the left ventricle lv of a normal heart h in systole is illustrated in fig1 . the left ventricle lv is contracting and blood flows outwardly through the tricuspid ( aortic ) valve av in the direction of the arrows . back flow of blood or “ regurgitation ” through the mitral valve mv is prevented since the mitral valve is configured as a “ check valve ” which prevents back flow when pressure in the left ventricle is higher than that in the left atrium la . the mitral valve mv comprises a pair of leaflets having free edges fe which meet evenly to close , as illustrated in fig1 . the opposite ends of the leaflets lf are attached to the surrounding heart structure along an annular region referred to as the annulus an . the free edges fe of the leaflets lf are secured to the lower portions of the left ventricle lv through chordae tendinae ct ( referred to hereinafter as the chordae ) which include plurality of branching tendons secured over the lower surfaces of each of the valve leaflets lf . the chordae ct in turn , are attached to the papillary muscles pm which extend upwardly from the lower portions of the left ventricle and intraventricular septum ivs . a number of structural defects in the heart can cause mitral valve regurgitation . regurgitation occurs when the valve leaflets do not close properly allowing leakage from the ventricle into the atrium . as shown in fig2 a , the free edges of the anterior and posterior leaflets normally meet along a line of coaptation c . an example of a defect causing regurgitation is shown in fig2 b . here an enlargement of the heart causes the mitral annulus to become enlarged , making it impossible for the free edges fe to meet during systole . this results in a gap g which allows blood to leak through the valve during ventricular systole . ruptured or elongated chordae can also cause a valve leaflet to prolapse since inadequate tension is transmitted to the leaflet via the chordae . while the other leaflet maintains a normal profile , the two valve leaflets do not properly meet and leakage from the left ventricle into the left atrium will occur . such regurgitation can also occur in patients who have suffered ischemic heart disease where the left ventricle does not contract sufficiently to effect proper closure . the present invention provides methods and devices for grasping , approximating and fixating tissues such as valve leaflets to treat cardiac valve regurgitation , particularly mitral valve regurgitation . the present invention also provides features that allow repositioning and removal of the device if so desired , particularly in areas where removal may be hindered by anatomical features such as chordae ct . such removal would allow the surgeon to reapproach the valve in a new manner if so desired . grasping will preferably be atraumatic providing a number of benefits . by atraumatic , it is meant that the devices and methods of the invention may be applied to the valve leaflets and then removed without causing any significant clinical impairment of leaflet structure or function . the leaflets and valve continue to function substantially the same as before the invention was applied . thus , some minor penetration or denting of the leaflets may occur using the invention while still meeting the definition of “ atraumatic ”. this enables the devices of the invention to be applied to a diseased valve and , if desired , removed or repositioned without having negatively affected valve function . in addition , it will be understood that in some cases it may be necessary or desirable to pierce or otherwise permanently affect the leaflets during either grasping , fixing or both . in some of these cases , grasping and fixation may be accomplished by a single device . although a number of embodiments are provided to achieve these results , a general overview of the basic features will be presented herein . such features are not intended to limit the scope of the invention and are presented with the aim of providing a basis for descriptions of individual embodiments presented later in the application . the devices and methods of the invention rely upon the use of an interventional tool that is positioned near a desired treatment site and used to grasp the target tissue . in endovascular applications , the interventional tool is typically an interventional catheter . in surgical applications , the interventional tool is typically an interventional instrument . in preferred embodiments , fixation of the grasped tissue is accomplished by maintaining grasping with a portion of the interventional tool which is left behind as an implant . while the invention may have a variety of applications for tissue approximation and fixation throughout the body , it is particularly well adapted for the repair of valves , especially cardiac valves such as the mitral valve . referring to fig3 a , an interventional tool 10 , having a delivery device , such as a shaft 12 , and a fixation device 14 , is illustrated having approached the mitral valve mv from the atrial side and grasped the leaflets lf . the mitral valve may be accessed either surgically or by using endovascular techniques , and either by a retrograde approach through the ventricle or by an antegrade approach through the atrium , as described above . for illustration purposes , an antegrade approach is described . the fixation device 14 is releasably attached to the shaft 12 of the interventional tool 10 at its distal end . when describing the devices of the invention herein , “ proximal ” shall mean the direction toward the end of the device to be manipulated by the user outside the patient &# 39 ; s body , and “ distal ” shall mean the direction toward the working end of the device that is positioned at the treatment site and away from the user . with respect to the mitral valve , proximal shall refer to the atrial or upstream side of the valve leaflets and distal shall refer to the ventricular or downstream side of the valve leaflets . the fixation device 14 typically comprises proximal elements 16 ( or gripping elements ) and distal elements 18 ( or fixation elements ) which protrude radially outward and are positionable on opposite sides of the leaflets lf as shown so as to capture or retain the leaflets therebetween . the proximal elements 16 are preferably comprised of cobalt chromium , nitinol or stainless steel , and the distal elements 18 are preferably comprised of cobalt chromium or stainless steel , however any suitable materials may be used . the fixation device 14 is coupleable to the shaft 12 by a coupling mechanism 17 . the coupling mechanism 17 allows the fixation device 14 to detach and be left behind as an implant to hold the leaflets together in the coapted position . in some situations , it may be desired to reposition or remove the fixation device 14 after the proximal elements 16 , distal elements 18 , or both have been deployed to capture the leaflets lf . such repositioning or removal may be desired for a variety of reasons , such as to reapproach the valve in an attempt to achieve better valve function , more optimal positioning of the device 14 on the leaflets , better purchase on the leaflets , to detangle the device 14 from surrounding tissue such as chordae , to exchange the device 14 with one having a different design , or to abort the fixation procedure , to name a few . to facilitate repositioning or removal of the fixation device 14 the distal elements 18 are releasable and optionally invertible to a configuration suitable for withdrawal of the device 14 from the valve without tangling or interfering with or damaging the chordae , leaflets or other tissue . fig3 b illustrates inversion wherein the distal elements 18 are moveable in the direction of arrows 40 to an inverted position . likewise , the proximal elements 16 may be raised , if desired . in the inverted position , the device 14 may be repositioned to a desired orientation wherein the distal elements may then be reverted to a grasping position against the leaflets as in fig3 a . alternatively , the fixation device 14 may be withdrawn ( indicated by arrow 42 ) from the leaflets as shown in fig3 c . such inversion reduces trauma to the leaflets and minimizes any entanglement of the device with surrounding tissues . once the device 14 has been withdrawn through the valve leaflets , the proximal and distal elements may be moved to a closed position or configuration suitable for removal from the body or for reinsertion through the mitral valve . fig4 illustrates the position of the fixation device 14 in a desired orientation in relation to the leaflets lf . this is a short - axis view of the mitral valve mv from the atrial side , therefore , the proximal elements 16 are shown in solid line and the distal elements 18 are shown in dashed line . the proximal and distal elements 16 , 18 are positioned to be substantially perpendicular to the line of coaptation c . the device 14 may be moved roughly along the line of coaptation to the location of regurgitation . the leaflets lf are held in place so that during diastole , as shown in fig4 , the leaflets lf remain in position between the elements 16 , 18 surrounded by openings o which result from the diastolic pressure gradient . advantageously , leaflets lf are coapted such that their proximal or upstream surfaces are facing each other in a vertical orientation , parallel to the direction of blood flow through mitral valve mv . the upstream surfaces may be brought together so as to be in contact with one another or may be held slightly apart , but will preferably be maintained in the vertical orientation in which the upstream surfaces face each other at the point of coaptation . this simulates the double orifice geometry of a standard surgical bow - tie repair . color doppler echo will show if the regurgitation of the valve has been reduced . if the resulting mitral flow pattern is satisfactory , the leaflets may be fixed together in this orientation . if the resulting color doppler image shows insufficient improvement in mitral regurgitation , the interventional tool 10 may be repositioned . this may be repeated until an optimal result is produced wherein the leaflets lf are held in place . once the leaflets are coapted in the desired arrangement , the fixation device 14 is then detached from the shaft 12 and left behind as an implant to hold the leaflets together in the coapted position . as mentioned previously , the fixation device 14 is coupled to the shaft 12 by a coupling mechanism 17 . fig5 a - 5b , 6 a - 6 b illustrate exemplary embodiments of such coupling mechanisms . fig5 a shows an upper shaft 20 and a detachable lower shaft 22 which are interlocked at a joining line or mating surface 24 . the mating surface 24 may have any shape or curvature which will allow or facilitate interlocking and later detachment . a snuggly fitting outer sheath 26 is positioned over the shafts 20 , 22 to cover the mating surface 24 as shown . fig5 b illustrates detachment of the lower shaft 22 from the upper shaft 20 . this is achieved by retracting the outer sheath 26 , so that the mating surface 24 is exposed , which allows the shafts 20 , 22 to separate . similarly , fig6 a illustrates a tubular upper shaft 28 and a detachable tubular lower shaft 30 which are interlocked at a mating surface 32 . again , the mating surface 32 may have any shape or curvature which will allow or facilitate interlocking and later detachment . the tubular upper shaft 28 and tubular lower shaft 30 form an outer member having an axial channel . a snuggly fitting rod 34 or inner member is inserted through the tubular shafts 28 , 30 to bridge the mating surface 32 as shown . fig6 b illustrates detachment of the lower shaft 30 from the upper shaft 28 . this is achieved by retracting the rod 34 to a position above the mating surface 32 which in turn allows the shafts 28 , 30 to separate . other examples of coupling mechanisms are described and illustrated in commonly assigned u . s . pat . no . 6 , 752 , 813 , incorporated herein by reference for all purposes . in a preferred embodiment , mating surface 24 ( or mating surface 32 ) is a sigmoid curve defining a male element and female element on upper shaft 20 ( or upper shaft 28 ) which interlock respectively with corresponding female and male elements on lower shaft 22 ( or lower shaft 30 ). typically , the lower shaft is the coupling mechanism 17 of the fixation device 14 . therefore , the shape of the mating surface selected will preferably provide at least some mating surfaces transverse to the axial axis of the a mechanism 19 to facilitate application of compressive and tensile forces through the coupling mechanism 17 to the fixation device 14 , yet causing minimal interference when the fixation device 14 is to be released from the upper shaft . the fixation device 14 is delivered to the valve or the desired tissues with the use of a delivery device . the delivery device may be rigid or flexible depending on the application . for endovascular applications , the delivery device comprises a flexible delivery catheter which will be described in later sections . typically , however , such a catheter comprises a shaft , having a proximal end and a distal end , and a fixation device releasably attached to its distal end . the shaft is usually elongate and flexible , suitable for intravascular introduction . alternatively , the delivery device may comprise a shorter and less flexible interventional instrument which may be used for trans - thoracic surgical introduction through the wall of the heart , although some flexibility and a minimal profile will generally be desirable . a fixation device is releasably coupleable with the delivery device as illustrated in fig3 a . the fixation device may have a variety of forms , a few embodiments of which will be described herein . fig7 a - 7d illustrate an embodiment of a fixation device 14 in various positions or configurations . fig7 a illustrates the fixation device 14 in a closed configuration for delivery through the patient &# 39 ; s vasculature and , in this example , through the mitral valve . the fixation device 14 includes a coupling member 19 which allows detachment of the fixation device 14 for implantation . in this example , the coupling member 19 is shown to include the lower shaft 22 and mating surface 24 of fig5 a - 5b , and therefore the coupling member 19 would function similarly as described above . the fixation device 14 also includes a pair of opposed distal elements 18 , each distal element 18 having an engagement surface 50 facing inwardly toward the opposed distal element 18 in the closed configuration . distal elements 18 preferably comprise elongate arms 53 , each arm having a proximal end 52 rotatably connected to the coupling member 19 and a free end 54 . suitable connections for arms 53 to coupling member 19 include pins , living hinges , or other known rotational connection mechanisms . in the closed configuration of fig7 a , free ends 54 point in a first direction such that the arms 53 and engagement surfaces 50 are nearly parallel to each other and to an axis 21 , and preferably are angled slightly inwardly toward each other . in a preferred embodiment , when tissue is not present between arms 53 , the arms 53 may be closed until free ends 54 either touch each other or engage shaft 12 when fixation device 14 is attached thereto , thereby minimizing the profile of the fixation device 14 for passage through a delivery device . fig7 b - 7c illustrate the fixation device 14 in an open position wherein the engagement surfaces 50 are disposed at a separation angle 56 apart , wherein the separation angle 56 is typically up to approximately 180 degrees , preferably up to 90 - 180 degrees , and arms 53 are disposed generally symmetrically relative to axis 21 . the arms 53 may be moveable to the open position by a variety of actuation mechanisms . for example , a plunger or actuator rod may be advanced through the coupling member 19 , as indicated by arrow 62 , so as to engage a spring or spring loaded actuation mechanism 58 which is attached to the distal elements 18 . by exerting a force against the actuation mechanism 58 , the distal elements 18 are rotated relative to coupling member 19 . the distal elements 18 may be held in this open position by the actuator rod against the resistance provided by the spring of the actuation mechanism 58 which biases the distal elements 18 toward the closed position of fig7 a when the distal elements 18 are less than 180 degrees apart . the spring loading of the actuation mechanism 58 resists outward movement of the actuation mechanism 58 and urges the device 14 towards the closed position . in this embodiment , proximal elements 16 comprise resilient loop - shaped wire forms biased outwardly and attached to the coupling member 19 so as to be biased to an open position shown in fig7 c but moveable rotationally inwardly when arms 53 are closed . the wire forms may be flexible enough to be rigidly attached to coupling member 19 and resiliently deflectable inwardly , or they may be attached by a rotational coupling such as a pin or living hinge . in use , leaflets lf are positioned between the proximal elements 16 and distal elements 18 . once , the leaflets lf are positioned between the proximal and distal elements 16 , 18 , the distal elements 18 may be closed , compressing the leaflets between engagement surfaces 50 and proximal elements 18 . depending upon the thickness of the leaflets , the arrangements of the leaflets , the position of the fixation device on the leaflets and other factors , the arms 53 may be maintained in the open position of fig7 b , moved to the fully closed position of fig7 a , or placed in any of various positions in between so as to coapt the leaflets lf and hold them in the desired position with the desired degree of force . in any case , the fixation device 14 will remain in place as an implant following detachment from the delivery catheter . in some situations , as previously mentioned , it may be desirable to reopen the fixation device 14 following initial placement . to reopen the device 14 , the actuator rod may be readvanced or reinserted through the coupling member 19 and readvanced to press against the actuation mechanism 58 , as previously indicated by arrow 62 in fig7 b . again , such advancement applies a force against the actuation mechanism 58 in the manner described above thus moving arms 53 outwardly to release force against leaflets and move engagement surfaces 50 away from proximal elements 16 . the leaflets are then free to move relative to fixation device 14 . the fixation device 14 may then be repositioned as desired and the actuator rod retracted to reclose the distal elements 18 to coapt the leaflets . under some circumstances , it may be further desirable to withdraw the fixation device 14 back through the valve or completely from the patient following initial insertion through the valve . should this be attempted with the clip in the closed or open positions illustrated in fig7 a - 7c , there may be a risk that arms 53 could interfere or become entangled with the chordae , leaflets or other tissues . to avoid this , the fixation element 14 is preferably adapted for inversion of arms 53 so that free ends 54 point in a second direction , opposite to the first direction in which the free ends 54 pointed in the closed position , each arm 53 forming an obtuse angle relative to axis 21 as illustrated in fig7 d . the arms 53 may be rotated so that the engagement surfaces 50 are disposed at a separation angle 56 of up to 360 degrees , and preferably at least up to 270 degrees . this may be accomplished by exerting a force against actuation mechanism 58 with a push rod or plunger extending through coupling member 19 as described above . in this embodiment , once the distal elements 18 have rotated beyond 180 degrees apart , the spring loading of the actuation mechanism 58 biases the distal elements 18 toward the inverted position . the spring loading of the actuation mechanism 58 resists outward movement of the actuation mechanism 58 and urges the device 14 towards the inverted position . with arms 53 in the inverted position , engagement surfaces 50 provide an atraumatic surface deflect tissues as the fixation device is withdrawn . this allows the device to be retracted back through the valve annulus without risk of injury to valvular and other tissues . in some cases , once the fixation device 14 has been pulled back through the valve , it will be desirable to return the device to the closed position for withdrawal of the device from the body ( either through the vasculature or through a surgical opening ). the embodiment illustrated in fig7 a - 7d is assembled from separate components composed of biocompatible materials . the components may be formed from the same or different materials , including but not limited to stainless steel or other metals , elgiloy ®, nitinol , titanium , tantalum , metal alloys or polymers . additionally , some or all of these components may be made of bioabsorbable materials that will be absorbed by surrounding tissues or will dissolve into the bloodstream following implantation . it has been found that in mitral valve repair applications the fixation devices of the invention are completely surrounded by tissue within a few months of implantation , after which the devices could dissolve or be absorbed without negative impact to the repair . in a further embodiment , some or all of the components may be molded as one part , as illustrated in fig8 a - 8b . here , the coupling member 19 , distal elements 18 and actuation mechanism 58 of the fixation device 14 are all molded from a polymer material as one moveable piece . fig8 a shows the fixation device 14 in the open position . advancement of an actuator rod 64 rotates the distal elements 18 relative to the coupling member 19 by a living hinge or by elastic deformation of the plastic at the point of connection between the elements 18 and the coupling member 19 . typically , this point of connection comprises a thinner segment of polymer to facilitate such bending . likewise , the actuation mechanism 58 coupled to the distal elements 18 in the same manner . fig8 b shows the fixation device 14 in the inverted position . fig9 illustrates another embodiment of a fixation device 14 . here , the fixation device 14 is shown coupled to a shaft 12 to form an interventional tool 10 . the fixation device 14 includes a coupling member 19 and a pair of opposed distal elements 18 . the distal elements 18 comprise elongate arms 53 , each arm having a proximal end 52 rotatably connected to the coupling member 19 and a free end 54 . the free ends 54 have a rounded shape to minimize interference with and trauma to surrounding tissue structures . preferably , each free end 54 defines a curvature about two axes , one being an axis 66 perpendicular to longitudinal axis of arms 53 . thus , the engagement surfaces 50 have a cupped or concave shape to surface area in contact with tissue and to assist in grasping and holding the valve leaflets . this further allows arms 53 to nest around the shaft 12 in the closed position to minimize the profile of the device . preferably , arms 53 are at least partially cupped or curved inwardly about their longitudinal axes 66 . also , preferably , each free end 54 defines a curvature about an axis 67 perpendicular to axis 66 or the longitudinal axis of arms 53 . this curvature is a reverse curvature along the most distal portion of the free end 54 . likewise , the longitudinal edges of the free ends 54 may flare outwardly . both the reverse curvature and flaring minimize trauma to the tissue engaged therewith . in a preferred embodiment suitable for mitral valve repair , the transverse width across engagement surfaces 50 ( which determines the width of tissue engaged ) is at least about 2 mm , usually 3 - 10 mm , and preferably about 4 - 6 mm . in some situations , a wider engagement is desired wherein the engagement surfaces 50 are larger , for example about 2 cm , or multiple fixation devices are used adjacent to each other . arms 53 and engagement surfaces 50 are configured to engage a length of tissue of about 4 - 10 mm , and preferably about 6 - 8 mm along the longitudinal axis of arms 53 . arms 53 further include a plurality of openings to enhance grip and to promote tissue ingrowth following implantation . the valve leaflets are grasped between the distal elements 18 and proximal elements 16 . in some embodiments , the proximal elements 16 are flexible , resilient , and cantilevered from coupling member 19 . the proximal elements are preferably resiliently biased toward the distal elements . each proximal element 16 is shaped and positioned to be at least partially recessed within the concavity of the distal element 18 when no tissue is present . when the fixation device 14 is in the open position , the proximal elements 16 are shaped such that each proximal element 16 is separated from the engagement surface 50 near the proximal end 52 of arm 53 and slopes toward the engagement surface 50 near the free end 54 with the free end of the proximal element contacting engagement surface 50 , as illustrated in fig9 . this shape of the proximal elements 16 accommodates valve leaflets or other tissues of varying thicknesses . proximal elements 16 include a plurality of openings 63 and scalloped side edges 61 to increase grip on tissue . the proximal elements 16 optionally include frictional accessories , frictional features or grip - enhancing elements to assist in grasping and / or holding the leaflets . in preferred embodiments , the frictional accessories comprise barbs 60 having tapering pointed tips extending toward engagement surfaces 50 . it may be appreciated that any suitable frictional accessories may be used , such as prongs , windings , bands , barbs , grooves , channels , bumps , surface roughening , sintering , high - friction pads , coverings , coatings or a combination of these . optionally , magnets may be present in the proximal and / or distal elements . it may be appreciated that the mating surfaces will be made from or will include material of opposite magnetic charge to cause attraction by magnetic force . for example , the proximal elements and distal elements may each include magnetic material of opposite charge so that tissue is held under constant compression between the proximal and distal elements to facilitate faster healing and ingrowth of tissue . also , the magnetic force may be used to draw the proximal elements 16 toward the distal elements 18 , in addition to or alternatively to biasing of the proximal elements toward the distal elements . this may assist in deployment of the proximal elements 16 . in another example , the distal elements 18 each include magnetic material of opposite charge so that tissue positioned between the distal elements 18 is held therebetween by magnetic force . the proximal elements 16 may be covered with a fabric or other flexible material as described below to enhance grip and tissue ingrowth following implantation . preferably , when fabrics or coverings are used in combination with barbs or other frictional features , such features will protrude through such fabric or other covering so as to contact any tissue engaged by proximal elements 16 . in an exemplary embodiment , proximal elements 16 are formed from metallic sheet of a spring - like material using a stamping operation which creates openings 63 , scalloped edges 61 and barbs 60 . alternatively , proximal elements 16 could be comprised of a spring - like material or molded from a biocompatible polymer . it should be noted that while some types of frictional accessories that can be used in the present invention may permanently alter or cause some trauma to the tissue engaged thereby , in a preferred embodiment , the frictional accessories will be atraumatic and will not injure or otherwise affect the tissue in a clinically significant way . for example , in the case of barbs 60 , it has been demonstrated that following engagement of mitral valve leaflets by fixation device 14 , should the device later be removed during the procedure barbs 60 leave no significant permanent scarring or other impairment of the leaflet tissue and are thus considered atraumatic . the fixation device 14 also includes an actuation mechanism 58 . in this embodiment , the actuation mechanism 58 comprises two link members or legs 68 , each leg 68 having a first end 70 which is rotatably joined with one of the distal elements 18 at a riveted joint 76 and a second end 72 which is rotatably joined with a stud 74 . the legs 68 are preferably comprised of a rigid or semi - rigid metal or polymer such as elgiloy ®, cobalt chromium or stainless steel , however any suitable material may be used . while in the embodiment illustrated both legs 68 are pinned to stud 74 by a single rivet 78 , it may be appreciated , however , that each leg 68 may be individually attached to the stud 74 by a separate rivet or pin . the stud 74 is joinable with an actuator rod 64 ( not shown ) which extends through the shaft 12 and is axially extendable and retractable to move the stud 74 and therefore the legs 68 which rotate the distal elements 18 between closed , open and inverted positions . likewise , immobilization of the stud 74 holds the legs 68 in place and therefore holds the distal elements 18 in a desired position . the stud 74 may also be locked in place by a locking feature which will be further described in later sections . in any of the embodiments of fixation device 14 disclosed herein , it may be desirable to provide some mobility or flexibility in distal elements 18 and / or proximal elements 16 in the closed position to enable these elements to move or flex with the opening or closing of the valve leaflets . this provides shock absorption and thereby reduces force on the leaflets and minimizes the possibility for tearing or other trauma to the leaflets . such mobility or flexibility may be provided by using a flexible , resilient metal or polymer of appropriate thickness to construct the distal elements 18 . also , the locking mechanism of the fixation device ( described below ) may be constructed of flexible materials to allow some slight movement of the proximal and distal elements even when locked . further , the distal elements 18 can be connected to the coupling mechanism 19 or to actuation mechanism 58 by a mechanism that biases the distal element into the closed position ( inwardly ) but permits the arms to open slightly in response to forces exerted by the leaflets . for example , rather than being pinned at a single point , these components may be pinned through a slot that allowed a small amount of translation of the pin in response to forces against the arms . a spring is used to bias the pinned component toward one end of the slot . fig1 a - 10b , 11 a - 11 b , 12 a - 12 b , 13 a - 13 b , and fig1 - 16 illustrate embodiments of the fixation device 14 of fig9 in various possible positions during introduction and placement of the device 14 within the body to perform a therapeutic procedure . fig1 a illustrates an embodiment of an interventional tool 10 delivered through a catheter 86 . it may be appreciated that the interventional tool 10 may take the form of a catheter , and likewise , the catheter 86 may take the form of a guide catheter or sheath . however , in this example the terms interventional tool 10 and catheter 86 will be used . the interventional tool 10 comprises a fixation device 14 coupled to a shaft 12 and the fixation device 14 is shown in the closed position . fig1 b illustrates a similar embodiment of the fixation device of fig1 a in a larger view . in the closed position , the opposed pair of distal elements 18 are positioned so that the engagement surfaces 50 face each other . each distal element 18 comprises an elongate arm 53 having a cupped or concave shape so that together the arms 53 surround the shaft 12 and optionally contact each other on opposite sides of the shaft . this provides a low profile for the fixation device 14 which is readily passable through the catheter 86 and through any anatomical structures , such as the mitral valve . in addition , fig1 b further includes an actuation mechanism 58 . in this embodiment , the actuation mechanism 58 comprises two legs 68 which are each movably coupled to a base 69 . the base 69 is joined with an actuator rod 64 which extends through the shaft 12 and is used to manipulate the fixation device 14 . in some embodiments , the actuator rod 64 attaches directly to the actuation mechanism 58 , particularly the base 69 . however , the actuator rod 64 may alternatively attach to a stud 74 which in turn is attached to the base 69 . in some embodiments , the stud 74 is threaded so that the actuator rod 64 attaches to the stud 74 by a screw - type action . however , the rod 64 and stud 74 may be joined by any mechanism which is releasable to allow the fixation device 14 to be detached from shaft 12 . fig1 a - 11b illustrate the fixation device 14 in the open position . in the open position , the distal elements 18 are rotated so that the engagement surfaces 50 face a first direction . distal advancement of the stud 74 relative to coupling member 19 by action of the actuator rod 64 applies force to the distal elements 18 which begin to rotate around joints 76 due to freedom of movement in this direction . such rotation and movement of the distal elements 18 radially outward causes rotation of the legs 68 about joints 80 so that the legs 68 are directly slightly outwards . the stud 74 may be advanced to any desired distance correlating to a desired separation of the distal elements 18 . in the open position , engagement surfaces 50 are disposed at an acute angle relative to shaft 12 , and are preferably at an angle of between 90 and 180 degrees relative to each other . in one embodiment , in the open position the free ends 54 of arms 53 have a span therebetween of about 10 - 20 mm , usually about 12 - 18 mm , and preferably about 14 - 16 mm . proximal elements 16 are typically biased outwardly toward arms 53 . the proximal elements 16 may be moved inwardly toward the shaft 12 and held against the shaft 12 with the aid of proximal element lines 90 which can be in the form of sutures , wires , nitinol wire , rods , cables , polymeric lines , or other suitable structures . the proximal element lines 90 may be connected with the proximal elements 16 by threading the lines 90 in a variety of ways . when the proximal elements 16 have a loop shape , as shown in fig1 a , the line 90 may pass through the loop and double back . when the proximal elements 16 have an elongate solid shape , as shown in fig1 b , the line 90 may pass through one or more of the openings 63 in the element 16 . further , a line loop 48 may be present on a proximal element 16 , also illustrated in fig1 b , through which a proximal element line 90 may pass and double back . such a line loop 48 may be useful to reduce friction on proximal element line 90 or when the proximal elements 16 are solid or devoid of other loops or openings through which the proximal element lines 90 may attach . a proximal element line 90 may attach to the proximal elements 16 by detachable means which would allow a single line 90 to be attached to a proximal element 16 without doubling back and would allow the single line 90 to be detached directly from the proximal element 16 when desired . examples of such detachable means include hooks , snares , clips or breakable couplings , to name a few . by applying sufficient tension to the proximal element line 90 , the detachable means may be detached from the proximal element 16 such as by breakage of the coupling . other mechanisms for detachment may also be used . similarly , a lock line 92 may be attached and detached from a locking mechanism by similar detachable means . in the open position , the fixation device 14 can engage the tissue which is to be approximated or treated . the embodiment illustrated in fig9 - 11 is adapted for repair of the mitral valve using an antegrade approach from the left atrium . the interventional tool 10 is advanced through the mitral valve from the left atrium to the left ventricle . the distal elements 18 are oriented to be perpendicular to the line of coaptation and then positioned so that the engagement surfaces 50 contact the ventricular surface of the valve leaflets , thereby grasping the leaflets . the proximal elements 16 remain on the atrial side of the valve leaflets so that the leaflets lie between the proximal and distal elements . in this embodiment , the proximal elements 16 have frictional accessories , such as barbs 60 which are directed toward the distal elements 18 . however , neither the proximal elements 16 nor the barbs 60 contact the leaflets at this time . the interventional tool 10 may be repeatedly manipulated to reposition the fixation device 14 so that the leaflets are properly contacted or grasped at a desired location . repositioning is achieved with the fixation device in the open position . in some instances , regurgitation may also be checked while the device 14 is in the open position . if regurgitation is not satisfactorily reduced , the device may be repositioned and regurgitation checked again until the desired results are achieved . it may also be desired to invert the fixation device 14 to aid in repositioning or removal of the fixation device 14 . fig1 a - 12b illustrate the fixation device 14 in the inverted position . by further advancement of stud 74 relative to coupling member 19 , the distal elements 18 are further rotated so that the engagement surfaces 50 face outwardly and free ends 54 point distally , with each arm 53 forming an obtuse angle relative to shaft 12 . the angle between arms 53 is preferably in the range of about 270 to 360 degrees . further advancement of the stud 74 further rotates the distal elements 18 around joints 76 . this rotation and movement of the distal elements 18 radially outward causes rotation of the legs 68 about joints 80 so that the legs 68 are returned toward their initial position , generally parallel to each other . the stud 74 may be advanced to any desired distance correlating to a desired inversion of the distal elements 18 . preferably , in the fully inverted position , the span between free ends 54 is no more than about 20 mm , usually less than about 16 mm , and preferably about 12 - 14 mm . in this illustration , the proximal elements 16 remain positioned against the shaft 12 by exerting tension on the proximal element lines 90 . thus , a relatively large space may be created between the elements 16 , 18 for repositioning . in addition , the inverted position allows withdrawal of the fixation device 14 through the valve while minimizing trauma to the leaflets . engagement surfaces 50 provide an atraumatic surface for deflecting tissue as the fixation device is retracted proximally . it should be further noted that barbs 60 are angled slightly in the distal direction ( away from the free ends of the proximal elements 16 ), reducing the risk that the barbs will catch on or lacerate tissue as the fixation device is withdrawn . once the fixation device 14 has been positioned in a desired location against the valve leaflets , the leaflets may then be captured between the proximal elements 16 and the distal elements 18 . fig1 a - 13b illustrate the fixation device 14 in such a position . here , the proximal elements 16 are lowered toward the engagement surfaces 50 so that the leaflets are held therebetween . in fig1 b , the proximal elements 16 are shown to include barbs 60 which may be used to provide atraumatic gripping of the leaflets . alternatively , larger , more sharply pointed barbs or other penetration structures may be used to pierce the leaflets to more actively assist in holding them in place . this position is similar to the open position of fig1 a - 11b , however the proximal elements 16 are now lowered toward arms 53 by releasing tension on proximal element lines 90 to compress the leaflet tissue therebetween . at any time , the proximal elements 16 may be raised and the distal elements 18 adjusted or inverted to reposition the fixation device 14 , if regurgitation is not sufficiently reduced . after the leaflets have been captured between the proximal and distal elements 16 , 18 in a desired arrangement , the distal elements 18 may be locked to hold the leaflets in this position or the fixation device 14 may be returned to or toward a closed position . such locking will be described in a later section . fig1 illustrates the fixation device 14 in the closed position wherein the leaflets ( not shown ) are captured and coapted . this is achieved by retraction of the stud 74 proximally relative to coupling member 19 so that the legs 68 of the actuation mechanism 58 apply an upwards force to the distal elements 18 which in turn rotate the distal elements 18 so that the engagement surfaces 50 again face one another . the released proximal elements 16 which are biased outwardly toward distal elements 18 are concurrently urged inwardly by the distal elements 18 . the fixation device 14 may then be locked to hold the leaflets in this closed position as described below . as shown in fig1 , the fixation device 14 may then be released from the shaft 12 . as mentioned , the fixation device 14 is releasably coupleable to the shaft 12 by coupling member 19 . fig1 illustrates the coupling structure , a portion of the shaft 12 to which the coupling member 19 of the fixation device 14 attaches . as shown , the proximal element lines 90 may remain attached to the proximal elements 16 following detachment from shaft 12 to function as a tether to keep the fixation device 14 connected with the catheter 86 . optionally , a separate tether coupled between shaft 12 and fixation device 14 may be used expressly for this purpose while the proximal element lines 90 are removed . in any case , the repair of the leaflets or tissue may be observed by non - invasive visualization techniques , such as echocardiography , to ensure the desired outcome . if the repair is not desired , the fixation device 14 may be retrieved with the use of the tether or proximal element lines 90 so as to reconnect coupling member 19 with shaft 12 . in an exemplary embodiments , proximal element lines 90 are elongated flexible threads , wire , cable , sutures or lines extending through shaft 12 , looped through proximal elements 16 , and extending back through shaft 12 to its proximal end . when detachment is desired , one end of each line may be released at the proximal end of the shaft 12 and the other end pulled to draw the free end of the line distally through shaft 12 and through proximal element 16 thereby releasing the fixation device . fig1 illustrates a released fixation device 14 in a closed position . as shown , the coupling member 19 remains separated from the shaft 12 of the interventional tool 10 and the proximal elements 16 are deployed so that tissue ( not shown ) may reside between the proximal elements 16 and distal elements 18 . while the above described embodiments of the invention utilize a push - to - open , pull - to - close mechanism for opening and closing distal elements 18 , it should be understood that a pull - to - open , push - to - close mechanism is equally possible . for example , distal elements 18 may be coupled at their proximal ends to stud 74 rather than to coupling member 19 , and legs 68 may be coupled at their proximal ends to coupling member 19 rather than to stud 74 . in this example , when stud 74 is pushed distally relative to coupling member 19 , distal elements 18 would close , while pulling on stud 74 proximally toward coupling member 19 would open distal elements 18 . the fixation device 14 may optionally include a covering . the covering may assist in grasping the tissue and may later provide a surface for tissue ingrowth . ingrowth of the surrounding tissues , such as the valve leaflets , provides stability to the device 14 as it is further anchored in place and may cover the device with native tissue thus reducing the possibility of immunologic reactions . the covering may be comprised of any biocompatible material , such as polyethylene terepthalate , polyester , cotton , polyurethane , expanded polytetrafluoroethylene ( eptfe ), silicon , or various polymers or fibers and have any suitable form , such as a fabric , mesh , textured weave , felt , looped or porous structure . generally , the covering has a low profile so as not to interfere with delivery through an introducer sheath or with grasping and coapting of leaflets or tissue . fig1 a - 17c illustrate a covering 100 on the fixation device 14 wherein the device 14 is in various positions . fig1 a shows the covering 100 encapsulating the distal elements 18 and the actuation mechanism 58 while the device 14 is in the open position . thus , the engagement surfaces 50 are covered by the covering 100 which helps to minimize trauma on tissues and provides additional friction to assist in grasping and retaining tissues . fig1 b shows the device 14 of fig1 a in the inverted position . the covering 100 is loosely fitted and / or is flexible or elastic such that the device 14 can freely move to various positions and the covering 100 conforms to the contours of the device 14 and remains securely attached in all positions . fig1 c shows the device 14 in the closed position . thus , when the fixation device 14 is left behind as an implant in the closed position , the exposed surfaces of the device 14 are substantially covered by the covering 100 . it may be appreciated that the covering 100 may cover specific parts of the fixation device 14 while leaving other parts exposed . for example , the covering 100 may comprise sleeves that fit over the distal elements 18 and not the actuation mechanism 58 , caps that fit over the distal ends 54 of the distal elements 18 or pads that cover the engagement surfaces 50 , to name a few . it may be appreciated that , the covering 100 may allow any frictional accessories , such as barbs , to be exposed . also , the covering 100 may cover the proximal elements 16 and / or any other surfaces of the fixation device 14 . in any case , the covering 100 should be durable to withstand multiple introduction cycles and , when implanted within a heart , a lifetime of cardiac cycles . the covering 100 may alternatively be comprised of a polymer or other suitable materials dipped , sprayed , coated or otherwise adhered to the surfaces of the fixation device 14 . optionally , the polymer coating may include pores or contours to assist in grasping the tissue and / or to promote tissue ingrowth . any of the coverings 100 may optionally include drugs , antibiotics , anti - thrombosis agents , or anti - platelet agents such as heparin , coumadin ® ( warfarin sodium ), to name a few . these agents may , for example , be impregnated in or coated on the coverings 100 . these agents may then be delivered to the grasped tissues surrounding tissues and / or bloodstream for therapeutic effects . as mentioned previously , the fixation device 14 optionally includes a locking mechanism for locking the device 14 in a particular position , such as an open , closed or inverted position or any position therebetween . it may be appreciated that the locking mechanism includes an unlocking mechanism which allows the device to be both locked and unlocked . fig1 - 21 illustrate an embodiment of a locking mechanism 106 . referring to fig1 , in this embodiment , the locking mechanism 106 is disposed between the coupling member 19 and the base 69 of the actuation mechanism 58 . the base 69 is fixedly attached to the stud 74 which extends through the locking mechanism 106 . the stud 74 is releasably attached to the actuator rod 64 which passes through the coupling member 19 and the shaft 12 of the interventional tool 10 . the base 69 is also connected to the legs 68 of the actuation mechanism 58 which are in turn connected to the distal elements 18 . fig1 also illustrates the proximal elements 16 , which in this embodiment straddle the locking mechanism and join beneath the locking mechanism 106 . the proximal elements 16 are shown supported by proximal element lines 90 . the proximal elements 16 are raised and lowered by manipulation of the proximal element lines 90 . in addition , lock lines 92 are shown connected with a release harness 108 of the locking mechanism 106 . the lock lines 92 are used to lock and unlock the locking mechanism 106 as will be described below . the proximal element lines 90 and lock lines 92 may be comprised of any suitable material , typically wire , nitinol wire , cable , suture or thread , to name a few . in addition , the proximal element lines 90 and / or lock lines 92 may include a coating , such as parylene . parylene is a vapor deposited pinhole free protective film which is conformal and biocompatible . it is inert and protects against moisture , chemicals , and electrical charge . fig1 provides a front view of the locking mechanism 106 of fig1 . however , here the proximal elements 16 are supported by a single proximal element line 90 which is through both of the proximal elements 16 . in this arrangement both of the elements are raised and lowered simultaneously by action of a single proximal element line 90 . whether the proximal elements 16 are manipulated individually by separate proximal element lines 90 or jointly by a single proximal element line 90 , the proximal element lines 90 may extend directly through openings in the proximal elements and / or through a layer or portion of a covering 100 on the proximal elements , or through a suture loop above or below a covering 100 . fig2 - 21 illustrate the locking mechanism 106 showing the locking mechanism 106 in the unlocked and locked positions respectively . referring to fig2 , the locking mechanism 106 includes one or more wedging elements , such as rolling elements . in this embodiment , the rolling elements comprise a pair of barbells 110 disposed on opposite sides of the stud 74 , each barbell having a pair of generally cylindrical caps and a shaft therebetween . the barbells 110 and the stud 74 are preferably comprised of cobalt chromium or stainless steel , however any suitable material may be used . the barbells 110 are manipulated by hooked ends 112 of the release harness 108 . when an upwards force is applied to the harness 108 by the lock line 92 ( illustrated in fig1 ), the hooked ends 112 raise the barbells 110 against a spring 114 , as shown in fig2 . this draws the barbells 110 up along a sidewall or sloping surface 116 which unwedges the barbells 110 from against the stud 74 . in this position , the stud 74 is free to move . thus , when the lock line 92 raises or lifts the harness 108 , the locking mechanism 106 is in an unlocked position wherein the stud 74 is free to move the actuation mechanism 58 and therefore the distal elements 18 to any desired position . release of the harness 108 by the lock line 92 transitions the locking mechanism 106 to a locked position , illustrated in fig2 . by releasing the upwards force on the barbells 110 by the hooked ends 112 , the spring 114 forces the barbells 110 downwards and wedges the barbells 110 between the sloping surface 116 and the stud 74 . this restricts motion of the stud 74 , which in turn locks the actuation mechanism 58 and therefore distal elements 18 in place . in addition , the stud 74 may include one or more grooves 82 or indentations which receive the barbells 110 . this may provide more rapid and positive locking by causing the barbells 110 to settle in a definite position , increase the stability of the locking feature by further preventing movement of the barbells 110 , as well as tangible indication to the user that the barbell has reached a locking position . in addition , the grooves 82 may be used to indicate the relative position of the distal elements 18 , particularly the distance between the distal elements 18 . for example , each groove 82 may be positioned to correspond with a 0 . 5 or 1 . 0 mm decrease in distance between the distal elements 18 . as the stud 74 is moved , the barbells 110 will contact the grooves 82 ; by counting the number of grooves 82 that are felt as the stud 74 is moved , the user can determine the distance between the distal elements 18 and can provide the desired degree of coaptation based upon leaflet thickness , geometry , spacing , blood flow dynamics and other factors . thus , the grooves 82 may provide tactile feedback to the user . the locking mechanism 106 allows the fixation device 14 to remain in an unlocked position when attached to the interventional tool 10 during grasping and repositioning and then maintain a locked position when left behind as an implant . it may be appreciated , however , that the locking mechanism 106 may be repeatedly locked and unlocked throughout the placement of the fixation device 14 if desired . once the final placement is determined , the lock line 92 and proximal element lines 90 are removed and the fixation device is left behind . fig2 , 24 a - 24 b illustrate another embodiment of a locking mechanism 106 . referring to fig2 , in this embodiment , the locking mechanism 106 is again disposed between the coupling member 19 and the base 69 of the actuation mechanism 58 . the base 69 is connected to the stud 74 which extends through the locking mechanism 106 , and connects to an actuator rod which extends through the coupling member 19 and the shaft 12 of the interventional tool 10 . the base 69 is also connected to the legs 68 of the actuation mechanism 58 which are in turn connected to the distal elements 18 . fig2 also illustrates the proximal elements 16 which manipulate the locking mechanism 106 in this embodiment . the locking mechanism 106 comprises folded leaf structures 124 having overlapping portions 124 a , 124 b , each folded structure 124 being attached to a proximal element 16 . in fig2 and fig2 a , the folded structures 124 are shown without the remainder of the locking mechanism 106 for clarity . proximal elements 16 are flexible and resilient and are biased outwardly . the folded leaf structures 124 include holes 125 ( fig2 b ) in each overlapping portion 124 a , 124 b so that the stud 74 passes through the holes 125 of the portions 124 a , 124 b as shown . the locking mechanism includes slots into which ends 123 of the folded leaf structures 124 are fixed . when the proximal elements 16 are in an undeployed position , as in fig2 , the folded leaf structures 124 lie substantially perpendicular to the stud 74 so that the holes 125 in each overlapping portion are vertically aligned . this allows the stud 74 to pass freely through the holes and the locking mechanism 106 is considered to be in an unlocked position . deployment of the proximal elements 16 , as shown in fig2 a , tilts the folded leaf structures 124 so as to be disposed in a non - perpendicular orientation relative to the stud 74 and the holes 125 are no longer vertically aligned with one another . in this arrangement , the stud 74 is not free to move due to friction against the holes of the folded leaf structure 124 . fig2 b provides a larger perspective view of the folded structures 124 in this position . thus , the locking mechanism 106 is considered to be in a locked position . this arrangement allows the fixation device 14 to maintain an unlocked position during grasping and repositioning and then maintain a locked position when the proximal elements 16 are deployed and the fixation device 14 is left behind as an implant . it may be appreciated , however , that the locking mechanism 106 may be repeatedly locked and unlocked throughout the placement of the fixation device 14 if desired . fig2 , 26 a - 26 b illustrate another embodiment of a locking mechanism 106 . referring to fig2 , in this embodiment , the locking mechanism 106 is again disposed between the coupling member 19 and the base 69 of the actuation mechanism 58 . and , the base 69 is connected to the stud 74 which extends through the locking mechanism 106 and connects to an actuator rod which extends through the coupling member 19 and the shaft of the interventional tool 10 . fig2 illustrates the proximal elements 16 which manipulate the locking mechanism 106 in this embodiment . the locking mechanism 106 comprises c - shaped structures 128 , each c - shaped structure 128 attached to a proximal element 16 . the c - shaped structures 128 hook around the stud 74 so that the stud 74 passes through the “ c ” of each structure 128 as shown in fig2 a - 26b . as shown , the structures 128 cross each other and the “ c ” of each structure 128 faces each other . a spring 130 biases the c - shaped structures into engagement with one another . when the proximal elements are in an undeployed position , as in fig2 a , the c - shaped structures 128 are urged into an orientation more orthogonal to the axial direction defined by stud 74 , thus bringing the “ c ” of each structure 128 into closer axial alignment . this allows the stud 74 to pass freely through the “ c ” of each structure 128 . deployment of the proximal elements 16 outwardly urges the c - shaped structures into a more angular , non - orthogonal orientation relative to stud 74 causing the sidewalls of the “ c ” of each structure 128 to engage stud 74 more forcefully . in this arrangement , the stud 74 is not free to move due to friction against the “ c ” shaped structures 128 . fig2 a - 22b illustrate a variation of the fixation device 14 described above in which the distal and proximal elements 16 , 18 on each side of the fixation device are movable laterally toward and away from each other to facilitate capture of more widely - separated leaflets or other tissue flaps . the coupling member 19 is bifurcated into two resilient and flexible branches 19 a , 19 b which are biased outwardly into the position shown in fig2 a , but which are movable to the position shown in fig2 b . as an alternative , branches 19 a , 19 b may be more rigid members connected to coupling member 19 by pins or hinges so as to be pivotable toward and away from each other . each of proximal elements 16 and distal elements 18 are coupled at their proximal ends to one branch 19 a or 19 b of the coupling member 19 . legs 68 are coupled at their proximal ends to base 69 , and therefore stud 74 , and at their distal ends to distal elements 18 , as described above . translation of stud 74 distally or proximally relative to coupling member 19 opens or closes distal elements 18 as in formerly described embodiments . a collar 131 is slidably disposed over coupling member 19 and has an annular groove 133 on its inner wall configured to slide over and frictionally engage detents 135 on branches 19 a , 19 b . a sheath 137 is positioned coaxially over shaft 12 and is slidable relative thereto to facilitate pushing collar 131 distally over coupling member 19 . in use , the embodiment of fig2 a - 22b is introduced with distal and proximal elements 16 , 18 in the closed position . collar 131 is pushed distally against , but not over , detents 135 so that branches 19 a , 19 b are disposed together and fixation device 14 has a minimal profile . when the user is ready to capture the target tissue ( e . g . valve leaflets ), sheath 137 is retracted so that collar 131 slides proximally over coupling member 19 . this allows branches 19 a , 19 b to separate into the position of fig2 a . actuator 64 is pushed distally so as to open distal elements 18 . tension is maintained on proximal element lines 90 ( not shown in fig2 a - 22b ) so that proximal elements 16 remain separated from distal elements 18 . when tissue is positioned between the proximal and distal elements , tension is released on proximal element lines 90 allowing the tissue to be captured between the proximal and distal elements . sheath 137 may then be advanced distally so that collar 131 urges branches 19 a , 19 b back together . sheath 137 is advanced until groove 133 in collar 131 slides over detents 135 and is frictionally maintained thereon as shown in fig2 b . sheath 137 may then be retracted from collar 131 . distal elements 18 may be closed , opened or inverted by advancing or retracting stud 74 via actuator 64 , as in the embodiments described above . it should be understood that the embodiment of fig2 a - 22b preferably includes a locking mechanism as described above , which has been omitted from the figures for clarity . in a further alternative of the embodiment of fig2 a - 22b , fixation device 14 may be configured to allow for independent actuation of each of the lateral branches 19 a , 19 b and / or distal elements 18 . in an exemplary embodiment , shaft 12 and coupling member 19 may be longitudinally split into two identical halves such that a first branch 19 a may be drawn into collar 131 independently of a second branch 19 b . similarly , actuator shaft 64 may be longitudinally split so that each half can slide independently of the other half , thus allowing one of distal elements 18 to be closed independently of the other distal element 18 . this configuration permits the user to capture one of the valve leaflets between one of the distal and proximal elements 16 , 18 , then draw the corresponding branch 19 a into the collar 131 . the fixation device 14 may then be repositioned to capture a second of the valve leaflets between the other proximal and distal elements 16 , 18 , after which the second branch 19 b may be drawn into collar 131 to complete the coaptation . of course , the closure of distal elements 18 may occur either before or after branches 19 a , 19 b are drawn into collar 131 . fig2 - 28 illustrate an additional embodiment of the fixation device 14 . as shown in fig2 , the fixation device 14 includes a coupling member 19 which couples the device 14 to the shaft 12 of the interventional tool 10 . here , the device 14 also includes a top coupler 150 attached to coupling member 19 and a bottom coupler 152 attached to the stud 74 so that the two couplers are axially moveable relative to one another . the distal elements 18 are rotatably attached to the top coupler 150 by upper pins 156 and rotatably attached to the bottom coupler 152 by lower pins 160 . when the bottom coupler 152 is advanced , the pins 156 , 160 are drawn apart . the upper pins 156 are disposed within slots 158 as shown . when the bottom coupler 152 is advanced distally relative to top coupler 150 , pins 156 , 160 are drawn apart . angling of the slots 158 causes the distal elements 18 to rotate toward the coupling member 19 as the pins 156 , 160 are drawn apart . relative movement of the couplers 150 , 152 may be achieved by any suitable mechanism including sliding or threading . fig2 illustrates the fixation device 14 in the closed position . here , the device 14 has a low profile ( width in the range of approximately 0 . 140 - 0 . 160 inches orthogonal to the axial direction defined by shaft 12 / stud 74 ) so that the device 14 may be easily passed through a catheter and through any tissue structures . to open the device 14 the bottom coupler 152 is then retracted or the couplers 150 , 152 brought toward one another to rotate the distal elements 18 outward . the components of the fixation device 14 may be formed from stainless steel or other suitable metal , such as by machining , or formed from a polymer , such as by injection molding . in addition , portions of the fixation device 14 , particularly the distal elements 18 , may be covered with a covering such as described above , to promote tissue ingrowth , reduce trauma , enhance friction and / or release pharmacological agents . alternatively , the device 14 may have a smooth surface which prevents cellular adhesion thereby reducing the accumulation of cells having potential to form an emboli . optionally , the fixation device 14 may include tissue retention features such as barbs 170 and / or bumpers 172 , illustrated in fig2 - 30 . the barbs 170 may extend from the engagement surfaces 50 of the distal elements 18 , as shown , and may be present in any number and any arrangement . thus , the barbs 170 will engage the leaflets or tissue during grasping to assist in holding the tissue either by frictional engagement , minor surface penetration or by complete piercing of the tissue , depending on the length and shape of the barbs 170 selected . alternatively or in addition , bumpers 172 may extend from the distal elements 18 . as shown in fig2 , each bumpers 172 may extend from the proximal end 52 of the distal element 18 and curve toward the free end 54 of the distal element 18 . or , as shown in fig3 , each bumper 172 may extend from the free end 54 and curve toward the proximal end 52 . bumpers 172 are preferably constructed of a resilient metal or polymer and may have any of various geometries , including a solid thin sheet or a loop - shaped wire form . the bumpers 172 may help to actively engage and disengage tissue from the barbs 170 during opening and closing of the fixation device 14 . further , to assist in grasping a tissue , the engagement surfaces 50 may have any texture or form to increase friction against the grasped tissue . for example , the surfaces 50 may include serrations , scales , felt , barbs , polymeric frictional elements , knurling or grooves , to name a few . fig3 illustrates the engagement surface 50 having a serrated edge 174 to improve grip on tissue engaged . fig3 also illustrates an embodiment of the fixation device 14 mounted on an interventional tool 10 or delivery catheter for ventricular approach to the mitral valve . here the device 14 is mounted on the shaft 12 with the engagement surfaces 50 facing distally relative to shaft 12 ( and facing upstream relative to the mitral valve ). thus , when the mitral valve is approached from the ventricular side , the engagement surfaces 50 can be pressed against the downstream surfaces of the valve without passing through the valve . it may be appreciated that any of the embodiments of the fixation device 14 described herein may be mounted on shaft 12 in this orientation for approach to any valve or tissue , including embodiments that include both proximal and distal elements . it may be appreciated that when the fixation device 14 is mounted on the shaft 12 in orientation illustrated in fig3 , the position of the distal elements and the proximal elements are reversed . in such instances it is useful to keep in mind that the distal elements contact the distal surface or downstream surface of the leaflets and the proximal elements contact the proximal surface or upstream surface of the leaflets . thus , regardless of the approach to the valve and the relative position of the proximal and distal elements on the fixation device , the proximal and distal elements remain consistent in relation to the valve . fig3 - 34 illustrate an additional embodiment of the fixation device 14 . as shown in fig3 , the fixation device 14 includes a coupling member 19 , proximal elements 16 and distal elements 18 which are each connected to a set of base components 186 . the distal elements 18 are connected to the base components 186 ( top base component 186 a and a bottom base component 186 b ) by extension arms 188 . in this embodiment , each distal element 18 is connected by two extension arms 188 in a crossed arrangement so that one extension arm 188 connects the distal element 18 to the top base component 186 a and the other extension arm 188 ′ connects the distal element 18 to the bottom base component 186 b . the top base component 186 a can be separated from the bottom base component 186 b by any suitable method which may be torque driven , spring driven or push / pull . increasing the separation distance between the base components 186 draws the distal elements 18 inwards toward the base components 186 , as shown in fig3 . this allows the tissue to be grasped between the distal elements 18 and proximal elements 16 while in an arrangement wherein the distal elements 18 are parallel to each other . this may prevent inconsistent compression of the tissue and may better accommodate tissues or leaflets of varying thicknesses . as shown in fig3 , the distal elements 18 may be drawn together and the proximal elements 16 may be retracted to form a low profile fixation device 14 . fig3 - 39 , 40 a - 40 d , 41 - 42 , 43 a - 43 c illustrate another embodiment of the fixation device 14 . in this embodiment , the device 14 is deliverable in the inverted position and moveable to the open position for grasping of the tissue . fig3 illustrates the fixation device 14 in the inverted position . the fixation device 14 includes a shaft 198 , proximal elements 16 and distal elements 18 . each distal element 18 has a proximal end 52 rotatably connected to the shaft 198 and a free end 54 . the fixation device 14 also includes an actuator rod 204 , a base 202 and a pair of deployment arms 200 attached to the base 202 as shown . in the inverted position , the extender 204 is extended and deployment arms 200 are disposed between the actuator rod 204 and the distal elements 18 . as shown in fig3 , the actuator rod 204 may be retracted so that the deployment arms 200 press against the distal elements 18 , rotating the distal elements 18 from the inverted position to the open position . the angle of the distal elements 18 may be adjusted by retracting or extending the actuator rod 204 various distances . as shown in fig3 , further retraction of the actuator rod 204 raises the distal elements 18 further . in the open position , tissue or leaflets may be grasped between the distal elements 18 and proximal elements 16 . fig3 illustrates the proximal elements 16 in their released position wherein the tissue or leaflet would be present therebetween . hereinafter , the tissue will be referred to as leaflets . in this embodiment , each distal element 18 includes an implant pledget 210 , typically press - fit or nested within each distal element 18 . the implant pledgets 210 will be attached to the leaflets by ties , such as sutures or wires , and will be used to hold the leaflets in desired coaptation . the implant pledgets 210 will then be separated from the fixation device 14 and will remain as an implant . to attach the implant pledgets 210 to the leaflets , the leaflets and implant pledgets 210 are punctured by fixation tools 220 , as shown in fig3 . the fixation tools 220 extend from the catheter 86 , pass through the leaflets and puncture the implant pledgets 210 . thus , the pledgets 210 are comprised of a puncturable material , such as structural mesh . the fixation tools 220 are used to deliver an anchor 222 as illustrated in larger view in fig4 a - 40d . fig4 a shows the fixation tool 220 including a sleeve 224 surrounding the fixation tool 220 and an anchor 222 loaded therebetween . in this embodiment , the anchor includes one or more flaps 228 which are held within the sleeve 224 . it may be appreciated that the anchor 222 may have any suitable form . additional exemplary embodiments of anchors are provided in commonly assigned u . s . pat . no . 6 , 752 , 813 incorporated herein for all purposes . a suture 226 is attached to the anchor 222 and extends through the sleeve 224 or on the outside of the sleeve 224 , as shown , to the catheter 86 . the fixation tools 220 are advanced so that the anchor 222 passes through the leaflet ( not shown ) and the pledget 210 , as shown in fig4 . referring now to fig4 b , the sleeve 224 is then retracted to expose the flaps 228 which releases the anchor 222 from the confines of the sleeve 224 . the flaps 228 extend radially outwardly , illustrated in fig4 c , by spring loading , shape memory or other self - expanding mechanism . thus , the flaps 228 are positioned against the distal side of the pledget 210 , the suture 226 passing through the pledget 210 and the leaflet , as shown in fig4 . at this point , the pledgets 210 can be removed from the distal elements 18 . by extending the actuator rod 204 distally , the base 202 draws the deployment arms 200 distally which returns the distal elements 18 to the inverted position , as shown in fig4 . since the pledgets 210 have been pierced by the fixation tools 220 and the anchors 222 have been deployed , the pledgets 210 and the leaflets disengage from distal elements 18 and remain in position . the proximal elements 16 may also be returned to their initial position as shown , using any of various mechanisms as have been described above in connection with other embodiments . referring now to fig4 d , the fixation tool 220 is then removed while the anchor 222 remains in place with suture 226 attached . the implant pledgets 210 are then separated from the fixation device 14 and left behind to maintain coaptation of the leaflets in the desired position . fig4 a - 43c illustrate the implant pledgets 210 from various perspective views . fig4 a provides a perspective top view showing that the pledgets 210 are connected by a link 230 that allows the pledgets 210 to be released from one side of the fixation device 14 . in addition , the sutures 226 are fixed together , either by knot tying or placement of a suture fastener 232 as shown . it may be appreciated that the suture fastener 232 may have any suitable form . additional exemplary embodiments of suture fasteners 232 are provided in commonly - assigned u . s . pat . no . 7 , 048 , 754 , which is incorporated herein by reference for all purposes . fig4 b provides a perspective bottom view showing the anchor 222 positioned against the bottom side of the pledget 210 . likewise , fig4 c provides a perspective side view also showing the anchor 222 positioned against the bottom side of the pledget 210 . fig4 a - 44b , 45 - 46 illustrate another embodiment of the fixation device 14 . as shown in fig4 a , the fixation device 14 is mounted on the shaft 12 and is comprised of distal elements 18 and a retention clip 36 comprised of a semi - rigid material having a folded shape . the material may be any suitable material providing rigidity with recoiling properties such as various metals or plastics . the folded shape is such that a fold 252 is directed distally and free ends 254 are directed proximally toward the distal elements 18 . penetration elements 256 are disposed near the free ends 254 and directed toward the shaft 12 . in addition , an opening 258 is located near the fold 252 , as illustrated in fig4 b which provides a perspectives view of the device 14 . referring back to fig4 a , the fold 252 is attached to an actuator rod 74 which passes through the shaft 12 and an arrow - shaped structure 260 is disposed on the shaft 12 between the free ends 254 , proximal to the opening 258 , as shown . in this arrangement , the fixation device 14 is advanced through the valve so that the distal elements 18 are disposed below the leaflets . the device may then be retracted proximally to capture the leaflets within the distal elements 18 . as shown in fig4 , retraction of the actuator rod 74 draws the retention clip 36 toward the distal elements 18 so that the sloping sides of the arrow - shaped structure 260 force the free ends 254 outward , away from the shaft 12 . further retraction of actuator rod 74 results in the sloping sides of arrow shaped structure 260 falling into the opening 258 in retention clip 36 , causing retention clip 36 to recoil back to the closed position as shown in fig4 , with the free ends 254 extending through the distal elements 18 . this allows the penetration elements 256 to penetrate the leaflets ( not shown ) to secure engagement therewith . the actuator rod 74 is then detached from the retention clip 36 and shaft 12 is detached from distal elements 18 which are left in place to hold the leaflets in a coapted arrangement . it may be appreciated that the foregoing embodiment may also include proximal elements 16 configured to be positioned on the upstream side of the valve leaflets to assist in the capture and fixation . such proximal elements may be mounted to shaft 12 so as to be removed following fixation of the leaflets , or the proximal elements may be connected to distal elements 18 and / or retention clip 36 to be implanted therewith . in further embodiments , the proximal elements may be manipulated to enhance gripping . for example , the proximal elements may be lowered to grasp leaflets or tissue between the proximal and distal elements , and then the proximal elements may be moved to drag the leaflets or tissue into the fixation device . in another example , the proximal elements may be independently lowered to grasp the leaflets or tissue . this may be useful for sequential grasping . in sequential grasping , one proximal element is lowered to capture a leaflet or tissue portion between the proximal and distal elements . the fixation device is then moved , adjusted or maneuvered to a position for grasping another leaflet or tissue portion between another set of proximal and distal elements . in this position , the second proximal element is then lowered to grasp this other leaflet or tissue portion . fig4 provides a perspective view of an embodiment of a delivery device or delivery catheter 300 which may be used to introduce and position a fixation device as described above . the delivery catheter 300 includes a shaft 302 , having a proximal end 322 and a distal end 324 , and a handle 304 attached to the proximal end 322 . a fixation device ( not shown ) is removably coupleable to the distal end 324 for delivery to a site within the body , typically for endovascular delivery to the mitral valve . thus , extending from the distal end 324 is a coupling structure 320 for coupling with a fixation device . also extending from the distal end 324 is an actuator rod 64 . the actuator rod 64 is connectable with the fixation device and acts to manipulate the fixation device , typically opening and closing the distal elements . such coupling to a fixation device is illustrated in fig4 . fig4 illustrates an embodiment of a fixation device 14 coupled to the distal end 324 of the delivery catheter 300 . the shaft 302 is shown having a nose 318 near its distal end 324 . in this embodiment , the nose 318 has a flanged shape . such a flanged shape prevents the nose 318 from being retracted into a guiding catheter or introducer as will be discussed in later sections . however , it may be appreciated that the nose 318 may have any shape including bullet , rounded , blunt or pointed , to name a few . extending from the nose 318 is a compression coil 326 through which the coupling structure 320 and actuator rod 64 pass . the actuator rod 64 is coupleable , as shown , with the stud 74 of the fixation device 14 . such coupling is illustrated in fig4 . fig4 illustrates a portion of the shaft 302 of the delivery catheter 300 and a fixation device 14 which is coupleable with the catheter 300 . passing through the shaft 302 is the actuator rod 64 . in this embodiment , the actuator rod 64 comprises a proximal extremity 303 and a distal extremity 328 , the distal extremity 328 of which is surrounded by a coil 330 . the proximal extremity 303 is typically comprised of stainless steel , nitinol , or elgiloy ®, to name a few , and may have a diameter in the range of 0 . 010 in . to 0 . 040 in ., preferably 0 . 020 in . to 0 . 030 in ., more preferably 0 . 025 in ., and a length in the range of 48 to 72 in . the distal extremity 328 may be tapered , is typically comprised of stainless steel , nitinol , or elgiloy ®, to name a few , and may have a diameter in the range of 0 . 011 to 0 . 025 in and a length in the range of 4 to 12 in . such narrowing increases flexibility of the distal end 324 of the actuator rod 64 . the actuator rod 64 further comprises a joiner 332 which is attached to the distal extremity 328 . the joiner 332 is removably attachable with stud 74 of the fixation device 14 . in this embodiment , the joiner 332 has internal threads which mate with external threads on the stud 74 of the fixation device 14 . as described previously , the stud 74 is connected with the distal elements 18 so that advancement and retraction of the stud 74 , by means of the actuator rod 64 , manipulates the distal elements . likewise , the coupling member 19 of the fixation device 14 mates with the coupling structure 320 of the catheter 300 . thus , the coupling member 19 and coupling structure 320 function as previously described in relation to fig6 a - 6b . referring back to fig4 , the fixation device 14 may also include a locking mechanism which includes a release harness 108 , as previously described in relation to fig1 - 21 . lock lines 92 are connected with the release harness 108 to lock and unlock the locking mechanism 106 as previously described . the lock lines 92 extend through the shaft 302 of the delivery catheter 300 and may connect with the release harness 108 in various arrangements as will be illustrated in later sections . similarly , proximal element lines 90 extend through the shaft 302 of the delivery catheter 300 and connect with the proximal elements 16 . the proximal elements 16 are raised and lowered by manipulation of the proximal element lines 90 as previously described . the proximal element lines 90 may connect with the proximal elements 16 in various arrangements as will be illustrated in later sections . referring back to fig4 , the handle 304 attached to the proximal end 322 of the shaft 302 is used to manipulate the coupled fixation device 14 and to optionally decouple the fixation device 14 for permanent implantation . as described , the fixation device 14 is primarily manipulated by the actuator rod 64 , proximal element lines 90 and lock lines 92 . the actuator rod 64 manipulates the distal elements 18 , the proximal element lines 90 manipulate the proximal elements 16 and the lock lines 92 manipulate the locking mechanism . in this embodiment , the actuator rod 64 may be translated ( extended or retracted ) to manipulate the distal elements 18 . this is achieved with the use of the actuator rod control 314 which will be described in later sections . the actuator rod 64 may also be rotated to engage or disengage the threaded joiner with the threaded stud 74 . this is achieved with the use of the actuator rod handle 316 which will also be described in later sections . further , the proximal element lines 90 may be extended , retracted , loaded with various amounts of tension or removed with the use of the proximal element line handle 312 . and , the lock lines 92 may be may be extended , retracted , loaded with various amounts of tension or removed with the use of the lock line handle 310 . both of these handles 310 , 312 will be described in more detail in later sections . the actuator rod handle 316 , actuator rod control 314 , proximal element line handle 312 and lock line handle 310 are all joined with a main body 308 within which the actuator rod 64 , proximal element lines 90 and lock lines 92 are guided into the shaft 302 . the handle 304 further includes a support base 306 connected with the main body 308 . the main body 308 is slideable along the support base 306 to provide translation of the shaft 302 . further , the main body 308 is rotatable around the support base 306 to rotate the shaft . fig5 illustrates a cross - sectional view of the delivery catheter shaft 302 of fig4 . in this embodiment , the shaft 302 has a tubular shape with inner lumen 348 and is comprised of a material which provides hoop strength while maintaining flexibility and kink resistance , such as a braided laminated material . such material may include stainless steel braided or coiled wire embedded in a polymer such as polyurethane , polyester , pebax , grilamid tr55 , and aesno to name a few . to provide further support and hoop strength , a support coil 346 is disposed within the lumen 348 of shaft 302 as illustrated in fig5 . passing through the support coil 346 are a variety of elongated bodies , including tubular guides and cylindrical rods . for example , one type of tubular guide is a compression coil 326 extending through lumen 348 from the proximal end 322 to the distal end 324 of the shaft 302 , and the actuator rod 64 extends through the compression coil 326 . therefore , the compression coil typically has a length in the range of 48 to 60 in . and an inner diameter in the range of 0 . 020 to 0 . 035 in . to allow passage of the actuator rod 64 therethrough . the actuator rod 64 is manipulable to rotate and translate within and relative to the compression coil 326 . the compression coil 326 allows lateral flexibility of the actuator rod 64 and therefore the shaft 302 while resisting buckling and providing column strength under compression . the compression coil may be comprised of 304v stainless steel to provide these properties . to provide additional tensile strength for the shaft 302 and to minimize elongation , a tension cable 344 may also pass through the support coil 346 . the tension cable 344 extends through lumen 348 from the proximal end 322 to the distal end 324 of the shaft 302 . therefore , the tension cable 344 typically has a diameter in the range of 0 . 005 in . to 0 . 010 in . and a length in the range of 48 to 60 in . in preferred embodiments , the tension cable 344 is comprised of 304v stainless steel . in addition , at least one lock line shaft 341 having a tubular shape may be present having a lock line lumen 340 through which lock lines 92 pass between the lock line handle 310 and the locking mechanism 106 . the lock line shaft 341 extends through lumen 348 from the proximal end 322 to the distal end 324 of the shaft 302 . therefore , the lock line shaft 341 typically has a length in the range of 48 to 60 in ., an inner diameter in the range of 0 . 016 to 0 . 030 in ., and an outer diameter in the range of 0 . 018 to 0 . 034 in . in preferred embodiments , the lock line shaft 341 is comprised of a 304v stainless steel coil however other structures or materials may be used which provide kink resistance and compression strength . similarly , at least one proximal element line shaft 343 having a tubular shape may be present having a proximal element line lumen 342 . proximal element lines 90 pass through this lumen 342 between the proximal element line handle 312 and the proximal elements 16 . thus , the proximal element line shaft 343 extends through lumen 348 from the proximal end 322 to the distal end 324 of the shaft 302 . therefore , the proximal element line shaft 343 typically has a length in the range of 48 to 60 in ., an inner diameter in the range of 0 . 016 to 0 . 030 in ., and an outer diameter in the range of 0 . 018 to 0 . 034 in . in preferred embodiments , the proximal element line shaft 343 is comprised of a 304v stainless steel coil however other structures or materials may be used which provide kink resistance and compression strength . in this embodiment , the elongated bodies ( compression coil 326 enclosed actuator rod 64 , tension cable 344 , lock line shaft 342 , proximal element line shaft 343 ) each “ float ” freely in inner lumen 348 within the support coil 346 and are fixed only at the proximal end 322 and distal end 324 of shaft 302 . the lumen 348 is typically filled and flushed with heparinized saline during use . alternatively or in addition , the lumen 348 may be filled with one or more fillers , such as flexible rods , beads , extruded sections , gels or other fluids . preferably the fillers allow for some lateral movement or deflection of the elongated bodies within lumen 348 but in some cases may restrict such movement . typically , the elongated bodies are fixed at the proximal and distal ends of the shaft and are free to move laterally and rotationally therebetween . such freedom of movement of the elongated bodies provides the shaft 302 with an increased flexibility as the elongated bodies self - adjust and reposition during bending and / or torquing of the shaft 302 . it may be appreciated that the elongated bodies may not be fixed at the proximal and distal ends . the elongated bodies are simply unconstrained relative to the shaft 302 in at least one location so as to be laterally moveable within the lumen 348 . preferably the elongated bodies are unrestrained in at least a distal portion of the catheter , e . g . 5 - 15 cm from the distal end 324 , so as to provide maximum flexibility in the distal portion . it may be appreciated , however , that alternate shaft 302 designs may also be used . for example , referring to fig5 , in this embodiment the shaft 302 again has a tubular shape with an inner lumen 348 and a support coil 346 disposed within the lumen 348 of shaft 302 . filling the inner lumen 348 within the support coil 346 is an extrusion 334 having lumens through which pass a variety of elongated bodies , including the compression coil 326 enclosed actuator rod 64 , tension cable 344 , lock line shafts 342 , and proximal element line shafts 343 , as shown . the support coil 346 and elongated bodies may have the same geometries and be comprised of the same materials as described above in relation to fig5 . alternatively , as shown in fig5 , the shaft 302 may include an internal partition 350 to create multiple lumens within the shaft 302 . for example , the partition 350 may have a central lumen 352 for passage of the actuator rod 64 , optionally surrounded by the compression coil 326 . in addition , the partition 350 may also create at least one lock line lumen 340 for passage of a lock line 92 and at least one proximal element line lumen 341 for passage of a proximal element line 90 . optionally , each of the lumens defined by partition 350 may be lined with a kink - resistant element , such as a coil as in previous embodiments . fig5 a - 52c illustrate embodiments of the nose 318 of the shaft 302 . in fig5 a , the nose 318 comprises a tip ring 280 and a lock ring 282 . in preferred embodiments , epoxy and pebax are deposited between the tip ring 280 and the lock ring 282 to bond them together . the lock ring 282 has a geometry to mate with the tip ring 280 to maintain relative alignment between the two . fig5 b illustrates another embodiment of the nose 318 of the shaft 302 . here , the tip ring 280 is covered by a soft tip 284 to provide a more atraumatic tip and a smoother transition to the shaft . as mentioned previously , when lock lines 92 are present , the lines 92 pass through at least one lock line lumen 340 between the lock line handle 310 and the locking mechanism 106 . the lock lines 92 engage the release harnesses 108 of the locking mechanism 106 to lock and unlock the locking mechanism 106 as previously described . the lock lines 92 may engage the release harnesses 108 in various arrangements , examples of which are illustrated in fig5 a - 53c . in each embodiment , two lock line lumens 340 are present within the shaft 302 of the delivery catheter 300 terminating at the nose 318 . the lumens 340 are disposed on alternate sides of the actuator rod 64 so that each lumen 340 is directed toward a release harness 108 . fig5 a illustrates an embodiment wherein two lock lines 92 , 92 ′ pass through a single lock line lumen 340 and are threaded through a release harness 108 on one side of the actuator rod 64 ( the actuator rod 64 is shown without surrounding housing such as coupling structure , for clarity ). the lock lines 92 , 92 ′ are then separated so that each lock line passes on an opposite side of the actuator rod 64 . the lock lines 92 , 92 ′ then pass through the release harness 108 ′ on the opposite side of the actuator rod 64 and continue together passing through a another single lock line lumen 340 ′. this lock line arrangement is the same arrangement illustrated in fig4 . fig5 b illustrates an embodiment wherein one lock line 92 passes through a single lock line lumen 340 , is threaded through a release harness 108 on one side of the actuator rod 64 , and is returned to the lock line lumen 340 . similarly , another lock line 92 ′ passes through another single lock line lumen 340 ′, is threaded through a different release harness 108 ′ located on the opposite side of the actuator rod 64 , and is returned to the another single lock line lumen 340 ′. fig5 c illustrates an embodiment wherein both lock lines 92 , 92 ′ pass through a single lock line lumen 340 . one lock line 92 is threaded through a release harness 108 on one side of the actuator rod 64 and is then passed through another lock line lumen 340 ′ on the opposite side of the actuator rod 64 . the other lock line 92 ′ is threaded through another release harness 108 ′ on the other side of the actuator rod 64 ′ and is then passed through the another lock line lumen 340 ′ with the previous lock line 92 . it may be appreciated that a variety of lock line arrangements may be used and are not limited to the arrangements illustrated and described above . the various arrangements allow the harnesses 108 to be manipulated independently or jointly , allow various amounts of tension to be applied and vary the force required for removal of the lock lines when the fixation device is to be left behind . for example , a single lock line passing through one or two lumens may be connected to both release harnesses for simultaneous application of tension . as mentioned previously , when proximal element lines 90 are present , the lines 90 pass through at least one proximal element line lumen 342 between the proximal element line handle 312 and at least one proximal element 16 . the proximal element lines 90 engage the proximal elements 16 to raise or lower the element 16 as previously described . the proximal element lines 90 may engage the proximal elements 16 in various arrangements , examples of which are illustrated in fig5 a - 54b . in each embodiment , two proximal element line lumens 342 are present within the shaft 302 of the delivery catheter 300 terminating at the nose 318 . the lumens 342 are disposed on alternate sides of the actuator rod 64 ( the actuator rod 64 is shown without surrounding housing such as coupling structure , for clarity ) so that each lumen 342 is directed toward a proximal element 16 . fig5 a illustrates an embodiment wherein one proximal element line 90 passes through a single proximal element line lumen 342 . the proximal element line 90 is threaded through an eyelet 360 of a proximal element 16 on one side of the actuator rod 64 , passes over the actuator rod 64 and is threaded through an eyelet 360 ′ of another proximal element 16 ′ on the other side of the actuator rod 64 . the proximal element line 90 then passes through another single proximal element line lumen 342 ′. this proximal element line arrangement is the same arrangement illustrated in fig4 . fig5 b illustrates an embodiment wherein one proximal element line 90 passes through a single proximal element line lumen 342 , is threaded through an eyelet 360 of a proximal element 16 on one side of the actuator rod 64 , and is returned to the proximal element line lumen 342 . similarly , another proximal element line 90 ′ passes through another single proximal element line lumen 342 ′ on the opposite side of the actuator rod 64 , and is returned to the another single proximal element line lumen 342 ′. it may be appreciated that a variety of proximal element line arrangements may be used and are not limited to the arrangements illustrated and described above . the various arrangements allow the proximal elements to be manipulated independently or jointly , allow various amounts of tension to be applied and vary the force required for removal of the proximal element lines when the fixation device is to be left behind . for example , a single proximal element line passing through one or two lumens in shaft 302 may be used for simultaneous actuation of both proximal elements . fig5 illustrates an embodiment of the handle 304 of the delivery catheter 300 . as mentioned previously , the actuator rod handle 316 , actuator rod control 314 , proximal element line handle 312 and lock line handle 310 are all joined with the main body 318 . the handle 304 further includes a support base 306 connected with the main body 308 . the main body 308 is slideable along the support base 306 to provide translation of the shaft 302 and the main body 308 is rotatable around the support base 306 to rotate the shaft . fig5 provides a partial cross - sectional view of the main body 308 of the handle 304 depicted in fig5 . as shown , the main body 308 includes a sealed chamber 370 within which the actuator rod 64 , proximal element lines 90 and lock lines 92 are guided into the shaft 302 . the sealed chamber 370 is in fluid communication with the inner lumen 348 of shaft 302 and is typically filled with saline and flushed with heparin or heparinized saline . the sealed chamber 370 has a seal 372 along its perimeter to prevent leakage and the introduction of air to the chamber 370 . any air in the chamber 370 may be bled from the chamber 370 by one or more luers 374 which pass through the main body 308 into the chamber 370 as illustrated in fig5 . in this embodiment , the handle 304 includes two such luers 374 , one on each side of the main body 308 ( second luer symmetrically positioned on backside of main body 308 in fig5 , hidden from view ). referring now to fig5 , the sealed chamber 370 also has various additional seals , such as an actuator rod seal 376 which surrounds the actuator rod 64 where the actuator rod 64 enters the sealed chamber 370 , and a shaft seal 378 which surrounds the shaft 302 where the shaft 302 enters the sealed chamber 370 . as mentioned previously , the lock lines 92 may be may be extended , retracted , loaded with various amounts of tension or removed using the lock line handle 310 . likewise , the proximal element lines 90 may be extended , retracted , loaded with various amounts of tension or removed using the proximal element line handle 312 . both of these handles 310 , 312 may be similarly designed to manipulate the appropriate lines 90 , 92 passing therethrough . fig5 illustrates an embodiment of a lock line handle 310 having lock lines 92 passing therethrough . the lock line handle 310 has a distal end 384 , a proximal end 382 and an elongate shaft 383 therebetween . the distal end 382 is positionable within the sealed chamber 370 so that the proximal end 382 extends out of the chamber 370 , beyond the main body 308 . the free ends of the lock lines 92 are disposed near the proximal end 382 , passing through the wall of the handle 310 near a threaded nub 390 . the handle 310 further includes a cap 388 which is positionable on the nub 309 . internal threading with the cap 388 mates with the threading on the threaded nub 390 so that the cap 388 holds the free ends of the lock lines 92 between the cap 388 and the nub 390 and / or other portions of the handle 310 by friction . the lock lines 92 pass through a central lumen ( not shown ) of the elongate shaft 383 , extend through the sealed chamber 370 ( as shown in fig5 ) and extend through the shaft 302 to the locking mechanism 106 . disposed near the distal end 384 of the handle 310 is at least one wing 392 . in the embodiment of fig5 , two wings 392 are present , each wing 392 disposed on opposite sides of the elongate shaft 383 . the wings 392 extend radially outwardly and curve proximally so that a portion is parallel to the elongate shaft 383 , as shown . it may be appreciated that the wings 392 may alternatively have the shape of solid or continuous protrusions which extend radially and have a portion which is parallel to the elongate shaft 383 . the wings 392 are used to hold the lock line handle 310 in a desired position which in turn holds the lock under a desired load of tension , as will be described further below . the handle 310 also includes a finger grip 386 near the proximal end 382 which extends radially outwardly in alignment with the radial extension of the at least one wing 392 . thus , the user may determine the orientation of the wings 392 within the sealed chamber 370 from the orientation of the finger grip 386 outside of the main body 308 . the finger grip 386 may also serve an ergonomic purpose to assist in manipulating the handle 310 . the portion of the wings 392 parallel to the elongate shaft 383 have grooves or serrations 394 . the serrations 394 are used to apply tension to the lock lines 92 . as shown in fig5 a , the lock line handle 310 is positioned within a semi - tube 400 which is disposed within the sealed chamber 370 . the semi - tube 400 comprises a top half 402 and a bottom half 404 , each half 402 , 404 having grooves or serrations 406 which mate with the serrations 394 of the wings 392 . thus , when the wings 392 are rotated to mate the serrations 394 , 406 , as shown in fig5 a , the elongate shaft 383 is held in place . likewise , the wings 392 may be rotated , as shown in fig5 b , so that the wings 392 are disposed between the halves 402 , 404 and the serrations 394 , 406 are disengaged . in this position , the shaft 383 may be translated to apply or release tension in the lock lines 92 . thus , tension in the lines 92 may be adjusted by rotating the shaft 383 to disengage the serrations 394 , 406 , translating the shaft 383 and then rotating the shaft 383 back to reengage the serrations 394 , 406 . alternatively , the finger grip 386 may be pulled to apply tension to the lock lines 92 . pulling the finger grip 386 translates the lock line handle 310 within the semi - tube 400 . such translation is achievable due to angling of the serrations 394 , 406 and flexibility of wings 382 . however , the angling of the serrations 394 , 406 prevents translation in the opposite direction , i . e . by pushing the finger grip 386 . therefore , to release tension from the lock lines 92 , the shaft 383 is rotated to disengage the serrations 394 , 406 , allowing translation of the shaft 383 , and then the shaft 383 is rotated back to reengage the serrations 394 , 406 . to remove the lock lines 92 , the cap 388 is removed from the threaded nub 390 exposing the free ends of the lock lines 92 . if one lock line 92 is present having two free ends , continuous pulling on one of the free ends draws the entire length of lock line 92 out of the catheter 300 . if more than one lock line 92 is present , each lock line 92 will have two free ends . continuous pulling on one of the free ends of each lock line 92 draws the entire length of each lock line 92 out of the catheter 300 . it may be appreciated that the proximal element line handle 312 has corresponding features to the lock line handle 310 and operates in the same manner as illustrated in fig5 a , 58 a - 58 b . it may also be appreciated that other mechanisms may be used for manipulating the lock lines 92 and proximal element lines 90 , such as including buttons , springs , levers and knobs . the actuator rod 64 may be manipulated using the actuator rod control 314 and the actuator rod handle 316 . fig5 provides a cross - sectional view of a portion of the handle 304 which includes the actuator rod control 314 and the actuator rod handle 316 . the actuator rod handle 316 is located at the proximal end of the handle 314 . the actuator rod handle 316 is fixedly attached to the proximal end of the actuator rod 64 . the actuator rod 64 is inserted through a collet 426 which is disposed within a holder 428 as shown . the holder 428 has external threads 434 which mate with internal threads 432 of the actuator rod control 314 . thus , rotation of the actuator rod control 314 causes the holder 428 to translate along the actuator rod control 314 by action of the threading , as will be described in more detail below . the actuator rod control 314 is rotatably coupled with the main body 308 of the handle 304 and is held in place by a lip 430 . referring to fig5 a , the actuator rod control 314 may be manually rotated in a clockwise or counter clockwise direction , as indicated by arrow 436 . rotation of the actuator rod control 314 translates ( extends or retracts ) the actuator rod 64 to manipulate the distal elements 18 of the fixation device 14 . specifically , rotation of the actuator rod control 314 causes the external threads 434 of the adjacent holder 428 to translate along the mated internal threads 432 of the actuator rod control 314 . rotation of the holder 428 itself is prevented by holding pins 424 which protrude from the holder 428 and nest into grooves 438 in the main body 308 of the handle 304 . as the holder 428 translates , each holding pin 424 translates along its corresponding groove 438 . since the collet 426 is attached to the holder 428 , the collet 426 translates along with the holder 428 . to simultaneously translate the actuator rod 64 , the actuator rod 64 is removably attached to the collet 426 by a pin 422 . the pin 422 may have any suitable form , including a clip - shape which partially wraps around the collet 426 as illustrated in fig5 . thus , rotation of the actuator rod control 314 provides fine control of translation of the actuator rod 64 and therefore fine control of positioning the distal elements 18 . referring to fig5 b , removal of the pin 422 , as shown , allows disengagement of the actuator rod handle 316 and fixedly attached actuator rod 64 from the collet 426 . once disengaged , the actuator rod 64 may be rotated , as indicated by arrow 440 , by manually rotating the actuator rod handle 316 . as described previously , rotation of the actuator rod 64 engages or disengages the threaded joiner 332 of the delivery catheter 300 from the threaded stud 74 of the fixation device 14 . this is used to attach or detach the fixation device 14 from the delivery catheter 300 . in addition , when the actuator rod 64 is in the disengaged state , the actuator rod 64 may optionally be retracted and optionally removed from the catheter 300 by pulling the actuator rod handle 316 and withdrawing the actuator rod 64 from the handle 304 . depending on the application , the location of the target site , and the approach selected , the devices of the invention may be modified in ways well known to those of skill in the art or used in conjunction with other devices that are known in the art . for example , the delivery catheter may be modified in length , stiffness , shape and steerability for a desired application . likewise , the orientation of the fixation device relative to the delivery catheter may be reversed or otherwise changed . the actuation mechanisms may be changed to be driven in alternate directions ( push to open , pull to close , or pull to open , push to close ). materials and designs may be changed to be , for example , more flexible or more rigid . and , the fixation device components may be altered to those of different size or shape . further , the delivery catheter of the present invention may be used to deliver other types of devices , particularly endovascular and minimally invasive surgical devices used in angioplasty , atherectomy , stent - delivery , embolic filtration and removal , septal defect repair , tissue approximation and repair , vascular clamping and ligation , suturing , aneurysm repair , vascular occlusion , and electrophysiological mapping and ablation , to name a few . thus , the delivery catheter of the present invention may be used for applications in which a highly flexible , kink - resistant device is desirable with high compressive , tensile and torsional strength . referring to fig6 , an embodiment of a multi - catheter guiding system 1 of the present invention is illustrated . the system 1 comprises an outer guide catheter 1000 , having a proximal end 1014 , a distal end 1016 , and a central lumen 1018 therethrough , and an inner guide catheter 1020 , having a proximal end 1024 , distal end 1026 and central lumen 1028 therethrough , wherein the inner guide catheter 1020 is positioned coaxially within the central lumen 1018 of the outer guide catheter 1000 , as shown . the distal ends 1016 , 1026 of catheters 1000 , 1020 , respectively , are sized to be passable to a body cavity , typically through a body lumen such as a vascular lumen . thus , the distal end 1016 preferably has an outer diameter in the range of approximately 0 . 040 in . to 0 . 500 in ., more preferably in the range of 0 . 130 in . to 0 . 320 in . the central lumen 1018 is sized for the passage of the inner guide catheter 1020 ; the distal end 1026 preferably has an outer diameter in the range of approximately 0 . 035 in . to 0 . 280 in ., more preferably 0 . 120 in to 0 . 200 in . the central lumen 1028 is sized for the passage of a variety of devices therethrough . therefore , the central lumen 1028 preferably has an inner diameter in the range of approximately 0 . 026 in . to 0 . 450 in ., more preferably in the range of 0 . 100 in . to 0 . 180 in . fig6 illustrates an interventional catheter 1030 positioned within the inner guide catheter 1020 which may optionally be included in system 1 , however other interventional devices may be used . the interventional catheter 1030 has a proximal end 1034 and a distal end 1036 , wherein an interventional tool 1040 is positioned at the distal end 1036 . in this embodiment , the interventional tool 1040 comprises a detachable fixation device or clip . optionally , the interventional catheter 1030 may also include a nosepiece 1042 having a stop 1043 , as shown . the stop 1043 prevents the interventional tool 1040 from entering the central lumen 1028 of the inner guide catheter 1020 . thus , the interventional catheter 1030 may be advanced and retracted until the stop 1043 contacts the distal end 1026 of the inner guiding catheter 1020 preventing further retraction . this may provide certain advantages during some procedures . it may be appreciated that in embodiments which include such a stop 1043 , the interventional catheter 1030 would be pre - loaded within the inner guide catheter 1020 for advancement through the outer guiding catheter 1000 or both the interventional catheter 1030 and the inner guiding catheter 1020 would be pre - loaded into the outer guiding catheter 1000 for advancement to the target tissue . this is because the stop 1043 prevents advancement of the interventional catheter 1030 through the inner guiding catheter 1020 . the outer guide catheter 1000 and / or the inner guide catheter 1020 are precurved and / or have steering mechanisms , embodiments of which will be described later in detail , to position the distal ends 1016 , 1026 in desired directions . precurvature or steering of the outer guide catheter 1000 directs the distal end 1016 in a first direction to create a primary curve while precurvature and / or steering of the inner guide catheter 1020 directs distal end 1026 in a second direction , differing from the first , to create a secondary curve . together , the primary and secondary curves form a compound curve . advancement of the interventional catheter 1030 through the coaxial guide catheters 1000 , 1020 guides the interventional catheter 1030 through the compound curve toward a desired direction , usually in a direction which will allow the interventional catheter 1030 to reach its target . steering of the outer guide catheter 1000 and inner guide catheter 1020 may be achieved by actuation of one or more steering mechanisms . actuation of the steering mechanisms is achieved with the use of actuators which are typically located on handles connected with each of the catheters 1000 , 1020 . as illustrated in fig6 , handle 1056 is connected to the proximal end 1014 of the outer guide catheter 1000 and remains outside of the patient &# 39 ; s body during use . handle 1056 includes steering actuator 1050 which may be used to bend , are or reshape the outer guide catheter 1000 , such as to form a primary curve . handle 1057 is connected to the proximal end ( not shown ) of the inner guide catheter 1020 and may optionally join with handle 1056 to form one larger handle , as shown . handle 1057 includes steering actuator 1052 which may be used to bend , arc or reshape the inner guide catheter 1020 , such as to form a secondary curve and move the distal end 1026 of the inner guide catheter 1020 through an angle theta , as will be described in a later section . in addition , locking actuators 1058 , 1060 may be used to actuate locking mechanisms to lock the catheters 1000 , 1020 in a particular position . actuators 1050 , 1052 , 1058 , 1060 are illustrated as buttons , however it may be appreciated that these and any additional actuators located on the handles 1056 , 1057 may have any suitable form including knobs , thumbwheels , levers , switches , toggles , sensors or other devices . other embodiments of the handles will be described in detail in a later section . in addition , the handle 1056 may include a numerical or graphical display 1061 of information such as data indicating the position the catheters 1000 , 1020 , or force on actuators . it may also be appreciated that actuators 1050 , 1052 , 1058 , 1060 and any other buttons or screens may be disposed on a single handle which connects with both the catheters 1000 , 1020 . fig6 a - 61d illustrate examples of positions that the catheters 1000 , 1020 may hold . referring to fig6 a , the outer guide catheter 1000 may be precurved and / or steered into a position which includes a primary curve 1100 . the primary curve 1100 typically has a radius of curvature 1102 in the range of approximately 0 . 125 in . to 1 . 000 in ., preferably in the range of approximately 0 . 250 in . to 0 . 500 in . or forms a curve in the range of approximately 0 ° to 120 °. as shown , when the position includes only a primary curve 1100 , the distal end 16 lies in a single plane x . an axis x , transversing through the center of the central lumen 18 at the distal end 16 , lies within plane x . referring to fig6 b , the inner guide catheter 1020 extends through the central lumen 1018 of the outer guide catheter 1000 . the inner guide catheter 1020 may be precurved and / or steered into a position which includes a secondary curve 1104 . the secondary curve 1104 typically has a radius of curvature 10600 in the range of approximately 0 . 050 in . to 0 . 750 in ., preferably in the range of approximately 0 . 125 in . to 0 . 250 in . or forms a curve in the range of approximately 0 ° to 180 °. the secondary curve 1104 can lie in the same plane as the primary curve 1100 , plane x , or it can lie in a different plane , such as plane z as shown . in this example , plane z is substantially orthogonal to plane x . axis z , transversing through the center of the central lumen 1028 of the inner guide catheter 1020 at the distal end 1026 , lies within plane z . in this example , axis x and axis z are at substantially 90 degree angles to each other ; however , it may be appreciated that axis x and axis z may be at any angle in relation to each other . also , although in this example the primary curve 1100 and the secondary curve 1104 lie in different planes , particularly in substantially orthogonal planes , the curves 1100 , 1104 may alternatively lie in the same plane . referring now to fig6 c , the inner guide catheter 1020 may be further manipulated to allow the distal end 1026 to move through an angle theta 1070 . the angle theta 1070 is in the range of approximately − 180 ° to + 180 °, typically in the range of − 90 ° to + 90 °, possibly in the range of − 60 ° to + 60 °, − 45 ° to + 45 °, − 30 ° to + 30 ° or less . as shown , the angle theta 1070 lies within a plane y . in particular , axis y , which runs through the center of the central lumen 1028 at the distal end 1026 , forms the angle theta 1070 with axis z . in this example , plane y is orthogonal to both plane x and plane z . axes x , y , z all intercept at a point within the central lumen 1028 which also coincides with the intersection of planes x , y , z . similarly , fig6 d illustrates movement of the distal end 1026 through an angle theta 1070 on the opposite side of axis z . again , the angle theta 1070 is measured from the axis z to the axis y , which runs through the center of the central lumen 1016 at the distal end 1026 . as shown , the angle theta 1070 lies in plane y . thus , the primary curve 1100 , secondary curve 1104 , and angle theta 1070 can all lie in different planes , and optionally in orthogonal planes . however , it may be appreciated that the planes within which the primary curve 1100 , secondary curve 1104 and angle theta 1070 lie may be mutually dependent and therefore would allow the possibility that some of these lie within the same plane . in addition , the outer guide catheter 1000 may be pre - formed and / or steerable to provide additional curves or shapes . for example , as illustrated in fig6 a , an additional curve 1110 may be formed by the outer guide catheter 1000 proximal to the primary curve 1100 . in this example , the curve 1110 provides lift or raises the distal end 1016 of the outer guide catheter 1000 , which in turn raises the distal end 1026 of the inner guide catheter 1020 . such lifting is illustrated in fig6 b . here , the system 1 is shown prior to lifting in dashed line wherein the axis y ′ passes through the intersection of axis z and axis x ′. after application of curve 1110 , the distal portion of the system 1 is lifted in the direction of axis z so that axis x ′ is raised to axis x ″ and axis y ′ is raised to axis y ″. this raises distal end 1026 to a desired height . the articulated position of the multi - catheter guiding system 1 illustrated in fig6 a - 61d and fig6 a - 62b is particularly useful for accessing the mitral valve . fig6 a - 63d illustrate a method of using the system 1 for accessing the mitral valve mv . to gain access to the mitral valve , the outer guide catheter 1000 may be tracked over a dilator and guidewire from a puncture in the femoral vein , through the inferior vena cava and into the right atrium . as shown in fig6 a , the outer guide catheter 1000 may be punctured through a fossa f in the interatrial septum s . the outer guide catheter 1000 is then advanced through the fossa f and curved by the primary curve 1100 so that the distal end 1016 is directed over the mitral valve mv . again , it may be appreciated that this approach serves merely as an example and other approaches may be used , such as through the jugular vein , femoral artery , port access or direct access , to name a few . positioning of the distal end 1016 over the mitral valve mv may be accomplished by precurvature of the outer guide catheter 1000 , wherein the catheter 1000 assumes this position when the dilator and guidewire are retracted , and / or by steering of the outer guide catheter 1000 to the desired position . in this example , formation of the primary curve 1100 moves the distal end 1016 within a primary plane , corresponding to previous plane x , substantially parallel to the valve surface . this moves the distal end 1016 laterally along the short axis of the mitral valve mv , and allows the distal end 1016 to be centered over the opening o between the leaflets lf . referring to fig6 b , the inner guide catheter 1020 is advanced through the central lumen 1018 of the outer guide catheter 1000 and the distal end 1026 is positioned so that the central lumen 1028 is directed toward the target tissue , the mitral valve mv . in particular , the central lumen 1028 is to be directed toward a specific area of the mitral valve mv , such as toward the opening o between the valve leaflets lf , so that a particular interventional procedure may be performed . in fig6 b , the inner guide catheter 1020 is shown in a position which includes a secondary curve 1104 in a secondary plane , corresponding to previous plane z . formation of the secondary curve 1104 moves the distal end 1026 vertically and angularly between the commissures c , directing the central lumen 1028 toward the mitral valve mv . in this position an interventional device or catheter 1030 which is passed through the central lumen 1028 would be directed toward and / or through the opening o . although the primary curve 1100 and the secondary curve 1104 may be varied to accommodate different anatomical variations of the valve mv and different surgical procedures , further adjustment may be desired beyond these two curvatures for proper positioning of the system 1 . referring to fig6 c , the distal end 1026 of the inner guide catheter 1020 may be positioned through an angle theta 1070 . this moves the distal end 1026 vertically and angularly through a theta plane , corresponding to previous plane y . movement of the distal end 1026 through the angle theta 1070 in either direction is shown in dashed line in fig6 b . such movement can be achieved by precurvature and / or by steering of the catheter 1020 . consequently , the central lumen 1028 can be directed toward the mitral valve mv within a plane which differs from the secondary plane . after such movements , the inner guide catheter 1020 will be in a position so that the opening of the central lumen 1028 at the end 1016 faces the desired direction . in this case , the desired direction is toward the center of and orthogonal to the mitral valve . in some instances , it is desired to raise or lower the distal end 1026 so that it is at a desired height in relation to the mitral valve mv . this may be accomplished by precurvature and / or by steering of the outer guide catheter 1000 to form additional curve 1110 . generally this is used to lift the distal end 1026 above the mitral mv wherein such lifting was illustrated in fig6 b . when the curvatures in the catheters 1000 , 1020 are formed by steering mechanisms , the steering mechanisms may be locked in place by a locking feature . locking can provide additional stiffness and stability in the guiding system 1 for the passage of interventional devices or catheters 1030 therethrough , as illustrated in fig6 . the interventional catheter 1030 can be passed through the central lumen 1028 toward the target tissue , in this case the mitral valve mv . positioning of the distal end 1026 over the opening o , as described above , allows the catheter 1030 to pass through the opening o between the leaflets lf if desired , as shown in fig6 d . at this point , any desired procedure may be applied to the mitral valve for correction of regurgitation or any other disorder . as described previously , the curvatures may be formed in the catheters 1000 , 1020 by precurving , steering or any suitable means . precurving involves setting a specific curvature in the catheter prior to usage , such as by heat setting a polymer or by utilizing a shape - memory alloy . since the catheters are generally flexible , loading of the catheter on a guidewire , dilator obturator or other introductory device straightens the catheter throughout the curved region . once the catheter is positioned in the anatomy , the introductory device is removed and the catheter is allowed to relax back into the precurved setting . to provide a higher degree of control and variety of possible curvatures , steering mechanisms may be used to create the curvatures and position the catheters . in some embodiments , the steering mechanisms comprise cables or pullwires within the wall of the catheter . as shown in fig6 a , the outer guide catheter 1000 may include a pullwire 1120 slidably disposed in lumens within the wall of the catheter 1000 extending to the distal end 1016 . by applying tension to the pullwire 1120 in the proximal direction , the distal end 1016 curves in the direction of the pullwire 1120 as illustrated by arrow 1122 . likewise , as shown in fig6 a , placement of the pullwire 1120 along the opposite side of the catheter 1000 will allow the distal end 1016 to curve in the opposite direction , as illustrated by arrow 1124 , when tension is applied to the pullwire 1120 . thus , referring to fig6 c , diametrically opposing placement of pullwires 1120 within the walls of the catheter 1000 allows the distal end 1016 to be steered in opposite directions . this provides a means of correcting or adjusting a curvature . for example , if tension is applied to one pullwire to create a curvature , the curvature may be lessened by applying tension to the diametrically opposite pullwire . referring now to fig6 d , an additional set of opposing pullwires 1120 ′ may extend within the wall of the catheter 1000 as shown . this combination of pullwires 1120 , 1120 ′ allows curvature of the distal end in at least four directions illustrated by arrows 1122 , 1124 , 1126 , 1128 . in this example , pullwires 1120 create the primary curve 1100 of the outer guide catheter 1000 and the pullwires 1120 ′ create the lift . it may be appreciated that fig6 a - 64d also pertain to the inner guide catheter 1020 . for example , in fig6 d , pullwires 1120 may create the secondary curve 1104 of the inner guide catheter 1020 and the pullwires 1120 ′ create the angle theta 1070 . such pullwires 1120 and / or pullwires 1120 ′ and associated lumens may be placed in any arrangement , singly or in pairs , symmetrically or nonsymmetrically and any number of pullwires may be present . this may allow curvature in any direction and about various axes . the pullwires 1120 , 1120 ′ may be fixed at any location along the length of the catheter by any suitable method , such as gluing , tying , soldering , or potting , to name a few . when tension is applied to the pullwire , the curvature forms from the point of attachment of the pullwire toward the proximal direction . therefore , curvatures may be formed throughout the length of the catheter depending upon the locations of the points of attachment of the pullwires . typically , however , the pullwires will be attached near the distal end of the catheter , optionally to an embedded tip ring 280 , illustrated in fig6 e . as shown , the pullwire 1120 passes through an orifice 286 in the tip ring 280 , forms a loop shape and then passes back through the orifice 286 and travels back up through the catheter wall ( not shown ). in addition , the lumens which house the pullwires may be straight , as shown in fig6 a - 64d , or may be curved . the outer guide catheter 1000 and inner guide catheter 1020 may have the same or different construction which may include any suitable material or combination of materials to create the above described curvatures . for clarity , the examples provided will be in reference to the outer guide catheter 1000 , however it may be appreciated that such examples may also apply to the inner guide catheter 1020 . in embodiments in which the catheter is precurved rather than steerable or in addition to being steerable , the catheter 1000 may be comprised of a polymer or copolymer which is able to be set in a desired curvature , such as by heat setting . likewise , the catheter 1000 may be comprised of a shape - memory alloy . in embodiments in which the catheter is steerable , the catheter 1000 may be comprised of one or more of a variety of materials , either along the length of the catheter 1000 or in various segments . example materials include polyurethane , pebax , nylon , polyester , polyethylene , polyimide , polyethylenetelephthalate ( pet ), polyetheretherketone ( peek ). in addition , the walls of the catheter 1000 may be reinforced with a variety of structures , such as metal braids or coils . such reinforcements may be along the length of the catheter 1000 or in various segments . for example , referring to fig6 a , the catheter 1000 may have a proximal braided segment 1150 , a coiled segment 1152 and distal braided segment 1154 . the proximal braided segment 1150 provides increased column strength and torque transmission . the coiled segment 1152 provides increased steerability . the distal braided segment 1154 provides a blend of steerability and torque / column strength . in another example , referring to fig6 b , the outer guiding catheter 1000 has a proximal double - layer braided segment 1151 and a distal braided segment 1154 . thus , the proximal double - layer segment 1151 comprises a multi - lumen tube 1160 ( having steering lumens 1162 for pullwires , distal ends of the steering lumens 1162 optionally embedded with stainless steel coils for reinforcement , and a central lumen 1163 ), an inner braided layer 1164 , and an outer braided layer 1166 , as illustrated in the cross - sectional view of fig6 c . similarly , fig6 d provides a cross - sectional view of the distal braided segment 1154 comprising the multi - lumen tube 1160 and a single braided layer 1168 . in a further example , referring to fig6 e , the inner guiding catheter 1020 comprises a multi - lumen tube 1160 without reinforcement at its proximal end , a single braided layer middle segment 1170 and a single braided layer distal segment 1171 . each of the single braided layer segments 1170 , 1171 have a multi - lumen tube 1160 and a single layer of braiding 1168 , as illustrated in cross - sectional view fig6 f . however , the segments 1170 , 1171 are comprised of polymers of differing durometers , typically decreasing toward the distal end . fig6 g illustrates an other example of a cross - section of a distal section of an outer guiding catheter 1000 . here , layer 1130 comprises 55d pebax and has a thickness of approximately 0 . 0125 in . layer 1131 comprises a 30 ppi braid and has a thickness of approximately 0 . 002 in . by 0 . 0065 in . layer 1132 comprises 55d pebax and has a thickness of approximately 0 . 006 in . layer 1133 comprises 30 ppi braid and has a thickness of approximately 0 . 002 in by 0 . 0065 in . and finally , layer 1134 comprises nylon 11 and includes steering lumens for approximately 0 . 0105 in . diameter pullwires 1120 . central lumen 1163 is of sufficient size for passage of devices . fig6 h - 65i illustrate additional examples of cross - sections of an inner guiding catheter 1020 , fig6 i illustrating a cross - section of a portion of the distal end and fig6 i illustrating a cross - section of a more distal portion of the distal end . referring to fig6 h , layer 1135 comprises 40d polymer and has a thickness of approximately 0 . 0125 in . layer 1136 comprises a 30 ppi braid and has a thickness of approximately 0 . 002 in . by 0 . 0065 in . layer 1137 comprises 40d polymer and has a thickness of approximately 0 . 006 in . layer 1138 comprises a 40 d polymer layer and has a thickness of approximately 0 . 0035 in . and finally , layer 1139 comprises a 55d liner . in addition , coiled steering lumens are included for approximately 0 . 0105 in . diameter pullwires 1120 . and , central lumen 1163 is of sufficient size for passage of devices . referring to fig6 i , layer 1140 comprises a 40d polymer , layer 1141 comprises a 35d polymer , layer 1142 comprises a braid and layer 1143 comprises a liner . in addition , coiled steering lumens 1144 are included for pullwires . and , central lumen 1163 is of sufficient size for passage of devices . fig6 a - 66c illustrate an embodiment of a keying feature which may be incorporated into the catheter shafts . the keying feature is used to maintain relationship between the inner and outer guide catheters to assist in steering capabilities . as shown in fig6 a , the inner guide catheter 1020 includes one or more protrusions 1400 which extend radially outwardly . in this example , four protrusions 1400 are present , equally spaced around the exterior of the catheter 1020 . likewise , the outer guide catheter 1000 includes corresponding notches 1402 which align with the protrusions 1400 . thus , in this example , the catheter 1000 includes four notches equally spaced around its central lumen 1018 . thus , the inner guide catheter 1020 is able to be translated within the outer guide catheter 1000 , however rotation of the inner guide catheter 1020 within the outer guide catheter 1000 is prevented by the keying feature , i . e . the interlocking protrusions 1400 and notches 1402 . such keying helps maintain a known correlation of position between the inner guide catheter 1020 and outer guide catheter 1000 . since the inner and outer guide catheters 1020 , 1000 form curvatures in different directions , such keying is beneficial to ensure that the compound curvature formed by the separate curvatures in the inner and outer guide catheters 1020 , 1000 is the compound curvature that is anticipated . keying may also increase stability wherein the curvatures remain in position reducing the possibility of compensating for each other . fig6 b illustrates a cross - sectional view of the outer guiding catheter 1000 of fig6 a . here , the catheter 1000 includes a notched layer 1404 along the inner surface of central lumen 1018 . the notched layer 1404 includes notches 1402 in any size , shape , arrangement and number . optionally , the notched layer 1404 may include lumens 1406 , typically for passage of pullwires 1120 . however , the lumens 1406 may alternatively or in addition be used for other uses . it may also be appreciated that the notched layer 1404 may be incorporated into the wall of the catheter 1000 , such as by extrusion , or may be a separate layer positioned within the catheter 1000 . further , it may be appreciated that the notched layer 1404 may extend the entire length of the catheter 1000 or one or more portions of the length of the catheter 1000 , including simply a small strip at a designated location along the length of the catheter 1000 . fig6 c illustrates a cross - sectional view of the inner guiding catheter 1020 of fig6 a . here , the catheter 1020 includes protrusions 1400 along the outer surface of the catheter 1020 . the protrusions 1400 may be of any size , shape , arrangement and number . it may be appreciated that the protrusions 1400 may be incorporated into the wall of the catheter 1020 , such as by extrusion , may be included in a separate cylindrical layer on the outer surface of the catheter 1020 , or the protrusions 1400 may be individually adhered to the outer surface of the catheter 1020 . further , it may be appreciated that the protrusions 1400 may extend the entire length of the catheter 1000 or one or more portions of the length of the catheter 1020 , including simply a small strip at a designated location along the length of the catheter 1020 . thus , the keying feature may be present along one or more specific portions of the catheters 1000 , 1020 or may extend along the entire length of the catheters 1000 , 1020 . likewise , the notches 1402 may extend along the entire length of the outer guiding catheter 1020 while the protrusions 1400 extend along discrete portions of the inner guiding catheter 1000 and vice versa . it may further be appreciated that the protrusions 1400 may be present on the inner surface of the outer guiding catheter 1000 while the notches 1402 are present along the outer surface of the inner guiding catheter 1020 . alternatively or in addition , one or more steerable portions of the catheter 1000 may comprise a series of articulating members 1180 as illustrated in fig6 a . exemplary embodiments of steerable portions of catheters comprising such articulating members 1180 are described in u . s . patent application ser . no . 10 / 441 , 753 incorporated herein by reference for all purposes . fig6 b illustrates the outer guide catheter 1000 having a steerable portion comprising articulating members 1180 at its distal end 1016 . briefly , referring to fig6 a , each articulating member 1180 may have any shape , particularly a shape which allows interfitting or nesting as shown . in addition , it is desired that each member 1180 have the capability of independently rotating against an adjacent articulating member 1180 . in this embodiment , the articulating members 1180 comprise interfitting domed rings 1184 . the domed rings 1184 each include a base 1188 and a dome 1186 . the base 1188 and dome 1186 have a hollow interior which , when the domed rings 1184 are interfit in a series , forms a central lumen 1190 . in addition , the dome 1186 allows each articulating member 1180 to mate against an inner surface of an adjacent domed ring 1184 . the interfitting domed rings 1184 are connected by at least one pullwire 1120 . such pullwires typically extend through the length of the catheter 1000 and at least one of the interfitting domed rings 1184 to a fixation point where the pullwire 1120 is fixedly attached . by applying tension to the pullwire 1120 , the pullwire 1120 arcs the series of interfitting domed rings 1184 proximal to the attachment point to form a curve . thus , pulling or applying tension on at least one pullwire , steers or deflects the catheter 1000 in the direction of that pullwire 1120 . by positioning various pullwires 1120 throughout the circumference of the domed rings 1184 , the catheter 1000 may be directed in any number of directions . also shown in fig6 a , each interfitting domed ring 1184 may comprise one or more pullwire lumens 1182 through which the pullwires 1120 are threaded . alternatively , the pullwires 1120 may be threaded through the central lumen 1190 . in any case , the pullwires are attached to the catheter 1000 at a position where a desired curve is to be formed . the pullwires 1120 may be fixed in place by any suitable method , such as soldering , gluing , tying , welding or potting , to name a few . such fixation method is typically dependent upon the materials used . the articulating members 1180 may be comprised of any suitable material including stainless steel , various metals , various polymers or co - polymers . likewise the pullwires 1120 may be comprised of any suitable material such as fibers , sutures , metal wires , metal braids , or polymer braids . as mentioned previously , manipulation of the guide catheters 1000 , 1020 is achieved with the use of handles 1056 , 1057 attached to the proximal ends of the catheters 1000 , 1020 . fig6 illustrates a preferred embodiment of handles 1056 , 1057 . as shown , handle 1056 is attached to the proximal end 1014 of outer guide catheter 1000 and handle 1057 is attached to the proximal end 1024 of inner guide catheter 1020 . inner guide catheter 1020 is inserted through handle 1056 and is positioned coaxially within outer guide catheter 1000 . in this embodiment , the handles 1056 , 1057 are not linked together as shown in the embodiment illustrated in fig6 . it may be appreciated that such handles 1056 , 1057 may alternatively be connected by external connecting rods , bars or plates or by an additional external stabilizing base . an embodiment of a stabilizing base will be described in a later section . referring back to fig6 , interventional catheter is inserted through handle 1057 and is positioned coaxially within inner guide catheter 1020 and outer guide catheter 1000 . each handle 1056 , 1057 includes two steering knobs 1300 a , 1300 b emerging from a handle housing 1302 for manipulation by a user . steering knobs 1300 a are disposed on a side of the housing 1302 and steering knobs 1300 b are disposed on a face of the housing 1302 . however , it may be appreciated that such placement may vary based on a variety of factors including type of steering mechanism , size and shape of handle , type and arrangement of parts within handle , and ergonomics to name a few . fig6 illustrates the handles 1056 , 1057 of fig6 with a portion of the housing 1302 removed to reveal the assemblies of the handles . each knob 1300 a , 1300 b controls a steering mechanism which is used to form a curvature in the attached catheter . each steering mechanism includes a hard stop gear assembly 1304 and a friction assembly 1306 . tension is applied to one or more pullwires by action of the hard stop gear assembly to form a curve in a catheter . tension is maintained by the friction assembly . when tension is released from the one or more pullwires the catheter returns to a straightened position . fig7 illustrates steering mechanisms within a handle wherein the housing 1302 is removed for clarity . here , steering knob 1300 a is attached to a hard stop gear assembly 1304 and a friction assembly ( not in view ) and steering knob 1300 b is attached to a separate hard stop gear assembly 1304 and friction assembly 1306 . steering knob 1300 a is attached to a knob post 1318 which passes through a base 1308 , terminating in a knob gear wheel 1310 . the knob gear wheel 1310 actuates the hard stop gear assembly 1304 , thereby applying tension to one or more pullwires 1120 . the knob gear wheel 1310 is a toothed wheel that engages a disk gear wheel 1312 . rotation of the steering knob 1300 a rotates the knob post 1318 and knob gear wheel 1310 which in turn rotates the disk gear wheel 1312 . rotation of the disk gear wheel 1312 applies tension to one or more pullwires extending through the attached catheter , in this example the outer guiding catheter 1000 . as shown , the outer guiding catheter 1000 passes through the base 1308 , wherein one or more pullwires 1120 extending through the catheter 1000 are attached to the disk 1314 . such attachment is schematically illustrated in fig7 . catheter 1000 is shown passing through base 1308 . a pullwire 1120 passing through a steering lumen 1162 in the catheter 1000 emerges from the wall of the catheter 1000 , passes through an aperture 1320 in the disk 1314 and is attached to an anchor peg 1316 on the disk 1314 . rotation of the disk 1314 ( indicated by arrow 1328 ) around disk post 1315 by action of the disk gear wheel 1312 , applies tension to the pullwire 1120 by drawing the pullwire 1120 through the aperture 1320 and wrapping the pullwire 1120 around the disk 1314 as it rotates . additional rotation of the disk 1314 applies increasing tension to the pullwire 1120 . to limit the amount of tension applied to the pullwire 1120 , to limit curvature of the catheter and / or to avoid possible breakage of the pullwire 1120 , the rotation of the disk 1314 may be restricted by hard stop peg 1322 which is attached to the disk 1314 and extends into the base 1308 . fig7 a - 72b illustrate how the hard stop peg 1322 is used to restrict rotation of disk 1314 . fig7 a - 72b provide a top view , wherein the disk 1314 is disposed on the base 1308 . the anchor peg 1316 is shown with the pullwire 1120 thereattached . a groove 1326 is formed in the base 1308 beneath the disk 1314 and forms an arc shape . the hard stop peg 1322 extends from the disk 1314 into the groove 1326 in the base 1308 . referring now to fig7 b , rotation of the disk 1314 around knob post 1318 , indicated by arrow 1330 , draws the pullwire 1120 through the aperture 1320 as previously described , wrapping the pullwire 1120 around the disk 1314 . as the disk 1314 rotates , the hard stop peg 1322 follows along the groove 1326 , as shown . the disk 1314 continues rotating until the hard stop peg 1322 reaches a hard stop 1324 . the hard stop 1324 is positioned in the groove 1326 and prevents further passage of the hard stop peg 1322 . thus , disk 1314 rotation may be restricted to any degree of rotation less than or equal to 360 degrees by positioning of the hard stop 1324 . in some instances , it is desired to restrict rotation of the disk 1314 to a degree of rotation which is more than 360 degrees . this may be achieved with another embodiment of the hard stop gear assembly 1304 . referring now to fig7 a - 73b , a portion of such a hard stop gear assembly 1304 is shown . fig7 a illustrates the base 1308 and the disk post 1315 positioned therethrough . also shown in the base 1308 is an aperture 1334 through which the knob post 1318 , knob gear wheel 1310 and friction assembly 1306 pass , and a passageway 1336 through which the catheter 1000 passes . in this embodiment of the hard stop gear assembly 1304 , a groove 1326 is also present in an arc shape around the disk post 1315 , however a ball 1332 is positioned in the groove 1326 rather than a hard stop peg 1322 . disk 1314 is positioned over the groove 1326 and the ball 1332 as shown in fig7 b . the disk 1314 , illustrated in fig7 c , has a groove 1356 in its surface which is positioned adjacent to the base 1308 , the groove 1356 having an arc shape similar to the groove 1326 in the base 1308 . the ball 1332 is not fixedly attached to the base 1308 or the disk 1314 and is therefore free to move along the channel formed by the groove 1326 in the base 1308 and the groove in the disk 1314 . fig7 a - 74f illustrate how rotation of the disk 1314 may be restricted by the ball 1332 to a degree of rotation which is more than 360 degrees . fig7 a - 74f illustrate the groove 1326 in the base 1308 wherein the groove 1326 has an arc shape around disk post 1315 . the groove 1326 does not form a complete circle ; a first groove end 1350 a and a second groove end 1350 b form a wall which prevent passage of the ball 1332 . it may be appreciated that the groove ends 1350 a , 1350 b may be any distance apart , shortening the length of the groove 1326 by any amount , and allowing the ball 1332 movement , and hence catheter deflection , to be adjusted to any desired amount . to begin , referring to fig7 a , the ball 1332 is positioned within the groove 1326 near the first groove end 1350 a . the disk 1314 has a matching groove 1352 ( shape illustrated in dashed line ) including a first groove end 1354 a and a second groove end 1354 b . the disk 1314 is positioned over the ball 1332 so that the ball 1332 is near the second groove end 1354 b . referring now to fig7 b , the disk 1314 may be rotated while the ball 1332 remains in place . here , the disk 1314 has rotated 90 degrees , as indicated by arrow 36000 and the position of the groove ends 1354 a , 1354 b . referring now to fig7 c , the disk 1314 may be further rotated while the ball 1332 remains in place . here , the disk 1314 has rotated 270 degrees , as indicated by arrow 36000 and the position of the groove ends 1354 a , 1354 b . the disk 1314 may continue rotating to 360 degrees , as shown in fig7 d , indicated by arrow 36000 . here , the first groove end 1354 a in the disk 1314 has contacted the ball 1332 and pushes the ball 1332 along groove 1326 in the base . referring now to fig7 e , the disk 1314 may be further rotated while the ball 1332 is pushed along the groove 1326 in the base 1308 by the first groove end 1354 a in the disk 1314 . here , the disk 1314 is shown to have rotated 540 degrees . referring to fig7 f , the disk 1314 rotates until the ball 1332 reaches the second groove end 1350 b of the base 1308 , providing a hard stop . in this position , the ball 1332 is held between the first groove end 1354 a of the disk 1314 and the second groove end 1350 b of the base 1308 and further rotation of the disk 1314 is prevented . thus , the disk 1314 was rotated approximately 660 degrees in this example . any maximum degree of rotation may be set by positioning of groove ends 1350 a , 1350 b and / or groove ends 1354 a , 1354 b . additionally , in some embodiments , rotation can be limited by adding more than one ball 1332 to the groove 1326 , for example , two , three , four , five , six , seven , eight , nine , ten or more balls may be used to limit travel and hence curvature . it may be appreciated that one or more pullwires 1120 are attached to the disk 1314 in a manner similar to that illustrated in fig7 . therefore , as the disk 1314 rotates , around disk post 1315 by action of the disk gear wheel 1312 , tension is applied to the pullwire 1120 by drawing the pullwire 1120 through the aperture 1320 and wrapping the pullwire 1120 around the disk 1314 as it rotates . additional rotation of the disk 1314 applies increasing tension to the pullwire 1120 . restriction of rotation as described above limits the amount of tension applied to the pullwire 1120 , to limit curvature of the catheter and / or to avoid possible breakage of the pullwire 1120 . as mentioned , each steering mechanism includes at least a hard stop gear assembly 1304 and a friction assembly 1306 . as described above , tension is applied to one or more pullwires by action of the hard stop gear assembly to form a curve in a catheter . tension is maintained by the friction assembly . fig7 illustrates an embodiment of a friction assembly 1306 . the friction assembly 1306 essentially holds a steering knob , in this example steering knob 1300 b , and the associated knob post 1318 in a rotated position . here , rotation of the knob 1300 b and post 1318 rotates attached knob gear wheel 1310 . the knob gear wheel 1310 actuates the hard stop gear assembly 1304 , thereby applying tension to one or more pullwires 1120 . the knob gear wheel 1310 is a toothed wheel that engages a disk gear wheel 1312 . rotation of the steering knob 1300 b rotates the knob post 1318 and knob gear wheel 1310 which in turn rotates the disk gear wheel 1312 . rotation of the disk gear wheel 1312 applies tension to one or more pullwires extending through the attached catheter , in this example the outer guiding catheter 1000 . the steering knob 1300 b and knob post 1318 are held in a rotated position by friction provided by a frictional pad 1370 . the frictional pad 1370 is positioned between ring 1372 attached to the knob post 1318 and a plate 1374 attached to the base 1308 . the knob post 1318 extends from the knob 1300 b through the ring 1372 , the frictional pad 1370 and then the plate 1374 . the plate 1374 has internal threads which mate with threads on the knob post 1318 . as the knob post 1318 rotates , the threads on the post 1318 advance through the threads on the plate 1374 . this draws the ring 1372 closer to the plate 1374 , compressing the frictional pad 1370 therebetween . frictional pad 1370 may be comprised of any o - ring or sheet material with desirable frictional and compressibility characteristics , such as silicone rubber , natural rubber or synthetic rubbers , to name a few . in preferred embodiments , an epdm rubber o - ring is used . reverse rotation of the knob post 1318 is resisted by friction of the frictional pad 1370 against the ring 1372 . the higher the compression of the frictional pad 1370 the stronger the frictional hold . therefore , as the steering knob 1300 b is rotated and increasing amounts of tension are applied to the pullwires 1120 , increasing amounts of friction are applied to the ring 1372 to hold the knob 1300 b in place . manual reverse rotation of the steering knob 1300 b releases tension on the pullwires 1120 and draws the ring 1372 away from the plate 1374 thereby reducing the frictional load . when tension is released from the pullwires 1120 the catheter 1000 returns toward a straightened position . it may be appreciated that each handle 1056 , 1057 includes a steering mechanism for each curve to be formed in the attached catheter . thus , as shown in fig6 , handle 1056 includes a steering mechanism to form the primary curve 1100 in outer guiding catheter 1000 and a steering mechanism to form the additional curve 1110 . likewise , handle 1057 includes a steering mechanism to form the secondary curve 1104 in inner guiding catheter 1020 and a steering mechanism to form the angle theta 1070 . some curves , such as the primary curve 1100 , secondary curve 1104 and additional curve 1110 each typically vary in curvature between a straight configuration and a curved configuration in a single direction . such movement may be achieved with single set of a hard stop gear assembly 1304 and a friction assembly 1306 . however , other curves , such as the angle theta 1070 , may be formed in two directions as shown in fig6 c - 61d . such movement is achieved with two sets of the hard stop gear assembly 1304 and the friction assembly 1306 , each set controlling curvature in a single direction . fig7 illustrates the presence of an additional set of the friction assembly 1306 ′. one or more pullwires 1120 ′, such as an opposing set as illustrated in fig6 d , extending within the wall of the catheter 1000 are attached to the disk 1314 ′ in the same manner as pullwires 1120 are attached to disk 1314 . the disks 1314 , 1314 ′ are arranged so that rotation of steering knob 1300 b in one direction applies tension to the pullwires 1120 via disk 1314 and rotation of steering knob 1300 b in the opposite direction applies tension to the pullwires 1120 ′ via disk 1314 ′. likewise , the additional friction assembly 1306 ′ is shown having a ring 1372 ′ attached to the knob post 1318 and a frictional pad 1370 ′ disposed between the ring 1372 ′ and the opposite side of the plate 1374 . therefore , as rotation of the steering knob 1300 b in the opposite direction applies tension to the pullwires 1120 ′ via disk 1314 ′, the frictional pad 1370 ′ applies tension to the ring 1372 ′ holding the knob post 1318 ′ in place . it may be appreciated that various other mechanisms may be used for tensioning and holding pullwires 1120 in place . example mechanisms that may alternatively be used include clutches , ratchets , levers , knobs , rack and pinions , and deformable handles , to name a few . fig7 illustrates an embodiment of an interventional system 3 of the present invention . an embodiment of the multi - catheter guiding system 1 of the present invention is shown comprising an outer guide catheter 1000 , having a proximal end 1014 and a distal end 1016 , and an inner guide catheter 1020 , having a proximal end 1024 and a distal end 1026 , wherein the inner guide catheter 1020 is positioned coaxially within the outer guide catheter 1000 , as shown . in addition , a hemostatic valve 1090 is disposed within handle 1056 or external to handle 1056 as shown to provide leak - free sealing with or without the inner guide catheter 1020 in place . the valve 1090 also prevents back bleeding and reduces the possibility of air introduction when inserting the inner guide catheter 1020 through the outer guide catheter 1000 . an example of a hemostatic valve 1090 is illustrated in fig7 a , however any suitable valve or hemostatic valve may be used to provide similar functions . in fig7 a , the valve 1090 has a first end 1091 , a second end 1092 and a lumen 1093 therethrough . the inner wall of lumen 1093 is preferably tapered toward end 1091 and may further include a plurality of tapered axial channels configured to receive the protrusions 1400 on the inner guide catheter 1020 . the first end 1091 is attached to the outer guide catheter 1000 and the second end 1092 is free . referring now back to fig7 , the distal ends 1016 , 1026 of catheters 1000 , 1020 , respectively , are sized to be passable to a body cavity , typically through a body lumen such as a vascular lumen . to assist in inserting the fixation device 14 through a hemostatic valve 1090 , a fixation device introducer may be used . for example , when the fixation device 14 is loaded on a delivery catheter 300 and an inner guide catheter 1020 , insertion of the fixation device 14 , delivery catheter 300 and inner guide catheter 1020 through an outer guide catheter 1000 involves passing the fixation device 14 through a hemostatic valve 1090 on the outer guide catheter 1000 . to reduce any trauma to the fixation device 14 by the hemostatic valve 1090 , a fixation device introducer may be used . an embodiment of a fixation device introducer 1420 is illustrated in fig7 b . the introducer 1420 includes a loading body 1422 and an insertion endpiece 1424 . the fixation device 14 is loaded into the loading body 1422 and into the insertion endpiece 1424 to approximately the dashed line 1428 . the insertion endpiece 1424 has a split end creating individual split sections 1430 , in this embodiment , four split sections 1430 . by compressing the split sections 1430 , the endpiece 1424 forms a taper . such a taper is then inserted through a hemostatic valve 1090 , so that the insertion endpiece 1424 creates a smooth passageway through the valve for the fixation device 14 . once the insertion endpiece 1424 is inserted through the valve 1090 , the fixation device 14 , and attached delivery catheter 300 and inner guide catheter 1020 , may then be advanced through the fixation device introducer 1420 . the fixation device introducer 1420 also includes a hemostatic valve within the loading body 1422 to prevent any backbleeding or leakage through the introducer 1420 . manipulation of the guide catheters 1000 , 1020 is achieved with the use of handles 1056 , 1057 attached to the proximal ends of the catheters 1000 , 1020 . as shown , handle 1056 is attached to the proximal end 1014 of outer guide catheter 1000 and handle 1057 is attached to the proximal end 1024 of inner guide catheter 1020 . inner guide catheter 1020 is inserted through handle 1056 and is positioned coaxially within outer guide catheter 1000 . an embodiment of the delivery catheter 300 of the present invention is inserted through handle 1057 and is positioned coaxially within inner guide catheter 1020 and outer guide catheter 1000 . therefore , a hemostatic valve 1090 is disposed within handle 1057 or external to handle 1057 as shown to provide leak - free sealing with or without the delivery catheter 300 in place . the valve 1090 functions as described above . the delivery catheter 300 includes a shaft 302 , having a proximal end 322 and a distal end 324 , and a handle 304 attached to the proximal end 322 . a fixation device 14 is removably coupled to the distal end 324 for delivery to a site within the body . the outer guide catheter 1000 and / or the inner guide catheter 1020 are precurved and / or have steering mechanisms to position the distal ends 1016 , 1026 in desired directions . precurvature or steering of the outer guide catheter 1000 directs the distal end 1016 in a first direction to create a primary curve while precurvature and / or steering of the inner guide catheter 1020 directs distal end 1026 in a second direction , differing from the first , to create a secondary curve . together , the primary and secondary curves form a compound curve . advancement of the delivery catheter 300 through the coaxial guide catheters 1000 , 1020 guides the delivery catheter 300 through the compound curve toward a desired direction , usually in a direction which will position the fixation device 14 in a desired location within the body . fig7 illustrates portions of another embodiment of an interventional system 3 of the present invention . handles 1056 , 1057 of the multi - catheter guiding system 1 of the present invention are shown . each handle 1056 , 1057 includes a set of steering knobs 1300 a , 1300 b , as shown . manipulation of the guide catheters 1000 , 1020 is achieved with the use of the steering knobs 1300 a , 1300 b attached to the proximal ends of the catheters 1000 , 1020 . handle 304 of the delivery catheter 300 is also shown , including the proximal element line handle 312 , the lock line handle 310 , the actuator rod control 314 and the actuator rod handle 316 , among other features . the handle 304 is supported by the support base 306 which is connected to the handle 1057 . it may be appreciated the above described systems 3 are not intended to limit the scope of the present invention . the systems 3 may include any or all of the components of the described invention . in addition , the multi - catheter guiding system 1 of the present invention may be used to introduce other delivery catheters , interventional catheters or other devices . likewise , the delivery catheter 300 may be introduced through other introducers or guiding systems . also , the delivery catheter 300 may be used to deliver other types of devices to a target location within the body , including endoscopic staplers , devices for electrophysiology mapping or ablation , septal defect repair devices , heart valves , annuloplasty rings and others . in addition , many of the components of the system 3 may include one or more hydrophilic coatings . hydrophilic coatings become slippery when wet , eliminate the need for separate lubricants . thus , such coatings may be present on the multi - catheter guiding system , delivery catheter , and fixation device , including the proximal elements and distal elements , to name a few . further , the system 3 may be supported by an external stabilizer base 1440 , an embodiment of which is illustrated in fig7 . stabilizer base 1440 maintains the relative positions of the outer guide , inner guide and delivery catheter during a procedure . in this embodiment , the base 1440 comprises a platform 1442 having a planar shape for positioning on or against a flat surface , such as a table or benchtop . the base 1440 further includes a pair of handle holders 1444 , 1448 , each attached to the platform 1442 and extending upwardly from the platform 1442 , either angularly or perpendicularly . handle holder 1444 includes a notch 1446 for holding the outer guiding catheter 1000 , as illustrated in fig7 , thereby supporting the handle 1056 . fig7 shows the handle 1056 attached to the outer guiding catheter 1000 positioned so that the proximal end 1014 of the outer guiding catheter 1000 rests in the notch 1446 . referring back to fig7 , handle holder 1448 includes an elongate portion 1452 having a trough 1450 and a hooked end 1454 . as shown in fig8 , handle 1057 rests on the elongate portion 1452 and the handle 304 rests on hooked end 1454 so that the inner guiding catheter 1020 extends from the handle 1057 to the handle 1056 and continues on within outer guiding catheter 1000 . the handle 304 is additionally supported by support base 306 , as shown . it may be appreciated that the stabilizer base 1440 may take a variety of forms and may include differences in structural design to accommodate various types , shapes , arrangements and numbers of handles . referring now to fig8 , kits 1500 according to the present invention comprise any of the components described in relation to the present invention . the kits 1500 may include any of the components described above , such as the outer guide catheter 1000 including handle 1056 , the inner guide catheter 1020 including handle 1057 , the delivery catheter 300 and the fixation device 14 and instructions for use ifu . optionally , any of the kits may further include any other system components described above , such as various interventional tools 1040 , or components associated with positioning a device in a body lumen , such as a guidewire 1202 , dilator 1206 or needle 1204 . the instructions for use ifu will set forth any of the methods as described above , and all kit components will usually be packaged together in a pouch 1505 or other conventional medical device packaging . usually , those kit components which will be used in performing the procedure on the patient will be sterilized and maintained within the kit . optionally , separate pouches , bags , trays or other packaging may be provided within a larger package , where the smaller packs may be opened separately to separately maintain the components in a sterile fashion . while the foregoing is a complete description of the preferred embodiments of the invention , various alternatives , substitutions , additions , modifications , and equivalents are possible without departing from the scope of the invention . for example , in many of the above - described embodiments , the invention is described in the context of approaching a valve structure from the upstream side — that is , the atrial side in the case of a mitral valve . it should be understood that any of the foregoing embodiments may be utilized in other approaches as well , including from the ventricular or downstream side of the valve , as well as using surgical approaches through a wall of the heart . moreover , the invention may be used in the treatment of a variety of other tissue structures besides heart valves , and will find usefulness in a variety of tissue approximation , attachment , closure , clamping and ligation applications , some endovascular , some endoscopic , and some open surgical . again , although the foregoing invention has been described in some detail by way of illustration and example , for purposes of clarity of understanding , it will be obvious that various alternatives , modifications and equivalents may be used and the above description should not be taken as limiting in scope of the invention which is defined by the appended claims .
the invention provides devices , systems and methods for tissue approximation and repair at treatment sites . the devices , systems and methods of the invention will find use in a variety of therapeutic procedures , including endovascular , minimally - invasive , and open surgical procedures , and can be used in various anatomical regions , including the abdomen , thorax , cardiovascular system , heart , intestinal tract , stomach , urinary tract , bladder , lung , and other organs , vessels , and tissues . the invention is particularly useful in those procedures requiring minimally - invasive or endovascular access to remote tissue locations , where the instruments utilized must negotiate long , narrow , and tortuous pathways to the treatment site . in addition , many of the devices and systems of the invention are adapted to be reversible and removable from the patient at any point without interference with or trauma to internal tissues .