fig1 is a perspective view of lead 10 according to the present invention , which is shown implanted in a heart 4 . as seen in this embodiment , an implantable pulse generator 2 is coupled to a lead 10 by connector 5 as is well known in the art . pulse generator 2 may be any model capable of sensing and stimulating two or more chambers of the heart 4 with at least one situated on the left side of heart 4 . as further seen , in this embodiment , lead 10 may feature include one or more ring electrodes disposed along the lead body . in the illustrated embodiment , two ring electrodes 7 ( right atrium ) and 9 ( left atrium ) are shown . this embodiment further includes a helix 28 which extends beyond the distal end of the lead 10 . upon deployment , the helix expands and wedges within the coronary sinus , cardiac veins , or another vessel . this ensures excellent contact is maintained between the electrode 28 and the heart while also maintaining the lead 10 at the predetermined site of implant . the present invention permits the lead 10 to reliably pace and / or sense the right atrium , the left atrium , the left ventricle or any combination thereof by the electrodes 7 , 9 , and 28 respectively . fig2 is a plan view of one embodiment of the inventive lead . the bipolar lead 10 of this embodiment is stylet - activated , and includes an active fixation mechanism . lead 10 further includes a flexible , elongate lead body 12 covered by an insulative sleeve , such as polyurethane or silicone rubber . terminal assembly 14 is provided at the proximal end for coupling lead 10 to an implantable pulse generator 2 ( fig1 ). terminal assembly 14 has sealing rings 16 and terminal pin 18 , all of a type known in the art . an anchoring sleeve 20 ( shown partially in cross - section ) may also be provided for suturing lead body 12 to body tissue . anchoring sleeve 20 and terminal assembly 14 are preferably fabricated from silicone rubber , although they may also be constructed of any other suitable biocompatible material known in the art . the lead 10 of fig2 is further shown to include stylet guide 22 and stylet assembly 24 coupled to terminal pin 18 . the stylet assembly 24 imparts stiffness to lead 10 during placement . the stylet further actuates fixation helix 28 in a manner described below . stylet guide 22 and stylet assembly 24 are typically discarded after use and before connection of terminal pin 18 to pulse generator 2 ( fig1 ). other types of stiffening members as known in the art may be used in the alternative for this purpose . with continued reference to fig2 , an electrode and fixation assembly designated generally as 26 is disposed at the distal end of lead body 12 . in the illustrated embodiment , lead 10 is of the multi - polar , single pass configuration as may be adapted for placement in the coronary sinus or another vessel . the assembly 26 includes a distal helix electrode 28 , and a ring electrode 9 positioned proximal to the distal end . as will be appreciated by those of ordinary skill in the art , helix electrode 28 and ring electrode 9 are coupled to separate , insulated lead conductors ( not shown in fig2 ) that extend substantially the length of lead body 12 . lead conductors are preferably configured as concentric multi - filar coils of a platinum - iridium alloy or any other suitable alloy , such as mp35n . this configuration allows for a longitudinal lumen that extends along the length of lead body 12 and that is adapted to receive stylet assembly 24 . the lead may include one or more additional electrodes such as right atrium electrode 7 ( fig1 ). fig3 illustrates a cutaway side view of the fixation assembly 26 of lead 10 with helix 28 deployed . in this embodiment , fixation assembly 26 includes a stylet socket 62 that is slidably disposed in a piston - like fashion within the cylindrical interior of helix sleeve 46 . stylet socket is preferably made of hard plastic , which is molded to retain helix 28 , which extends axially outward from stylet socket 62 . stylet socket 62 includes a coupling member such as axially - oriented slot 66 formed therein , which may include a flared opening 68 corresponding to screwdriver tip 25 of stylet 24 . the embodiment of fig3 further includes a conductor coil 42 which defines a lumen for stylet 24 . conductor 42 terminates at helix sleeve 46 . in one embodiment , helix sleeve 46 is made of machined polysulfone , and is provided with a rectangular slot 48 which allows the diameter of the coil defined by inner conductor 42 to increase at a “ dog - leg ” point designated generally as 90 . distally from “ dog - leg ” point 90 , inner conductor 42 coils around the outer surface of helix sleeve 46 toward the distal end of helix sleeve 46 , and is electrically coupled , e . g ., by spot or laser welding , to helix 28 . fixation assembly 26 may be retained within helix sleeve 46 by means of a substantially cylindrical helix seal 70 which may be formed of molded silicone rubber . helix seal 70 is provided with a helical lumen or channel 72 extending from front to back , through which helix 28 is able to pass . helical lumen 72 in helix seal 70 may be initially sealed at the distal end 76 . when helix 28 advanced into helix seal 70 from the back , helix seal 70 guides helix 28 forward , such that the pointed tip of helix 28 pierces point 76 of lumen 72 . when helix 28 is screwed back out , the resiliency of silicone rubber seal 70 is such that lumen 72 effectively seals itself . this self - sealing arrangement is believed to be advantageous in that it prevents body fluids from entering electrode and fixation assembly 26 . helix 28 may be advanced and retracted using an embodiment of stylet 24 having a flattened tip 25 . rotation of the stylet imparts rotation to the helix assembly , causing the straightened helix to advance or retract . upon exiting the distal end of the lead , the helix expands into a helical shape that makes solid contact with the vessel wall . the embodiment of fixation assembly and stylet illustrated in fig3 are substantially described in u . s . pat . nos . 5 , 522 , 874 and 5 , 522 , 875 respectively to gates , and which are hereby incorporated by reference in their entireties . transvenous implantation of lead 10 may be accomplished using conventional lead introduction techniques . during the implantation procedure , stylet 24 is used to provide stiffness to lead body 12 , facilitating manipulation of lead 10 through the patient &# 39 ; s venous system . helix 28 is maintained in its most retracted position until the distal end of lead 10 including fixation assembly 26 is brought into contact with the desired coronary sinus , great vein , or other stimulation site . since helix 28 is contained completely within the electrode and fixation assembly 26 , it is prevented from damaging tissue as lead 10 is advanced through the venous system . once the desired electrode positioning is achieved , stylet 24 is rotated in the appropriate direction to cause helix 28 to advance through helical channel 72 within helix seal 70 , eventually piercing a sealed portion at the distal end of helical channel 72 in the manner discussed above . continued rotation of helix 28 will cause further advancement , so that helix 28 extends to its full diameter , engaging the endocardial vessel wall . in this way , electrode and fixation assembly 26 , and in particular , helix electrode 28 , is secured in contact with the desired stimulation site . to later remove or re - locate the lead , helix 28 can be released without significantly damaging the cardiac tissue by rotating stylet 24 in the opposite direction . helix 28 re - assumes a compressed configuration when retracted within the lead inner lumen . fig4 is a cross - sectional view illustrating an alternative embodiment of the inventive lead . in this embodiment , fixation helix 28 is coupled to coiled conductor 100 . the helix 28 is advanced or retracted out of a chamber or inner recess 102 in the distal end of the lead body 106 by rotation of the coiled conductor 100 . this type of coil mechanism is disclosed in commonly assigned u . s . pat . no . 4 , 106 , 512 to bisping with improvements thereto disclosed in commonly assigned u . s . pat . no . 4 , 311 , 153 to smits , in u . s . pat . no . 4 , 886 , 074 to bisping , and in u . s . pat . no . 5 , 837 , 006 to ocel , all hereby incorporated by reference in their entireties . in these “ bisping ” leads and the commercial embodiments thereof , rotation of the proximal end of a fixed pin 104 or other helix guide structure is utilized to impart rotational motion to the proximal end of coiled conductor 100 . this rotation is , in turn , translated into axial advancement and retraction of the helix out of , and into , distal chamber 102 . upon exiting distal chamber 102 of lead 10 , helix 28 expands into a helical shape wherein the helix is forced against a vessel wall such as the wall of the coronary sinus . yet another embodiment of a helix as may be employed with the current invention is shown in commonly - assigned u . s . pat . no . 4 , 570 , 642 to kane et al . hereby incorporated by reference in its entirety . according to this embodiment , the helix is fixed on a member slidably located within a chamber of the distal end of the pacing lead . a cylindrical stylet is employed to distally advance the slidable member within the chamber . this , in turn , exposes the fixation helix so that it may be screwed into the myocardium by rotation of the entire lead body . fig5 is a plan view of fixation assembly 26 at distal end 12 of lead 10 implanted in a vessel such as the coronary sinus . as shown , helix 28 is sized to wedge against the coronary sinus walls 6 when deployed . the helix defines a lumen that permits the unimpeded flow of blood , as depicted by arrow 8 . this uninterrupted blood flow prevents the formation of thrombosis and possible necrosis of the tissue , which may , in turn , cause stagnation in the vessel such that the health of the surrounding tissue is negatively impacted . fig6 is a plan view of yet another embodiment of helix 28 wherein the helix has a decreasing diameter . this embodiment may be adapted for use in a portion of a vessel wherein the vessel is decreasing in size , for example . in the alternative , a helix having an increasing diameter towards the helix distal end may be utilized . any other type of size variations along the length of the helix may likewise be utilized , such that only a portion of the helix diameter exceeds the diameter of the lead body . although the lead of fig1 is shown as a pacing lead , one skilled in the art will appreciate that the current invention may be employed with many other embodiments of implantable leads , catheters , or other elongated implantable medical devices ( imds ) that are to be maintained chronically at a desired implant site . for example , a defibrillation lead connected to a defibrillator 2 , as substantially described in u . s . pat . no . 5 , 549 , 642 to min , et al . and incorporated herein by reference in its entirety , may usefully employ the current invention . alternatively , a helix formed of a non - conductive or conductive material may be employed to affix the distal end of a drug - delivery lead within the coronary sinus or another vessel . in yet another invention , the distal end of the fixation helix may be utilized to attach the associated imd to tissue within a cardiac chamber such as the right ventricle . many other alternative embodiments are also contemplated within the scope of the current invention . in yet another embodiment of the current lead system , the lead body carries a sensing device such as sensor 110 ( fig5 ) to be placed in the coronary sinus or great vein . this is as substantially described in u . s . pat . no . 5 , 129 , 394 to mehra and incorporated herein by reference in its entirety . according to the described embodiment , a method and apparatus is provided for sensing in vivo blood pressure proportional to the left ventricular pressure . the measured pressure can be used to detect ventricular tachyarrhythmias or the cardio vascular status associated with congestive heart failure . pressure measurements can also be used to adjust the rate at which pacing pulses are delivered . a lead with a pressure sensor near its distal end is placed transvenously through the coronary sinus and located in the coronary vein or great vein . the pressure that is sensed in that location is proportional to the left ventricular pressure . values representing the left ventricular pulse , systolic and diastolic pressures , as well as the differentiated rate of change , dp / dt , gross rate of change , δp / δt , and mean or average pressure values are all , or selectively , developed by software algorithms and implemented in microprocessor - based control circuitry . in one preferred embodiment , one or more of the values are utilized in software - implemented algorithms to cause a pacemaker to pace the heart at a required rate to achieve a desired cardiac output . alternatively , these left ventricular pressure - related values may be employed to confirm the absence of mechanical pumping action of the heart , which , in conjunction with other cardiac signals , confirm the existence of a tachyarrhythmia requiring anti - tachy pacing , cardioversion or defibrillation . many other types of sensors may be carried on a lead configured according to the current invention . such sensors may measure o 2 saturation , temperature , flow , impedance , stroke volume , ph , and / or any of the other types of physiologic measurements known in the art . these sensors may be deployed , positioned and firmly anchored in the coronary sinus , middle and / or great cardiac vein , or another vessel using the current invention . although a specific embodiment of the invention has been disclosed , this is done for purposes of illustration only , and is not intended to be limiting with regards to the scope of the invention . it is contemplated various substitutions , alterations and / or modifications may be made to the disclosed embodiment without departing from the spirit and scope of the invention . such modifications may include substituting elements or components that perform substantially the same function in substantially the same way to achieve substantially the same result as those described herein .
a transvenous implantable medical device adapted for implantation in a body , and which is particularly adapted for use in a vessel such as the coronary sinus or cardiac great vein . the implantable medical device may take the form of a lead or catheter , and includes an extendable distal fixation member such as a helix . in one embodiment , the fixation member is a helix constructed of a shape memory metal or other super - elastic material . upon deployment , the helix assumes a predetermined helix shape larger than the diameter of the lead body diameter . the helix functions to wedge or fix the lead within the vessel in a manner that does not impede the flow of blood through the vessel . the helix may be retracted for ease of repositioning and / or removal . in one embodiment of the invention , the fixation member may be advanced using a stiffening member such as a stylet . in another embodiment , the helix is coupled to a coiled conductor such that rotation of the conductor extends or retracts the helix . according to yet another aspect of the invention , a helix lumen including a flexible fluid - tight seal may be utilized to house the helix when it is in the retracted position .