examples of an implementation of the present invention will now be described with reference to the drawings fig1 - 5 . in the figures , reference 10 generally refers to the screw lead of the system according to the present invention . the lead 10 comprises a lead body 12 which structure is in itself known , usually a polyurethane sheath to reduce friction when the catheter is inserted into a guide catheter , and to provide better sensitivity and better transmission of torque torsion . the diameter of the sheath of the lead body 12 is chosen to be thin enough to be compatible with the sub - selection catheters of veins of the coronary network , typically less than or equal to 5 french ( 1 . 65 mm ). the lead 10 is terminated at its distal end by a helical anchoring screw 14 made of a conductive material , connected through a metal tip 16 to an inner conductor 18 such as a spiral conductor providing electrical continuity between the anchoring screw 14 that is an electrode for collection and stimulation and a generator located at the proximal end ( not shown ) of the lead 10 . it should be understood that lead body 12 made of a polyurethane sheath provides rigidity in torsion to transmit torque from the proximal end to the distal end and to rotate the screw 14 to make it penetrate into the heart tissue . the conductive material of the screw is advantageously a niti alloy ( nitinol ), which has a capacity to transmit a sufficient torque for the intended application . the main advantage of this material is its extreme fatigue endurance . the disadvantage of nitinol is its relative high electrical resistance , but this drawback may be compensated by a bi - material structure comprising a silver core ( for electrical conductivity ) wrapped or coated by nitinol ( for properties of resistance to mechanical stress ) such that the less mechanically tough material ( silver ) is encapsulated in a sheath of nitinol . for bipolar stimulation , the lead is also provided with a ring electrode 20 connected to the generator by a separate conductor ( not shown ) in a manner well known to persons of ordinary shell in the art . the anchoring screw 14 is advantageously carried out with a distal portion 22 formed of non - touching turns over a length of about 1 . 5 to 2 mm . the distal portion 22 is connected to the lead body 12 via a mechanical transition portion 24 having flexibility in flexion , for example , a part formed by adjacent turns in the absence of stress of the screw . the purpose of this transition portion 24 is to introduce between the screw 14 itself ( the part that will penetrate into the tissues ) and the lead body 12 an elastic function to limit the mechanical action of the distal part of the lead 10 on the cardiac tissues and / or the veins . advantageously , this elastic feature ( i ) does not alter the torque transmission between the lead body 12 and the screw 14 under the two aspects of efficacy and safety ( coring effect ); ( ii ) does not alter the transmission of the electrical pulse , and ( iii ) is extremely resistant to flexion / compression events . on the other hand , the screw 14 is advantageously insulated over its length , for example , by a coating of parylene , except on the last millimeter of the distal part , which is the only electrically active part of the screw 14 . this structure reduces the stimulation surface and thereby reduces the risk of phrenic nerve stimulation . this electrically active part will also be buried deep into the wall of the epicardium , thereby concentrating the electric flow to the target tissue and stimulate a deep and more physiological zone . a long screw ( in the order of 10 - 15 mm ) penetrates deeply into the ventricular wall and performs a localized endocardial stimulation ensuring during stimulation a faster wave of depolarization from the endocardium to the epicardium . to avoid the risk of coring , the internal lumen of the flexible portion of the screw 14 is equipped with a silicone cartridge ( possibly filled with a steroid ) to maximize the effect of abutment to the transmission of torque . in the illustrated drawings , the screw 14 is an active screw playing ( at least at its distal end ) the role of a stimulation electrode . alternatively , the screw 14 is an electrically passive screw used for anchoring the lead 10 against the wall of the epicardium . the lead 10 may be provided at its end with a distal electrode in the shape of a ring electrode , a second electrode , or other suitable configurations . for the implantation of the lead 10 in the chosen stimulation site , in accordance with a preferred embodiment of the present invention , a guide catheter 26 with a double curvature is used . with reference to fig2 , the guide catheter 26 is illustrated with the lead 10 inserted inside . the distal portion 28 of the guide catheter 26 is open at its end , so as to bring out the distal end of the lead 10 and its anchoring screws 14 by relative axial movement of the lead body 12 inside the guide catheter 26 . in addition , a stylet 30 is inserted inside an inner lumen 32 of the lead 10 so as to stiffen it and straighten the natural curvature of the catheter 26 by more or less axially sliding the stylet 30 within the lead 10 . as indicated above , the catheter 26 has at its distal end 28 a double curvature , each curvature being inscribed in a separate area 38 and 40 . the curved surface 38 is an orientation curvature that follows the natural curvature of the coronary veins during the progression of the catheter 26 into the coronary sinus , while the curved surface 40 is a curve for supporting the orientation of the distal portion of the lead 10 once the site of stimulation is reached . more specifically , this supporting curvature 40 has the effect of directing the axis of the anchoring screw 14 not in line with the target vein 34 , but instead , as shown in fig3 ( after removal of the catheter 26 ), to the wall facing the epicardium 36 of the target vein . according to this method , the anchoring of the screw 14 and the subsequent screwing of the screw 14 along a direction d makes an angle a with the axial general direction of the lead 10 , roughly corresponding to the direction of progression of target vein 34 . the implantation procedure of the screw 14 at the selected site will now be described . this procedure is described in its most complete aspect , but it should be understood by persons of ordinary skill in the art that certain steps or the use of certain elements may be omitted , adapted , or modified without deviating from the scope of the present invention . according to one embodiment , a technique called otw ( over - the - wire ) is used . otw involves introducing into the coronary sinus and then in the coronary network a very thin guide wire provided at its distal end with a flexible termination that is not traumatic . previously , the practitioner arranges a main catheter to reach the outlet of the coronary sinus , insert the guide wire into the catheter , and pushed into the coronary venous system . the practitioner inserts the guide catheter 26 according to the invention . the guide catheter 26 may be used as a sub - selection catheter to choose , under fluoroscopy , the path of the venous network that will allow reaching the target vein corresponding to the chosen stimulation site . the self - orientation of the catheter 26 during this phase of positioning results from the principle of least energy , especially during the “ left turn ” in the area of intersection of the great cardiac vein and a lateral vein . the self - orientation of the orientation curve locally generates enough torque to force the orientation of the support curvature in the desired position . the predominance of the torque effect of the orientation curvature relatively to the support curvature is related to the fact that , in terms of dimensions : the radius of curvature of orientation is greater than the support radius curvature , and the length of the orientation curvature is greater than the support curvature length . the distance between the area generating the drive torque ( orientation curvature ) and the area to be controlled ( support curvature ) is thus extremely limited ( a few millimeters ). it should be noted that the present invention requires a single catheter to determine the relative positions of the two curvatures . thus , as stated above , the lead solution of the present invention is not operator - dependent : the practitioner just pushes catheter into the target vein for the catheter 26 to self - orient in the desired position after a few beats , frees both hands for the screwing operation , while ensuring a secure and accurate positioning of the screw 14 and holding it in this position during the screwing phase that follows . according to one embodiment , a hollow dilator catheter is used in the sub - region to establish a gradual transition between the guide wire and the tip of the sub - catheter , particularly to prevent the catheter tip , while sliding on the guide wire , from crashing against the wall of the vein , for example , where a curvature is met at a blocking point in the course of traversing the tortuous vein . this dilator catheter is advantageously preformed in its distal part to facilitate cannulation of the lateral veins . this option allows to compensate the self - positioning of the sub - catheter into the left atrium as it moves into the large vein ( because of the principle of least energy , but implemented in the great cardiac vein ). this behavior of the dilator catheter enables placement of a left atrial lead even in the proximal part of the great cardiac vein . once the desired stimulation site is reached , the practitioner slides the lead 10 inside the catheter 26 until the distal end of the lead 10 and its anchoring screws 14 emerge from the corresponding end of the catheter 26 ( configuration illustrated in fig2 ). because of the double curvature described above , the distal end of catheter 26 , the distal orifice of the catheter 26 is directed toward the epicardium 36 making an angle a compared to the general direction of the target vein . the catheter 26 is introduced into the lead 10 until it emerges from the catheter housing and its anchoring screw 14 comes in contact with the epicardium . an initial mapping is conducted to electrically test the contact point ( s ) and validate the chosen stimulation site . if the position is not satisfactory , the practitioner moves the catheter along the vein and test a new site until a suitable location is found . the final anchoring is obtained by imparting an axial rotation to the lead body in the case of a fixed screw lead . for a pin - driven lead , the axial rotation is imparted to the connector plug , where at the proximal side the connection plug is secured to a conductor extending axially within the lead body . the surgeon holds in one hand the proximal end of the lead body and turns a pin at the proximal end with the other hand , directly or through the intermediary of a tool . the pin is secured to an axial conductor extending within the lead body , and this conductor is free in rotation and is connected at its distal end to the connector plug deployment mechanism of the screw . another possibility is to introduce a specific screwing stylet into the lumen 32 of the lead body , especially in case when the sheath does not have a sufficient torsional rigidity to drive the screw directly from the proximal end . in an alternative embodiment , a retractable screw is used instead of a fixed screw . in this case , the rotation first deploys the screw out of its slot and subsequently penetrates the screw into the wall of the epicardium . after the screw 14 is anchored into the wall of epicardium , the catheter 26 is removed . the removal of the catheter 26 is performed according to a standard procedure of cutting through a slitter tool , as described , for example in , ep 2039390 a1 and its us counterpart u . s . published application 2009 / 0071012 ( sorin crm s . a . s . formerly known as ela medical ). the final and definitive installed configuration is illustrated in fig3 . advantages of using the present invention include the following improvements over the prior known coronary venous leads : the quality of the fixation for anchoring screws ; the stability of the electrical contact with the tissue regardless of the size of the vein ; the ability to map large portions of the vein before the final fixation ; the possibility to expand the exploitable part of the vein , particularly towards the proximal part of the venous system , known to be the least exposed to the risk of phrenic nerve stimulation , but having with traditional leads , the disadvantage of a lower stability due to a larger diameter ; the concentration of the electrical stimulation in a deep region of the epicardium , decreasing the risk of phrenic nerve stimulation ; the improved extraction capacity , by a simple unscrewing of the distal end ; the mechanical simplicity of the system , a low manufacturing cost and a high reliability . one skilled in the art will appreciate that the present invention can be practiced by other than the embodiments disclosed herein , which are provided for purposes of illustration and not of limitation .
a system implantable in the coronary venous system , including a pacing lead with an anchoring screw is disclosed . the system includes a stimulation lead for stimulating a left heart cavity of a patient , and a removable catheter for implanting the lead . the lead has at least one stimulation electrode having an anchoring screw that penetrates into the epicardial tissue of the patient . the catheter tube is a pre - shaped tube with two curvatures in the absence of stress . the two curvatures are inscribed in two separate surfaces for self - orientating the distal end of the catheter tube into the target vein and maintaining the axis of the anchoring screw towards the epicardial wall during the screwing of the lead head .