Abstract:
The lead configuration enhances the sensing characteristics of the lead and provides for stable location of the electrodes in the coronary sinus. The J-shaped bend in the distal portion of the lead body spaces the distal tip of the lead body less than about 0.9 inches laterally from the portion of the lead body that is proximal to the bend. The tip of the lead body is provided with a pacing/sensing electrode and the curved portion of the J-shaped bend carries an elongated coil electrode that serves as an indifferent electrode for pacing and sensing. For left atrial pacing, the lead tip electrode is located adjacent the wall of the coronary sinus closest to the left atrium, and the indifferent electrode is located adjacent the opposite wall of the coronary sinus, closer to the left ventricle. To enhance spatial distribution of the indifferent electrode and provide for greater averaging of the ventricular signal, which in turn reduces the far field of the ventricular signal, the indifferent electrode extends over 10-50 millimeters or multiple spaced indifferent electrodes are used.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to implantable electrical leads and more particularly for implantable leads intended for use in the coronary sinus of a patient&#39;s heart. 
     Recently there has been an increased interest in the placement of cardiac pacing and sensing electrodes in the coronary sinus, particularly for purposes of bi-atrial and bi-ventricular pacing. In this context, a number of configurations have been proposed in order to assist in placement and retention of the lead and its electrodes in desired locations within the coronary sinus. Early coronary sinus leads such as the Medtronic Model 6992 Lead had a generally straight lead body configuration and employed a non-conductive tip extending distally from the distal-most electrode as a mechanism for assisting in the insertion of the lead in the coronary sinus and for retaining it in the coronary sinus after insertion. More recently, it has been proposed to provide a body of a coronary sinus lead with a pre-formed sinusoidal or helical configuration in order to allow the lead to expand into contact with the walls of the coronary sinus and thereby retain the lead, much in the same fashion as has been employed in the context of spinal stimulation leads. Coronary sinus leads having such a pre-formed configuration are disclosed in U.S. Pat. No. 5,423,865 issued to Bowald et al. and U.S. Pat. No. 5,476,498 issued to Ayers. Spinal cord stimulation leads having similar pre-formed configurations are disclosed in U.S. Pat. No. 4,374,527 issued to Iversen and U.S. Pat. No. 4,414,986 issued to Dickhudt. 
     An alternative approach to fabrication of coronary sinus leads has been to provide the distal portion of the lead with a curved configuration corresponding to some extent to the curved configuration of the coronary sinus and great vein. For example, a coronary sinus lead having a continuous multi-radius curvature is disclosed in U.S. Pat. No. 5,433,729 issued to Adams et al. Similar configurations are illustrated in U.S. Pat. No. 5,423,772 issued to Lurie and in U.S. Pat. No. 5,445,148 issued to Jaraczewski. An alternative configuration employing two spaced 45° bends is disclosed in U.S. Pat. No. 5,683,445 issued to Swoyer. 
     SUMMARY OF THE INVENTION 
     In the context of coronary sinus leads, it is believed that further improvements in lead configuration can still be made in order to enhance both the sensing characteristics of the coronary sinus lead and to provide for stable location of electrodes in the coronary sinus. The lead of the present invention is intended to accomplish these goals by means of an improved lead body and electrode configuration. In a preferred embodiment, the lead is pre-formed to display a small radius, J-shaped bend in its distal end. In particular, the J-shaped bend is preferably configured such that the distal tip of the lead is spaced less than about 0.9 inches laterally from the portion of the lead proximal to the J-shaped bend. In such a lead, the tip of the lead is provided with a pacing and sensing electrode and the curved portion of the J-shaped distal portion of the lead carries an elongated coil electrode which serves as the indifferent electrode for pacing and sensing. This configuration is optimized to allow placement of the lead in portions of the coronary sinus having a wide variety of diameters. 
     For example, if the lead is placed in a portion of the coronary sinus having a relatively larger diameter, the lead can be placed such that the distal tip of the lead is curved back more proximally such that the J-shaped curve is compressed to display a reduced radius of curvature, bracing the lead within the coronary sinus and stabilizing the location of the tip electrode. In portions of a coronary sinus having a lesser diameter, the lead may be implanted with the distal tip of the lead directed distally relatively to the lead body such that the J-shaped bend is opened to display a greater radius of curvature, which also braces the lead within the coronary sinus and stabilizes the location of the tip electrode.. In either configuration, the pre-formed J-shaped bend serves to cause the lead to extend across the width of the coronary sinus and to brace the electrode located at the distal end of the lead against the wall of the coronary sinus. 
     Preferably, for purposes of left atrial pacing, the lead is located so that the tip electrode is located adjacent the wall of the coronary sinus closest to the left atrium. Given the configuration of the lead this necessarily results in the elongated coil indifferent electrode being located at least in part adjacent the opposite wall of the coronary sinus, closer to the left ventricle. The indifferent electrode in preferred embodiments extends over a length of at least about 10 millimeters, in order to provide a large surface area electrode which in turn provides some averaging of the ventricular signal due to the spatial dispersion of the electrode. In other embodiments, the coil electrode may be extended over a substantially greater distance, for example 20 to 50 millimeters in order to further enhance the spatial distribution of the indifferent electrode and provide for a greater averaging of the ventricular signal, in turn reducing the relatively high far field of the ventricular signal relative to the atrial signal and assisting in accurate discrimination between atrial and ventricular signals sensed by the lead. As an alternative, rather than employing a single longer coil electrode, spatial dispersion may be accomplished by provision of multiple spaced indifferent electrodes proximal to the tip electrode to accomplish averaging of the ventricular signal. 
     In analyzing the ventricular signal sensed in leads generally corresponding to those according to the present invention, the inventors have determined that the ventricular signals sensed at the ends of the indifferent electrodes generally display the highest slew rate, and that this slew rate can be reduced if the end of the indifferent electrode is curved such that it extends generally perpendicular to the axis of the coronary sinus, directed generally away from the ventricle. In order to accomplish this result, in some embodiments, the lead may be configured to employ a longer electrode, for example, 20 millimeters or more in length, and the lead body may be preformed so that as implanted, both ends of the indifferent electrode are curved away from the coronary sinus wall closer to the ventricle and toward the coronary sinus wall adjacent the atrium when the lead is implanted. This may be accomplished by providing a second, preformed bend proximal to the J-shaped bend at the distal end of the lead and directed in an opposite direction or it may be accomplished by other mechanisms, for example, by manufacturing the lead such that the curved portion of the lead carrying the elongated coil electrode is of greater rigidity than the portion of the lead immediately proximal thereto which in turn will encourage the lead to display a similar configuration as implanted. 
     An additional mechanism for reducing the slew rate of the ventricular signals sensed at the ends of the indifferent electrode is to provide a conductivity reducing coating on one or both end portions of the indifferent electrode. This mechanism may be employed as a substitute or in addition to provision of a spatially dispersed indifferent electrode and/or configuring the indifferent electrode so that the ends of the electrodes are directed away from the ventricles. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of a first embodiment of a lead according to the present invention. 
     FIG. 2 is a cross-sectional view of the distal portion of the lead of FIG.  1 . 
     FIGS. 3 and 4 illustrate alternative implantation methods for use in conjunction with the lead of FIG. 1, allowing it to be adapted to portions of a coronary sinus having different diameters. 
     FIG. 5 illustrates the distal portion of an alternative embodiment of a lead according to the present invention, employing an elongated indifferent electrode configured such that the ends of the electrode are directed away from the wall of the coronary sinus adjacent the ventricles, as implanted. 
     FIGS. 6 and 7 illustrate alternate implantation techniques for the lead of FIG. 7 allowing the lead to be accommodated to portions of the coronary sinus having different internal diameters. 
     FIG. 8 illustrates an alternate embodiment of the lead in which spatial dispersion of the electrode is accomplished by provision of multiple indifferent electrodes spaced along the lead body. 
     FIG. 9 illustrates yet another alternative embodiment of the present invention in which spatial dispersion of the indifferent electrode is accomplished by means of multiple electrodes located along the lead body. 
     FIG. 10 illustrates an additional alternative embodiment of the present invention in which one or more ends of the indifferent electrode are provided with a conductivity reducing coating in order to reduce the slew rate of ventricular signals sensed at one or both ends of the electrode. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a plan view of a first embodiment of an electrical lead according to the present invention. The lead is provided with an elongated outer insulative sheath  10  which encases two concentrically located, mutually insulated coiled conductors. At the proximal end is located an in-line bipolar connector assembly  30 . Connector assembly  30  may correspond to the IS-1 connector standard and is provided with a connector ring  34 , a connector pin  38  and two sets of sealing rings  32  and  36  which serve to seal the connector assembly within the bore of an associated implanted pacemaker and to prevent fluid leakage between the connector ring  34  and the connector pin  38 . The distal portion  20  of the lead has a generally J-shaped configuration, and includes a pacing/sensing electrode  22  located at the distal tip of the lead and an elongated indifferent electrode  12 , extending around the curved portion of the J-shaped distal portion  20  of the lead. Electrode  12  in the illustrated embodiment takes the form of a continuation of one of the two coiled conductors within the outer insulative sheath  10 , and extends proximally within the lead to connector assembly  30 , where it is coupled to connector ring  34 . The second coiled conductor within the lead body is located concentrically within and insulated from coiled conductor  12 , and extends from the tip electrode  22  to the connector assembly  30  where it is coupled to connector pin  38 . Also illustrated is a stylet  42  inserted through stylet guide  40  into connector pin  38  which stylet may be employed to straighten the lead or to adjust the curvature of the distal portion of the lead to facilitate its installation in the coronary sinus. An anchoring sleeve  16  is also illustrated mounted around the sheath  10 . 
     FIG. 2 is a cross-sectional view through the J-shaped distal portion  20  of the lead of FIG.  1 . In this view, it can be seen that the outer sheath  10  encases conductor  12 , the exposed portion of which serves as the indifferent electrode, which in turn encases inner insulative sheath  42 , which insulates inner coiled conductor  40  from the outer conductor/indifferent electrode  12 . In order to maintain the lead in the J-shaped configuration illustrated, one or more of inner conductor  42 , outer conductor/indifferent electrode  12 , inner insulative sheath  42  and outer insulative sheath  10  may be pre-formed to display the desired configuration. Conductors  12  and  40  may be any of the numerous conductor types known for use in conjunction with cardiac pacing leads, and in particular may be platinum or tantalum coated MP35N alloy wire. Outer and inner insulative sheaths  10  and  42  may be fabricated of biocompatible plastic such as polyurethane or silicone rubber. As visible in cross-section, tip electrode  22  is provided with a distal-facing bore in which monolithic controlled release device  24  is located. Monolithic controlled release device  24  may correspond to any of the various types of monolithic controlled release devices known to the art including those described in U.S. Pat. No. 5,282,844 issued to Stokes et al., U.S. Pat. No. 4,972,848 issued to DiDomenico et al. and U.S. Pat. No. 4,506,680 issued to Stokes, all incorporated herein in their entireties and preferably elutes an anti-inflammatory steroid such as sodium dexamethasone phosphate or the like in order to reduce irritation of tissue adjacent the electrode. Electrode  22  is also provided with a proximally facing bore in which the distal end of inner conductor  40  is located, along with a crimping core  28 . Conductor  40  is coupled to electrode  22  by means of crimps (not illustrated) compressing the lead between electrode  22  and the crimping core  28 . Also visible are two plastic bands  43  and  44  which may also be fabricated of polyurethane or silicone rubber and which encircle the inner insulative sleeve  42  distal to the distal end of conductor/electrode  12 . 
     As illustrated, the preferred configuration for this particular embodiment of the lead according to the present invention is a J-shaped bend extending over an arc of approximately 90 to 150 degrees, preferably about 130 degrees. The lead is most preferably configured such that the exposed portion of tip electrode  22  is displaced a distance “B” laterally from the lead body proximal to the curved portion of the J-shaped bend and extends a distance “A” proximally from the distal most portion of the J-shaped bend. In such embodiments the distance “A” may be, for example between about 0.25 and 0.5 inches, while distance “B” may be, for example, between about 0.6 and about 0.9 inches. In the particular embodiment illustrated, configuring the J-shaped distal bend in this fashion facilitates its use in the coronary sinus as illustrated in more detail in FIG.  3  and FIG. 4 below. 
     FIG. 3 illustrates schematically the coronary sinus  100  of a patient&#39;s heart, as viewed looking at the posterior surface of the heart. The lead is illustrated entering the ostium  102  of the coronary sinus and is located in this figure in a portion of the coronary sinus that has a relatively larger interior diameter. In this case, the lead is implanted in such a fashion that the distal tip of the lead is directed back proximally, with the tip electrode  22  located adjacent a wall of the coronary sinus  100  closest to the left atrium. In this configuration, the J-shaped bend is somewhat compressed, and the resilience of the lead body tends to cause the lead to expand against the walls of the coronary sinus to brace the lead, maintaining electrode  22  in its desired position. In this view, the elongated indifferent electrode  12  is located such that its proximal end lies generally along the wall of the coronary sinus  102  closer to the ventricle and its distal end is curved and directed away from the wall of the coronary sinus closer to the ventricle. 
     FIG. 4 illustrates the lead of FIG. 1 as implanted in a more distal portion of the coronary sinus  100  of the patient&#39;s heart. The lead is shown entering the ostium  102  the coronary sinus, but in this case is located with the distal tip of the lead extending distally, rather than proximally, with the J-shaped bend in this case being opened, rather than compressed. This configuration allows the lead to be implanted in portions of the coronary sinus having a relatively smaller diameter. The resiliency of the J-shaped bend in this case also tends to brace the lead within the coronary sinus and maintain electrode  22  in its desired location. It should be noted that in this configuration, like the configuration illustrated in FIG. 3, the proximal end of electrode  12  lies alongside the wall of the coronary sinus closer to the ventricle while the distal end of electrode  12  is directed away from the wall of the coronary sinus closer the ventricle and toward the wall of the coronary sinus adjacent the atrium. 
     Implanting the lead as illustrated in FIG.  3  and FIG. 4 is accomplished by inserting a stylet into the lead and advancing the lead to the ostium of the coronary sinus. In order to accomplish the implant configuration illustrated in FIG. 3, the stylet is withdrawn to a point slightly proximal to the beginning of the curved portion of the J-shaped distal end  20  of the lead, and the lead is advanced into the coronary sinus with the curved portion of the J-shaped bend being the most distally located portion of the lead. The implantation configuration of FIG. 4 is accomplished in a similar fashion, with the exception that the stylet is advanced to a point adjacent the tip electrode  22  of the lead and the lead is advanced into the coronary sinus with the tip electrode  22  being the distal-most portion of the lead. The stylet may then be withdrawn to allow the curvature of the distal end to display itself to the degree allowed by the coronary sinus, bracing the tip electrode in its desired location. 
     While all of the embodiments illustrated in the Figures include an indifferent electrode it should be understood that the configuration of the J-shaped curve as illustrated in FIGS. 1-4 is also valuable in the context of a unipolar pacing lead having only a tip electrode. Similarly, the J-shaped configuration illustrated is also believed valuable in the context of leads having additional electrodes and/or physiologic sensors. In alternative embodiments, the exposed coil electrode may serve as a defibrillation electrode in addition or as an alternative to serving as an indifferent electrode. 
     FIG. 5 illustrates an alternative embodiment of a lead according to the present invention, employing an electrode configured such that both the proximal and distal ends of the indifferent electrode are intended to be directed away from the wall of the coronary sinus closer to the ventricle and toward the wall of the coronary sinus adjacent the atrium as implanted, in order to reduce the slew rate of the ventricular signal sensed by the indifferent electrode. In this case, the lead  200  is formed with its distal end including a J-shaped bend  202  which may correspond in configuration to the J-shaped bend of the lead of FIG.  1 . Proximal to the J-shaped bend  202  is a second, oppositely directed curved portion  204  which may be pre-formed into the lead body by means of a curvature pre-formed in any of the conductors and/or insulators of the lead body. Alternatively, the lead may be configured to display a curved configuration proximal to the J-shaped bend  202  by the expedient of a flexibility transition, such that the body of the lead  200  is more flexible proximal to the J-shaped bend  202 , which again will encourage the lead to display the configuration illustrated from the wall of the coronary sinus adjacent the ventricles and toward the wall A of the coronary sinus most closely adjacent the atrium. 
     FIG. 8 illustrates an alternative embodiment in which the indifferent electrodes are dispersed along the lead body in order to accomplish averaging of the ventricular signal. Preferably the electrodes are dispersed over a distance of at least about 20 mm along the lead proximal to the tip electrode. The lead  300  may be provided with a curved configuration including a first J-shaped bend  302  which may correspond to the configuration of the J-shaped bends of the leads of FIGS. 1 and 5. Proximal to the J-shaped bend  302  is a second curved portion  304 , and proximal to the second curved portion  304  is a third oppositely directed curved portion  306  winch may correspond to the pre-formed curved portion  304  of the lead in FIG.  5 . Alternatively, the lead may be constructed so that the flexibility of the lead proximal to the second curved portion  304  is substantially reduced, in order that the lead will display the curvature illustrated when implanted in the patient&#39;s coronary sinus. Located along the curved portion of the J-shaped bend  302  and along the second curved portion  304 , tip electrode  312  is shown located adjacent the wall of the coronary sinus adjacent the atrium while electrodes  308  and  310  are shown located in contact with the wall closer to the ventricle and have their distal and proximal ends, respectively, curved and directed away from the wall closer to the ventricle. As illustrated, the lead is configured as it would appear if implanted in a relatively smaller diameter portion of the coronary sinus, with the tip of the lead directed generally distally. However, as discussed in conjunction with the leads of FIGS. 1 and 5, in larger diameter portions of the coronary sinus, the lead may be implanted such that the tip of the lead is directed proximally. 
     FIG. 9 illustrates yet another alternative embodiment of the lead according to the present invention accomplishing dispersion of the indifferent electrode by means of the provision of multiple indifferent electrodes spaced from one another along the lead body. The lead  400  is provided with a curved configuration including a J-shaped bend  402  which may correspond to the J-shaped bends of the leads in FIGS. 1 and 5 and a second oppositely directed bend  404  which may correspond to the oppositely directed bends  204  and  306  of the lead in FIGS. 5 and 8. In this case, the indifferent electrode takes the form of two coiled electrodes including a relatively shorter coiled electrode  403  and a second coiled electrode  406  located proximal to the curved portion  404  of the lead body. As implanted, tip electrode  408  is shown located adjacent the wall A of the coronary sinus most closely to the atria. As illustrated, the tip of the lead  400  is directed proximally as would be expected in the context of a lead implanted in a larger diameter portion of the coronary sinus. However, the distal tip of the lead could also be directed distally as discussed above in conjunction with implantation of a lead in smaller diameter portions of the coronary sinus. 
     FIG. 10 illustrates yet another embodiment of a lead according to the present invention employing an alternative mechanism to minimize the contribution of the ventricular signal. In this case, the lead  500  has a physical configuration generally identical to that of the lead illustrated in FIG. 1, with a single J-shaped bend  502  extending over the distal portion of the lead. The lead is shown implanted with the tip electrode  504  adjacent the wall of the coronary sinus most adjacent the atrium. In this case, the elongated coiled indifferent electrode  506  is provided with a coating of a voltage attenuating material such as tantalum or tantalum oxide extending over a length “D” of the electrode  506  adjacent the proximal end of the electrode and optionally over a length “C” of the electrode  506  adjacent its distal end. Provision of the voltage attenuating coating reduces slew rates associated with ventricular signals sensed by the distal portions of the leads, and to provide a result similar to that provided by configuring the lead so that the proximal and distal portions of the indifferent electrodes are configured so that they curve away from the wall of the coronary sinus closer to the ventricles and toward the wall of the coronary sinus adjacent the atrium. Such a coating may also be applied to one or both end portions of any of the electrodes illustrated in FIGS. 1-9, in order to enhance the benefits provided by the specific electrode configurations employed by the leads.