Abstract:
A joint for a cardiac stimulation lead is disclosed that connects a lead body and a coil conductor with an isodiametric junction. The lead body includes a counterbore disposed at its distal end. The lead body&#39;s counterbore securably receives the inner insulator of the coil conductor. Alternatively, the coil conductor includes a counterbore disposed at its proximal end. The coil conductor&#39;s counterbore securably receives the distal end of the lead body.

Description:
FIELD OF INVENTION 
     The present invention relates to implantable medical leads, and more particularly implantable pacing/defibrillation leads for applications such as cardiac pacemaking or cardioversion, including heart stimulation and monitoring. 
     BACKGROUND OF INVENTION 
     Implantable leads can be used to pass an electric current through the myocardium to alleviate arrhythmias, for example using the methods of cardioversion for tachycardia, defibrillation for ventricular fibrillation, and other methods depending on the particular arrhythmia. Alleviation of arrhythmias can be accomplished transvenously by implanting leads in the heart. The implantable leads form an electrical connection between a pulse generator or other electronic device and the heart. 
     Leads typically include one or more electrodes at the lead&#39;s distal end. The electrodes are designed to form an electrical connection with a tissue or organ. A flexible conductor electrically connects the electrode to the pulse generator. Commonly, the flexible conductor takes the form of a single or multifilar wire coil. Although, stranded or solid cables are also used. Regardless of the form, an insulating layer of material typically surrounds the flexible conductors. Together, the flexible conductor and the insulating layer form the lead body. The lead body electrically and mechanically couples the pulse generator at its proximal end to the electrode at its distal end. 
     Transvenous cardioversion and defibrillation leads employ cardioversion and defibrillation electrodes, respectively. These electrodes are typically configured as elongated metal coils. Transvenous pacing leads, cardiac ablation catheters and other electrode bearing leads and catheters may also employ coil electrodes. Leads having coil electrodes are commonly manufactured by winding the wire into a helix around the exterior surface of the lead body. The winding of wire around the lead body typically creates a region of increased diameter relative to the lead body. The increased diameter is usually twice the wire&#39;s diameter. Alternatively, a lead body may be attached to a separate coil electrode. A collar or transition is typically provided at the juncture of the lead body and a separate coil electrode. The collar or transition mechanically stabilizes the junction between the lead body and the separate coil electrode. The collar or transition also typically creates a region of increased diameter. The increased diameter resulting from the above methods is detrimental to the patient because they require an increased diameter introducer for implantation. The use of an increased diameter introducer increases the trauma to tissues during implantation. The increased diameter introducer also limits the size of the vein in which the electrode may be introduced. In addition, the collar or transition complicates the explanting of the lead by potentially “hanging-up” on a removal sheath used for this purpose and thereby, increases the risk to the patient. Alternatively, if no sheath is used, a danger of having the collar or transition “hanging-up” on fibrotic tissue exists during explanting. Thus, there is a need to provide a coil electrode having a uniform diameter junction with the lead body to produce an isodiametric lead. 
     The present invention meets the above needs and provides additional advantages and improvements that will be evident to those skilled in the art. 
     SUMMARY OF THE INVENTION 
     The present invention provides a lead that is substantially isodiametric over the region where the lead body transitions to coiled electrode. The present invention eliminates the need to use an increased diameter introducer to allow passage of a lead&#39;s region of increased diameter and reduces or eliminates the possibility of a region of increased diameter creating a shoulder capable of “hanging-up” on the introducer, removal sheath or fibrotic tissue during implanting and explanting. 
     The lead includes a lead body and a coil electrode. The lead body includes at least one conductor and an elongated, flexible polymeric lead insulator surrounding the conductor. The lead body may also include additional pacing and/or sensing conductors. The individual conductors may be single wires or a plurality of wires. The lead insulator generally defines an outside diameter, an internal lumen and a counterbore at its distal end. The coil electrode includes a wire wound as a helix around an inner insulator. The inner insulator can define one or more additional lumens. The coil electrode has a coil diameter substantially equal in size to the outside diameter of the lead insulator. The coil electrode is electrically coupled to the conductor. The wire helix may be electrically coupled to the conductor by spirally winding the shocking coil around the shocking conductor, welding, crimping or a conductive adhesive. The inner insulator is secured within the counterbore of the lead insulator. The inner insulator may be frictionally secured, adhesively bonded or welded within the counterbore of the lead insulator. If the lead body has additional pacing or sensing conductors, a distal end of the pacing or sensing conductors extending distally beyond the counterbore in the distal end of the lead insulator and into the lumen of the inner insulator. Thereby, the lead insulator and the inner insulator continuously electrically insulate the pacing and/or sensing conductors from the coil electrode. 
     Alternatively, the inner insulator of the coil electrode defines the counterbore at its proximal end instead of the lead body defining a counterbore at its distal end. In this later embodiment, the lead insulator is secured within the counterbore of the inner insulator. Again, the lead insulator may be frictionally secured, adhesively bonded or welded within the counterbore of the inner insulator. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a plan view of an embodiment for an isodiametric cardioversion/defibrillation lead in which an embodiment of the present invention is practiced; 
     FIG. 2 illustrates a greatly enlarged sectional side view showing an embodiment of the connection between the distal end of the coil electrode and the proximal end the lead body of the lead of FIG.  1 . 
     FIG. 3 illustrates a greatly enlarged sectional side view showing an embodiment of the connection between the proximal end of the coil electrode and the distal end of the lead body of the lead of FIG. 1; and 
     FIG. 4 illustrates a greatly enlarged sectional side view showing another embodiment of the connection between the proximal end of the coil electrode and the distal end of the lead body of the lead of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is applicable to a variety of implantable medical devices for providing an electric current to selected body tissues or transmitting signals from a sensing electrode to the medical device. The invention is described in the context of a defibrillation or cardioversion electrode designed for transvenous implantation. The appended claims are not intended to be limited to any specific example or embodiment described in this patent. It will be understood by those skilled in the art that the present invention may be used to secure electrodes to lead bodies to produce a wide variety of leads including, but not limited to, sensing leads, pacing leads, defibrillation leads, and other medical leads both unipolar and multipolar. Further, in the drawings described below, reference numerals are generally repeated where identical elements appear in more than one figure. 
     FIG. 1 illustrates an embodiment of a lead  10  made in accordance with the present invention. Lead  10  includes a lead body  12 , a coil electrode  14 , a second coil electrode  15 , a tip electrode  11  and a lead connector pin  16 . Lead  10  is generally configured to transmit an electric signal from a pulse generator (not shown) to the heart. Further, lead  10  is configured to permit insertion through a selected vein and the guiding of the electrodes to a target locations in or on the heart. Typically, lead body  12  is a flexible, elastomeric structure round in cross-section, but could be any number of materials, sizes and shapes appropriate for specific applications. The pulse generator may be a cardiac rhythm management device, such as a cardioverter/defibrillator, a pacemaker, or a sensing/diagnostic instrument. Lead connector pin  16  is provided at the proximal end of lead body  12 . Lead connector pin  16  is configured to form an electrical connection with the cardiac rhythm management device. Typically, the lead connector pin conforms to the international standard IS-1 when used to connect a lead to a pacemaker, although, it could take any number of forms known to those skilled in the art. 
     FIG.  2  and FIGS. 3 and 4 illustrate the details alternative embodiments of region  18  and region  19  in FIG. 1, respectively. Lead body  12  includes a flexible polymeric lead insulator  22  surrounding at least one defibrillating conductor  28  and at least one pacing conductor  29 . In the embodiment of FIG. 1, a defibrillating conductor  27 , shown in FIGS. 3 and 4, is electrically coupled to defibrillating electrode  14  and a second defibrillating conductor  28 , shown in FIG. 2, is electrically coupled to second defibrillating electrode  15 . Lead insulator  22  is generally configured to insulate the conductors and present a smooth biocompatible external surface to body tissues. Thus, lead insulator  22 , either alone or in combination with an inner insulator  26 , described below, is typically coextensive with the conductors. The material of lead insulator  22  is typically selected based on biocompatibility, biostability and durability for the particular application. Lead insulator  22  may be silicone, polyurethane, polyethylene, polyimide, PTFE, ETFE, or other materials known to those skilled in the art. Typically, the conductors are in the form of a cables and/or coils. The cable or coil may be made up of one or more conductive wires or filars. The conductors may be composed of stainless steel, MP35N, drawn-brazed-strand (DBS), platinum alloy, or other conductive materials known to those skilled in the art. The number, size, and composition of the conductors will depend on particular application for the lead. Regardless of the conductors used, lead body  12  should be capable of readily conforming to the irregular passageways and shapes of the cardiovascular system. Accordingly, the lead body should have enough flexibility to permit the lead body to flex easily, and elastically. 
     Coil electrodes  14  and  15  are provided near the distal end of lead body  12 . To stimulate the heart, coil electrodes  14  and  15  may be positioned within the right atrium or right ventricle, or at other positions within or on the heart appropriate for particular applications. Coil electrodes  14  and  15  typically include a wire  24  wound as a helix around an inner insulator  26 . Wire  24  may be composed of a biocompatible conducting material, such as stainless steel, MP35N, DBS, platinum allow or other electrically conductive materials known to those skilled in the art. Wire  24  is electrically connected to conductors  27  and  28  when used in coil electrodes  14  and  15 , respectively. The electrical connection can be a weld, by crimping, by an electrically conductive adhesive, by intertwining the conductor and the wire or by other methods known to those skilled in the art. Inner insulator  26  provides the framework around which the wire is wound and, in addition, can electrically isolate conductors  28  and  29  that typically extend through lumen distally beyond the defibrillation conductor  27 . Thus for purposes of the present invention, although inner insulator  26  typically functions as an insulator, it is not necessary for inner insulator  26  to function as an insulator. Inner insulator  26  may function solely as a structure on which wire  24  is wound to forming a coil electrode or alternatively, as a structure on which a pre-wound wire  24  is placed to define a structure for connecting the coil electrode to the lead body. Inner insulator  26  is typically coextensive with wire  24 , although it can extend proximally and/or distally beyond wound wire  24  as appropriate for a particular application. Inner insulator  26  may be made from a variety of materials including silicone, polyurethane, polyethylene, polyimide, PTFE, ETFE, or other materials known to those skilled in the art. Inner insulator  26  is typically selected based on biocompatibility, biostability and durability. Inner insulator  26  is generally configured to receive wire  24  such that the shape and coil diameter  40  of the wound wire is substantially corresponds the shape and outside diameter  42  of the lead body&#39;s insulator. 
     FIG. 2 illustrates the details of an embodiment of the junction between a proximal end of lead body  12  and a distal end of coil electrode  14  within region  18  of FIG.  1 . The embodiment of FIG. 2 joins the proximal end of lead body  12  to the distal end of coil electrode  14  by inserting inner insulator  26  into a counterbore  30  in lead insulator  22  at the proximal end of lead body  12 . Counterbore  30  can be mechanically cut, integrally molded or formed by other means known to those skilled in the art within the proximal end of lead body  22 . Inner insulator  26  has its distal end dimensioned to fit within counterbore  30  at the proximal end of lead insulator  22  such that inner insulator  26  may be secured in counterbore  30 . Inner insulator  26  is typically secured within counterbore  30  using an appropriate adhesive for the materials and application. Alternatively, inner insulator  26  could be secured within counterbore  30  by friction, welding, or thermal or chemical bonding of the insulators with one another, or by configuring the distal end of inner insulator  26  and counterbore  30  to mechanically interlock. The embodiment of FIG. 2 shows second defibrillating conductor  28  and pacing conductor  29  extending beyond coil electrode  14  to second coil electrode  15  and tip electrode  1 , respectively. 
     FIG. 3 illustrates details of an embodiment of the junction between a distal end of lead body  12  and a proximal end of coil electrode  14  within region  19  of FIG.  1 . The embodiment of FIG. 3 joins the distal end of lead body  12  to the proximal end of coil electrode  14  by inserting inner insulator  26  into a counterbore  32  in lead insulator  22  at the distal end of lead body  12 . Counterbore  32  can be mechanically cut, integrally molded or formed by other means known to those skilled in the art within the distal end of lead body  22 . Inner insulator  26  has its proximal end dimensioned to fit within counterbore  32  at the distal end of lead insulator  22  such that inner insulator  26  may be secured in counterbore  32 . Inner insulator  26  is typically secured within counterbore  32  using an appropriate adhesive for the materials and application. Alternatively, inner insulator  26  could be secured within counterbore  32  by friction, welding, or thermal or chemical bonding of the insulators with one another, or by configuring the proximal end of inner insulator  26  and counterbore  32  to mechanically interlock. The embodiment shows the electrical connection of conductor  27  to the wire  24  over a wound region  52  wherein wire  24  is wound around conductor  28 . Alternatively, conductor  28  can be wound around wire  24  or other methods of electrically connecting discussed above could be used. 
     FIG. 4 illustrates details of another embodiment of the junction between a distal end of lead body  12  and a proximal end of coil electrode  14  within region  19  of FIG.  1 . The particular embodiment joins lead body  12  to coil electrode  14  by inserting a reduced diameter portion at the distal end of lead body  12  into a counterbore  34  in the proximal end of inner insulator  26 . Counterbore  34  can be mechanically cut, integrally molded or formed by other means known to those skilled in the art within the proximal end of inner insulator  26 . The distal end of lead insulator  22  is adapted to fit within counterbore  34  at the proximal end of coil electrode  14  such that inner insulator  26  may be secured in counterbore. The distal end of lead insulator  22  is typically secured within counterbore  34  using an appropriate adhesive for the materials and application. Alternatively, lead insulator  22  could be secured within counterbore  34  by welding, thermal or chemical bonding of the insulators with one another, or by configuring the proximal end of lead insulator  22  and counterbore  34  to mechanically interlock. The embodiment shows the electrical connection of conductor  27  to the wire  24  over a wound region  44  wherein wire  24  is wound around conductor  28  and inner insulator  26  bringing wire  24  into contact with conductor  27 . Alternatively, the other methods of electrically connecting conductor  27  to wire  24  discussed above could be used. 
     As noted above, the use of a defibrillation/pacing electrode as described herein is for exemplary purposes only. It will be understood by those skilled in the art how to apply the present invention to a variety of medical leads.