Abstract:
A method for securing a coil or cable conductor to an electric element including an implantable electric element having a longitudinal edge electrically coupled to a coil or cable conductor. The coil or cable having filars with ends configured to contact the longitudinal edge of the electric element. The ends secured to the longitudinal edge by welding, soldering or an electrically conductive adhesive.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to lead assemblies for medical devices, and more specifically to a method and apparatus for providing a secure electrical connection between wound elements, as found in unifilar and multifilar coil conductors, and electric elements, such as lead connector pins, electrodes, sensors and various other elements employed in lead assemblies for implantable medical devices. 
     BACKGROUND OF THE INVENTION 
     Implantable leads form an electrical connection between a pulse generator or other electronic device and a tissue or structure in the body. For example, leads transmit electric signals used to stimulate cardiac or nerve tissue in one direction and signals generated by sensors placed in proximity to particular organs or tissues in the opposite direction. Leads typically include one or more electric elements at the lead&#39;s distal end. The electric elements are designed to form an electrical connection with a tissue or organ. Most leads also include a lead connector pin at the lead&#39;s proximal end. Lead connector pins are adapted to electrically and mechanically connect leads to the pulse generators or other electronic medical devices. A flexible conductor connects the electric element to the lead connector pin. Commonly, the flexible conductor takes the form of a single or multifilar wire coil. Although, there is an increasing interest in using stranded cables as conductors. Regardless of the form, the flexible conductors are typically surrounded by an insulating layer of material. Together, the flexible conductor and the insulating layer form the lead body. The lead body couples the lead connector pin at the proximal end with the electric element at the distal end. 
     Manufacturing leads is costly. Forming a secure electrical junction between the conductors and electric elements has proven difficult and time consuming. Laser welds are commonly used to connect the filars or wires that make up the conductors to electric elements. The conductor&#39;s filars are typically helically wound into a coil for increased reliability. Laser welding the coiled filars to electric elements typically requires that the end of a coil be ground flat. Grinding the ends flat allows sufficient contact between the coil and the electrical element to weld the two together with a butt joint. Grinding increases the time, complexity and cost of manufacture. Further, welding requires the synchronized rotation of the conductor and electric element to weld at the various points around their circumference. The rotating also adds to the time, complexity and costs of manufacture. Alternatively, ring electrodes are connected to a conductor by etching away a region of insulator, applying a coating of electrically conductive adhesive, and then placing the ring electrode around the conductor. This method is also time consuming and expensive. Hence, there exists a need to improve the manufacturing techniques used to secure electric elements to conductors in leads to reduce the time, complexity and cost. 
     In addition, current manufacturing techniques do not allow welding an electrical element to a coil without adding elements that increase the lead&#39;s diameter near the weld. In application, a uniform diameter weld would result in a smaller lead. A smaller diameter lead is desired to allow placement in restricted spaces such as cardiac veins or the epidural space to reduce the effects of implanted lead on the patient. Further, a smaller lead allows for a smaller introducer that reduces the trauma associated with implantation and similarly a smaller removal sheath when explanting the lead. Hence, there exists a need to reduce the diameter of the welds used to secure electric elements to conductors in implantable medical leads. 
     The present invention meets these needs and provides other advantages and improvements that will be evident to those skilled in the art. 
     SUMMARY OF THE INVENTION 
     The present invention provides a uniform diameter junction for an implantable lead and reduces the time, complexity and costs of producing implantable electrical leads by allowing the use of a straight line weld of the conductors to the electric elements. In addition, the junction typically results in a uniform diameter connection between the lead body and the electric element. 
     In accordance with the present invention, a method and lead design are provided for longitudinally securing the cut ends of a conductor to an electric element. The present invention&#39;s method for manufacturing an implantable medical device leads includes a conductor having at least one filar and an electric element having a longitudinal edge. The electric element can be a ring electrode, a terminal pin, a splice ring, a terminal ring, a lead connector pin, a sensor or other implantable medical device commonly attached to leads. The filars can be spirally wound into the conductor at a substantially constant pitch. The filars are cut in a direction parallel to a longitudinal axis of the conductor to form at least one collinear cut end. The collinear cut end is parallel to the longitudinal axis of the conductor. The ends are secured to the longitudinal edge of the electric element to provide an electrical connection. The cut ends can be secured to the electrical element by laser welding, resistance welding, soldering, swaging, electrically conductive adhesives, micro arc welding or by other methods known to those skilled in the art. In addition, the longitudinal edge can combine with a second edge to define a notch. The second edge is configured to have a pitch corresponding to the pitch of the filars. The corresponding pitch allows one of the plurality of filars to abut the second edge over the distance that the electric element and the conductor are coextensive. Further, the plurality of filars can embedded in an elongated, flexible elastomeric insulator. The insulator can define a lumen adapted to receive a stylet for guiding the lead into the patient. A portion of the insulator may be removed from the conductor&#39;s proximate end prior to welding. Typically, the insulator is removed mechanically or by chemical etching. 
     The present invention further discloses an implantable lead for a medical device. The implantable lead includes at least one conductor and one or more electric elements. The conductor has one or more filars wherein each filars terminate in an end. The ends are typically generated by cutting using any of a number of techniques known to those skilled in the art. The ends are cut so as to be collinearly oriented in a direction parallel to a long axis of the conductor. The filars can be spirally wound into the conductor at a substantially constant pitch. The electrical element also has a longitudinal edge. The longitudinal edge is configured to contact the cut ends and the cut ends are secured to the longitudinal edge, typically in a laser-welding step. When the filars are wound at a substantially constant pitch, the electrical element can have a second edge having a pitch corresponding to the pitch of the filars. The longitudinal edge and a second edge of the electric element cooperate to define a notch extending inwardly from one end of the electric element. The notch is shaped so that one of the plurality of filars abuts the second edge over the distance that the electric element and the conductor are coextensive. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an implantable lead in which an embodiment of the present invention is practiced; 
     FIG. 2A illustrates a fragmentary view of a unifilar conductor used in a unipolar lead of FIG. 1; 
     FIG. 2B illustrates a fragmentary view of a multifilar conductor used in a unipolar lead as in FIG. 1; 
     FIG. 3 illustrates a fragmentary view of a multifilar conductor used in a bipolar lead as in FIG. 1; 
     FIG. 4 is a perspective drawing illustrating an embodiment of a ring electrode; 
     FIG. 5A is a perspective drawing illustrating an embodiment of the interconnection between the conductor and the ring electrode illustrated in FIG. 4; and 
     FIG. 5B is a side elevation drawing of the interconnection illustrated in FIG.  5 A. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is applicable to a variety of implantable medical devices utilizing an electric current to stimulate selected body tissues or to transmit signals from a sensor or electrode contacting selected tissue to the medical device. The invention is described in the context of an electrode on a cardiac pacing lead as a specific example for illustrative purposes only. The appended claims are not intended to be limited to any specific end use, example or embodiment described in this specification. It will be understood by those skilled in the art that the invention may be used to provide electrically and mechanically secure connections between wound conductors and electrical elements in a wide variety of implantable leads including, but not limited to, pacing leads, sensing leads, defibrillation leads, unipolar leads, multipolar leads, and leads with extendable positive helix fixation electrodes. 
     FIG. 1 illustrates a unipolar lead  10  made in accordance with the present invention. Lead  10  consists of an electrode assembly  11 , a lead body  12 , and a lead connector pin  18 . Lead  10  is designed to facilitate insertion through a selected vein and then guiding electrode assembly  11  into the right ventricle of the heart or alternatively into a branch of the great coronary vein. Electrode assembly  11  then provides a pacing electrical stimulus to the heart. For exemplary purposes, electrode assembly  11  includes a tip electrode  14 , a ring electrode  16  and tines  15 . Electrode assembly  11 , as shown, is configured to be secured within the trabeculae of the right ventricle by tines  15 . Tip electrode  14  is typically a cathode. Ring electrode  16  can be an anode or a sensor for measuring biological parameters. Lead body  12  is typically elongated and flexible enabling the lead to be directed through the veins and heart of the patient. In its most basic form, lead body  12  includes one or more conductors (described in more detail below) covered by an insulator. The conductors transmit an electrical current to and/or from a tissue. The insulator prevents electrical leakage or short circuits. The insulator can be any of a variety of materials, including silicone, polyurethanes, fluoropolymers or other polymeric materials known to those skilled in the art. The insulators are generally selected based on biocompatibility, biostability and durability. Lead connector pin  18  is configured to be received by a pulse generator (not shown). The pulse generator may itself be implantable. Typically, the lead connector pin conforms to IS- 1  when used to connect the lead to a pacemaker. The pulse generator can be a neurological stimulator, a cardiac pacemaker, a defibrillator, or other device transmitting an electrical stimulus to a tissue or organ. 
     FIGS. 2A and 2B illustrate details of unifilar and multifilar wound conductors. A unifilar conductor  20  and a multifilar conductor  24  are both shown in unipolar embodiments. The conductors typically extend the length of lead body  12 . Conductors electrically and, to a lesser degree, mechanically connect lead connector pin  18  to the electrodes  14  and sensor  16 . The conductors are typically composed of single or multiple small wires or filars. The filars are typically made of stainless steel, MP35N, drawn-brazed-strand (DBS) or other electrically conductive materials known those skilled in the art. The filars typically range in size from 0.001 inch to 0.015 inch in thickness and typically are round, square or rectangular in cross-sectional shape. Unifilar conductor  20 , shown in FIG. 2A, has a single wire or filar  21  wound around a central axis  22  to define a lumen. The helical winding of filar  21  around axis  22  creates a wound diameter and a pitch. The wound diameter defined as the diameter of the entire coil in cross section. Coiled conductors used in pacing leads typically have wound diameters between 0.010 inch and 0.125 inch, depending on the specific application. The pitch defined as a distance  23  a filar travels along the conductor&#39;s longitudinal axis in making one full wind around the axis. The pitch can vary with the physical dimensions and characteristics of the filar and/or the requirements for a particular application. Multifilar conductor  24 , as shown in FIG. 2B, has more than one filar. Specifically, multifilar conductor  24  is a trifilar conducting coil constructed of three wires or filars  28  spiral wound in parallel around a central axis  25 . The winding of filars  27  around axis  25  also creates a pitch. The pitch defined as a distance  26  a particular filar travels along the conductor&#39;s longitudinal axis in making one full wind around the axis. The pitch can vary with the number of filars  27 , the physical characteristics of the filars and/or the requirements of the application. 
     FIG. 3 illustrates a fragment of a bipolar lead  30 . A bipolar lead has two conductors. Bipolar lead  30  has an inner conductor coil  31  coaxially disposed within the outer conductor coil  32 . When using the lead body design of FIG. 3, outer conductor coil  32  is typically connected to a proximal sensing electrode and inner conductor coil  31  is connected to a distal tip electrode  14  (FIG.  1 ). The inner and outer coils of bipolar lead  30  can be either unifilar or multifilar. Inner conductor coil  31  has a smaller wound diameter than outer conductor coil  32 . An insulator  33  is disposed between inner conductor coil  31  and outer conductor coil  32  and around conductor coil  32 . Insulator  33  can define a lumen (not shown) for insertion of a stylet to stiffen the lead during implantation. The difference between the two conductors&#39; wound diameters is typically sufficient to allow the electrical insulation of the two conductors from one another. Thus, insulator  33  electrically isolates inner conductor coil  31  from the outer conductor coil  32 . An outer insulator  34  electrically isolates the conductors from the lead&#39;s environment. Alternatively, a bipolar conductor could be configured having two separate unifilar or multifilar conductors wound in parallel (not shown). The parallel wound bipolar conductor would have two alternating electrically isolated spiral wound conductors wound in parallel about the longitudinal axis and having the same wound diameter. 
     FIG. 4 illustrates the proximal end of an electric element  40 . Electric element  40  is shown as a ring electrode like electrode  16  of FIG. 1 for illustrative purposes. The proximal end of a sensing electrode, the distal end of a lead connector pin, or any other electric element would be interchangeable with the ring electrode for purposes of the present invention. Electric elements found in implantable leads are typically made from stainless steel, MP35N or other biocompatible materials. In the embodiment shown, electric element  40  includes an exposed region  41  designed to electrically contact a tissue structure. Exposed region  41  is in electrical communication with a longitudinal edge  42 . Longitudinal edge  42  can be integral with or distinct from exposed region  41  depending on the nature of the particular electric element. Longitudinal edge  42  is substantially parallel to a longitudinal axis  45  of electrical element  40 . Further, longitudinal edge  42  can be spaced a distance from longitudinal axis  45  substantially equivalent to winding radius of the filars. Longitudinal edge  42  is configured to allow cut ends of filars to abut to longitudinal edge  42  to facilitate an electrical connection between longitudinal edge  42  and the cut ends. Longitudinal edge  42  is also configured to allow the cut ends of the filars to be welded to longitudinal edge  42 . In other embodiments, longitudinal edge  42  can be configured to allow the cut ends of the filars to be secured thereto using an electrically conductive adhesives, crimping or other methods of connecting cut ends to electric elements known to those skilled in the art. A second edge  43  can also be provided on the electric element. Second edge  43  cooperates with longitudinal edge  42  to form a notch  44 . Second edge  43  may be configured with a pitch corresponding to the pitch of the wound filars. When the pitch of second edge  43  corresponds to the pitch of the wound filars, second edge  43  can contact a filar  53  (shown in FIG. 5B) over a distance  58  that the electric element and the wound filar are coextensive. 
     FIGS. 5A and 5B illustrate the connection between an electrical element  40  and multifilar conductor coil  24 . At least one end  41  is generated by cutting the distal end of the conductor coil along the coil&#39;s longitudinal axis. The coil is typically cut by trimming, grinding, laser cutting or by other means known to those skilled in the art. When there are a plurality of ends, the ends  41  are oriented collinearly with one another. For purposes of the present invention, a plurality of collinear ends means the ends are sufficiently collinear to allow all ends to be secured to longitudinal edge  42  of electrode  40 . A single collinear end means the end is cut in a configuration allowing the end to be secured longitudinal edge  42 . The actual number of ends generated by cutting is typically equivalent to the number of filars in the conductor coil. That is, cutting a unifilar conductor produces one end and cutting a trifilar conductor typically produces three ends. Although, the number of ends can vary from the number of filars, such as when in bipolar conductors are wound in parallel (as described above but not shown). If the conductor has an insulator, the cutting of the conductor coil can either be preceded or followed by the removing a portion of the insulator from the cut ends. The insulator can be removed mechanically, by chemical etching, or by other methods known to those of skill in the art. Longitudinal edge  42  of electric element  40  is then secured to the at least one end  41 . When ends  41  are secured to longitudinal edge  42 , a mandrel (not shown) may be inserted through a lumen defined along the longitudinal axis of the conductor and the longitudinal axis of electric element  40 . As discussed above, the ends can be secured by welding, electrically conductive adhesives or by other methods known to those skilled in the art. When secured by welding the ends can be secured by a single weld  53  extending over distance  52  or by a series of welds  53  extending over distance  52 . 
     This invention has been described herein in considerable detail in order to comply with the patent statutes and to provide those skilled in the art with the information needed to apply the novel principles and to construct and use such specialized components as are required. However, it is to be understood that the invention can be carried out by specifically different equipment and devices, and that various modifications, both as to the equipment and operating procedures, can be accomplished without departing from the invention&#39;s scope.