Abstract:
An apparatus and method for laser stripping coated cables for endocardial defibrillation leads comprising a jig for holding at least one insulated wire, the jig having a base plate, a linear stripping area on the plate, a first clasp mounted on the plate for holding a first end of the wire, at least two primary pins mounted on the plate on a first side of the linear stripping area, at least one secondary pin mounted on the plate on a second side of the linear stripping area, and a second clasp mounted on the plate for holding a second end of the wire; and a laser effective to remove insulation from the insulated wire, the laser being mounted to effectively remove insulation in the linear stripping area.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to implantable cardiac defibrillation leads, and more particularly to a defibrillation lead having a coated cable conductor therein and to a method of manufacturing for such leads. An apparatus for manufacturing cables by selective laser removal of insulation is described. 
     2. Description of the Related Art 
     Implantable medical devices for treating irregular contractions of the heart with electrical stimuli are well known in the art. Some of the most common forms of such implantable devices are defibrillators and pacemakers. 
     Defibrillators are implantable medical devices used to treat fibrillation, a condition characterized by rapid, chaotic electrical and mechanical activity of the heart&#39;s excitable myocardial tissue that results in an instantaneous cessation of blood flow from the heart. Defibrillation is a technique employed to terminate fibrillation by applying one or more high energy electrical pulses to the heart in an effort to overwhelm the chaotic contractions of individual tissue sections and to restore the normal synchronized contraction of the total mass of tissue. 
     A pacemaker, or pacer, is an implantable medical device that delivers low energy electrical pulses to stimulate a patient&#39;s heart to beat at a desired rate in instances where the heart itself is incapable of proper self-regulation. This occurs when the heart&#39;s natural pacemaker, which causes the rhythmic electrical excitation of the heart and pumping of blood, malfunctions due to age or disease. Demand pacing is a process used to maintain normal beating of a heart having this condition. 
     Various types of leads for defibrillators and demand pacers have been suggested in the prior art. For example, large electrical patches sewn to the exterior surface of the heart have been used to deliver defibrillation pulses to the heart. Implantation of such patch electrodes requires opening of the patient&#39;s chest during thoracic surgery. For pacing, pulses may be applied to the heart with the use of a pacer lead having an exposed metal surface, or demand pacer electrode, extending through a vein and into the heart. 
     Those involved in the medical arts recognized that prior art defibrillators required a high threshold level of energy for effective defibrillation, which limited the useful life-span of the devices and, more significantly, posed a significant risk of causing electrolysis of the blood and myocardial damage. It was realized that the defibrillation electrode configuration played an important role in the amount of energy needed to achieve successful defibrillation. This led to the development of transvenous defibrillation leads having long coil-shaped defibrillation electrodes for implantation into the right ventricle of the heart through a vein. For example, U.S. Pat. No. 4,922,927, the entire disclosure of which is incorporated herein by reference, discloses a defibrillation electrode made up of a plurality of separate wires wound side-by-side to form a tight coil. The coil was disposed upon an insulated tubular member and had a length sufficient to extend throughout the entire length of the ventricular chamber to provide sufficient electrode surface area for defibrillation. 
     Transvenous cardiac stimulation leads, such as the device of U.S. Pat. No. 4,922,927, were configured to also carry a demand pacing electrode. Thus, a single device implantable in one surgical procedure could provide defibrillation and pacing pulses for heart patients suffering from both irregular heart beat and, at times, cardiac fibrillation. This eliminated the need for multiple and complex surgical procedures to attach the prior art electrodes required for both types of treatments. 
     Another defibrillation electrode configuration for use with dual purpose transvenous leads is disclosed in U.S. Pat. Nos. 5,476,502 and 5,374,287 to Rubin, which are also incorporated herein by reference in their entireties. The “Rubin” catheter included either a helical or lance shaped defibrillation electrode for delivering a defibrillation pulse directly to the interior of the septum of the patient&#39;s heart. The length of the helix-shaped electrode to be screwed into the septum from the right ventricle, about 0.5 cm to 1.0 cm, was substantially shorter than the conventional coiled transvenous defibrillation electrodes. 
     Despite these developments there continues to be a need for a lead capable of providing both high voltage defibrillation and effective demand pacing with a smaller lead diameter to minimize obstruction in the veins leading to the heart. One such lead has been developed by some of the inventors herein and others. A commonly-assigned patent application has been filed entitled Endocardial Defibrillation Lead with Looped Cable Conductors, attorney docket no. ITM-609 US, the disclosure of which is incorporated herein by reference. This lead has a looped cable conductor for conducting high voltage defibrillating shocks to the heart and a coil conductor for conducting low voltage pacing pulses. These two conductors are carried in separate lumens within a lead body. Additional lumens may be provided for additional conductors if additional functions are desired. The looped cable conductor has insulation which must be accurately removed at selected locations. 
     SUMMARY OF THE INVENTION 
     We have invented a method of manufacturing an implantable defibrillation lead with an elongated, flexible lead body having folded cable conductors and an apparatus for performing this method. According to our invention, a jig supports an insulated cable conductor in a looped configuration, exposing selected portions of the conductor over a linear stripping area. A laser selectively removes insulation from the cable. The cable is then folded into a doubled configuration and inserted into a lead body of an endocardial lead. 
     In a preferred embodiment, there is provided an implantable endocardial defibrillation lead having a looped cable conductor for conducting at least high voltage defibrillation shocks. A coil electrode is connected to an elongated, flexible, electrically non-conductive lead body and is supplied with electrical power for delivering electrical shocks to the heart through a looped cable conductor that extends through the lead body and is associated with a power source. 
     Depending upon the desired application for the lead, the invention may also be used with a pacer and, thus, include any of a variety of pacer electrodes and sensors that are presently available or may become available. Such devices, if used, would be disposed upon the lead, insulated from the defibrillator electrode segments and electrically connected with a second electrical conductor that extends through the lead body and provides electrical power to the pacer electrode. The lead may also include a ground electrode disposed upon the lead a distance from the other electrodes to receive the pulses delivered to the heart tissue and transmit them back through a third electrical conductor extending through the lead. The coil electrode and looped cable conductor may also serve a dual function as a ground electrode and conductor. 
     The invention may also be adapted for fixation of the distal end of the lead to the heart to achieve selective positioning of the electrode or electrodes. A variety of currently available passive and active fixation mechanisms, or that may become available, may be used with the invention, such as tines or a fixation screw for securing the distal end of the lead within the heart. 
     Moreover, multiple coil defibrillation electrodes may be used, for example, for placement in the ventricle and in the superior vena cava of a patient. The defibrillation electrode may be energized through a single cable conductor, in which case insulation must be removed from more than one area of the conductor. Furthermore, if the defibrillation coil or coils are used both for defibrillation an as an anode for cardiac pacing, low and high voltage connections to the cardiac stimulator are usually provided. This would require multiple areas without insulation at the proximal end of the lead as well. Our method and apparatus accurately prepares a cable conductor for use in a defibrillation lead. 
     The apparatus of our invention comprises a jig for holding at least one insulated wire, the jig having a base plate, a linear stripping area on the plate, a first clasp mounted on the plate for holding a first end of the wire, at least two primary pins mounted on the plate on a first side of the linear stripping area, at least one secondary pin mounted on the plate on a second side of the linear stripping area, and a second clasp mounted on the plate for holding a second end of the wire; and a laser effective to remove insulation from the insulated wire, the laser being mounted to effectively remove insulation in the linear stripping area. 
     The characteristics and advantages of the present invention described above, as well as additional features and benefits, will be readily apparent to those skilled in the art upon reading the following detailed description and referring to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a detailed description of the preferred embodiments of the invention, reference will now be made to the accompanying drawings wherein: 
     FIG. 1 is a plan view of an implantable defibrillation and pacing lead. 
     FIG. 2 is a perspective view of a cable conductor used in the lead. 
     FIG. 3 is a partial section of a distal end of the lead of FIG. 1 with a window for allowing connection of a cable conductor to a defibrillation electrode. 
     FIG. 4 is a plan view of the assembled inner sleeve and cable conductor at the window. 
     FIG. 5 is a through section of the window of FIG. 4, taken along line  5 — 5 . 
     FIG. 6 is a partial through section of the proximal end of the lead. 
     FIG. 7 is a perspective view of an apparatus for stripping insulation from a cable conductor according to the present invention. 
     FIG. 8 is a perspective view of the apparatus of FIG. 7 with laser according to our invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The presently preferred embodiments of the invention are shown in the above-identified figures and described in detail below. In describing the preferred embodiments, like or identical reference numerals are used to identify common or similar elements. The figures are not necessarily to scale and certain features and certain views of the figures may be shown exaggerated in scale or in schematic form in the interest of clarity and conciseness. 
     FIG. 1 illustrates a plan view of an endocardial high voltage cable lead  14 . A ventricular tip cathode or electrode  22  and shock coil  24  are located at distal end  44  of the lead  14 . At a proximal end  46  of the lead there is a high voltage connector  48  and a low voltage connector  50 , preferably an IS-1 (international standard one) connector. The two connectors  48 ,  50  are joined at a junction  52  which is covered by an insulative boot  54 . A lead body  56  extends between the distal end  44  and the proximal end  46 . A suture sleeve  58  is slidingly received on the lead body  56  and conventionally provides additional support for the lead  14  where it is inserted in a blood vessel of a patient. At the tip cathode  22 , tines  60  may be provided to help secure the lead  14  within the heart. Other well known active or passive fixation devices, such as helical screws, may be provided. Such features are well known in the art and need not be further described herein. 
     The shock coil  24  comprises a segment  62  of coiled wire, preferably multi-filar, more preferably tri-filar. A distal cap  64  secures one end of the segment  62 , while a proximal sleeve  66  secures the other end. More detail concerning the shock coil  24  will be provided hereafter. 
     Regarding the proximal end  46  of the lead  14 , the low voltage connector  50  is provided with annular sealing rings  68 ,  70  to prevent body fluids from injuring the connector, when the connector is inserted into the implantable device. Between the sealing rings  68 ,  70 , a lead connector  72  may be provided. A pin connector  74  is located at the proximal end of the lead, thus providing two electrical contacts for the low voltage connector  50 . Through these connectors  72 ,  74 , the electrical condition of the heart may be sensed, particularly of the ventricle, if the distal end of the lead  14  is implanted therein. In addition, pacing pulses and other low voltage therapy may be provided through these connectors to the tip cathode  22 . As will be more fully explained below, the shock coil  24  may be used as a low voltage anode or indifferent electrode if bipolar sensing or pacing is desired. Alternatively, a conventional low voltage ring electrode could be provided near the distal end of the lead. 
     The high voltage connector  48  also has annular sealing rings  76 , but is usually provided only with a pin connector  78 . The electrical path for high voltage shocks is usually between this pin connector  78  through an electrical conductor to the shock coil  24  and back through the heart to a can of the implantable medical device (not shown). However, an additional coiled electrode could be provided, forming a bipolar shock electrode. Where two coiled shock electrodes are used, they are frequently placed on the lead such that one would be in the ventricle and the other in the atrium or superior vena cava. Multi-filar coiled connectors have heretofore been used to conduct the electrical current for the shock to one or more shock coils. 
     In a preferred embodiment, a looped cable conductor is provided. The cable conductor  80  is illustrated in prospective view in FIG.  2 . The cable conductor  80  comprises a conductive multi-strand wire  82 . Preferably, most of the wire  82  has insulation  84 . A middle section of the wire  86  is stripped of insulation, and then the cable conductor is folded back on itself, forming a loop or bend  92  at the middle section  86 . Each end  88 ,  90 , of the conductor is also stripped of insulation. As a consequence of the looped construction described, the conductor  80  forms a redundant system, as either side of the conductor is capable of carrying current to the shock coil  24 . If additional electrodes are wanted, additional locations on the wire  82  may be stripped of insulation. The exposed areas must be accurately placed so that two exposed areas come together when the wire  82  is folded. 
     We will describe the distal end  44  of the lead  14  in greater detail, in connection with FIG.  3 . FIG. 3 is a partial through-section of the distal end  44 . As can be seen in FIG. 3, the tip cathode  22  comprises a shank  94  which extends into the distal cap  64 , and into the lead body  56 . The tines  60  are formed on the distal cap  64 . In addition, the distal cap  64  captures a distal end  112  of the coil segment  62 . Within the shank  94 , a stopped bore  96  receives a crimp plug  98  and a coil conductor  100 . The coil conductor  100  is a conventional low voltage conductor which extends from the tip cathode  22  to the pin connector  74  and electrically couples the cathode  22  and the pin connector  74 . The shank  94  is crimped over the crimp plug  98  to secure the conductor  100  between the crimp plug and the shank. 
     The coil conductor  100  passes through a first lumen  102  in the lead body  56 . Preferably this lumen is non-coaxial, that is, it is offset from the axis of the lead body  56 . However, to receive the shank  94  symmetrically with respect to the lead body, a stopped bore  104  is provided in the distal end of the lead body. This stopped bore is coaxial with the axis of the lead body itself. A second lumen  106  is provided to receive the looped cable conductor  80 . Preferably, this lumen is also non-coaxial with respect to the lead body and may be smaller in diameter than the first lumen  102 . Additional lumens may be provided where additional looped cables are connected to other electrodes, such as a second shock electrode. 
     A window  108  cuts through a portion of the lead body  56  to expose the second lumen  106 . An arcuate crimp sleeve  110  fills this window  108  and captures the stripped middle section  86  of the cable conductor  80 . A proximal end  114  of the coil segment  62  extends over the arcuate crimp sleeve  110  and is covered by the proximal sleeve  66 . This proximal end  114  preferably extends for a plurality of loops proximal to the arcuate crimp sleeve. In multi-filar coils, each filer should form the loops proximal to the arcuate crimp sleeve. This extension proximal to the crimp sleeve relieves mechanical stresses, and reduces the possibility of a mechanical failure adjacent the crimp sleeve. A circumferential bead of adhesive  116  seals the distal cap  64  to the coil segment  62  and underlying lead body  56 . A similar adhesive bead  118  likewise seals the proximal sleeve  66  to the coil segment  62  and lead body  56 . 
     Further detail of the window and lumens can be seen in FIGS. 4 and 5. FIG. 4 is a top plan view of the window  108  with crimp sleeve  110 , with the cable conductor  80  shown in phantom lines. FIG. 5 is a plan through section of the multilumen lead body. 
     Once the crimp sleeve  110  has been positioned in the lead body, the proximal sleeve  66  can be slid onto the lead body. The coiled segment  62  is then placed on the lead body with the proximal end extending past the crimp sleeve  110 . The coil  62  is then laser welded to the crimp sleeve. The proximal sleeve  66  is brought up over the proximal end of the coil  62  and secured with adhesive, as described above. 
     The proximal end  46  of the lead is shown in FIG. 6, showing a partial through section of a plan view of the distal end  46  of the lead. The boot  54  encloses an assembly connecting the two connectors  48 ,  50 . A crimp connector  136  is connected to a coiled conductor  138  which is electrically and mechanically connected to the pin connector  78  of the high voltage connector  48 . The coil conductor  138  passes through an insulating sleeve  140 . The low voltage connector  50  has a coaxial lead segment  142 . The coil conductor  100 , described above in connection with the distal end of the lead, passes co-axially down the lead segment  142 , that is, the axis of the coil  100  and the axis of the lead segment  142  coincide. An inner tubing  144  surrounds the coil conductor  100 . A return low voltage coil conductor  146  surrounds the inner tubing  144  and is connected proximally at one end to the ring connector  72  and at a distal end  150  to the crimp connector  136 . An outer tubing  148  encases the return coil  146 . 
     An apparatus and jig for preparing the cable  80  are illustrated in FIGS. 7 and 8. In FIG. 7 a jig  160  is illustrated in perspective view. The jig  160  comprises a base plate  162  having a linear stripping area  164 . The linear stripping area  164  has slot  166  through the plate  162 . A laser beam is directed to exposed areas of the conductor  80  to remove insulation at selected areas. The jig  160  is preferably configured so that a plurality of cables  80  can be manufactured at one time. In the illustrated embodiment, four cables could be installed in the jig for installation removal. A single-cable jig is illustrated in FIG.  8 . For clarity of explanation, the components for a single cable conductor  80  will be described, but it is to be understood that this could be replicated as often as desired. 
     With this understanding, it can be seen that jig  160  has a first clasp  168  adjacent the linear stripping area  164 . This clasp is used to grasp an end of the conductor  80 , as can be seen in FIG.  8 . The clasp comprises a first post  170  with an elastomeric sleeve  172  thereon and a second post  174  spaced away from the first post  170 . The second post  174  also has an elastomeric sleeve  176 . When the end of the conductor  80  is placed between first and second post, the elastomeric sleeves press against the conductor  80  and hold the end in a desired location. On the opposite side of the linear stripping area  164  from the first clasp  168 , there is a plurality of primary pins  178 . The number of primary pins  178  is a function of the desired of configuration of the conductor  80 . 
     On the same side of the linear stripping area  164  as the first clasp  168 , there are secondary pins  180 . As will be explained below, sets of secondary pins may be provided to accommodate different lengths of conductors  180 . There is also a set of tertiary pins  182 , on the same side of the linear stripping area  164  as the secondary pins  180 , but placed much closer to the linear stripping area, and preferably adjacent the linear stripping area. 
     Finally, there is a second clasp  184  for grasping the second end of the conductor  80 . Like the first clasp  168 , the second clasp  184  comprises a third post  186  enclosed in an elastomeric sleeve  188  and a fourth post  190 , also enclosed in an elastomeric sleeve  192 . Shield bars  194 ,  196  are provided which can be placed over the conductor  80 , as seen in FIG. 8, and adjacent the linear stripping area. These shield bars serve to block exposure to laser radiation and to conduct heat away from the area being irradiated by laser light. This allows a well defined area on the conductor  80  to be stripped of insulation. Additional lower shield bars  196  are provided below the conductor  80  and serve a similar function to the upper shield bars  194 . In our preferred embodiment, the laser radiation is provided from below the base plate  162 . In this configuration, the base plate  162  serves an additional shield for the conductor  80 . It is easier to remove the vapors resulting from the incineration of the insulation on the conductor  80  which results from exposure to the laser radiation. Index pins  198  are provided for the removable placement of the upper shield bars  194 . Each of these pins  198  engages a respective bore  200  in an upper shield bar  194 . 
     The jig  160  is loaded with a conductor  80 , as will be more fully described below, and then placed on a work table  202  which has a opening (not shown) at least exposing the linear stripping area  164 . A laser  204 , mounted below the work table  202 , focuses on selected parts of the conductor  80  to burn away the insulation at those selected parts. A suitable laser is manufactured by Lumonics Corporation of Livonia, Mich. The laser  204  is controlled by a laser control apparatus  206 . A displacement mechanism  208  is also under the control of the laser control  206 . The laser control apparatus  206  both turns the laser beam on and off and causes the displacement mechanism  208  to linearly displace the laser  204  along linear stripping area  164  and to remove insulation at selected locations on the conductor  80 . In general, insulation is removed from conductor  80  every second time the conductor passes over the linear stripping area  164 . 
     We will now describe how the conductor  80  is installed in the jig  160 . On the end of the conductor  80  is placed in the first clasp  168  and the conductor is taking across the linear stripping area  164 , around a first of the primary pins  178 , back across the stripping area  164  around a tertiary pin  182 , across the stripping area  164 , and around a primary pin  178 . The conductor  80  is then extended across the stripping area  164  and to a secondary pin  180  which is, as illustrated, a substantial and selected distance away from the linear stripping area. The conductor is then brought back across the stripping are  164 , around a third primary pin, back to a secondary pin  180 , and then back to a fourth primary pin  178 . 
     It can be seen in FIG. 7 that several sets of secondary pins  180  may be provided. For instance, a first set  210  of secondary pins  180  may be provided at a selected distance from the stripping are  164 . A second set  212  and a third set  214  of secondary pins may also be provided. A particular set of secondary pins is used depending on the overall length of the cardiac lead that is being constructed. Cardiac leads are different lengths to accommodate different physiologies in patients. The distance of the secondary pins  180  from the primary pins  178  is related to the length of lead desired. 
     After passing around the fourth primary pin  178 , the conductor again crosses the stripping area  164 , passes around the second tertiary pin  182 , crosses the stripping area  164 , passes around the fifth and final primary pin  178 , and is secured in the second clasp  184  after crossing the stripping are  164  for a final time. This pattern may be duplicated as often as desired so that more than one conductor may be manufactured substantially the same time. In the illustrated embodiment of FIG. 7, four conductors could be processed at the same time. 
     It can be seen by an examination of the apparatus thus described that there is generally one more primary pin than there are both tertiary pins and a set of secondary pins used in any desired set up. Of course, cables could be installed using fewer pins, and the tertiary pins could be omitted. Tertiary pins are used when it is desired to have a cable with two connection locations are desired adjacent the approximate end of the lead. 
     Those skilled in the art will recognize from the foregoing description that the cable lead of our invention can be used in cardiac leads in other configurations without departing from the teachings of our invention. 
     While preferred embodiments of the present invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit or teachings of this invention. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of this system and apparatus are possible and are within the scope of the invention. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims which follow, the scope of which shall include all equivalents of the subject matter of the claims.