Abstract:
An implantable endocardial defibrillation lead having an elongated lead body with multiple lumens therein. Windows, cut through the lead body, provide access to selected ones of the lumens at selected locations along the lead body. In addition, a method and an apparatus for forming windows in a multilumen lead body are disclosed. A ferromagnetic stylet is inserted into a selected lumen. The lead body is oriented in a jig by application of an electromagnetic field. A grinder or punch cuts a window into the selected lumen.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to implantable cardiac stimulation devices and systems for regulating the contraction of a heart. More particularity, the invention relates to a defibrillation lead, and more particularly to a defibrillation lead having multiple lumens therein and to a method of manufacturing for such leads. 
     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 conductors are connected to pacing or defibrillation electrodes or to sensors or other devices at selected locations along the length of the lead body. To connect the electrodes or other devices to a conductor, it is frequently necessary to cut a window through the lead body to gain access to a selected lumen. Because lead bodies are often made of silicon rubber and are very flexible, it is difficult to make these windows in a replicable fashion. 
     SUMMARY OF THE INVENTION 
     We have invented an implantable defibrillation lead with an elongated, flexible lead body having multiple lumens and windows at selected locations along the lead body, the windows providing access to selected lumens. We have also invented a method of manufacturing such leads and an apparatus for performing this method. According to our invention, a jig with an electromagnetic table supports a lead body. A ferromagnetic stylet, inserted in a selected lumen of the lead body orients the lead body in the jig when the lead body is placed within the magnetic field of the electromagnet. Mechanical grinding wheels then remove material at selected locations to form the windows. Alternatively, a punch could also form the windows. 
     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. In one embodiment of the invention, the lead includes tines. A small fixation screw for securing the distal end of the lead within the heart, wherein the fixation screw also functions as a pacer stimulating and sensing electrode, could be used. 
     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 manufacturing windows in lead bodies according to the present invention. 
     FIG. 8 is a cross sectional view of a multilumen lead and ferromagnetic stylet according to our invention. 
     FIG. 9 is a cross sectional view as in FIG. 8, showing two magnets. 
     FIG. 10 is a cross sectional view as in FIG. 8, showing a punch. 
     FIG. 11 is a cross sectional view as in FIG. 8, showing two cutters. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The presently preferred embodiment 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 . 
     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  is cut through a portion of the lead body  56  to expose the second lumen  106 . An apparatus and method for forming this window will be further discussed below. 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  1   10  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; preferably two loops. In multi-filar coils, each filar 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 . 
     We will now describe an apparatus for preparing a window in the lead body  56 . A cutting apparatus  150  is illustrated in perspective view in FIG. 7. A jig  152  is mounted on a base plate  153 . The jig  152  has a sliding table  154  which holds a support beam  156  by means of end brackets  158 , 160 . Machine screws  162  fasten the end brackets  158  to the table  154 . Machine screws  164  connect the support beam  156  to the end brackets  158 . A groove  166  runs longitudinally along the support beam  156  for receiving and supporting a lead body  56 . Magnets  168  are mounted in the support beam  156  to attract a ferromagnetic stylet inserted in a lumen in the lead body. These magnets  168  are preferably fixed magnets but may also be electromagnets. Suitable fixed magnets are rare earth magnets available from Duracore. A back plate  170  mounted on the support beam  156  helps to prevent the lead from being displaced by the action of end cutter used to make a window in the lead body. In the illustrated embodiment, a slot  172  allows the cutter to pass through the back plate  170  during the cutting operation. 
     Two ball bearing slides  174 , 176  support the table  154  which is fastened thereto by machine screws  177 . The ball bearing slides  174 ,  176  are free to reciprocate smoothly between pillow blocks  178 , 180 , 182 ,  184  which support respective pairs of slide rods  186 ,  188  and  190 , 192 . The ball bearing slides  174 ,  176  enable the jig  152  to be moved smoothly in a first linear direction which we will call the Z direction. This movement brings the lead body  56  into contact with a grinding wheel  200 . The position of the grinding wheel  200  can be adjusted in two other mutually orthogonal directions which we will call X and Y directions, thus providing a complete range of adjustment for making the required window in the lead body  56 . In our preferred embodiment, this cutter comprises a grinder  194 . The grinder  194  comprises a grinder motor  196  which turns a shaft  198 . The grinding wheel  200  is mounted on the end of this rotating shaft  198 . The motor is supported by a motor mount  202  which has a horizontal micrometer  204  for adjusting the position of the grinding wheel  200  in the X or horizontal direction. A vertical micrometer  206  is also provided for adjusting the position of the grinding wheel  200  in a vertical or Y direction. A base  208  is fastened to the horizontal micrometer  204  and supports an upright mounting plate  210 . In its turn, the upright mounting plate  210  supports the vertical micrometer  206  which is attached to the motor  196 . As a safety feature, a shield  214  is mounted to a shield bracket  212  which shield bracket is also connected to the motor  196 . A live center  216  rides against the end of the shaft  198  to reduce vibration. 
     In operation, a lead body is placed in the groove  166 . The position of the grinding wheel  200  is carefully adjusted using the horizontal and vertical micrometers  204 ,  206 . With the grinding wheel spinning  200 , the table supporting the support beam  156  slides horizontally in the Z direction, thus causing the lead body  56  to pass under the grinding wheel  200  and cutting the desired window in the lead body. The lead body is properly oriented by the action of the magnets  168  on the ferromagnetic stylet in the lead body  56 . 
     This can be seen more clearly in FIG. 8 which shows a lead body  56  in cross section mounted on the support beam  156 . The ferromagnetic stylet  220  is in the first lumen  102 . The second lumen  106  is oriented properly by action of the magnet  168  on the ferromagnetic stylet  220 . Sliding the table  154  in the Z direction shown brings the lead body  56  into contact with the grinding wheel  200 , cutting the window  108 . 
     An alternative configuration is illustrated in cross section in FIG.  9 . In FIG. 9 the lead body  56  is shown oriented toward the magnet  168  by magnetic action on the ferromagnetic stylet  122  such that the second lumen  106  may be cut by the cutter. A second magnet  222  is also provided. This magnet  222  is preferably an electromagnet connected to a power supply  224 . Of course, electromagnets could be used for both first and second magnets. When the electromagnet  222  is activated, the ferromagnetic stylet  220  responds to both magnetic fields and readjusts the position of the lead body  56  such that a third lumen  107  can be cut. Of course, if an electromagnet is also used for the first magnet  168 , that magnet may be turned off when the second magnet  222  is turned on. 
     It will be recognized that other types of cutters may be used in place of a grinder wheel  200 . For example, a punch  226  or knife edge could be utilized as illustrated in FIG.  10 . In addition, multiple cutters could be utilized as illustrated in FIG.  11 . The cutters may be made movable rather than the table  154 , allowing windows to be cut in different lumens without reorienting the lead body  56 . Alternatively, it may be desired to cut more than one window into the same lumen. Multiple parallel cutters would allow such an operation to be done in a single step. 
     Those skilled in the art will recognize from the foregoing description that the multilumen lead with windows of our invention can be used in cardiac leads in other configurations without departing from the teachings of our invention. For example, more then one looped cable conductor could be provided for bipolar defibrillation shocks. Low voltage connections could be provided to some, all or none of such looped cable conductors. 
     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.