Abstract:
A medical electrical lead that includes a lead body having a plurality of lead body lumens, an electrode head assembly fixedly engaged with the lead body, a first conductor extending within a first lead body lumen of the plurality of lead body lumens, and a first electrode, positioned along the electrode head assembly, having a deformation coupling the first electrode to the first conductor and transferring traction forces applied to the lead body to the electrode head assembly. A second electrode extends along the electrode head assembly and the lead body and a second conductor extends within a second lead body lumen of the plurality of lead body lumens. An attachment member couples the second electrode and the second conductor and transfers traction forces applied to the lead body to the electrode head assembly

Description:
REFERENCE TO PRIORITY APPLICATION  
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/284,430, entitled “MEDICAL ELECTRICAL LEAD”, incorporated herein by reference in its entirety.  
       CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0002]    Cross-reference is hereby made to commonly assigned related U.S. Applications, filed concurrently herewith, docket number P-10009, entitled “INSULATING MEMBER FOR A MEDICAL ELECTRICAL LEAD AND METHOD FOR ASSEMBLY”; P-10010, entitled “DRIVE SHAFT SEAL FOR A MEDICAL ELECTRICAL LEAD”; P-10012, entitled “IMPLANTABLE MEDICAL LEAD HAVING A RETRACTION STOP MECHANISM”; and P-10051, entitled “MEDICAL ELECTRICAL LEAD”. 
     
    
     
       FIELD OF THE INVENTION  
         [0003]    The present invention relates generally to a medical electrical lead, and, more particularly, the present invention relates to an apparatus for transferring traction forces exerted on an implantable medical electrical lead.  
         BACKGROUND OF THE INVENTION  
         [0004]    A wide assortment of implantable medical devices (IMDs) are presently known and in commercial use. Such devices include cardiac pacemakers, cardiac defibrillators, cardioverters, neurostimulators, and other devices for delivering electrical signals to a portion of the body and/or receiving signals from the body. Pacemakers, for example, are designed to operate so as to deliver appropriately timed electric stimulation signals when needed, in order to cause the myocardium to contract or beat, and to sense naturally occurring conduction signals in the patient&#39;s heart.  
           [0005]    Devices such as pacemakers, whether implantable or temporary external type devices, are part of a system for interacting with the patient. In addition to the pacemaker device, which typically has some form of pulse generator, a pacing system includes one or more leads for delivering generated stimulation pulses to the heart and for sensing cardiac signals and delivering those sensed signals back to the pacemaker. As is known, pacemakers can operate in either a unipolar or bipolar mode, and can pace the atria or the ventricles. Unipolar pacing requires a lead having only one distal electrode for positioning in the heart, and utilizes the case, or housing of the implanted device as the other electrode for the pacing and sensing operations. For bipolar pacing and sensing, the lead typically has two electrodes, a tip electrode disposed at the distal end of the lead, and a ring electrode spaced somewhat back from the distal end. Each electrode is electrically coupled to a conductive cable or coil, which carries the stimulating current or sensed cardiac signals between the electrodes and the implanted device via a connector.  
           [0006]    Combination devices are available for treating cardiac arrhythmias that are capable of delivering shock therapy, for cardioverting or defibrillating the heart in addition to cardiac pacing. Such a device, commonly known as an implantable cardioverter defibrillator or “ICD”, uses coil electrodes for delivering high-voltage shock therapies. An implantable cardiac lead used in combination with an ICD may be a quadrapolar lead equipped with a tip electrode, a ring electrode, and two coil electrodes. A quadrapolar lead requires four conductors extending the length of the lead body in order to provide electrical connection to each electrode.  
           [0007]    In order to perform reliably, cardiac pacing leads need to be positioned and secured at a targeted cardiac tissue site in a stable manner. One common mechanism for securing an electrode position is the use of a rotatable fixation helix. The helix exits the distal end of the lead and can be screwed into the body tissue. The helix itself may serve as an electrode or it may serve exclusively as an anchoring mechanism to locate an electrode mounted on the lead adjacent to a targeted tissue site. The fixation helix may be coupled to a drive shaft that is further connected to a coiled conductor that extends through the lead body as generally described in U.S. Pat. No. 4,106,512 to Bisping et al. A physician rotates the coiled conductor at a proximal end to cause rotation of the fixation helix via the drive shaft. As the helix is rotated in one direction, the helix is secured in the cardiac tissue. Rotation in the opposite direction removes the helix from the tissue to allow for repositioning of the lead at another location.  
           [0008]    Removal of a chronically implanted lead is sometimes necessary, for example, due to a medical complication associated with the implanted lead system or due to the need to implant a new type of lead system. However, after a lead has been implanted in a patient&#39;s body for a period of time, fibrotic tissue growth typically encapsulates the lead, strongly adhering the lead to the surrounding tissue. As a result, considerable traction applied to the proximal end of the lead may be necessary to pull the lead free. Reinforcement of some type, extending along the lead body, is beneficial in preventing breakage or partial disassembly of the lead during extraction. Several such reinforcement mechanisms are disclosed, for example, in U.S. Pat. No. 5,231,996 to Bardy et al.  
           [0009]    In the context of implantable cardiac leads, the use of cabled or stranded conductors in place of commonly used coiled conductors provides increased tensile strength. Exemplary cabled or stranded conductors are disclosed in U.S. Pat. No. 5,760,341 issued to Laske et al., and U.S. Pat. No. 5,246,014 to Williams et al. The improved tensile strength exists substantially between the electrode and the connector that the cabled or stranded conductor is coupled between.  
           [0010]    In leads having an active fixation device, such as a fixation helix, the fixation device is generally housed in a relatively rigid electrode head member to provide support needed in securing the fixation device within the body tissue. The rigid electrode head member is coupled to a lead body that is more flexible for allowing easier passage through the cardiovascular structures. To improve the extractability of a lead of this type, it is desirable to transfer tensile force directly to the relatively rigid electrode head. Providing features that make a lead easier to extract allows the clinician to complete the associated surgical procedure more safely and in less time.  
         SUMMARY OF THE INVENTION  
         [0011]    The present invention is directed to a medical electrical lead including a lead body having a plurality of lead body lumens, and an electrode head assembly fixedly engaged with the lead body. A first conductor extends within a first lead body lumen of the plurality of lead body lumens, and a first electrode is positioned along the electrode head assembly, and has a deformation coupling the first electrode to the first conductor and transferring traction forces applied to the lead body to the electrode head assembly.  
           [0012]    In accordance with another aspect of the present invention, the medical electrical lead includes a second electrode extending along the electrode head assembly and the lead body, a second conductor extending within a second lead body lumen of the plurality of lead body lumens, and an attachment member coupling the second electrode and the second conductor and transferring traction forces applied to the lead body to the electrode head assembly.  
           [0013]    By coupling the conductors to the electrode head assembly, the present invention enables traction forces applied to the proximal end of the lead body to be transferred to the electrode head assembly via the cabled conductors rather than to the electrodes, the coiled conductor or the joint between the electrode head assembly and the lead body. By providing at least two cable connections to the electrode head assembly, redundant reinforcement is provided ensuring tensile integrity of the lead even if one cable connection should fail. Thus, features included in the present invention improve the reliability and durability of an implantable medical lead during extraction. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a plan view of an implantable cardiac lead that may be utilized in accordance with the present invention;  
         [0015]    [0015]FIG. 2 is a cross-sectional view of a multi-lumen lead body shown in FIG. 1;  
         [0016]    [0016]FIG. 3 is a side cut away view of a distal end of the lead shown in FIG. 1 showing a cable connected to a ring electrode and an electrode head assembly;  
         [0017]    [0017]FIG. 4 is a side, cut-away view of the distal end of the lead shown in FIG. 1 showing a second cable connected to a coil electrode and the electrode head assembly;  
         [0018]    [0018]FIG. 5 is a perspective view of an attachment member used for interlocking with a coil electrode and a cable in a distal end of a lead according to the present invention; and,  
         [0019]    [0019]FIG. 6 is a perspective view of the electrode head assembly according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]    [0020]FIG. 1 is a plan view of a lead that may be utilized in accordance with the present invention, embodied as a transvenous cardiac defibrillation lead. As illustrated in FIG. 1, a lead  10  according to the present invention includes an elongated lead body  12  having a connector assembly  16  at a proximal end of the lead  10  for connecting to an implantable device, and an electrode head assembly  14  at a distal end of the lead  10  for carrying one or more electrodes. Lead  10  is shown as a quadrapolar lead including, at or near the distal end, a helical tip electrode  30 , a ring electrode  50 , a right ventricular (RV) defibrillation coil  38  and a superior vena cava (SVC) defibrillation coil  40 . The helical tip electrode  30  and ring electrode  50  may be utilized to sense cardiac signals and/or deliver pacing pulses to a patient. One of the defibrillation coils  38  or  40  serves as the cathode while the other serves as the anode during delivery of a defibrillation shock to a patient as a result of a detected tachycardia or fibrillation condition.  
         [0021]    The lead body  12  takes the form of an extruded tube of biocompatible plastic such as silicone rubber. Multiple lumens located within the lead body  12  carry four insulated conductors from the connector assembly  16  to the corresponding electrodes  30 ,  50 ,  38  and  40  located at or near the distal end of the lead  10 . The multi-lumen lead body  12  may correspond generally to that disclosed in U.S. Pat. No. 5,584,873 issued to Shoberg et al., incorporated herein by reference in its entirety. Three of the insulated conductors carried by lead body  12  are preferably stranded or cabled conductors, each electrically coupled to one of the ring electrode  50 , the RV coil  38  and the SVC coil  40 . The cabled conductors are preferably inextensible or minimally extensible and may correspond generally to the conductors disclosed in U.S. Pat. No. 5,246,014, issued to Williams et al., incorporated herein by reference in its entirety. A fourth, coiled conductor extends the length of the lead body  12  and is coupled to the helical tip electrode  30 .  
         [0022]    In this embodiment, the helical tip electrode  30  functions as an electrode for cardiac pacing and/or sensing and as an active fixation device for anchoring the lead  10  in a desired position. In other embodiments that may employ the present invention, a helical tip may function only as an active fixation device. Therefore, the helical tip electrode  30  may also be referred to herein as a “fixation helix.” In other embodiments, the lead  10  may possess other types of passive or active fixation mechanisms, such as hooks or tines.  
         [0023]    The connector assembly  16  has multiple connector extensions  18 ,  20 , and  22  arising from a trifurcated connector sleeve, typically formed of silicone rubber. The connector extensions  18 ,  20 , and  22  couple the lead  10  to an implantable medical device such as an implantable cardioverter defibrillator (ICD).  
         [0024]    Connector extension  20  is shown as a bipolar connector including a connector ring  24  and a connector pin  25 . Connector extension  20  houses the cabled conductor that is electrically coupled to the connector ring  24  at the proximal lead end and to the ring electrode  50  at the distal lead end. The connector extension  20  also houses the coiled conductor that is electrically coupled to the connector pin  25  and extends to the tip electrode  30 . During a lead implant or explant procedure, rotation of the connector pin  25  relative to the connector assembly  16  causes corresponding rotation of the coiled conductor and advancement or retraction of the helical tip electrode  30  in the fashion generally described in U.S. Pat. No. 4,106,512 to Bisping et al., incorporated herein by reference in its entirety. By advancing the helical tip electrode  30 , the electrode  30  can be actively fixed in cardiac tissue. A stylet  32  may be advanced within an inner lumen of the coiled conductor to the distal end of the lead  10  to aid in lead placement during an implant procedure.  
         [0025]    The connector extension  18  carries a single connector pin  52  that is electrically coupled to an insulated cable extending the length of the lead body  12  and electrically coupled to the RV coil  38 . The connector extension  22  carries a connector pin  42  that is electrically coupled to a respective insulated cable that is further coupled to the SVC coil  40 .  
         [0026]    [0026]FIG. 2 is a cross-sectional view of a multi-lumen lead body of the lead of FIG. 1. As illustrated in FIG. 2, the lead body  12  includes four lumens  102 ,  122 ,  124 , and  126 . Lumen  102  carries the coiled conductor  26  that is coupled to the helical tip electrode  30 . The conductor  26  is shown surrounded by insulation tubing  120 . A stylet  32  may be advanced within the lumen  34  of the coiled conductor  26  during implantation procedures. Lumen  122  carries an insulated cable conductor  110  that is electrically coupled at a proximal end to the connector ring  24  and at a distal end to the ring electrode  50 . Lumen  124  carries an insulated cable conductor  112  that is electrically coupled at a proximal end to the connector pin  52  and at a distal end to the RV coil  38 . Lumen  126  carries an insulated cable conductor  114  that is electrically coupled at a proximal end to the connector pin  42  and at a distal end to the SVC coil  40 .  
         [0027]    [0027]FIG. 3 is a side cutaway view of the distal end of the lead  10  showing a detailed view of the electrode head assembly  14  and the electrodes  30 ,  50  and  38 . The molded, tubular electrode head assembly  14  includes two members, a distal electrode head assembly  113  and a proximal electrode head assembly  111 . The distal and proximal electrode head assemblies  113  and  111  are preferably formed from a relatively rigid biocompatible plastic. For example, assemblies  113  and  111  may be fabricated from molded polyurethane. The proximal electrode head assembly  111  is coupled to the multi-lumen lead body  12 , typically formed from a relatively more compliant plastic such as silicone rubber, at a joint  140 . The lumen  104  within the proximal electrode head assembly  111  communicates with the lumen  102  within the lead body  12  for carrying the coiled conductor  26  extending between the tip electrode  30  and the connector ring  24 . In FIG. 3, the ring electrode  50  is shown coupled to the cable  110 , and the RV coil  38  is shown positioned on the outer diameter of the proximal electrode head assembly  111  and the lead body  12 .  
         [0028]    [0028]FIG. 3 further shows the helical tip electrode  30  electrically coupled to the coiled conductor  26  via a drive shaft  100 . The electrode  30  and drive shaft  100  are preferably fabricated of a biocompatible metal such as platinum iridium alloy. The coiled conductor  26  extends to the proximal connector assembly  16 . Rotation of the connector pin  25  at the proximal end of coiled conductor  26  causes corresponding rotation of the distal end of the coiled conductor  26  to, in turn, cause rotation of the drive shaft  100 . This rotation results in extension or retraction of helical tip electrode  30 . A guide  28  actuates the helical tip  30  as it is advanced or retracted. The lead  10  may include a drive shaft seal  109  encircling the drive shaft  100 . The drive shaft seal  109 , which may be formed of silicone or any other elastomer, is housed within the proximal electrode head assembly  111 .  
         [0029]    According to the present invention, as illustrated in FIG. 3, the ring electrode  50  is coupled to the cable  110  via two deformations  220 . During assembly, a tool is used to press the ring electrode  50  against the cable  110  creating indentations or crimp-like deformations  220 , which ensure the electrical coupling of the ring electrode  50  to the cable  110 . Ring electrode  50  is captured between the proximal and distal electrode head assemblies  111  and  113  when the assemblies  111  and  113  are bonded together. In this way, traction forces applied at the proximal lead end are transferred to the electrode head assembly  14  in part via the cable  110  that is coupled to the ring electrode  50  via deformations  220 .  
         [0030]    As illustrated in FIGS. 3 and 4, the RV coil  38  is positioned on an outer surface  140  of the proximal electrode head assembly  111  and the lead body  12 . As illustrated in FIG. 4, a cross-groove crimp sleeve, or attachment member  224 , provides electrical connection of cable  112  to the RV coil  38  and mechanical connection to the proximal electrode head assembly  111 . The attachment member  224  is fabricated of a conductive biocompatible metal such as titanium or platinum. The attachment member  224  provides a tubular portion for receiving the cable  112  and a groove, running perpendicular to the tubular portion, for receiving one or more coils of RV coil  38  in a manner as generally described in U.S. Pat. No. 5,676,694 to Boser et al., and in U.S. Pat. No. 6,016,436 to Bischoff et al., both patents incorporated herein by reference in their entirety.  
         [0031]    [0031]FIG. 5 is a perspective view of an attachment member for interlocking with a coil electrode and a cable in a distal end of a lead, according to the present invention. As illustrated in FIG. 5, the attachment member  224  according to the present invention includes a cross-groove  228  for receiving one or more coils of RV coil  38  and a tubular receiving portion  226  having a lumen  232  for receiving the cable conductor  112 . The RV coil  38  may be welded or brazed within the groove  228 . Alternatively, this connection may be made by crimping or otherwise compressing the groove  228  around RV coil  38  to provide an electrical and mechanical coupling to the coil  38 . The cable  112  may be coupled to the attachment member  224  by crimping the receiving portion  226 , or staking, welding, brazing or otherwise mechanically and electrically coupling the cable  112  to the sleeve  224 .  
         [0032]    [0032]FIG. 6 is a perspective view of a proximal electrode head assembly according to the present invention. As illustrated in FIG. 6, the proximal electrode head assembly  111  includes a recess  234  for retaining the attachment member  224 . The attachment member  224  is maintained within the recess  234  by a biocompatible plastic tube surrounding the proximal end  239  of the assembly  111 . The RV coil  38  is positioned over the proximal end  239  with one or more coils interlocking with cross-groove  228  of the attachment member  224  (FIG. 5) residing in recess  234 . A second recess  236  is provided for retaining the cable  110  that is coupled to ring electrode  50 , which is positioned over the distal end  238  of the assembly  111 . The deformations  220  (FIG. 3) electrically couple the ring electrode  50  to the cable  110  residing in recess  236  and thereby couple the cable  110  to the electrode head assembly  14  once the ring electrode  50  is captured between proximal and distal electrode head assemblies  111  and  113  as shown in FIG. 3.  
         [0033]    In addition, as illustrated in FIG. 6, the recess  234  includes an opening so that once attachment member  224  is inserted within the recess  234 , opening  235  is adjacent to the lumen  232  so that the cable conductor  112  is inserted within opening  235  and lumen  232  and positioned at the receiving portion  226 .  
         [0034]    Thus, two connections are provided to the electrode head assembly  14 , one by the cable  110  residing in recess  236  coupled to ring electrode  50  and the other by the cable  112  interlocking with the attachment member  224  residing in recess  234 . This double connection to the electrode head assembly from the cables  110  and  112 , which extend proximally to connector assembly  16 , provides improved tensile strength to lead  10  for better withstanding extraction forces applied during lead removal. Traction forces applied to the proximal end of lead  10  will be transferred via the cables  110  and  112  to the electrode head assembly  111 , preventing separation of lead body  12  from the electrode head assembly  111  or other lead breakage. A redundant lead strengthening mechanism is provided by having two cable connections to the electrode head assembly  14  so that, should one connection fail, the remaining connection will prevail, thereby ensuring tensile integrity of the lead  10 .  
         [0035]    The lead described above with respect to the present invention is a quadrapolar high-voltage lead of the type that may be used in conjunction with an implantable cardioverter defibrillator. However, it will be understood by one skilled in the art that any or all of the inventive aspects described herein may be incorporated into other types of lead systems. For example, one or more of the aspects may be included in a multipolar pacing lead having any combination of a tip electrode, one or more ring electrodes, and/or one or more coil electrodes for use in pacing, sensing, and/or shock delivery. Alternatively, drug-delivery or other electrical stimulation leads may employ aspects of the present invention for improving the lead extraction characteristics. As such, the above disclosure should be considered exemplary, rather than limiting, with regard to the following claims.