Apparatus for transferring traction forces exerted on an implantable medical lead

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

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'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'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] FIG. 1 is a plan view of an implantable cardiac lead that may be utilized in accordance with the present invention;

[0015] FIG. 2 is a cross-sectional view of a multi-lumen lead body shown in FIG. 1;

[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] 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] 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] FIG. 6 is a perspective view of the electrode head assembly according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[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] 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] 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] 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] 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] 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.

Claims

1. A medical electrical lead, comprising: 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.

2. The medical electrical lead of claim 1, further comprising: 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.

3. The medical electrical lead of claim 2, wherein the attachment member includes a receiving portion having an attachment member lumen receiving the second conductor, and the electrode head assembly includes a recess retaining the attachment member.

4. The medical electrical lead of claim 3, the receiving portion being one of either crimped, staked, welded or brazed to mechanically and electrically coupled the second conductor to the attachment member.

5. The medical electrical lead of claim 3, wherein the attachment member includes a cross-groove receiving one or more coils of the second electrode.

6. The medical electrical lead of claim 5, wherein the second electrode is welded or brazed within the cross-groove to couple the second electrode to the attachment member.

7. The medical electrical lead of claim 5, wherein the cross-groove is compressed about the second electrode to couple the second electrode to the attachment member.

8. The medical electrical lead of claim 3, wherein the attachment member is retained within the recess by a biocompatible plastic tube surrounding the electrode head assembly.

9. The medical electrical lead of claim 3, wherein the electrode head assembly includes a second recess retaining the first conductor.