Implantable medical lead having a retraction stop mechanism

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-10013, entitled “APPARATUS FOR TRANSFERRING TRACTION FORCES EXERTED ON AN IMPLANTABLE MEDICAL LEAD”; 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 a retraction stop mechanism of a medical electrical lead for preventing over-retraction of a rotatable helical tip electrode.

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 electrical stimulation signals when needed, in order to cause the myocardium to con-tract 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 signals to the heart and for sensing cardiac signals and delivering those sensed signals from the heart 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, one disposed substantially at the distal tip end of the lead, and the other 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 electrical 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] One problem that can arise with the use of such a lead is over-retraction of the helix during lead repositioning. Repositioning of the lead may be required during an implant procedure if poor electrical contact is made with the targeted cardiac tissue, resulting in higher than desired stimulation thresholds or poor sensing. The physician must retract the helix by applying turns to the coiled conductor in the appropriate direction. The physician may not have tactile feedback or fluoroscopic image indicating when the helix has dislodged from the heart tissue and is fully retracted. In many cases, the physician will perform additional turns of the coiled conductor in order to ensure the helix is safely removed from the heart tissue before applying tension to the lead to relocate it. Excessive turns, however, can cause deformation of the fixation helix rendering it unusable. In such cases, the lead must then be removed and replaced by a new lead.

[0009] To address the problem of over-retraction, a retraction stop mechanism may be provided within the distal lead head. An exemplary retraction stop mechanism that includes a fixed stop formed of a plurality of fixed cam and axial stop surfaces and a movable stop formed of a like plurality of rotatable cam and axial stop surfaces is disclosed in U.S. Pat. No. 5,837,006 to Ocel et al.. This stop effectively prevents over-retraction.

[0010] However, many considerations are taken into account when optimizing the design of a lead. For example, minimizing lead size is important since a smaller device is more readily implanted within the cardiac structures or coronary vessels of a patient. Moreover, providing features that make a lead easier to implant and extract allows the clinician to complete the associated surgical procedure more safely and in less time. Finally, an optimized lead design requires a minimum number of parts that may be assembled using techniques that are relatively simple and low cost. It is therefore desirable to provide a medical lead having a retraction stop mechanism that requires a minimal amount of space, can be constructed from a minimal number of parts, and is easily manufactured and verified.

SUMMARY OF THE INVENTION

[0011] The present invention is directed to a medical lead having a helical tip electrode mounted on a drive shaft. The helical tip electrode and drive shaft are housed within an electrode head assembly at the distal end of the lead. The electrode head assembly is bonded to a lead body having at least a center lumen for carrying a coiled conductor that is coupled at its distal end to the drive shaft and at its proximal end to a connector pin. Applying turns to the connector pin effectively turns the coiled conductor resulting in rotation of the drive shaft and advancement or retraction of the helical tip electrode. When enough turns are applied in the appropriate direction to cause full retraction of the helical tip electrode, a movable flange portion located on the drive shaft engages a fixed retraction flange located on the electrode head assembly so that rotation of the drive shaft is absorbed by a conductor of the lead.

[0012] The movable flange portion is provided as an extension in the proximal direction from a cylindrical body formed near the distal end of the drive shaft. The geometry of the movable flange portion allows it to be incorporated in a one-piece, machined drive shaft eliminating the need for additional parts, welds, or weld inspections. The fixed retraction flange is provided as a protrusion from the distal end of the electrode head assembly. The fixed retraction flange may be incorporated in a one-piece, molded proximal electrode head assembly, eliminating the need for additional parts or bonding processes.

[0013] The present invention thus provides an effective retraction stop mechanism comprising two components that require a minimal amount of space within the distal end of the lead. By minimizing the size of the retraction stop mechanism, over all lead size may be reduced. Furthermore, the two component retraction stop mechanism included in the present invention does not require additional bonding or welding procedures, resulting in a lead manufacturing process that is easily accomplished at a low cost.

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 of the lead shown in FIG. 1;

[0016]
FIG. 3 is a side cut away view of a distal end of the lead shown in FIG. 1;

[0017]
FIG. 4 is a perspective view of a retraction stop mechanism of an implantable cardiac lead according to the present invention;

[0018]
FIG. 4A is a planar view of a front surface of the retraction stop mechanism of FIG. 4; and

[0019]
FIG. 5 is an enlarged, perspective, partially cut-away view of the retraction stop mechanism of FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

[0020]
FIG. 1 is a plan view of an implantable cardiac 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 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 and 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 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. 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 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. Reference is made to U.S. Pat. No. 4,217,913 to Dutcher, incorporated herein by reference in its entirety. Therefore, the helical tip electrode 30 may also be referred to herein as a “fixation helix”.

[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 bi-polar 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 its proximal end and to the ring electrode 50 at its distal 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 is provided with four lumens 102, 122,124, and 126. Lumen 102 carries the coiled conductor 26 that is coupled to the helical tip electrode 30. In accordance with the present invention, the conductor 26 is shown surrounded by an insulation tubing 120. A stylet 32 may be advanced within the lumen 34 of the coiled conductor 26. Lumen 122 carries an insulated cable 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 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 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 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 electrode 30 as the helical tip electrode 30 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 electrode head assembly 14.

[0029]
FIG. 4 is a perspective view of a retraction stop mechanism of an implantable cardiac lead according to the present invention. FIG. 4A is a planar view of a front surface of the retraction stop mechanism of FIG. 4. As illustrated in FIG. 4, the drive shaft 100 includes a distal stem 44 for coupling to the helical tip electrode 30. A proximal stem 46 is provided for coupling to the coiled conductor 26. As illustrated in FIGS. 4 and 4A, an axial stop surface, or flange portion 240 extends in a proximal direction from a front surface 107 of a movable stop, or engaging member 106, that is formed as a cylindrical body near the distal end of the drive shaft 100. The drive shaft 100 and engaging member 106 with the flange portion 240 may be machined as one component, eliminating additional parts, welding processes or weld inspections needed for providing a movable retraction stop.

[0030] As illustrated in FIGS. 3 and 4, the distal end of the proximal electrode head assembly 111 includes a fixed retraction flange 242 that includes an axial stop surface 246. The fixed retraction flange 242 is a distal protrusion positioned within the electrode head assembly 14. The electrode head assembly 14, including the fixed retraction flange 242 may be formed as a single, molded polyurethane component. Therefore, implementing the fixed retraction flange 242 in lead 10 does not require additional parts or bonding procedures during lead assembly.

[0031]
FIG. 5 is an enlarged, perspective, partially cut-away view of a retraction stop mechanism according to the present invention. As illustrated in FIGS. 3 and 5, as the connector pin 25 at the proximal end of coiled conductor 26 is rotated in a first, clockwise direction so as to retract the helical tip electrode 30, this rotation of the connector pin 25 in the first direction causes the drive shaft 100 to rotate in the first direction. As the drive shaft 100 rotates, the electrode 30 and the engaging member 106 are also rotated in the first direction. As the electrode 30 is rotated in the first direction, the electrode 30 advances through the guide 28, causing the electrode 30 to be advanced through the electrode head assembly 14 in a direction shown by arrow A, so as to be advanced towards the electrode head assembly 14, thereby retracting the electrode 30 from the cardiac tissue and within the electrode head assembly 14.

[0032] At the same time, the rotation of the drive shaft 100 in the first direction also causes the engaging member 106 to be rotated in the first direction, while at the same time, the movement of the electrode 30 through the guide 28 causes the engaging member 106 to also be advanced within the electrode head assembly 14 in the direction A. Furthermore, the rotation of the drive shaft 100 in the first direction results in the engaging member 106 being rotated about the drive shaft 100 so that as engaging member 106 advances in the direction A, the flange 240 engages against the fixed retraction flange 242 upon complete retraction of the helical tip electrode 30, so that the torque resulting from extra turns applied to the connector pin 25 after the helical tip electrode 30 is completely retracted within distal assembly 113 will, therefore, not be transmitted to the helical tip electrode 30. Rather, additional torque is absorbed by the coiled conductor 26. Deformation of the helical tip electrode 30 is thereby avoided, allowing repositioning of the lead 10.

[0033] As the connector pin 25 at the proximal end of coiled conductor 26 is rotated in a second, counterclockwise direction in order to advance of the helical tip electrode 30 within the cardiac tissue to secure the lead, this rotation of the connector pin 25 in the second direction causes rotation of the drive shaft 100 in the second direction. As the drive shaft 100 rotates, the electrode 30 and the engaging member 106 are also rotated in the second direction. As the electrode 30 is rotated in the second direction, the electrode 30 advances through the guide 28, causing the electrode 30, to be advanced through the electrode head assembly 14 in a direction shown by arrow B, away from the electrode head assembly 14, so that the electrode 30 is advanced outward from the distal end of the electrode head assembly 14 and is inserted within the cardiac tissue.

[0034] At the same time, the rotation of the drive shaft 100 in the second direction also causes the engaging member 106 to be rotated in the second direction, while at the same time, the movement of the electrode 30 through the guide 28 causes the engaging member 106 to also be advanced within the electrode head assembly 14 in the direction B. Furthermore, the rotation of the drive shaft 100 in the second direction results in the engaging member 106 being rotated about the drive shaft 100 so that as engaging member 106 advances in the direction B, the flange portion 240 disengages from against the fixed retraction flange 242. As a result, when the drive shaft 100 is rotated in the in the second direction, opposite the first direction, the retraction stop mechanism of the present invention does not prevent rotation of the engaging member 106, allowing advancement of the helical tip electrode 30 through the electrode head assembly 14 in the direction B.

[0035] According to the present invention, the flange 240 and the axial stop surface 246 are compact such that little space within the electrode head assembly 14 is required to provide a retraction stop mechanism. Furthermore, the fixed retraction flange 242 and the engaging member 106 have geometries that may be incorporated directly into the molded electrode head assembly 14 and the machined drive shaft 100, respectively, without requiring additional parts or bonding or welding procedures. The retraction stop mechanism of the present invention is advantageously located proximal to the stem 44 allowing the welded joint between the helical tip electrode 30 and the stem 44 to be easily inspected. Thus, the assembly procedures for a lead having a retraction stop mechanism in accordance with the present invention are kept simple and are easily verified, resulting in a more reliable lead.

[0036] The lead described above employing a retraction stop mechanism in accordance with the present invention is a quadrapolar high-voltage lead of the type that may be used for pacing, cardioversion and defibrillation. 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 of the retraction stop mechanism described herein may be included in any unipolar or multipolar pacing lead having a rotatable fixation device and any combination of one or more tip, ring or coil electrodes for use in pacing, sensing, and/or shock delivery. Alternatively, any drug-delivery or other electrical stimulation lead that benefits from having a retraction stop mechanism may employ aspects of the present invention. As such, the above disclosure should be considered exemplary, rather than limiting, with regard to the following claims.

Implantable medical lead having a retraction stop mechanism

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REFERENCE TO PRIORITY APPLICATION

Provisional Applications (1)