Implantable medical device lead including a unifilar coiled cable

A medical device lead includes a flexible body having a proximal region with a proximal end, and a distal region with a distal end. A connector is coupled to the proximal end of the flexible body of the lead to electrically and mechanically connect the lead to an implantable pulse generator. The medical device lead also includes an electrode in the distal region of the flexible body, and a cable conductor having a proximal end electrically coupled to the connector and a distal end electrically coupled to the electrode. The cable conductor consists of a single helically coiled filar including a plurality of co-radial turns and having an outer diameter of less than about 0.020 inch (0.508 mm).

TECHNICAL FIELD

The present disclosure relates to implantable medical devices. More particularly, the present disclosure relates to a medical device lead including an unifilar coiled cable configured to reduce electrode heating in MRI environments.

BACKGROUND

Magnetic resonance imaging (MRI) is a non-invasive imaging procedure that utilizes nuclear magnetic resonance techniques to render images within a patient's body. Typically, MRI systems employ the use of a magnetic coil having a magnetic field strength of between about 0.2 to 3 Teslas (T). During the procedure, the body tissue is briefly exposed to RF pulses of electromagnetic energy in a plane perpendicular to the magnetic field. The resultant electromagnetic energy from these pulses can be used to image the body tissue by measuring the relaxation properties of the excited atomic nuclei in the tissue.

During imaging, the electromagnetic radiation produced by the MRI system may be picked up by implantable device leads used in implantable medical devices such as pacemakers or cardiac defibrillators. This energy may be transferred through the lead to the electrode in contact with the tissue, which may lead to elevated temperatures at the point of contact. The degree of tissue heating is typically related to factors such as the length of the lead, the conductivity or impedance of the lead, and the surface area of the lead electrodes. Exposure to a magnetic field may also induce an undesired voltage on the lead.

SUMMARY

Disclosed herein are various embodiments of a medical device lead including a small diameter unifilar coiled cable, as well as medical device systems including such a lead.

In Example 1, a medical device lead includes a flexible body having a proximal region with a proximal end, and a distal region with a distal end. A connector is coupled to the proximal end of the flexible body of the lead to electrically and mechanically connect the lead to an implantable pulse generator. The medical device lead also includes an electrode in the distal region of the flexible body, and a cable conductor having a proximal end electrically coupled to the connector and a distal end electrically coupled to the electrode. The cable conductor consists of a single helically coiled filar including a plurality of co-radial turns and having an outer diameter of less than about 0.020 inch (0.508 mm).

In Example 2, the medical device lead according to Example 1, wherein a pitch of the helically coiled filar is about one to about two times a diameter of the filar.

In Example 3, the medical device lead according to either Example 1 or 2, wherein the pitch of the helically coiled filar varies along at least a portion of the cable conductor.

In Example 4, the medical device lead according to any of Examples 1-3, wherein a diameter of the filar is less than about 0.003 inch (0.076 mm).

In Example 5, the medical device lead according to any of Examples 1-4, and further comprising a dielectric mandrel extending through and coaxially with the helically coiled filar.

In Example 6, the medical device lead according to any of Examples 1-5, wherein the flexible body comprises a plurality of lumens, and wherein the cable conductor extends through one of the plurality of lumens.

In Example 7, a medical device lead includes a flexible body having a proximal region with a proximal end and a distal region with a distal end. A connector is coupled to the proximal end of the flexible body of the lead to electrically and mechanically connect the lead to an implantable pulse generator. A tip electrode is at the distal end of the flexible body, and one or more ring electrodes are in the distal region of the flexible body. The medical device lead further includes a coiled conductor having a proximal end electrically coupled to the connector and a distal end electrically coupled to the tip electrode, and one or more cable conductors each having a proximal end electrically coupled to the connector and a distal end electrically coupled to one of the one or more ring electrodes. Each cable conductor consists of a single helically coiled filar including a plurality of co-radial turns. An outer diameter of each of the cable conductors is less than an outer diameter of the coiled conductor.

In Example 8, the medical device lead according to Example 7, wherein the outer diameter of each of the one or more cable conductors is less than about 0.020 inch (0.508 mm).

In Example 9, the medical device lead according to either Example 7 or 8, wherein, for each of the one or more cable conductors, a pitch of the helically coiled filar is about one to about two times a diameter of the filar.

In Example 10, the medical device lead according to any of Examples 7-9, wherein the pitch of the helically coiled filar of at least one of the one or more cable conductors varies along at least a portion of the cable conductor.

In Example 11, the medical device lead according to any of Examples 7-10, wherein, for each of the one or more cable conductors, a diameter of the filar is less than about 0.003 inch (0.076 mm).

In Example 12, the medical device lead according to any of Examples 7-11, and further comprising a dielectric mandrel extending through and coaxially with each helically coiled filar.

In Example 13, the medical device lead according to any of Examples 7-12, wherein the flexible body comprises a plurality of lumens, and wherein the coiled conductor and the one or more cable conductors extend through different lumens.

In Example 14, the medical device lead according to any of Examples 7-13, wherein the tip electrode comprises a fixation helix.

In Example 15, a medical device lead includes a flexible body having a proximal region with a proximal end, and a distal region with a distal end. A connector is coupled to the proximal end of the flexible body of the lead to electrically and mechanically connect the lead to an implantable pulse generator. One or more electrodes are in the distal region of the flexible body and are configured to deliver pacing signals and/or sense electrical activity of cardiac tissue. One or more cable conductors each have a proximal end electrically coupled to the connector and a distal end electrically coupled to one of the one or more electrodes. Each cable conductor consists of a single helically coiled filar including a plurality of co-radial turns. The outer diameter of each of the one or more cable conductors is less than about 0.020 inch (0.508 mm).

In Example 16, the medical device lead according to Example 15, wherein, for each of the one or more cable conductors, a pitch of the helically coiled filar is about one to about two times a diameter of the filar.

In Example 17, the medical device lead according to either Example 15 or 16, wherein the pitch of the helically coiled filar of at least one of the one or more cable conductors varies along at least a portion of the cable conductor.

In Example 18, the medical device lead according to any of Examples 15-17, wherein, for each of the one or more cable conductors, a diameter of the filar is less than about 0.003 inch (0.076 mm).

In Example 19, the medical device lead according to any of Examples 15-18, and further comprising a dielectric mandrel extending through and coaxially with each helically coiled filar.

In Example 20, the medical device lead according to any of Examples 15-19, wherein the filar comprises an insulative coating.

DETAILED DESCRIPTION

FIG. 1is a perspective view of an implantable medical device (IMD)10in accordance with one embodiment. The IMD10includes a pulse generator12and a cardiac lead14. The lead14operates to convey electrical signals between the heart16and the pulse generator12. The lead14has a proximal region18and a distal region20. The lead14includes a lead body, or flexible body22, extending from the proximal region18to the distal region20. The proximal region18is coupled to the pulse generator12and the distal region20is coupled to the heart16. The distal region20includes an extendable/retractable fixation helix24, which will be discussed in greater detail with respect to subsequent drawings, and which locates and/or secures the distal region20within the heart16. In one alternative embodiment, the distal region20includes a plurality of tines or other structures for fixation of the lead14relative to the heart20(e.g., in a coronary vein or ventricular trabeculae). In another alternative embodiment, the lead14is configured as a neural lead including electrode cuffs for coupling the lead14to a nerve, or configured for insertion into a spinal cord.

The distal region20of the lead14has an axially compact design that accommodates a dedicated bipolar electrode configuration. The lead14may alternatively have other electrode configurations. As will be explained in further detail herein and shown in additional figures, one or more conductors that electrically couple the connector in the proximal region18of the lead14to one or more electrodes in the distal region20of the lead14are configured to minimize energy pickup in MRI environments to reduce heating at the electrodes.

The pulse generator12typically includes a connector header13that couples the pulse generator12to the lead14. The connector header13typically contains one or more bores17that is/are able to receive a connector (not shown) that is part of a connector assembly (not shown, but see40inFIG. 2, discussed herein) formed near the proximal region18of the lead14, wherein electrical contacts (not shown) of the connection header13couple with lead contacts (not shown) of the connector assembly (not shown).

The connection header13can be attached to a hermetically sealed enclosure15that contains a battery, electronic circuitry, and other components known to those skilled in the art. Electrical contacts (not shown) in the connection header13can be a type known to those skilled in the art that are electrically connected via feedthroughs (not shown) mounted to extend through the hermetically sealed enclosure15in order to electrically couple the lead14with pulse generator12.

The pulse generator12can be implanted subcutaneously within an implantation location or pocket in the patient's chest or abdomen. In embodiments in which the lead14is a neural lead, the pulse generator may alternatively be implanted at the patient's back or buttocks. The pulse generator12may be any implantable medical device known in the art or later developed, for delivering an electrical therapeutic stimulus to the patient. In various embodiments, the pulse generator12is a pacemaker, an implantable cardioverter/defibrillator (ICD), a cardiac resynchronization (CRT) device configured for bi-ventricular pacing, and/or includes combinations of pacing, CRT, and defibrillation capabilities.

The lead body22can be made from a flexible, biocompatible material suitable for lead construction. In various embodiments, the lead body22is made from a flexible, electrically insulative material. In one embodiment, the lead body22is made from silicone rubber. In another embodiment, the lead body22is made from polyurethane. In various embodiments, respective segments of the lead body22are made from different materials, so as to tailor the lead body22characteristics to its intended clinical and operating environments. In various embodiments, proximal and distal ends of the lead body22are made from different materials selected to provide desired functionalities.

The heart16includes a right atrium26, a right ventricle28, a left atrium30and a left ventricle32. The heart16includes an endothelial inner lining or endocardium34covering the myocardium36. In some embodiments as illustrated, the fixation helix24, located at the distal region20of the lead, penetrates through the endocardium34, and is imbedded within the myocardium36. Alternatively, the lead14may be configured as a passive fixation lead as discussed herein. In one embodiment, the IMD10includes a plurality of leads14. For example, it may include a first lead14adapted to convey electrical signals between the pulse generator12and the right ventricle28, and a second lead (not shown) adapted to convey electrical signals between the pulse generator12and the right atrium26. Additional leads may also be employed. For example, in various embodiments, a coronary venous lead (not shown) may be utilized for stimulating a left atrium30and/or a left ventricle32of the heart16.

In the illustrated embodiment shown inFIG. 1, the fixation helix24penetrates the endocardium34of the right ventricle28and is imbedded in the myocardium36of the heart16. In some embodiments, the fixation helix24is electrically active and thus can be used to sense the electrical activity of the heart16or to apply a stimulating pulse to the right ventricle28. In other embodiments, the fixation helix24is not electrically active. In still other embodiments, the lead14is fixed relative to the heart16using passive structures (e.g., tines, spirals, etc.).

During operation, the lead14can be configured to convey electrical signals between the IMD12and the heart16. For example, in those embodiments in which the IMD12is a pacemaker, the lead14can be utilized to deliver electrical stimuli for pacing the heart16. In those embodiments in which the IMD12is an implantable cardiac defibrillator, the lead14can be utilized to deliver electric shocks to the heart16in response to an event such as a heart attack or arrhythmia. In some embodiments, the IMD12includes both pacing and defibrillation capabilities.

The electrical signals are carried between the IMD12and electrodes at the distal region20by one or more conductors extending through the lead14. The one or more conductors are electrically coupled to a connector suitable for interfacing with the IMD12at the proximal region18of the lead14and to the one or more electrodes at the distal region20. According to various embodiments, the one or more conductors include coiled cables consisting of a single filar and having a small outer diameter. In some embodiments, the coiled cables are configured to deliver low voltage signals to the one or more electrodes. The coil pitch may be small (e.g., one to two times the cable filar diameter) to minimize effects of magnetic resonance imaging (MRI) scans on the functionality and operation of the lead14.

FIG. 2is an isometric illustration of a lead14according to some embodiments. A connector assembly40is disposed at or near the proximal region18, or proximal end, of the lead14. The connector assembly40includes a connector42and a terminal pin44. The connector42is configured to be coupled to the lead body22and is configured to mechanically and electrically couple the lead14to the connection header13on the pulse generator12(seeFIG. 1). In various embodiments, the terminal pin44extends proximally from the connector42and in some embodiments is coupled to a conductor member (not visible in this view) that extends longitudinally through the lead body22such that rotating the terminal pin44relative to the lead body22causes the conductor member to rotate within the lead body22. In some embodiments, the terminal pin44includes an aperture (not shown) extending therethrough in order to accommodate a guide wire or an insertion stylet.

A distal assembly46is disposed at or near the distal region20or distal end of the lead14or lead body22. Depending on the functional requirements of the IMD10(seeFIG. 1) and the therapeutic needs of a patient, the distal region20of the lead14may include one or more electrodes. In the illustrated embodiment, the distal region20includes one or more coil electrodes48and49that can function as shocking electrodes for providing, for example, a defibrillation shock to the heart16. In some embodiments, the coil electrodes48and49include a coating that is configured to control (i.e., promote or discourage) tissue ingrowth. In various embodiments, the lead14may include only a single coil electrode. In various other embodiments, the lead14also includes one or more low-voltage electrodes (e.g., ring electrodes), such as electrode47, along the lead body22in lieu of or in addition to the coil electrodes48,49. When present, the low-voltage electrodes operate as relatively low-voltage, pace/sense electrodes. As will be appreciated by those skilled in the art, a wide range of electrode combinations may be incorporated into the lead14within the scope of the various embodiments.

The distal assembly46includes a housing50, within which the fixation helix24, or helical electrode, is at least partially disposed. As will be explained in greater detail herein, the housing50accommodates a mechanism that enables the fixation helix24to move distally and proximally relative to the housing50, but that includes structure (not seen in this view) that limits distal travel of the fixation helix24(relative to the housing50) in order to reduce or prevent over-extension of the fixation helix24. As noted herein, the fixation helix24operates as an anchoring means for anchoring the distal region20of the lead14within the heart16. In alternative embodiments, the lead14is fixed relative to the heart16using passive structures (e.g., tines, spirals, etc.).

In some embodiments, the fixation helix24, or helical electrode, is electrically active, and is used as a low-voltage, pace/sense electrode. In some embodiments, the fixation helix24is made of an electrically conductive material such as ELGILOY™, MP35N™, tungsten, tantalum, iridium, platinum, titanium, palladium, stainless steel as well as alloys of these materials.

The lead14is one exemplary implementation of a lead in accordance with the present disclosure, and other configurations for the lead14are also possible. For example, while coil electrodes48,49are shown adjacent to each other, the coil electrode49may alternatively be disposed more proximally on the lead14. As another example, the lead14may include a plurality of annular electrodes along the distal region20for providing pacing and/or sensing signals to adjacent tissue.

FIG. 3is a perspective view of a portion of the lead14according to embodiments of the present disclosure. The lead14includes a coil conductor60and coiled cable conductors62and64. In the illustrated embodiment, the lead14includes a lead body having a plurality of lumens66,68, and70. The coil conductor60passes through the lumen66, the coiled cable conductor62passes through the lumen68, and the coiled cable conductor64passes through the lumen70. In some embodiments, the lumens66,68,70extend substantially parallel from the connector40at the proximal region18to the distal region20.

The coil conductor60is adapted for connection to the pulse generator12at the proximal region18of the lead14. For example, the coil conductor60may be electrically connected to the connector42. In the embodiment shown, the coil conductor60extends in parallel through the lead14with the coiled cable conductors62,64. The longitudinal axis of the coil conductor60is offset from the longitudinal axes of the coiled cable conductors62,64. In some embodiments, the coil conductor60is electrically coupled to one or more electrodes in the distal region20of the lead14. For example, in some implementations the coil conductor60may be electrically coupled to the fixation helix24and/or the ring electrode47. The coil conductor60may alternatively or additionally be connected to other electrodes. To reduce the amount of MRI-induced energy that is transmitted to the electrodes connected to the coil conductor60, the turns of the coil conductor60may be tightly wound to maximize the inductance of the coil. In some embodiments, to minimize the space between adjacent turns and maximize the number of turns, the coil conductor60is unifilar. In other embodiments, the coil conductor60is multifilar.

The coiled cable conductors62,64are also adapted for connection to the pulse generator12at the proximal region18of the lead14, for example via electrical connection to the connector42. In some embodiments, the coiled cable conductors62,64are configured to carry low voltage signals between the pulse generator12and one or more electrodes in the distal region20. For example, with regard to the embodiment of the lead14shown inFIG. 2, the coiled cable conductors62and/or64may be connected to the proximal end and/or distal end of the coil electrodes48,49. In this way, the coiled cable conductors62,64operate to carry sensing and/or pacing signals between the pulse generator12and the coil electrodes48,49. In alternative embodiments, coiled cable conductors62and/or64may be connected to the ring electrode47and/or fixation helix24.

While two coiled cable conductors62,64are shown, the lead14may alternatively include any number of coiled cable conductors62,64. For example, in one alternative configuration, the lead14includes four cable conductors, each connected to one of the proximal or distal ends of the coil electrodes48,49. In another alternative configuration, the lead14includes a plurality of annular electrodes in the distal region, and a coiled cable conductor is connected to each of the plurality of annular electrodes.

Exposure of the lead14to magnetic resonance imaging (MRI) fields can result in localized heating of the electrodes at the distal region18due to excitation of the lead conductors (e.g., coiled cable conductors62,64). Conductors with high inductance (>1 μH) are more resistant to excitation in MRI fields. The inductance of the conductor is determined by its geometric properties, including whether the conductor is straight or coiled. For a coiled or wound conductor, such as the coiled cable conductors62,64, several parameters influence its inductance, including the coil pitch, the outer diameter of the coil52, the cross-sectional area of the coil52, and the number of filars comprising the coil52. For example, in some embodiments, the coil pitch (i.e., the distance between the centers of adjacent coil turns) may be small (e.g., one to two times the cable filar diameter). The conductive coil62is shown having a pitch of approximately equal to the filar diameter inFIG. 3. Thus, the dimensions and characteristics of the coil52may be selected to minimize the effects of magnetic resonance imaging (MRI) fields on the performance and response of the lead14.

The coiled cable conductors62,64may have an outer diameter d of less than about 0.020 inch (0.508 millimeter (mm)). For example, in some exemplary implementations, the outer diameter d of the coiled cable conductors62,64are in the range of about 0.008 inch to about 0.014 inch (0.203-0.356 mm). In some embodiments, the coiled cable conductors62,64each consist of a single filar of conductive material (i.e., unifilar) that is helically coiled with a plurality of co-radial turns. The turns of the coiled cable conductors62,64may be closely wound. For example, in some embodiments, the coiled cable conductors62,64have a pitch of between about one and two times the filar diameter. The pitch may be consistent along the length of the coiled cable conductors62,64, or may be varied along at least a portion of the coiled cable conductors62,64. One exemplary approach to incorporating variable pitch sections into the coiled cable conductors62,64is described in U.S. Publication 2009/0149933, entitled “Implantable Lead Having a Variable Coil Conductor Pitch,” which is hereby incorporated by reference in its entirety. In some embodiments, the filar of the coiled cable conductors62,64has a diameter of between about 0.0007 inch and 0.003 inch (0.018-0.076 mm). One exemplary material suitable for coiled cable conductors62,64is MP35N including a silver core. Other exemplary materials suitable for coiled cable conductors62,64include, but are not limited to, MPTa (MP35N with tantalum), platinum-clad Ta, platinum-clad MP35N, MP35N, and Nitinol. In some embodiments, the filar of each of the coiled cable conductors62,64is insulated.

A plurality of leads including unifilar coiled cable conductors as described were exposed to an MRI environment, and the heating at the electrode attached to each of the unifilar coiled cable conductors was measured. For comparison, similar leads including bifilar and trifilar coiled cable conductors were also exposed to an MRI environment, and the associated electrodes were tested for heating. In each case, the coiled cable conductors were connected to the distal end of the distal coil electrode (e.g., coil electrode48inFIG. 2). The results, shown in Table 1 below, demonstrated that unifilar coiled cable conductors transmit significantly less MRI-induced energy to electrodes than corresponding multifilar configurations.

The coiled cable conductors62,64with a small outer diameter d and having a small pitch may be prone to damage during construction and use. For example, unifilar coils, such as coiled cable conductors62,64, may not transmit torque well, and the forces typically encountered by the lead14can cause the coiled cable conductors62,64to experience stress concentrations in portions of the coiled cable conductors62,64, which can lead to premature fatigue of the coiled cable conductors62,64. To prevent this from occurring, the coiled cable conductors62and/or64may be formed about a flexible, non-conductive mandrel72that is retained after manufacturing and during use. In some embodiments, the mandrel72is comprised of a polymeric material, such as expanded polytetrafluoroethylene (ePTFE), layered ePTFE, polytetrafluoroethylene (PTFE), polyethylene terephthalate (PETE), ethylene/tetrafluoroethylene copolymer (ETFE), fluorinated ethylene propylene (FEP), polyether ether ketone (PEEK), polyamides, polyimides, para-aramid synthetic fibers, and polyurethane. The mandrel72increases the axial pull strength of the coiled cable conductors62,64for later manufacturing processes and during chronic implantation. That is, the mandrel72improves the strength of the coiled cable conductors62,64with respect to forces along the longitudinal axes of the coiled cable conductors62,64. This improved axial pull strength is provided by the flexible and resilient mandrel72substantially filling the inner diameter of the coiled cable conductors62,64. During manufacturing, the coiled cable conductors62,64may be wrapped around the mandrel72in a tightly-wound configuration. In alternative embodiments, the mandrel72is removed from the coiled cable conductors62,64after manufacturing.