Medical electrical stimulation lead including expandable coiled fixation element

A medical lead includes a coiled conductor portion that defines at least part of an outer surface of the lead and an expandable coiled fixation element that defines at least a part of the outer surface of the lead. The expandable coiled fixation element is configured to expand from a first dimension in a first state to a second dimension in a second state in a direction away from the coiled conductor portion. In some examples, the expandable coiled fixation element comprises a shape memory material.

TECHNICAL FIELD

The disclosure relates to medical leads, and, in particular, fixation of medical leads.

BACKGROUND

Electrical stimulation systems may be used to deliver electrical stimulation therapy to patients to treat a variety of symptoms or conditions. Some electrical stimulation systems have been proposed to address symptoms or conditions such as chronic pain, tremor, movement disorders, psychological disorders, multiple sclerosis, spinal cord injury, cerebral palsy, amyotrophic lateral sclerosis, dystonia, torticollis, epilepsy, pelvic floor disorders, gastroparesis, muscle stimulation (e.g., functional electrical stimulation (FES) of muscles) or obesity. In some examples, an electrical stimulation system includes an electrical stimulator that delivers electrical stimulation signals to a target stimulation site within a patient via at least one electrode of one or more electrical stimulation leads.

The electrical stimulation lead may be implanted in a patient on a temporary or permanent basis such that at least one stimulation electrode is positioned proximate to a target stimulation site. The target stimulation site may be, for example, a nerve or other tissue site, such as a spinal cord, pelvic nerve, pudendal nerve, stomach, bladder, or within a brain or other organ of a patient, or within a muscle or muscle group of a patient.

SUMMARY

In general, the disclosure is directed to a medical electrical stimulation lead that includes at least one coiled conductor that defines at least part of an outer surface of the medical lead, and an expandable coiled fixation element that also defines at least part of the outer surface of the medical lead. In some examples, the expandable coiled fixation element is physically separate from the at least one coiled conductor. The expandable coiled fixation element defines a plurality of turns, and at least one of the turns is configured to expand away from the coiled conductor from a first dimension in a first state of the fixation element to a second dimension in a second state of the fixation element. When expanded, the at least one of the turns of the coiled fixation element is configured to engage with tissue of a patient to help fix a position of the lead relative to a target stimulation site. Also described herein are systems including the electrical stimulation lead, methods for implanting the medical lead, and methods of forming the coiled fixation element.

In one example, the disclosure is directed to a system comprising medical lead comprising a coiled conductor that defines at least part of an outer surface of the medical lead, an electrode electrically connected to the coiled conductor, and an expandable coiled fixation element that defines at least part of the outer surface of the medical lead. The expandable coiled fixation element defines a plurality of turns, and at least one of the turns is configured to expand away from the coiled conductor from a first dimension in a first state to a second dimension in a second state.

In another example, the disclosure is directed to a medical lead comprising means for conducting electrical stimulation signals, wherein the means for conducting electrical stimulation signals comprises a coiled portion defining at least part of an outer surface of the medical lead, means for generating electrical stimulation therapy, wherein the means for generating electrical stimulation therapy is electrically connected to the means for conducting electrical stimulation signals, and means for fixing the means for conducting electrical stimulation signals to tissue of a patient, the means for fixing being coiled and defining at least part of the outer surface of the medical lead. The means for fixing defines a plurality of turns and at least one of the turns is configured to expand away from the coiled portion of the means for conducting from a first dimension in a first state to a second dimension in a second state.

In another example, the disclosure is directed to a method comprising implanting a medical lead in a patient, the medical lead comprising a coiled conductor that defines at least part of an outer surface of the medical lead, an electrode electrically connected to the coiled conductor, and an expandable coiled fixation element that defines at least part of the outer surface of the medical lead, wherein the expandable coiled fixation element defines a plurality of turns, and at least one of the turns is configured to expand away from the coiled conductor from a first dimension in a first state to a second dimension in a second state. The method further comprises applying thermal energy to the expandable coiled fixation element via a thermal energy source to cause the expandable coiled fixation element to expand away from the coiled conductor.

In another example, the disclosure is directed to a method comprising coiling a conductor to define a coiled conductor portion that defines at least part of an outer surface of a medical lead, and coiling an elongated member to define an expandable coiled fixation element that defines at least part of the outer surface of the medical lead, wherein the expandable coiled fixation element is configured to expand from a first dimension in a first state to a second dimension in a second state.

DETAILED DESCRIPTION

In some electrical stimulation applications, it may be desirable to minimize migration of a medical electrical stimulation lead (also referred to herein as a “lead,” a “medical lead,” and a “stimulation lead”) following implantation in a patient at a target stimulation site. For example, it may be desirable for one or more electrodes of the lead to remain proximate to the target stimulation site in order to provide adequate and reliable stimulation of the target stimulation site. Movement of stimulation electrodes of a lead from a target stimulation site may reduce electrical coupling between the electrode and the target stimulation site, possibly undermining therapeutic efficacy of the electrical stimulation therapy. In examples described herein, a lead includes an expandable coiled fixation element that is configured to expand from a first dimension (e.g., a first outer profile) in a first state of the fixation element to a second dimension (e.g., a second outer profile) in a second state of the fixation element to engage with tissue of a patient and help minimize lead migration following implantation of the lead in the patient, e.g., such that the one or more electrodes are positioned to deliver electrical stimulation signals to the target stimulation site. The coiled fixation element may be at least partially retractable, such as by stretching the coiled conductors to elongate the coiled fixation element, as discussed in further detail below, or by applying a force to the expanded fixation element (e.g., via a sheath that surrounds the coiled fixation element).

The expandable coiled fixation element may help ensure the electrodes of the lead deliver electrical stimulation to the target stimulation site as intended, which may be particularly useful if the lead is being used to test electrical stimulation therapy on the patient. Electrical stimulation therapy may be tested on a patient in order to determine whether the patient is responsive to electrical stimulation therapy, whether the patient is a candidate for successful long-term electrical stimulation therapy or to determine if electrical stimulation delivered with particular stimulation parameter values provides efficacious therapy to the patient. In some applications, the expandable coiled fixation element is configured to fix the lead such that the electrodes of the lead remain substantially co-located with a target stimulation site, e.g., substantially fixed to surrounding tissue, in order to help ensure the target tissue site is being stimulated, as opposed to a non-target tissue site. In addition, in some examples, fixing the lead may help maintain a minimum distance between the electrode and a nerve in order to help prevent inflammation to the nerve from the electrical stimulation.

The stimulation lead may be, for example, a test electrical stimulation lead (also referred to herein as a “test lead” or a “trial lead”) in which an outer surface of the lead is at least partially defined by at least one coiled conductor that is configured to transmit electrical stimulation signals from an electrical stimulator at a proximal end of the conductor to an electrode at a distal portion of the conductor. Each coiled conductor may comprise example, an electrically conductive member surrounded by electrical insulation. In some examples, the electrical insulation defines at least a portion of the outer surface of the lead.

A test lead may be used to deliver electrical stimulation therapy to a patient on a trial basis, e.g., prior to surgical implantation of a fully implantable electrical stimulation lead that is used for chronic stimulation delivery. In some examples, the test lead is a percutaneous medical lead that is not intended to be fully implanted in the patient. Instead, a distal portion of the test lead may be implanted in the patient and a proximal portion of the lead may be external to the patient and electrically connected to an electrical stimulator. The distal portion of the lead may be implanted in the patient for the duration of a test period, in which electrical stimulation is delivered to the patient via the one or more electrodes of the test lead. In other examples, the test lead may be fully implanted in the patient (e.g., the entire length of the lead from the proximal end to the distal end may be implanted in the patient).

While the entire test lead may not be implanted in the patient, at least a portion of the lead including the one or more electrodes may be implanted in the patient. A test lead may be simplified relative to a lead intended for long-term implantation in a patient (also referred to as a “chronic lead”) and may include a smaller profile (e.g., a smaller outer diameter or other perimeter), such that the test lead may be less invasive than the chronic lead. For example, as discussed in further detail below, the test lead may not include an outer jacket that encloses the conductor (coiled or uncoiled) and defines a smooth outer surface of the lead. The test lead may also be referred to as a temporary electrical stimulation lead or, when it is used to evaluate peripheral nerve stimulation, a “peripheral nerve evaluation lead,” or when it is used to evaluate percutaneous nerve stimulation, a “percutaneous nerve evaluation lead.”

Testing electrical stimulation therapy on a patient with a smaller profile test lead may be advantageous in some examples. For example, the smaller profile test lead may enable the test lead to be implanted (fully or partially) in the patient in a clinic, non-hospital setting, rather than in a hospital setting, which may be less intimidating to a patient and may also be more cost efficient. For example, a relatively small needle (e.g., an 18-20 gauge needle) may be used to implant some example test leads described herein, which may be used outside of a hospital setting. In addition, for some patients, the non-hospital setting procedure and the smaller size of the test lead may be less of an obstacle to the testing of the electrical stimulation therapy than a procedure that is required to be performed in a hospital and/or a procedure that requires the implantation of a relatively large lead.

FIG. 1is a conceptual diagram illustrating an example therapy system10that includes electrical stimulator12electrically connected to electrical stimulation lead14. In the example shown inFIG. 1, lead14includes two conductors16A,16B, which are at least partially coiled around core18(shown in phantom lines inFIG. 2B), and electrodes22A,22B (collectively referred to as “electrodes22”). Lead14further includes coiled fixation element24(also shown inFIGS. 2A and 2B) that is coiled with conductors16(collectively referred to as “conductors16”). Lead14is separated into two segments inFIG. 1for ease of illustration; the two segments may ordinarily be connected to each other, and the alignment of the segments is illustrated by an assembly line.FIGS. 2A and 2Bfurther illustrate lead14and coiled fixation element24, and are also referred to below in the description of lead14.

In some examples, electrical stimulator12is configured to be implanted in a patient. In other examples, electrical stimulator12is configured to be carried external to a patient. For example, electrical stimulator12may be an external trial stimulator that is used to determine whether electrical stimulation therapy provides efficacious therapy to the patient, to determine whether the patient is a candidate for long-term electrical stimulation therapy, or to select one or more electrical stimulation parameters for long term therapy for the patient.

Electrical stimulator12is configured to generate and deliver a programmable stimulation signal (e.g., in the form of electrical pulses or a continuous time signal) that is delivered to a target stimulation site within a patient by lead14, and more particularly, via electrodes22of lead14. In some examples, electrical stimulator12may also be referred to as a signal generator or a neurostimulator. In some examples, electrical stimulator12may also include a sensing module that is configured to sense one or more physiological parameters of the patient via one or more electrodes22or a separate set of electrodes. Although one lead14is shown inFIG. 1, in other examples, electrical stimulator12may be coupled to two or more leads, e.g., to support delivery of electrical stimulation to multiple target stimulation sites within a patient, such as in the case of bilateral stimulation.

Lead14is configured to deliver electrical stimulation signals generated by electrical stimulator14to tissue of a patient proximate the one or more electrodes22. Proximal end14A of lead14may be both electrically and mechanically coupled to electrical stimulator12either directly or indirectly (e.g., via a lead extension). In some examples, the entire lead14, from proximal end14A to distal end14B, may be configured to be implanted in a patient. In other examples, only a portion of lead14including distal end14and electrodes22is configured to be implanted in a patient. Lead14may be flexible in some examples, which may enable lead14to accommodate a plurality of different implantation sites within a patient, as well as decrease the irritation to adjacent tissue.

In the example shown inFIG. 1, lead14includes conductors16A and16B that are each at least partially coiled around core18to define coiled portion17. In one example, only a portion of each of the conductors16A,16B is coiled, such that coiled portion17is only on a segment of lead14, and a proximal portion of the respective conductor16A,16B adjacent proximal end14A of lead14is not coiled, as shown inFIG. 1. In other examples, the proximal portion of each of the conductors16A,16B may be at least partially coiled, and, in some examples, the entire length of conductors16A,16B may be coiled from end to end.

Conductors16A,16B are configured to deliver electrical stimulation signals from electrical stimulator12to electrodes22A,22B, respectively. Conductors16A,16B each include an electrically conductive member surrounded by an electrically insulative material. The electrically conductive member can be formed from, for example, a stainless steel, such as MP35N alloy. The electrically insulative material may be any suitable biocompatible electrically insulative material, such as ethylene tetrafluoroethylene (ETFE), polytetrafluoroethylene (PTFE), silicone rubber, polyurethane, fluoropolymer, other suitable polymers, and the like. In the example shown inFIG. 1, electrodes22A,22B are defined by removing part of the electrically insulative material from each conductor16A,16B, respectively, thereby exposing the electrically conductive member, and mechanically and electrically connecting electrically conductive collar to the exposed electrically conductive members of the conductors16. The electrically conductive collars may define the outer surface of electrodes22that contact tissue of a patient when distal end14B of lead14is implanted in the patient, in other examples, electrodes22of lead14may be defined by, for example, uninsulated portions of the electrically conductive members of conductors16. In this example, the exposed electrically conductive members of conductors16may define the outer surface of electrodes22that contact tissue of a patient when distal end14B of lead14is implanted in the patient.

In the example shown inFIG. 1, electrodes22are immediately adjacent to distal end14B of lead14and are positioned along a longitudinal outer surface of lead14(e.g., in contrast to a tip electrode that is at a distal tip of lead14). In other examples, electrodes22can have other positions along lead14, such as closer to middle portion of lead14(e.g., midway between proximal and distal ends14A,14B, respectively). In addition, while two electrodes22A,22B are shown inFIG. 1, in other examples, lead14may include any suitable number of electrodes, with or without electrically conductive collars. For example, lead14may include more than two conductors that define one or more respective electrodes, where the conductors are at least partially coiled (e.g., coaxially coiled and/or coiled together), and each conductor may define at least one respective electrode. As another example, lead14may include a single conductor that defines one electrode, which may be used to test unipolar electrical stimulation therapy. In the case of a unipolar stimulation lead with a single electrode (or multiple electrodes of a single polarity), the return path for the stimulation may be through the body of the patient, e.g., to an external ground pad or the like.

Lead14further includes electrical contacts23A,239,23C (collectively referred to as “electrical contacts23”) near proximal end14A of lead14. Electrical contacts23A,239are configured to electrically connect conductors16A,16B, respectively, to electrical stimulator12, and, in particular, stimulation module32of electrical stimulator12. Electrical contact23is configured to electrically connect expandable coiled fixation element24to electrical stimulator12, and, in particular, stimulation module32of electrical stimulator12. In the example shown inFIG. 1, electrical contacts23A,23B are defined by removing part of the electrically insulative material from each conductor16A,16B, thereby exposing the electrically conductive member. In some examples, an electrically conductive collar is mechanically and electrically connected to the exposed electrically conductive members of the conductors16. The electrically conductive collars may define the outer surface of electrical contacts23A,23B that contact respective electrical contacts of electrical stimulator12when proximal end14A of lead14is introduced in opening26defined by electrical stimulator12(e.g., opening26in a header of electrical stimulator12). Electrical contact23C may be defined by an outer surface of elongated member25(described in further detail below) or an electrically conductive collar electrically and mechanically connected to elongated member25that is introduced in opening26of electrical stimulator12.

InFIG. 1, a proximal portion of lead14including proximal end14A is illustrated as being aligned with proximal end opening26defined by electrical stimulator16. Electrical contacts that are electrically connected to stimulation module32may be positioned within opening26, such that when proximal end14A of lead14is introduced in opening26and electrical contacts23contact respective electrical contacts in opening26, electrical contacts23electrically connect stimulation module32to electrodes and expandable fixation element24.

Coiled portion17(also referred to as a “coiled conductor portion”) of lead14is defined by a plurality of turns (at least two turns) of conductors16, and defines inner surface20A (FIG. 2B) and outer surface20B. As noted above, each conductor16A,16B may have an electrically insulative outer layer (e.g., a sheath, coating or the like), which may electrically insulated conductors16from each other. In some examples, at least some of the turns of conductors16are not mechanically connected to each other, such that the turns may move relative to each other. That is, the distance between adjacent turns may increase or decrease depending on the force applied to the ends of coiled portion17, such that coiled portion17of conductor16can increase and decrease in length LC, which is measured in a direction substantially parallel to a longitudinal axis of coiled portion17. In some examples, increasing a length of coiled portion17may decrease the radius of curvature of the turns. As discussed in further detail below, this feature of lead14may aid in explanation of lead14from a patient by, for example, decreasing the extent to which expandable fixation element24extends away from outer surface20B of coiled conductor17when elongated.

In some examples, none of the turns of coiled portion17are mechanically connected to each other. In other examples, some of the adjacent turns of coiled portion17are mechanically connected to each other, e.g., adhered or welded together. For example, the last two or three turns at either end of coiled portion17may be mechanically connected to each other.

In examples in which at least some of the adjacent turns of coiled portion17of conductor16are movable relative to each other, the coiled configuration of portion17may help accommodate axial forces placed on lead14, e.g., help absorb the axial forces to help prevent migration of lead14(e.g., distal end14B of lead14). The axial forces may be applied, for example, in a direction substantially parallel to longitudinal axis15(FIG. 2B) of lead14, such as from tugging or pulling on a proximal end14A of lead14. For example, when lead14is implanted in a patient and mechanically connected to electrical stimulator12, relative movement between lead14and the stimulator12may generate axial forces that pull on lead14. As another example, when lead14is implanted such that distal end14B is implanted in the patient and proximal end14A is carried external to the patient, forces applied to proximal end14A, or anywhere along a length of lead14, from ordinary activities of the patient may generate axial forces that pull on lead14. Because coiled portion17may stretch and compress, coiled portion17may accommodate some relative movement between distal end14B of lead14and proximal end14A of lead14.

Lead14may be, for example, a test lead in which an outer surface of lead14is at least partially defined by coiled conductors16. In the example shown inFIG. 1, conductors16define an outer surface of lead14that contacts tissue of the patient when lead14is at least partially implanted in the patient. For example, in the example shown inFIG. 1, at least a portion of outer surface20B of coiled portion17of conductors16is configured to directly contact tissue of the patient when lead14is at least partially implanted in the patient. In some examples, the entire outer surface20B of coiled portion17of conductors16is configured to directly contact tissue of the patient when lead14is at least partially implanted in the patient.

In contrast to some leads configured for chronic implantation (e.g., long-term, non-temporary implantation, such as on the order of years) in a patient, lead14does not include an outer jacket (e.g., an outer electrically insulative jacket) in which conductors16of lead14are positioned, where the outer jacket defines an outer surface of the lead. That is, in the example shown inFIG. 1, an outer jacket is not positioned between coiled portion17of conductors16and tissue of the patient when lead14is implanted in the patient. Rather, at least a portion of the outer surface of lead14is defined by coiled portion17of conductors16, such that coiled conductors16contact tissue of the patient when lead14is implanted in the patient. While conductors16each include an electrically conductive member surrounded by an electrically insulative material, at least a portion of coiled portion17of conductors16is not disposed within an outer jacket that is separate from the electrical insulative material of conductors16. Conductors16may each be electrically insulated along their respective lengths, but no additional electrical insulation may be provided around that portion (or entire) coiled portion17of conductors16by a physically separate outer jacket. In some examples, no portion of conductors16is disposed within a common outer jacket that encloses coiled portion17. The absence of an outer jacket or the like in which at least coiled portion17conductors16is placed may help decrease the profile of lead14, e.g., by decreasing the total outer perimeter (e.g., an outer profile or outer diameter) of lead14, which may help decrease the invasiveness of lead14when at least the portion of lead14including a part of coiled portion17of conductor16is implanted in a patient. In addition, an absence of the outer jacket may also help increase the ease with which lead14can be extended, e.g., to retract coiled fixation element24back from the second dimension to the first dimension.

As discussed above, conductors16are wrapped around core18to define coiled conductor portion17. Core18is configured to increase the structural rigidity and stiffness of the section of lead14including the coiled portion17. Increasing the structural rigidity and stiffness of the coiled portion17of conductor16may increase the ease with which lead14may be manipulated by a clinician, e.g., as distal end14B of lead14is being guided to a target stimulation site within a patient. In some examples, core18may be formed from a material that is more structurally rigid than coiled portion17of conductor16. Accordingly, in these examples, coiled portion17of conductor16may adopt the curvature or other shape of core18when core18is disposed within coiled portion17of conductor16. In one example, core18is substantially cylindrical and has a substantially circular cross-section (e.g., measured in a direction substantially perpendicular to the longitudinal axis of core18).

In some examples, core18is formed from a biocompatible material, such as a metal (e.g., a shape memory metal such as Nitinol), a polymer, and the like. For example, core18may be a metal stylet. In some examples, the configuration of core18(e.g., the size and material) is selected such that lead14can be manipulated (e.g., to navigate and steer lead14through tissue) from its proximal end by a clinician as the clinician implants lead14in a patient. For example, a thickness and material of core18can be selected to define a self-supporting core18. However, a self-supporting core18is not present in all examples. Rather, the positioning of core18within the space defined by the inner surface20A defined by coiled portion17of conductor16may be sufficient to increase the rigidity and stiffness of the section of lead14including the coiled portion17. Core18may occupy a part of or the entire space defined by the inner surface20A (FIGS. 2A and 2B) defined by coiled portion17, such that core18engages with coiled portion17of conductor18as portion17flexes.

In some examples in which only a portion of conductors16is coiled, core18may have a length (measured in a direction parallel to its longitudinal axis) that is substantially equal to (e.g., equal to or nearly equal to) lengthLCof the coiled section of conductor16. LengthLCof the coiled conductor portion17is the length of the coil defined by conductor16, rather than the length of the conductor16required to define the coil (prior to defining the coil), and is measured in a direction substantially parallel to (e.g., nearly parallel or parallel to) longitudinal axis15(FIG. 2B) of lead14. In other examples, core18may have a length that is less than or greater than the lengthLCof coiled portion17of conductors16.

In some examples, an outer perimeter of core18defines the radius of curvature of the turns of coiled portion17of conductors16. For example, during manufacture of lead14, conductor16may be wrapped around core18to defined coiled portion17, such that inner surface20A defined by coiled portion17is directly adjacent to an outer surface of core18.

In some examples, core18may be removed from lead14after lead14is implanted in the patient, e.g., after lead14has been introduced into the patient and guided through tissue until electrodes22A,22B of lead14are positioned at a target tissue site. In this way, core18may act as a stylet or guide wire that is used as an implant tool for implanting lead14in a patient. In order to further aid the implantation of lead14in the patient, the withdrawal of core18from the patient, core18may include a handle at its proximal end (which may remain outside of the patient even after lead14is implanted in the patient). The handle may have any suitable structure that enables a clinician to better grasp core18.

In other examples, core18may not be used to implant lead14and conductor16, or at least coiled portion17of conductor16, may be sufficiently structurally rigid to enable lead14to be relatively easily manipulated by a clinician. And instead, lead14may define a hollow central lumen in place of core18during implantation of lead14in the patient. In these examples, coiled portion17of conductor16may be defined by, for example, wrapping conductor16around core18or another form, and subsequently removing core18from the inner lumen of coiled portion16or by wrapping conductor16around a form that defines an opening configured to receive a stylet.

Lead14includes coiled fixation element24, which is defined by a plurality of turns of an elongated member25. In the example shown inFIGS. 1-2B, coiled fixation element24and coiled portion17of conductors16are coaxial. At least one of the turns of fixation element24is configured to expand from a first dimension in a first state (e.g., a particular configuration or structure of fixation element24) to a second dimension in a second state (e.g., another particular configuration or structure of fixation element24). In this way, the profile of fixation element24may increase between the first and second states of fixation element24. The dimension of fixation element24may be measured, for example, in a direction substantially perpendicular (e.g., perpendicular or nearly perpendicular) to longitudinal axis15(FIG. 2B) of lead14. As discussed in further detail below, fixation element24may be configured to expand from the first dimension in the first state to the second dimension in the second state in response to the application of a threshold level of thermal energy. When lead14is implanted in a patient, the force applied against fixation element24by surrounding tissue may prevent fixation element24from expanding fully to the second dimension. However, fixation element24may still expand and may still configured to try to expand to the second dimension in the second state.

Each turn of fixation element24defines a loop of elongated member25. The expansion of the one or more turns of fixation element24, during the transition from the first state to the second state of fixation element24, is in a direction away (e.g., radially outward) from coiled portion17of conductor16, such that coiled fixation element24increases in size (e.g., the profile, such as the outer diameter, of the turns may increase) in the expanded state, in this way, coiled fixation element24is configured to expand in order to engage with surrounding tissue to help inhibit migration of lead14from an initial implant site. For example, fixation element24may engage with tissue in order to help inhibit migration of electrode22from a target stimulation site within the patient.

In some cases, elongated member25may be a wire, such as an electrically conductive wire. Elongated member25can comprise any suitable biocompatible material, such as, for example, a biocompatible shape memory material, such as Nitinol. A shape memory material is configured to remember an original shape and return to the original shape (from another shape) upon the application of thermal energy. As discussed in further details below, the original shape can be the second, expanded state of fixation element24. In examples in which elongated member25comprises a shape memory material, thermal contact23C can be directly or indirectly (e.g., via an intermediate layer) thermally connected to a proximal end or portion of elongated member25. The contact23C may define a part of a pathway for introducing thermal energy into elongated member25in order to cause expandable coiled fixation element24to expand from the first dimension in a first state to a second dimension in a second state. In some examples, the thermal energy is applied to elongated member25by applying electrical energy to elongated member25via contact23C; the resistance in the material from which elongated member25is formed to the electrical energy generates the thermal energy. In this way, the thermal energy source that provides the thermal energy that causes fixation element24to expand from the first dimension to the second dimension may be an electrical energy source.

In the example shown inFIG. 1, coiled fixation element24is co-axially wound with conductors16and is located within coiled conductor portion17. For example, elongated member25may be wrapped around core18(FIG. 2B) and coiled alongside conductors16to define coiled fixation element24, such that in the first state, all of the turns of coiled fixation element24are adjacent turns of coiled portion17of conductors16. In this way, coiled fixation element24may be wound within windings of conductors16and each of the turns (defined by windings of elongated member25) may be interposed (e.g., positioned between) between adjacent windings of one or more conductors16within coiled portion17. In some examples, the turns of fixation element24may be arranged in a helical pattern. Coiled fixation element24may be directly adjacent core18in the example shown inFIG. 1, or, in other examples, may be separated from core18, e.g., by a sheath or the like wrapped around core18.

In examples in which coiled fixation element24is wound within (e.g., between) windings of conductors16such that fixation element24is interposed with conductors16, as shown inFIG. 1, coiled portion17of conductors16and coiled fixation element24may have substantially similar outer perimeters. For example, coiled fixation element24may be wound in alternating courses with conductors16A,16B, or in another interleaved pattern. By sizing coiled fixation element24to have substantially the same (e.g., the same or within about 10%) outer perimeter as coiled conductor portion17, as shown inFIG. 1, the inclusion of coiled fixation element24in lead14may not contribute to the overall outer perimeter of lead14, thereby minimizing the invasiveness of lead14attributable to the presence of fixation element24. Thus, winding elongated member25within windings of conductors16may be useful for adding a fixation element24to lead14without increasing the invasiveness of lead14.

Elongated member25can have any suitable length relative to conductor16. A suitable length can be selected to be a length that enables a sufficient number of turns of coiled fixation element24to fix lead14to be defined. Ends of elongated member25are at any position relative to coiled conductor portion17suitable for defining coiled fixation element24. In some examples, a proximal end of elongated member25is aligned with proximal end14A of lead14(which may correspond to proximal ends of conductors16in some examples). However, in other examples, the proximal end of elongated member25may be positioned closer to coiled conductor portion17than proximal end14A of lead14. A distal end of elongated member25may terminate at a portion of lead14distal to coiled conductor portion17, as shown inFIG. 1. For example, distal end25B of elongated member25may be distal to coiled conductor portion17but proximal to electrodes22, or distal to both coiled conductor portion17and electrodes22. In other examples, the distal end of elongated member25may terminate proximal to the distal-most end of coiled conductor portion17or may be aligned with the distal-most end of coiled conductor portion17.

In some examples, one or both ends of elongated member25are secured to coiled portion17in order to fix the relative position between coiled fixation element24and conductor16. For example, one or both ends of elongated member25can be crimped, adhered, welded, or otherwise mechanically connected to conductor16. In other examples, coiled fixation element24and conductor16remain sufficiently fixed relative to each other without the aid of a separate securing mechanism. For example, once coiled, elongated member retains its coiled shape as coiled fixation element24, such that turns of conductor16hold turns of coiled fixation element24in place and limit movement of coiled fixation element24in a direction parallel to a longitudinal axis of lead. Core member18limits movement of coiled fixation element24in a direction perpendicular to a longitudinal axis of lead14.

In the example shown inFIG. 1, coiled fixation element24is as tightly coiled as conductors16within coiled portion17of lead14. For example, for every one turn of coiled fixation element24, there may be one turn of each of the conductors16. In other examples, however, coiled fixation element24and conductors16may have different relative densities of coils. For example, in some examples, coiled fixation element24may not be as tightly coiled as coiled conductors16, e.g., for every two turns of each conductor16, there may be one turn of coiled fixation element24. As another example, conductors16may not be as tightly coiled as fixation element24, e.g., for every two turns of elongated member25, there may be one turn of conductors16. Other relative densities are contemplated.

In some examples, as shown inFIG. 1, when fixation element24is in the first state, the turns of coiled portion17of conductor16and the turns of coiled fixation element24have substantially similar (e.g., identical or nearly identical) radii of curvature (e.g., measured in a cross section from an inner surface of the respective turn to longitudinal axis15of lead14), the second state, as shown inFIGS. 2A and 2B, a subset of turns24A-24J (some, but not all, of the turns) of coiled fixation element24extend away from coiled portion17of conductors16, such that subset of turns24A-24J of coiled fixation element24are no longer immediately adjacent turns of coiled portion17of conductors16and have different radii of curvature than turns of coiled portion17.

FIG. 2Ais a conceptual illustration of electrical stimulation lead14shown inFIG. 1, in which expandable coiled fixation element24is in a second state, which is also referred to herein as an expanded state. In the second state, turns24A-24J have a different, larger dimension compared to coiled fixation element24in the first state (shown inFIG. 1).

FIG. 2Bis a larger view of coiled fixation element24in the second state, and coiled conductor portion17. As shown inFIG. 29, when coiled fixation element24is in the second state, turns24A-24J extend away from coiled conductor portion17, whereas other turns, such as turns24K-24M of coiled fixation element24do not extend away from coiled conductor portion17to the same extent as turns24A-24J. In the example shown inFIGS. 2A and 2B, turns24K-24M do not expand and have the same radius of curvature in the first and second states of fixation element24. In examples in which the turns of coiled fixation element have the same radius of curvature as conductors16within coiled portion17in the first state, turns24K-24M have the same radius of curvature in the first or second states. In addition, in some examples, the proximal and distal ends of elongated member25, from which coiled fixation element24is defined, stay in substantially the same position (e.g., nearly or completely the same position) in the first and second states of fixation element24.

In the second state of coiled fixation element, turns24A-24J of fixation element24extend away from coiled portion17of conductors16and are configured to engage with surrounding tissue to help fix lead14to surrounding tissue and help prevent lead14from migrating from a target stimulation site following implantation in the patient. Moreover, in the second state of fixation element24, the turns24A-24J of coiled fixation element24that extend away from coiled portion17define a relatively smooth, curvilinear surface that may not cause irritation to surrounding tissue. The curvilinear surfaces of expanded turns24A-24J that engage with surrounding tissue help reduce tissue ingrowth around the expanded turns24A-24J, which may help increase the ease with which lead14may be explanted from the patient. This may be useful if for example, lead14is a test lead. In comparison to some existing methods of fixing medical leads, such as suturing lead14to surrounding tissue, coiled fixation element24may permit implantation of lead4in a patient via a minimally invasive surgery, which may allow for reduced pain and discomfort for the patient, as well as a quicker recovery time.

Coiled fixation element24can have other configurations in other examples. For example, in some other examples, coiled fixation element24may be defined by a single turn of elongated member25, and the single turn may expand away from coiled portion17of conductor16in the second state. In addition, in some other examples, in the first state, the turns of coiled fixation element24do not contact coiled portion17of conductors16when fixation element24is in the first state. In addition, in some other examples, the turns of coiled portion17of conductor16and fixation element24have different radii of curvature when fixation element24is in the first state. For example, the coils of fixation element24may have a greater radius of curvature than the coils of coiled portion17of conductor16and may, for example, wrap around at least a portion of coiled portion17of conductor16. Other examples of coiled fixation element24in which coiled fixation element24is not coiled alongside conductor16and/or includes turns having a different radius of curvature than turns of coiled conductor17are described below with respect toFIGS. 3-5.

In the example shown inFIGS. 2A and 2B, one segment of consecutive turns24A-24J of coiled fixation element24expand away from coiled portion17of conductors16in the second state of fixation element24. In other examples, another arrangement of turns of coiled fixation element24may expand away from coiled portion17in the second state. For example, in another example, every other turn of coiled fixation element24for the entire length of coiled portion17or for a part of the length of coiled portion17may expand away from coiled portion17of conductors16in the second state. As another example, two segments of a plurality of consecutive turns of coiled fixation element24expand away from coiled portion17of conductors16in the second state of fixation element24. The segments may be axially displaced from each other along longitudinal axis15of lead14. For example, the segment of consecutive turns24A-24J shown inFIGS. 2A and 2Bmay be a first segment of turns, and fixation element24may include a second segment of expandable turns closer to distal end149of lead14, but still axially aligned with coiled portion17of conductors16.

As discussed above, in some examples, such as when coiled fixation element24is formed from a shape memory material, coiled fixation element24is configured to expand upon application of a thermal energy to fixation element24. For example, fixation element24may be formed from an electrically conductive elongated member25, and, upon the application of electrical energy to a proximal end of elongated member25(e.g., contact23C positioned at the proximal end), the electrical energy traverses through elongated member25to the at least one expandable turn of coiled fixation element24, which expands away from coiled portion17of conductors16in response to the heat generated by the resistance in elongated member25to the electrical energy. The electrical energy can be, for example, an electrical current having an amplitude on the order of milliamps (mA). The current amplitude can be selected to not cause any physiologically significant stimulation of the patient's tissue. In some examples, the physiological significance can be indicated by perception of the stimulation by the patient, modulation of a nerve of the patient, elicitation of some motor response (e.g., a toe flexation or an anal sphincter contraction) from the patient, or any combination thereof. In some examples, the electrical energy that is used to cause expansion of fixation element24from the first dimension in the first state to the second dimension in the second state can be provided by electrical stimulator12or a separate device. In this way, a source of electrical energy may also be a thermal energy source.

In other examples, the thermal energy may be provided by, for example, body heat transferred to coiled fixation element24from tissue surrounding fixation element24when lead14(e.g., the entire lead or just a distal portion) is implanted in a patient.

Coiled fixation element24can have any suitable location relative to electrodes22. For example, lead14may include one or more coiled fixation elements24proximal to electrodes22, as shown inFIG. 1, distal to electrodes22, or lead14may include more than one coiled fixation element (e.g., two fixation elements) that are located both proximal and distal to electrodes22. In some examples, coiled fixation element24between electrodes22or both proximal and distal to electrodes22may help fix the portion of lead14comprising electrodes22to adjacent tissue, which may help better secure electrodes22at a target tissue site compared to a more proximal located fixation element24.

When expandable fixation element24is in the first state in which the turns of expandable fixation element24are not expanded, lead14may assume a relatively low profile (e.g., a relatively small outer perimeter). The lower profile of lead14may permit it to be percutaneously implanted in a patient via an introducer (e.g., a needle), which may be less invasive than some proposed surgical implantation techniques, which may require introducing lead14through an incision. That is, in some examples, when fixation element24is in the first state, lead14is sized to be received in and traverse through a lumen of an introducer that is used to percutaneously implant at least a distal portion of lead14in a patient. The introducer may self-define an opening through skin of the patient to access the target stimulation site, and this self-defined opening may be less invasive than an incision. The introducer may be, for example, a needle, such as an 18, 19 or 20 gauge needle. The size of the introducer that is selected may depend upon the size of conductor16, as well as upon the presence or absence of an outer jacket in which conductor16is positioned.

In the example shown inFIG. 1, electrical stimulator12includes processor30, stimulation module32, memory34, power source36, and telemetry module38. In other examples, electrical stimulator12may include a fewer or greater number of components. Lead14is configured to be electrically coupled to stimulation module32, such that stimulation module32can deliver electrical stimulation signals to a patient via electrodes22of lead14. Proximal end14A of lead14may be configured to be directly electrically and mechanically connected to electrical stimulator12, as shown inFIG. 1, or to a lead extension that electrically and mechanically connects to electrical stimulator.

In general, electrical stimulator12comprises any suitable arrangement of hardware, alone or in combination with software and/or firmware, to perform the techniques attributed to electrical stimulator12and processor30, stimulation module32, and telemetry module38. In various examples, processor30can include any one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or any other equivalent integrated or discrete logic circuitry, as well as any combinations of such components.

Electrical stimulator12may also include memory34, which includes any volatile or non-volatile media, such as a random access memory (RAM), read only memory (ROM), non-volatile RAM (NVRAM), electrically erasable programmable ROM (EEPROM), flash memory, and the like. Memory34may store instructions for execution by processor30. In some examples, memory34also stores one or more stimulation therapy programs that specify stimulation parameter values for the electrical stimulation therapy provided by electrical stimulator12.

Although processor30, stimulation module32, and telemetry module38are described as separate modules, in some examples, processor30, stimulation module32, and telemetry module38can be functionally integrated. In some examples, processor30, stimulation module32, telemetry module38correspond to individual hardware units, such as ASICs, DSPs, FPGAs, or other hardware units.

Stimulation module32is configured to generate and deliver electrical stimulation to tissue of a patient via one or more electrodes22of lead14. In some examples, processor30controls stimulation module32by selectively accessing and loading at least one stimulation therapy programs from memory34to stimulation module32. In some cases, a clinician or patient may select a particular one of the stimulation therapy programs from a list using a medical device programming device (also referred to herein as a “programmer”). Processor30may receive the selection from the medical device programming device via telemetry module38.

Stimulation module32is configured to generate and deliver stimulation therapy, i.e., electrical stimulation, according to stimulation parameters. In some examples, stimulation module32delivers therapy in the form of electrical pulses. In such examples, relevant stimulation parameters may include a voltage amplitude, a current amplitude, a pulse rate, a pulse width, a duty cycle, or the combination of electrodes of lead14with which stimulation module32delivers the stimulation signals to tissue of the patient. In other examples, stimulation module32delivers electrical stimulation in the form of continuous waveforms. In such examples, relevant stimulation parameters may include a voltage amplitude, a current amplitude, a frequency, a shape of the stimulation signal, a duty cycle of the stimulation signal, or the combination of electrodes with which stimulation module32delivers the stimulation signals to tissue of the patient.

Telemetry module38includes any suitable hardware, firmware, software or any combination thereof for communicating with another device, such as a medical device programming device. Processor30is configured to control telemetry module38to exchange information with the medical device programmer and/or another device external to electrical stimulator12. Under the control of processor30, telemetry module38may receive downlink telemetry, e.g., patient input, from and send uplink telemetry, e.g., an alert, to a programming device with the aid of an antenna, which may be internal and/or external to outer housing40of electrical stimulator12. In some examples, electrical stimulator12may be configured to communicate with other devices, external to the patient or implanted in the patient, such as other electrical stimulators, control devices, or sensors, via telemetry module38.

Power source36is configured to deliver operating power to the components of electrical stimulator12. Power source36may include a battery and a power generation circuit to produce the operating power. In some examples, the battery may be rechargeable to allow extended operation.

Although not shown inFIG. 1, in some examples, therapy system10may also include a medical device programmer that is configured to program electrical stimulator12. The programmer may be, for example, a dedicated or general purpose computing device (e.g., a handheld computing device or a workstation) that permits a clinician to program electrical stimulation therapy for delivery to a patient by electrical stimulator12. For example, using the programmer, the clinician may specify electrical stimulation parameters for use by electrical stimulator12in the generation and delivery of electrical stimulation therapy, such as the voltage or current amplitude and frequency of the electrical stimulation signals generated by electrical stimulator12and delivered to the patient or the shape of the stimulation signal, the duty cycle of the stimulation signal, or the combination of electrodes of with which electrical stimulator12delivers stimulation to the patient. The medical device programmer may communicate with electrical stimulator12via cables or a wireless communication.

Therapy system10may be used to deliver electrical stimulation to any suitable target stimulation site in a patient. For example, the target stimulation site may be a tissue site proximate to a sacral nerve, an occipital nerve, or a tissue site proximate to any other suitable nerve, organ, muscle or muscle group in the patient, which may be selected based on, for example, the particular condition that therapy system10is implemented to address. For example, therapy system10may be used to deliver electrical stimulation therapy to a pudendal nerve, a perineal nerve or other areas of the nervous system, in which cases, lead14may be implanted and substantially fixed proximate to the respective nerve. As further examples, lead14may be positioned for temporary or chronic spinal cord stimulation for the treatment of pain, for peripheral neuropathy or post-operative pain mitigation, ilioinguinal nerve stimulation, intercostal nerve stimulation, gastric stimulation for the treatment of gastric mobility disorders and obesity, muscle stimulation (e.g., functional electrical stimulation (FES) of muscles), for mitigation of other peripheral and localized pain (e.g., leg pain or back pain), or for deep brain stimulation to treat mood or psychological disorders, movement disorders, and other neurological disorders.

FIG. 3is a conceptual illustration of a part of an example electrical stimulation lead50, which is similar to lead14ofFIG. 1, but includes a different configuration of expandable coiled fixation element52. As with lead14, lead50includes conductor16and coiled portion17of conductor16is shown inFIG. 3. Rather than being coiled alongside conductor16as with elongated member25shown inFIG. 1, elongated member54, from which coiled fixation element52is defined, is wrapped around a part of the outer surface of coiled portion17of conductor16, e.g., elongated member54is disposed circumferentially about the outer surface of coiled conductor portion17, to define a plurality of turns. Coiled fixation element52and coiled conductor portion17are coaxial in the example shown inFIG. 3. In some examples, coiled fixation element52is immediately adjacent coiled conductor portion17. In other examples, coiled fixation element24is separated from coiled conductor portion17by a separator, such as a sheath that is positioned around all or part of coiled conductor portion17.

In some examples, as shown inFIG. 3, elongated member54is wrapped only around a part of coiled conductor portion17, such that coiled fixation element52only partially overlaps with coiled conductor portion17. In other examples, elongated member54is wrapped around the entire coiled conductor portion17, such that there is complete overlap between coiled conductor portion17and coiled fixation element52. For example, proximal and distal portions of coiled conductor portion17may substantially align with (e.g., completely align with or generally align with) proximal and distal portions, respectively, of coiled fixation element52.

InFIG. 3, coiled fixation element52is in the second, expanded state in which a subset of turns52A-52F extends radially away from coiled portion17of conductor16, while distal-most and proximal-most turns of coiled fixation element52remain unexpanded. In the second, expanded state, turns52A-52F have a greater radius of curvature (e.g., measured from a center longitudinal axis15of lead50to the inner surface of the turn) than the nonexpandable turns of coiled fixation element, e.g.,52G-52J, and coiled conductor portion17. In the first state, subset of turns52A-52F is closer to coiled conductor portion17than in the second state. For example, in the first state, subset of turns52A-52F may lie against coiled portion17, e.g., as shown with respect to nonexpandable turns52G-52J inFIG. 3.

In both the first and second states, coiled fixation element52defines at least part of an outer, exterior surface of lead50that contacts tissue of a patient when the portion of lead50including coiled fixation element52is implanted in the patient. In addition, in some examples, coiled conductor portion17also defines a part of the outer, exterior surface of lead50.

In some examples, coiled fixation element52and conductors16remain sufficiently fixed relative to each other without the aid of a separate securing mechanism. For example, core member18may limit movement of coiled fixation element52in a direction perpendicular to longitudinal axis15of lead14. In addition, in some examples, at least the proximal and/or distal non-expandable turns (e.g., turns52G-52J) of coiled fixation element52may be more tightly coiled around coiled conductor portion17than the middle turns of coiled fixation element52, which may help limit movement of coiled fixation element52in a direction parallel to longitudinal axis15of lead50. As with elongated member25(FIG. 1), due to the properties of the material from which elongated member54is formed in some examples, elongated member54may be configured to retains its coiled shape once coiled, without the application of an uncoiling force.

In other examples, one or both ends55A,55B of coiled fixation element52may be secured to coiled conductor portion17in order to fix the relative position between coiled fixation element52and conductor16. For example, one or both ends55A,55B of fixation element52of can be crimped, adhered, welded, or otherwise mechanically connected to conductor16. As an example, a retainer ring can be positioned over ends one or both ends55A,55B of coiled fixation element52and around a part of coiled conductor portion17in order to secure coiled fixation element52to coiled conductor portion17. The retainer ring can be formed from any suitable material, such as a metal or polymer, and can be attached to coiled fixation element52using any suitable technique, such as by adhering, welding or crimping the cap to coiled fixation element52.

An example of lead60that includes expandable coiled fixation element62connected to coiled conductor portion17with a retainer ring64is shown inFIG. 4. As with expandable fixation element52(FIG. 3), fixation element62is disposed circumferentially about the outer surface of the coiled conductor portion17. In the example shown inFIG. 4, only a proximal end of coiled fixation element62is mechanically fixed to coiled conductor portion17with retainer ring64. Retainer ring64can be, for example, a metal or polymer shrink tube. As shown inFIG. 4, when a separate retainer ring64is used to fix expandable coiled fixation element62to coiled conductor portion17, even the distal-most turns of fixation element62may expand to the second dimension in the second state without increasing the possibility of axial movement of fixation element62(in a direction substantially parallel to longitudinal axis15of lead60) relative to coiled conductor portion17.

In other examples of lead60, a retainer ring can have another configuration, such as another position relative to fixation element62. For example, a second retainer ring64can be positioned at distal end62B of expandable coiled fixation element62. In these examples, a middle portion of fixation element62, which is positioned between proximal and distal ends of fixation element62, expands from a first dimension in a first state to a second dimension in a second state. As another example, in some examples of lead60, retainer ring64may be positioned to mechanically connect a distal end of fixation element62to coiled conductor portion17, and a proximal end may be free to move, e.g., a turn of coiled fixation element62including the proximal end may be configured to expand from a first dimension in a first state to a second dimension in a second state. In another example, retainer ring64may be positioned to mechanically connect a middle portion of coiled fixation element62to coiled conductor portion17, and distal and proximal ends of coiled fixation element62may be free to move, e.g., distal-most and proximal-most turns of coiled fixation element62may be configured to expand from a first dimension in a first state to a second dimension in a second state.

In the example shown inFIG. 4, elongated member66is positioned around an outer surface of coiled conductor portion17to define coiled fixation element62. Coiled fixation element62is double stranded, such that for every turn of elongated member66around coiled conductor portion17, there are two adjacent portions of elongated member66. For example, as shown inFIG. 3, turn62A of coiled fixation element62includes two adjacent portions66A,669of elongated member66.

Coiled fixation element62is configured to expand from a first dimension in a first state to a second dimension in a second state. InFIG. 4, coiled fixation element62is in the second, expanded state in which turns of coiled fixation element62extend radially away from coiled portion17of conductor16. In the second, expanded state, turns of coiled fixation element62have a greater radius of curvature (e.g., measured from a center longitudinal axis of coiled fixation element62, coiled conductor portion17, or both, to the outer surface of the turn) than in the first state. For example, in the first state, turns of coiled fixation element62may lie against coiled portion17.

In both the first and second states, coiled fixation element62defines at least part of an outer, exterior surface of lead60that contacts tissue of a patient when the portion of lead60including coiled fixation element62is implanted in the patient. In addition, in some examples, such as the one shown inFIG. 4, coiled conductor portion17also defines a part of the outer, exterior surface of lead60.

FIG. 5Ais a conceptual illustration of a part of an example electrical stimulation lead70, which is similar to lead14ofFIG. 1, but includes an expandable coiled fixation element72that has a different configuration than expandable coiled fixation element24. As with lead14, lead70includes coiled conductors16and coiled portion17of conductor16is shown inFIG. 5A. Coiled fixation element72is defined by elongated member74, which is coiled alongside coiled conductors16A,16B (e.g., as with elongated member25of lead14) for part of the length (measured along the x-axis direction, where orthogonal x-z axes are shown inFIG. 5Afor ease of description of the figure only) of lead70, and is wrapped around a part of the outer surface of coiled portion17of conductor16(e.g., as with elongated members54,66of leads50,60, respectively) for another part of the length of lead70. In the example shown in HG5A, elongated member74is coiled alongside coiled conductors16A,16B within segments75A,75B of lead70and wrapped around a part of the outer surface of coiled conductors16A,16B (and, therefore, coiled portion17of conductor16) within segment76of lead70. In the example shown inFIG. 5A, segment76is between segments75A,75B. In other examples, however, there may only be one segment75A,75B or more than one segment76.

Within segments75A,75B of lead70, elongated member70is coiled with conductors16in one direction and defines a portion of fixation element72that does not expand when coiled fixation element72expands from a first dimension in the first state to a second dimension in the second state. Coiled fixation element72and coiled conductor portion17are coaxial in the example shown inFIG. 5A. Within segments75A,75B, the outer surface of lead70that may contact tissue of a patient when lead70is implanted in the patient is defined by both elongated member74, which is coiled to define coiled expandable fixation element72, and conductors16A,16B.

In contrast to segments75A,75B of lead70, within segment76, elongated member74is wrapped around the outer surface of conductors16in more than one direction to define a portion of fixation element72that expands from the first dimension to the second dimension. Coiled fixation element72is shown in the expanded state inFIG. 5A. In some examples, an inner surface of coiled fixation element72is immediately adjacent an outer surface of coiled conductor portion17within segment76. In other examples, the inner surface of coiled fixation element72is separated from the outer surface of coiled conductor portion17by a separator, such as a sheath that is positioned around all or part of coiled conductor portion17.

Within segment76, the outer surface of lead70that may contact tissue of a patient when lead70is implanted in the patient is defined by coiled expandable fixation element72. For example, elongated member74may be disposed about the outer surface of conductors16to define a plurality of turns, including turns78A-78D (collectively referred to as “turns78”), as shown inFIG. 5A. However, elongated member74is not wrapped around conductors16in a single direction to define turns78, such that turns78do not define a helical configuration, e.g., as some examples of turns of coiled fixation element24may define (FIG. 2A, 2B). Instead, within segment76, elongated member74is wrapped around conductors16in two directions to define noncontinuous turns of expandable coiled fixation element72. The noncontinuous turns of expandable coiled fixation element72may be useful for, for example, dislodging lead70from tissue ingrowth because the tissue may find a straight path through coiled fixation element72.

In the example shown inFIG. 5A, elongated member74is wrapped around the outer surface of conductors16in a first circumferential direction to define one turn78A, and then member74is wrapped back around the outer surface of conductors16in a second circumferential direction that is opposite to the first direction to define another turn78B. Thereafter, member74is wrapped around the outer surface of conductors16in the first circumferential direction to define turn78C, and subsequently wrapped back around the outer surface of conductors16in the second circumferential direction that is opposite to the first direction to define another turn78D. This wrapping of elongated member74in alternating directions may continue for as many turns as desired, which may be selected based on the desired length (measured in a direction parallel to a longitudinal axis of lead70) of the expanded portion of coiled expandable fixation element72. In addition, any pattern of wrapping in the first and second circumferential directions may be used instead of or in addition to, the alternating pattern shown inFIG. 5A.

InFIG. 5A, coiled fixation element72is in the second, expanded state in which a subset of turns (including turns78A-78D) extend radially away from coiled portion17of conductor16, while distal-most and proximal-most turns of coiled fixation element72remain unexpanded. In the second, expanded state, the expanded turns have a greater radius of curvature than the nonexpandable turns of coiled fixation element72. In the first state, the subset of turns that expand is closer to coiled conductor portion17than in the second state. For example, in the first state, subset of turns78A-78D and the other expanded turns may sit against coiled portion17.

In the second, expanded state shown inFIG. 5A, turns78may have any suitable dimension relative to each other. In some examples, all of the turns78may have the same dimensions in the x-axis, z-axis, and y-axis dimensions. In other examples, at least two turns78may have different dimensions in one, two, or all three of the x-axis, z-axis, and y-axis dimensions. Turns78of different dimensions may help increase variability of tissue with which coiled fixation element72may engage with in order to help fix electrodes22A,22B at a target tissue site.

In some examples, coiled fixation element72and conductors16remain sufficiently fixed relative to each other without the aid of a separate securing mechanism. For example, the wrapping of elongated member74and conductors16together may help fix the relative position of an inner surface of.

FIG. 5Bis an illustration of coiled expandable fixation element72of lead70ofFIG. 5A, and illustrates the wrapping of elongated member74in different directions to define turns of fixation element72that expand away from conductors16in the second state of fixation element72.

In some examples, a portion of conductors16that extends through the section of lead70with coiled fixation element72may be uncoiled, e.g., may be relatively straight. For example, rather than wrapping around coiled conductor portion17, as shown inFIG. 5A, coiled fixation element72may wrap around un-coiled (e.g., substantially straight) conductors16. This may help reduce the outer perimeter of lead70through the portion with coiled fixation element72because conductors16may have a smaller profile (e.g., smaller outer perimeter) when uncoiled. In some examples in which a portion of conductors16that extends through the section of lead70with coiled fixation element72is uncoiled, when coiled fixation element72is in the first, non-expanded state, coiled fixation element72may not protrude past the outer surface of lead70defined by portions of conductor16distal and proximal to coiled fixation element72. In some examples, the uncoiled portion may be positioned between, for example, two coiled sections of conductors16to which coiled fixation element72may be mechanically connected, such that when a clinician pulls on a proximal end of lead70, conductors16elongate and decrease a profile of an expanded coiled fixation element72.

As discussed above, in some examples, a lead that includes an expandable coiled fixation element that defines a part of the outer surface of the lead can be percutaneously implanted in a patient with the aid of an introducer. The introducer may be configured to define a pathway from an entry point in the skin of the patient to a target stimulation site for the electrodes of the lead.FIG. 6Aillustrates an example introducer assembly80, which includes introducer needle82and stylet84, which is disposed inside of lumen86defined by introducer needle82.FIG. 6Billustrates introducer needle82andFIG. 6Cillustrates stylet84. WhileFIGS. 6A-6Care described with respect to lead14(FIG. 1), in other examples, introducer assembly80may be used to implant any lead including an expandable coiled fixation element in a patient.

Needle82includes a pointed tip82A that helps define a pathway through tissue of the patient as needle82is guided through the tissue. In some examples, the pointed tip82A of needle82is sharp enough to define a percutaneous opening, e.g., without the aid of a previously defined incision, for needle82. Stylet84may be disposed inside of introducer needle82as needle82is introduced into the patient in order to help prevent coring of tissue by needle82as needle82is advanced through tissue. In other examples, however, an introducer that is used to implant lead14may not include stylet84. For example, only introducer needle82may be introduced into the patient in order to define a pathway through tissue of the patient.

Lumen86of needle82is configured to receive lead14including expandable coiled fixation element24. In some examples, needle82is configured such that lumen86is sized to receive lead14while expandable fixation element24is in the first state, i.e., prior to expansion of expandable fixation element24to the second dimension in the second state. In some cases, the inner surface of needle82that defines lumen86may interact with expandable fixation element24to help retain the first state of expandable fixation element24.

FIG. 7is a flow diagram illustrating an example technique for implanting a lead that includes an expandable coiled fixation element that defines a part of the outer surface of the lead in a patient. WhileFIG. 7is described with respect to lead14shown inFIG. 1, in other examples, the technique shown inFIG. 7can be used to implant other leads, such as lead50(FIG. 3), lead60(FIG. 4) or other leads. In addition, whileFIG. 7is described with reference to introducer assembly80ofFIG. 6A, in other examples, other introducer assemblies can be used to implant a lead including an expandable coiled fixation element. In addition, if desired, a surgical technique that includes implanting lead14through an incision in the patient may also be used, if desired. However, an introducer assembly may be less invasive than the surgical techniques using an incision.

In accordance with the example technique shown inFIG. 7, introducer assembly80is introduced into tissue of a patient and a distal end (which includes pointed tip82A) of needle82is guided to target stimulation site within the patient (90). In some examples, the target stimulation site is a tissue site that is proximate the target nerve to be modulated by the electrical stimulation therapy delivered via electrodes22of lead14. Introducer assembly80may be inserted into the patient percutaneously or via an incision. Needle82defines a pathway through tissue of the patient from an entry point in the skin of the patient to the target stimulation site. Prior to, after, or as introducer assembly80is guided to the target stimulation site, lead14is introduced into lumen86of needle82(92). In particular, distal end14B of lead14is introduced into lumen86before proximal end14A. If stylet84is positioned in lumen86, stylet84may be removed from lumen86prior to introduction of lead14into lumen86.

Lead14is advanced through lumen86of needle82until electrodes22adjacent to distal end14B of lead14are positioned proximate to the target stimulation site. Positioning of introducer needle82and/or lead14may be aided by imaging techniques, such as by fluoroscopy using markers (e.g. radio-opaque or otherwise visible) on lead14or using ultrasound. The markers may also help indicate a location of coiled fixation element24with respect to one or more points of introducer needle82(e.g., tip82A of needle82). Distal end14B of lead14may be advanced through lumen86of needle82until at least distal end14B protrudes past tip82A of needle82and into tissue of the patient and expandable fixation element24is deployed from needle82(i.e., is advanced past tip82A of needle82). In other examples, expandable fixation element24may be deployed from needle82by withdrawing needle82(in a direction away from the patient), thereby exposing lead14. In either example, after electrodes22of lead14are at the target stimulation site, introducer needle82may be withdrawn from the patient, leaving lead14at least partially within the patient.

As discussed above, proximal end14A of lead14may be electrically and mechanically connected to electrical stimulator12, which may be carried external to the patient or implanted in the patient. In some examples, after lead14is at the target stimulation site and introducer needle82is withdrawn (92), proximal end14A of lead14remains outside of the patient and may be electrically and mechanically connected to an external electrical stimulator12. In other examples, after lead14is at the target stimulation site and introducer needle82is withdrawn (92), proximal end14A of lead may be implanted in the patient and may be electrically and mechanically connected to an implanted electrical stimulator12.

In accordance with the technique shown inFIG. 7, coiled fixation element24is expanded from a first dimension in the first state to the second dimension in a second state (94). In some examples, coiled fixation element24may be expanded to the second state before introducer needle82is withdrawn (92), while in other examples, coiled fixation element24may be expanded after introducer needle is withdrawn (92). Expanding coiled fixation element24prior to complete withdrawal of needle82from the patient, but after deployment of fixation element24from lumen86, may help fix the position of lead14during withdrawal of needle82from the patient, which may generate tugging and pulling forces along lead14in an axial direction (e.g., along longitudinal axis15).

In some examples, immediately upon deployment into body tissue, coiled fixation element24remains in the first state, in which turns of fixation element24do not extend away from coiled conductor portion17. In these examples, in order to expand coiled fixation element24into the second state (94), thermal energy is applied to coiled fixation element24. In the case of coiled fixation element24comprised of a shape memory material, the thermal energy may be sufficient to bring coiled fixation element24to a temperature greater than or equal to its transition temperature for changing shape, which is described in further detail below with reference toFIG. 8. As discussed above, thermal energy may be applied to coiled fixation element24by applying electrical energy (e.g., electrical current) to elongated member25; in this example, the resistance in the material from which member25is formed to the electrical energy generates the thermal energy.

In one example, elongated member25is electrically conductive, and upon the application of electrical energy to a contact23A near the proximal end of elongated member25, the electrical energy traverses through elongated member25to the at least one expandable turn of coiled fixation element24, which expands away from coiled portion17in response to the heat generated by the electrical energy. In some examples, electrical stimulator12is electrically connected to elongated member25and provides the electrical energy that generates the thermal energy that causes coiled fixation element24to expand from the first dimension in the first state (e.g., as shown inFIG. 1) to the second dimension in the second state (e.g., as shown inFIGS. 2A and 2B). In other examples, a device with an electrical energy source separate from electrical stimulator12is electrically connected to elongated member25and provides the electrical energy that generates the thermal energy that causes coiled fixation element24to expand.

Regardless of the source of electrical energy, the current provided to elongated member25to cause expansion of coiled fixation element24from the first state to the second state may be less than about 12.5 mA, such as a current in a range of about 1 mA to about 12.5 mA. In some examples, the energy level may be selected so as to not activate any physiological response from the patient, and may be selected to be under a perception threshold of the patient.

In another example, in order to expand coiled fixation element24into the second state (94), body heat from tissue surrounding coiled fixation element24provides the thermal energy that causes coiled fixation element24to expand from the first state to the second state. For example, elongated member25may be comprised of a shape memory material that is configured to revert to shape of the second state (e.g., in which at least one turn extends away from coiled conductor portion17) upon exposure to a temperature of about 33.2° C. to about 38.2° C. (about 92° F.-to about 101° F.), such as about 34.4° C.-to about 37.8° C. (about 94° F.-to about 100° F.), or about 35.4° C.-to about 37.8° C. (about 96° F.-to about 100° F.).

In the second state, at least one of the turns of coiled fixation element24extends away from coiled conductor portion17(e.g., radially away from coiled conductor portion17), such that, when lead14is implanted in tissue of the patient, the expanded turns of coiled fixation element24engage with surrounding tissue to substantially fix electrodes22proximate to the stimulation target site. In some examples, two or more of the turns of fixation element24extends away from coiled conductor portion17in the second state, and, in other examples, all of the turns of fixation element24extends away from coiled conductor portion17in the second state.

In some examples in which lead14includes core18, after coiled fixation element24is expanded to increase its profile (94), core18may be removed from lead14and from the patient. For example, a clinician may pull on a proximal end of core18(e.g., that remains outside of the patient) and pull the proximal end of core18in a direction away from the patient. As discussed above, core18may provide structural rigidity to lead14, e.g., to enable a clinician to better manipulate lead14during implantation of lead14in the patient. Flexibility of lead14imparted to lead14after removal of core18may be more comfortable to the patient in some examples. Thus, in some examples, it may be desirable to remove core18after lead14is implanted in the patient.

In accordance with the technique shown inFIG. 7, after lead14is substantially secured in place with the aid of coiled fixation element24in the second, expanded position, electrical stimulator12may deliver electrical stimulation to the patient via electrodes22of lead14(96). As discussed above, the stimulation may be, in some examples, electrical stimulation that is delivered on a trial, temporary basis in order to evaluate the efficacy of the electrical stimulation therapy. In other examples, the stimulation delivered by electrical stimulator12via lead14may be chronic, long-terra stimulation (e.g., on the order of months or years).

Upon determination, e.g., by a clinician, that lead14should be explanted from the patient, the clinician, manually or with the aid of a device, may withdraw lead14from patient. In the technique shown inFIG. 7, the clinician pulls on proximal end14A of lead14to withdraw lead14from the patient (98). Due to the coiled nature of coiled fixation element24and coiled conductor portion17around which coiled fixation element24is positioned, pulling on proximal end14A of lead14may elongate coiled conductor portion17of lead14along longitudinal axis15, thereby causing coiled fixation element24to contract towards coiled fixation element17. When coiled fixation element24contracts towards coiled conductor portion17, coiled fixation element24may contract towards the first state and at least partially disengage with surrounding tissue. At least partially disengaging coiled fixation element24from surrounding tissue may help reduce the extent to which coiled fixation element24fixes lead14in place. In this way, lead14may be configured to aid explanation of lead14from patient14.

When proximal end14A of lead14is pulled to cause coiled fixation element24to contract towards coiled fixation element17, coiled fixation element24may contract back to the first state. However, in other examples, coiled fixation element24may contract from the second state towards the first state (in which the turns of coiled fixation element24are closer to coiled conductor portion17), but may not completely return back to the first state (e.g., may not have the same turn radius as coiled conductor portion17in the case of lead14or may not completely lie against coiled conductor portion17in the case of leads50,60).

The order of steps shown inFIG. 7is merely one example of a method of implanting a lead including an expandable coiled fixation element. In other examples, the steps may be performed in a different order.

As discussed above, in some examples, an expandable coiled fixation element of a medical lead is formed from a shape memory material. A shape memory material may be, for example, a shape memory alloy, which may also be referred to as a smart metal, memory metal, memory alloy, or smart alloy. In one example, an expandable coiled fixation element described herein is formed from a nickel titanium (NiTi) shape memory alloy. The shape memory material selected for the expandable coiled fixation element may have a one-way memory effect in some examples. With a one-way memory effect shape memory material, a material may remember one shape, which may be referred to as its original shape. The memory may be deformed from its original shape to a second shape while the material is in a cold state (e.g., a temperature below the transition temperature of the material). The material will retain the second shape until it is heated above the transition temperature of the material. In response to being heated to the transition temperature of the material, the material will revert back to its original shape. Once the material cools after heating to the transition temperature, the material will retain the original shape until deformed again. The original shape may, for example, define the coiled fixation element in the second, expanded state, and the second shape may, for example, define the coiled fixation element in the first state.

In another example, the shape memory material selected for the expandable coiled fixation element may have a two-way memory effect. With a two-way memory effect shape memory material, the material may remember two different shapes: a first shape at a first temperature (or a first range of temperatures) and a second shape at a second temperature (or a second range of temperatures). With a two-way memory effect shape memory material, the material may be deformed in a cold state (e.g., a temperature below the first temperature or range of temperatures), and will retain the deformed shape until it is heated above the first transition temperature of the material. At the first transition temperature, the material may revert to the first shape. Once the material cools after heating, the material will retain its first shape until deformed again or until heated to the second transition temperature, at which time, the material may revert to the second shape. Once the material cools after heating, the material will retain its second shape until a force is applied to further deform the material.

FIG. 8is a flow diagram of an example technique for forming an expandable coiled fixation element of a medical lead. WhileFIG. 8is described with respect to lead14shown inFIG. 1, in other examples, the technique shown inFIG. 8can be used to form coiled fixation elements of other leads, such as lead50(FIG. 3), lead60(FIG. 4) or other leads.

In accordance with the technique shown inFIG. 8, while elongated member25is at or above the transition temperature of the shape memory material from which elongated member25is formed, elongated member25is manipulated to define coiled fixation element24in the second state in which coiled fixation element24has the second dimension (100). Elongated member25may be coiled manually or with the aid of a semi-automated or automated device.

After coiling elongated member25to define coiled fixation element24having the second dimension in the second state (100), elongated member25may be deformed (e.g., straightened) and coiled with conductors16to define lead14that may look like lead14shown inFIG. 1, in which coiled fixation element24is in the first state (102). For example, elongated member25can placed adjacent to conductor16and both elongated member25and conductor16can be wrapped around core18. In some examples, core18remains within the lumen defined by the coiled fixation element24defined by elongated member25and coiled conductor portion17when lead14is implanted in a patient. In other examples, core18may be removed from the lumen after the coil defined by elongated member25and conductor16are formed. After defining lead14including coiled fixation element24in the first state, lead14may be implanted in the patient while coiled fixation element24is in the first state.

In other examples, after defining a coiled fixation element in the second state with an elongated member, the elongated member can be subsequently coiled around coiled conductor portion17to define the coiled fixation element in the first state. Examples of such coiled fixation elements are described above with respect to coiled fixation elements52,66, and72ofFIGS. 3-5, respectively.