EP4683706A1

EP4683706A1 - Distal end fixation for implantable medical device

Info

Publication number: EP4683706A1
Application number: EP24709516.9A
Authority: EP
Inventors: Thomas A. Anderson; Jason D. HAMACK
Original assignee: Medtronic Inc
Current assignee: Medtronic Inc
Priority date: 2023-03-20
Filing date: 2024-02-28
Publication date: 2026-01-28
Also published as: WO2024194708A1; CN120731108A

Abstract

A device comprising: an elongated housing extending from a proximal end to a distal end along a longitudinal axis; a first electrode and a second electrode extending distally from the distal end of the elongated housing; and one or more tissue retention features defined by the distal end of the elongated housing. Each tissue retention feature may include a first opening disposed on the distal end of the elongated housing, a second opening disposed on an outer surface of the elongated housing between the proximal end and the distal end, and a channel connecting the first opening and the second opening. One or more openings of the first opening or the second opening is configured to allow ingrowth of the wall tissue into the channel via the one or more openings.

Description

DISTAL END FIXATION FOR IMPLANTABLE MEDICAL DEVICE

[0001] This application claims the benefit of U.S. Provisional Patent Application Serial No. 63/491,204, filed March 20, 2023, the entire content of which is incorporated herein by reference.

TECHNICAL FIELD

[0002] The disclosure relates to medical devices, and more particularly to fixation mechanisms of medical devices.

BACKGROUND

[0003] Various types of implantable medical devices (IMDs) have been implanted for treating or monitoring one or more conditions of a patient. Such IMDs may be adapted to monitor or treat conditions or functions relating to heart, muscle, nerve, brain, stomach, endocrine organs or other organs and their related functions. Such IMDs may be associated with leads that position electrodes at a desired location or may be leadless with electrodes integrated with and/or attached to the device housing. These IMDs may have the ability to wirelessly transmit data either to another device implanted in the patient or to another instrument located externally of the patient, or both.

[0004] A cardiac pacemaker is an IMD configured to deliver cardiac pacing therapy to restore a more normal heart rhythm. Such IMDs sense the electrical activity of the heart, and deliver cardiac pacing based on the sensed electrical activity, via electrodes. Some cardiac pacemakers are implanted a distance from the heart and coupled to one or more leads that intravascularly extend into the heart to position electrodes with respect to cardiac tissue. Some cardiac pacemakers are sized to be completely implanted within one of the chambers of the heart and may include electrodes integrated with or attached to the device housing rather than leads. Some cardiac pacemakers provide dual chamber functionality, by sensing and/or stimulating the activity of both atria and ventricles, or other multi-chamber functionality. A cardiac pacemaker may provide multi-chamber functionality via leads that extend to respective heart chambers, or multiple cardiac pacemakers may provide multi-chamber functionality by being implanted in respective chambers. SUMMARY

[0005] In general, this disclosure is directed to implantable medical devices (IMDs) configured to sense and deliver electrical signals to tissue of a patient via a plurality of electrodes at or near a distal end of an elongated housing of the IMD. More particularly, this disclosure is directed to IMDs where the distal end of the elongated housing of the IMD defines one or more tissue retention features. Each tissue retention feature may be configured to facilitate growth of tissue into the tissue retention feature to affix IMD to the tissue, e.g., to inhibit unintended rotation and/or dislodgement of the IMD from the tissue. [0006] In some examples, a single IMD is implanted in one chamber of a heart of the patient and is able to sense in and/or deliver cardiac pacing to more than one chamber, which may avoid the need for a leaded device or multiple smaller devices to provide such functionality, which may reduce the amount of material implanted within the patient. In some examples, such an implantable medical device includes a distal electrode that is configured to penetrate through wall tissue of the heart chamber in which the device is implanted, and into wall tissue of another heart chamber. In addition to the distal electrode, the device includes a reference electrode and one or more proximal electrodes configured to contact the wall tissue of the heart chamber. The distal electrode may be a helix configured to penetrate tissue of the patient. The distal electrode may be configured to sense in and/or deliver cardiac pacing to one chamber of the heart and the one or more proximal electrodes may be configured to sense in and/or deliver cardiac pacing to another separate chamber of the heart.

[0007] The IMD may include an elongated housing extending from a proximal end to a distal end. The electrodes can be connected to a distal end of the elongated housing. As described herein, the IMD may include one or more tissue retention features defined by the distal end of the elongated housing. Each tissue retention feature may include a first opening disposed on the distal end of the elongated housing, a second opening disposed on a side of the elongated housing (e.g., between the proximal end and the distal end), and a channel connecting the first opening to the second opening. Each tissue retention feature may allow growth of tissue into the channel via one or more of the first opening or the second opening. Tissue growth within tissue retention features may improve contact between the proximal electrode and the tissue relative to another electrode placed on the distal end of the elongated housing. The improved contact may improve performance by, e.g., reducing pacing thresholds for the proximal electrode. The tissue growth within the tissue retention features may further improve performance of the IMD by preventing unintended rotation and/or dislodgment of the IMD from tissue of the patient, thereby improving the consistency of the sensing and/or pacing capabilities of the electrodes. [0008] In some examples, this disclosure is directed to a fixation device comprising: an elongated body extending distally from a distal end of a housing of an implantable medical device (IMD), the elongated body comprising: a proximal end located at the distal end of the IMD; and a helix extending distally from the proximal end and defining one or more coils, wherein a distal end of the helix is configured to penetrate into tissue of a patient; and one or more tissue retention features defined by the distal end of the housing, each tissue retention feature comprising: a first opening disposed on the distal end of the housing; a second opening disposed on an outer surface of the housing, wherein the outer surface is proximal to the distal end of the housing and disposed along a perimeter of the housing; and a channel connecting the first opening and the second opening, wherein one or more openings of the first opening or the second opening is configured to allow tissue growth into the channel via the one or more openings.

[0009] In some examples, this disclosure is directed to a device comprising: an elongated housing extending from a proximal end to a distal end along a longitudinal axis, the elongated housing being configured to be implanted wholly within a chamber of a heart; a first electrode extending distally from the distal end of the elongated housing, the first electrode comprising an elongated body defining a helix, wherein a distal end of the helix is configured to penetrate wall tissue of the chamber; a second electrode extending distally from the distal end of the elongated housing, wherein the second electrode is configured to be placed in contact with the wall tissue of the chamber without penetrating the wall tissue; and one or more tissue retention features defined by the distal end of the elongated housing, each tissue retention feature comprising: a first opening disposed on the distal end of the elongated housing; a second opening disposed on an outer surface of the elongated housing between the proximal end and the distal end; and a channel connecting the first opening and the second opening, wherein one or more openings of the first opening or the second opening is configured to allow ingrowth of the wall tissue into the channel via the one or more openings. [0010] In some examples, this disclosure is directed to a device comprising: an elongated housing extending from a proximal end to a distal end along a longitudinal axis, the elongated housing being configured to be implanted wholly within a chamber of a heart; a first electrode extending distally from the distal end of the elongated housing, the first electrode comprising an elongated body defining a helix, wherein a distal end of the helix is configured to penetrate wall tissue of the chamber; a second electrode extending distally from the distal end of the elongated housing, wherein the second electrode is configured to be placed in contact with the wall tissue of the chamber without penetrating the wall tissue; and one or more tissue retention features defined by the distal end of the elongated housing, each tissue retention feature comprising: a first opening disposed on the distal end of the elongated housing; a second opening disposed on an outer surface of the elongated housing between the proximal end and the distal end; and a channel connecting the first opening and the second opening, wherein one or more openings of the first opening or the second opening is configured to allow ingrowth of the wall tissue into the channel via the one or more openings.

[0011] In some examples, this disclosure is directed to a method comprising: implanting a device within a first chamber of a heart of a patient, wherein the device comprises: an elongated housing extending from a proximal end to a distal end along a longitudinal axis, the elongated housing being configured to be implanted wholly within a first chamber of a heart; a first electrode extending distally from the distal end of the elongated housing, the first electrode comprising an elongated body defining a helix, wherein a distal end of the helix is configured to penetrate first wall tissue of the first chamber; a second electrode extending distally from the distal end of the elongated housing, wherein the second electrode is configured to be placed in contact with the first wall tissue of the first chamber without penetrating the first wall tissue; one or more tissue retention features defined by the distal end of the elongated housing, each tissue retention feature comprising: a first opening disposed on the distal end of the elongated housing; a second opening disposed on an outer surface of the elongated housing between the proximal end and the distal end; and a channel connecting the first opening and the second opening, wherein one or more openings of the first opening or the second opening is configured to allow ingrowth of the first wall tissue into the channel via the one or more openings; and signal generation circuitry within the elongated housing, the signal generation circuitry being coupled to the first electrode and the second electrode; delivering, by the signal generation circuitry, cardiac pacing to a second chamber of the heart via the first electrode, wherein the second chamber of the heart is separate from the first electrode; and delivering, by the signal generation circuitry, cardiac pacing to the first chamber of the heart via the second electrode.

[0012] This summary is intended to provide an overview of the subject matter described in this disclosure. It is not intended to provide an exclusive or exhaustive explanation of the methods and systems described in detail within the accompanying drawings and description below.

BRIEF DESCRIPTION OF DRAWINGS

[0013] The details of one or more examples of this disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of this disclosure will be apparent from the description and drawings, and from the claims.

[0014] FIG. 1 is a conceptual diagram illustrating an example device implanted in the heart of a patient, in accordance with one or more aspects of this disclosure.

[0015] FIG. 2A is a perspective diagram illustrating the example device of FIG. 1 with a plurality of tissue retention features.

[0016] FIG. 2B is a perspective diagram illustrating a top-down view of the example device of FIG. 2 A.

[0017] FIG. 3A is a cross-section diagram illustrating a cross-section view of an example configuration of the device of FIG. 2A, the cross-section being taken along line A-A of FIG. 2B and along a plane parallel to the longitudinal axis of the example device. [0018] FIG. 3B is a cross-section diagram illustrating a cross-section view of another example configuration of the device of FIG. 2A, the cross-section being taken along line A-A of FIG. 2B and along a plane parallel to the longitudinal axis of the example device. [0019] FIG. 3C is a cross-section diagram illustrating a cross-section view of another example configuration of the device of FIG. 2A, the cross-section being taken along line A-A of FIG. 2B and along a plane parallel to the longitudinal axis of the example device.

[0020] FIG. 4A is a perspective diagram illustrating a top-down view of another example of the device of FIG. 1 with tissue retention features having flexible pins. [0021] FIG. 4B is a cross-section diagram illustrating a cross-section view of the example device of FIG. 4A, the cross-section being taken along line B-B of FIG. 4A and along a plane parallel to the longitudinal axis of the example device.

[0022] FIG. 5 is a functional block diagram illustrating an example configuration of the device of FIG. 1.

[0023] FIG. 6 is a flow diagram illustrating an example process for sensing a cardiac electrical signal and delivering cardiac pacing therapy to a heart of a patient via an example device of any of FIGS. 1-5.

DETAILED DESCRIPTION

[0024] In general, this disclosure is directed to distal end configurations for implantable medical devices (IMDs). More particularly, this disclosure is directed to IMDs having a distal end with one or more features for fixation of the IMD with respect to patient tissue, and/or a plurality of electrodes configured to sense electrical signals from and to deliver electrical stimulation (e.g., cardiac pacing) to tissue of a patient.

[0025] FIG. 1 is a conceptual diagram illustrating an example device 104 implanted in the heart 102 of a patient, in accordance with one or more aspects of this disclosure. Device 104 is shown implanted in the right atrium (RA) of the patient’s heart 102 in a target implant region 106, such as the triangle of Koch, in heart 102 of the patient with a distal end of device 104 directed toward the left ventricle (LV) of the patient’s heart 102. Although in the example of FIG. 1 the distal end of device 104 is directed toward the LV, the distal end may be directed to other targets, such as interventricular septum of heart 102. Target implant region 106 may lie between the bundle of His and the coronary sinus and may be adjacent the tricuspid valve.

[0026] Device 104 includes a distal end 110 and a proximal end 116. Distal end 110 includes a first electrode 112, and a second electrode 114. First electrode 112 may define a helical shape, e.g., as illustrated in FIG. 1. First electrode 112 extends from distal end 110 and may penetrate through the wall tissue of a first chamber (e.g., the RA in the illustrated example) into wall tissue of a second chamber (e.g., ventricular myocardium 108 of the LV in the illustrated example). Second electrode 114 may be disposed on a ramp extending distally from distal end 110 and is configured to be placed in contact with the wall tissue of the first chamber without penetration of the wall tissue of the first chamber by second electrode 114. Second electrode 114 may contact the wall tissue of the first chamber as first electrode 112 penetrates the wall tissue of the first chamber.

[0027] The configuration of electrodes 112 and 114 illustrated in FIG. 1 allows device 104 to sense cardiac signals and/or deliver cardiac pacing to multiple chambers of heart 102, e.g., the RA and ventricle(s) in the illustrated example. In this manner, the configuration of electrodes 112 and 114 may facilitate the delivery of A-V synchronous pacing by single device 104 implanted within the single chamber, e.g., the RA. While device 104 is implanted at target implant region 106 to sense in and/or pace the RA and ventricle(s) in the example shown in FIG. 1, a device having an electrode configuration in accordance with the examples of this disclosure may be implanted at any of a variety of locations to sense in and/or pace any one, two or more chambers of heart 102. For example, device 104 may be implanted at region 106 or another region, and first electrode 112 may extend into tissue, e.g., myocardial tissue, of the LV or interventricular septum to, for example, facilitate the delivery of A-V synchronous pacing. Furthermore, a device having an electrode configuration in accordance with the examples of this disclosure may be implanted at any of a variety of locations within a patient for sensing and/or delivery of therapy to other patient tissue. In some examples, first electrode 112 extends into the tissue of heart 102 at region 106 and affix device 104 to the tissue of heart 102.

[0028] Additionally, the anti-rotation features and/or functionality described herein are described primarily in the context of a cardiac pacemaker configured to be implanted in one chamber and deliver pacing and sense in that chamber and an additional chamber. However, the anti-rotation features and/or functionality described herein may be included on any implantable medical device, such as an implantable stimulator or implantable lead configured to be fixed at any location or tissue of the body. For example, an implantable stimulator or implantable lead may include one or more tissue retention features on a distal end, the one or more tissue retention features being configured to prevent or inhibit unintended rotation and/or dislodgement of the implantable stimulator or implantable lead from tissue of the patient.

[0029] FIG. 2A is a perspective diagram illustrating device 104. Device 104 includes a housing 202 that defines a hermetically sealed internal cavity. Housing 202 may be formed from a conductive material including titanium or titanium alloy, stainless steel, MP35N (a non-magnetic nickel-cobalt-chromium-molybdenum alloy), platinum alloy or other bio-compatible metal or metal alloy, or other suitable conductive material. In some examples, housing 202 is formed from a non-conductive material including ceramic, glass, sapphire, silicone, polyurethane, epoxy, acetyl co-polymer plastics, polyether ether ketone (PEEK), a liquid crystal polymer, other biocompatible polymer, or other suitable non- conductive material.

[0030] Housing 202 extends between distal end 204 and proximal end 206 along longitudinal axis 210. Housing 202 may be cylindrical or substantially cylindrical but may be other shapes, e.g., prismatic, or other geometric shapes. Housing 202 may include a delivery tool interface member 208, e.g., at proximal end 206, for engaging with a delivery tool during implantation of device 104. At distal end 204, housing 202 may define a face 212 of housing 202. Face 212 may define a distal end major surface. Face 212 may be orthogonal to longitudinal axis 210. In some examples, face 212 is slanted, e.g., face 212 defines a reference plane that is not orthogonal to longitudinal axis 210.

[0031] Distal end 204 defines a plurality of tissue retention features 220. Each tissue retention feature 220 may include a first opening 222A disposed on face 212, a second opening 222B disposed on the side of housing 202 (or a side in the case of shapes of housing 202 other than cylindrical), and a channel (not pictured) connecting first opening 222 A and second opening 222B. Each tissue retention feature 220 may be configured to retain tissue within the channel. The tissue may grow into the channel via one or more of first opening 222A or second opening 222B. Ingrown tissue within tissue retention features 220 may further affix device 104 to tissue of the patient and may inhibit unintended rotation and/or dislodgement of device 104 within the tissue. While FIG. 2A illustrates distal end 204 defining four tissue retention features 220, other examples of distal end 204 may include one, two, three, or five or more tissue retention features 220. Tissue retention features 220 may be spaced equally around an outer perimeter of distal end 204. In some examples, one or more tissue retention features 220 are disposed circumferentially adjacent to second electrode 114. In some examples, one tissue retention feature 220 is disposed directly opposite second electrode 114 (e.g., is separated from second electrode 114 by 180 degrees).

[0032] Each of openings 222A, 222B (collectively referred to as “openings 222”) of each tissue retention feature 220 may be entirely enclosed by distal end 204 (e.g., distal end 204 defines the entirety of each of openings 222 and each of openings 222 is separated from another opening or feature by material of distal end 204). For example, openings 222 may be connected only via the channel of the tissue retention feature 220 and each tissue retention feature 220 may be separated from another tissue retention feature 220. Each of openings 222 may be sized to facilitate ingrowth of tissue into the channel. Each of openings 222 may define maximum length and/or width, e.g., to prevent excess ingrown tissue within the channel. Excess ingrown tissue may impede removal of the device 104 from the tissue by the clinician. The ingrown tissue within tissue retention features 220 may be removable from tissue retention features 220 as a part of the removal of the device 104 from the tissue without requiring the clinician to perform additional steps, e.g., relative to another device 104 without tissue retention features 220.

[0033] Distal end 204 may include one or more ramps 214. Second electrode 114 may be disposed on ramp 214. Ramp 214 extends from a first end that is fixedly attached to housing 202 at or near distal end 204 (e.g., attached to face 212), to a second end that is more distal than the first end. Ramp 214 may be disposed radially outwards of first electrode 112 relative to longitudinal axis 210. Ramp 214 may extend around at least a portion of a perimeter of housing 202. Ramp 214 may extend up to 180 degrees around longitudinal axis 210 and along the perimeter of housing 202. Ramp 214 may define a partial helix, e.g., wound in a same direction and/or in different directions around longitudinal axis 210 as a helix and/or coil defined by first electrode 112.

[0034] Ramp 214 may be an anti-rotation feature in addition to tissue retention features 220. Ramp 214 may increase compression of the tissue and/or increase the friction or other fixation force between the tissue and device 104 and/or first electrode 112. The increase in fixation force(s) may be sufficient to resist rotation of first electrode 112 by movement of the tissue of heart 102 but may not be sufficient to resist rotation of first electrode 112 by the clinician, e.g., to remove device 104 from heart 102. The amount of force the tissue exerts on first electrode 112 and/or the amount of force ramp 214 exerts on the tissue may vary based on movement of heart 102, movement of device 104, movement of fluid within heart 102, size of heart 102, a number of ramp(s) 214 on face 212, presence of additional anti-rotation feature(s), or the like. Ramp 214 may be or may include features of any of the example ramps described in commonly owned U.S.

Provisional Patent Application No. 63/485,174, filed February 15, 2023, and entitled “DISTAL END FIXATION FOR IMPLANTABLE MEDICAL DEVICE,” the entirety of which is herein incorporated by reference.

[0035] First electrode 112 may include one or more coatings (e.g., electrically insulative coating(s)) configured to define a first electrically active region 216, or first electrode 112 may otherwise define first electrically active region 216. In some examples, first electrically active region 216 is more proximate to the second, e.g., distal, end of first electrode 112. In the example of FIG. 2A, first electrically active region 216 includes the distal end of electrode 112. Second electrode 114 may include one or more coatings configured to define a second electrically active region 217 on an outer surface of second electrode 114. In some examples, as illustrated in FIG. 2A, second electrical active region 217 forms a ring around a therapeutic substance dispensing device 215 on second electrode 114. Second electrode 114 may include, but is not limited to, a button electrode, a spring electrode, or any other suitable type or shape of electrode.

[0036] First and second electrodes 112 and 114 may be formed of an electrically conductive material, such as titanium, platinum, iridium, tantalum, stainless steel or alloys thereof. First and second electrodes 112 and 114 may be coated with an electrically insulating coating, e.g., a parylene, polyurethane, silicone, epoxy, or other insulating coating, to reduce the electrically conductive active surface area of first and second electrodes 112 and 114, and thereby define first and second electrically active regions 216 and 217. Defining first and second electrically active regions 216 and 217 by covering portions with an insulating coating may increase the electrical impedance of first and second electrodes 112 and 114 and thereby reduce the current delivered during a pacing pulse that captures the cardiac tissue. A lower current drain conserves the power source, e.g., one or more rechargeable or non-rechargeable batteries, of device 104.

[0037] In some examples, first and second electrodes 112 and 114 include an electrically conducting material coating on first and second electrically active regions 216 and 217 to define the active regions. For example, first and second electrically active regions 216 and 217 may be coated with titanium nitride (TiN). First and second electrodes 112 and 114 may be made of substantially similar material or may be made of different material from one another.

[0038] In the example of FIG. 2A, first electrode 112 takes the form of a helix or a coil. First electrode 112 may be an elongated body defining a helix. In some examples, a helix is an object having a three-dimensional shape like that of a wire wound uniformly in a single layer around a cylindrical or conical surface or mandrel such that the wire would be in a straight line if the surface were unrolled into a plane. First electrode 112 may extend from face 212 from a proximal end to a distal end, e.g., defining first electrically active region 216. The proximal end may be a location along first electrode 112 where first electrode 112 extends distally past distal end 204 of device 104.

[0039] Second electrode 114 is disposed on distal end 204 and may include a button electrode, e.g., as illustrated in FIG. 2A, or any other suitable type or shape of electrode. In some examples, device 104 includes a plurality of second electrodes 114 (e.g., two or more second electrodes 114) disposed on distal end 204 of housing 202. The plurality of second electrodes 114 may be equally spaced around a circumference of distal end 204. At least one of the plurality of second electrodes 114 may be disposed on ramps (e.g., on two or more ramps 214). In some examples, each of the plurality of second electrodes 114 is disposed on ramps. Each ramp 214 may include a single second electrode 114 or two or more second electrodes 114. In some examples, second electrode 114 is disposed at a predetermined angle, e.g., about longitudinal axis 210, away from first end of first electrode 112.

[0040] In some examples, first electrode 112 includes one or more additional antirotation features. The additional anti-rotation features may include a shape of first electrode 112, dimensions (e.g., outer diameter, pitch, or the like) of first electrode 112, one or more features disposed on an outer surface of first electrode 112, or the like. The shape and/or dimensions of first electrode 112 may include a geometric shape of first electrode 112, a varying diameter configuration of first electrode 112, a varying pitch configuration of first electrode 112, a waveform configuration of first electrode 112, or any combination herein. The one or more anti-rotation features disposed on first electrode 112 may include, but are not limited to, elongate darts, barbs, or tines. In some examples, the anti-rotation features include bumps, ridges, and/or other texturing disposed on one or more surfaces of ramp 214 and/or of face 212. The one or more anti-rotation features may resist rotation of first electrode 112 (e.g., by penetrating the tissue, by increasing the friction between first electrode 112 and the tissue, or the like) alone or in conjunction with other anti-rotation features (e.g., ramp 214, tissue retention features 220).

[0041] As illustrated in FIG. 2A, first electrode 112 may be a helix extending distally from face 212 and revolving around longitudinal axis 210 in a counter-clockwise direction (i.e., “wound” in a counter-clockwise direction, and ramp 214 may define partial helix extending distally from face 212 and revolving around longitudinal axis 210 in a clockwise direction, although in other examples the first electrode 112 and ramp 214 may revolve around longitudinal axis 210 in different directions (e.g., first electrode 112 revolves around longitudinal axis 210 in a clockwise direction and ramp 214 revolves around longitudinal axis 210 in a counter-clockwise direction) or first electrode 112 and ramp 214 may revolve around longitudinal axis 210 in a same direction.

[0042] First and second electrodes 112 and 114 may vary in size and shape in order to enhance tissue contact of first and second electrically active regions 216 and 217. For example, first electrodes 112 may have a round cross-section or could be made with a flatter cross-section (e.g., oval or rectangular) based on tissue contact specifications. In some examples, second electrode 114 defines an outer surface that varies in size and shape (e.g., an oval outer surface, an outer surface with a larger diameter, or the like) in order to enhance tissue contact of second electrically active region 217.

[0043] The size and shape of first electrode 112 may be determined at least in part by stiffness requirements. For example, stiffness requirements may vary based on the expected implantation requirements, including the tissue into which the electrodes are implanted or contact, as well as how long device 104 is intended to be implanted.

[0044] The distal end of first electrode 112 can have a conical, hemi-spherical, or slanted edge distal tip with a narrow tip diameter, e.g., less than 1 millimeter (mm), for penetrating into and through tissue layers. The distal end of first electrode can be a sharpened or angular tip or sharpened or beveled edges, but the degree of sharpness may be constrained to avoid a cutting action that could lead to lateral displacement of the distal end of first electrode 112 and undesired tissue trauma. In some examples, first electrode 112 defines a maximum diameter at its base that interfaces with housing distal end 204. In such examples, the outer diameter of the helix defined by first electrode 112 may decrease from housing distal end 204 to the distal end of first electrode 112. In some examples, the diameter of first electrode 112 varies from housing distal end 204 to the distal end of first electrode 112. The varying diameter may cause first electrode 112 to resist rotation within the tissue of heart 102.

[0045] The outer dimensions of first electrode 112 can be substantially straight and cylindrical, with first electrode 112 being rigid in some examples. First electrode 112 may have flexibility in lateral directions, being non-rigid to allow some flexing with heart motion. In a relaxed state, when not subjected to any external forces, first electrode 112 can be configured to maintain a distance between first electrically active region 216 and housing distal end 204.

[0046] Distal end of first electrode 112 can pierce through one or more tissue layers to position first electrically active region 216 within a desired tissue layer, e.g., the ventricular myocardium 108 or interventricular septum. Accordingly, first electrode 112 extends a distance from housing distal end 204 corresponding to the expected pacing site depth and may have a relatively high compressive strength along its longitudinal axis, which may be substantially similar to or coincident with longitudinal axis 210, to resist bending in a lateral or radial direction when a longitudinal, axial, and/or rotational force is applied, e.g., to the proximal end 206 of housing 202 to advance device 104 into the tissue at target implant region 106. By resisting bending in a lateral or radial direction, first electrode 112 can maintain a spacing between a plurality of windings of first electrode 112 when first electrode 112 is a helix electrode. The spacing may be a pre-determined pitch of first electrode 112 and may vary from distal end 204 to the distal end of first electrode 112. First electrode 112 may be longitudinally non-compressible. First electrode 112 may also be elastically deformable in lateral or radial directions when subjected to lateral or radial forces, however, to allow temporary flexing, e.g., with tissue motion, but returns to its normally straight position when lateral forces diminish. In some examples, when first electrode 112 is not exposed to any external force, or to only a force along its longitudinal axis (substantially similar to or coincident with longitudinal axis 210), first electrode 112 retains a straight, linear configuration as shown.

[0047] All, substantially all, or a portion of housing 202 may function as an electrode 218, e.g., an anode, during pacing and/or sensing. In some examples, electrode 218 circumscribes a portion of housing 202 at or near proximal end 206. Electrode 218 can fully or partially circumscribe housing 202. FIG. 2A shows electrode 218 extending as a singular band around the outer perimeter of housing 202. Electrode 218 can also include multiple segments spaced a distance apart along a longitudinal axis 210 of housing 202 and/or around a perimeter of housing 202. In some examples, electrode 218 is disposed on face 212 or on ramp 214 disposed on face 212. In some examples, second electrode 114 is disposed on a first ramp 214 and electrode 218 may be disposed on a second ramp 214. [0048] When housing 202 is formed from a conductive material, such as a titanium alloy, portions of housing 202 may be electrically insulated by a non-conductive material, such as a coating of parylene, polyurethane, silicone, epoxy or other biocompatible polymer, or other suitable material. For the portions of housing 202 without the non- conductive material, one or more discrete areas of housing 202 with conductive material can be exposed to define electrode 218.

[0049] When housing 202 is formed from a non-conductive material, such as a ceramic, glass or polymer material, an electrically-conductive coating or layer, such as a titanium, platinum, stainless steel, alloys thereof, a conductive material may be applied to one or more discrete areas of housing 202 to form electrode 218.

[0050] In some examples, electrode 218 is a component, such as a ring electrode, that is mounted or assembled onto housing 202. Electrode 218 may be electrically coupled to internal circuitry of device 104 via electrically-conductive housing 202 or an electrical conductor when housing 202 is a non-conductive material. In some examples, electrode 218 is located proximate to proximal end 206 of housing 202 and can be referred to as a proximal housing -based electrode. Electrode 218 can also be located at other positions along housing 202, e.g., located proximately to distal end 204 or at other positions along longitudinal axis 210.

[0051] In some examples, second electrode 114 or electrode 218 is paired with first electrode 112 for sensing ventricular signals and delivering ventricular pacing pulses. In some examples, second electrode 114 is paired with electrode 218 or first electrode 112 for sensing atrial signals and delivering pacing pulses to atrial tissue (e.g., to the atrial endocardium) in target implant region 106. In other words, electrode 218 is paired, at different times, with first electrode 112 and/or second electrode 114 for either ventricular or atrial functionality, respectively. In some examples, first and second electrodes 112 and 114 are paired with each other, with different polarities, for atrial and ventricular functionality.

[0052] In some examples, second electrode 114 is configured as an atrial cathode electrode for delivering pacing pulses to the atrial tissue, e.g., at target implant region 106 in combination with electrode 218. Second electrode 114 and electrode 218 may also be used to sense atrial P-waves for use in controlling atrial pacing pulses (delivered in the absence of a sensed P-wave) and for controlling atrial- synchronized ventricular pacing pulses delivered using first electrode 112 as a cathode and electrode 218 as the return anode.

[0053] A distal end of first electrode 112 can be configured to rest within a ventricular myocardium of the patient, and second electrode 114 can be configured to contact an atrial endocardium of the patient without penetration of the atrial endocardium. Device 104 may include more or fewer electrodes than two electrodes. In some examples, device 104 includes one or more second electrodes 114 along housing distal end 204. For example, device 104 may include two or three electrodes configured for atrial functionality like second electrode 114, and the three electrodes may be substantially similar or different from one another. Spacing between a plurality of second electrodes 114 may be at an equal or unequal distance. Second electrode(s) 114 may be individually selectively coupled to sensing and/or pacing circuitry enclosed by housing 202 for use as an anode with first electrode 112 or as an atrial cathode electrode, or may be electrically common and not individually selectable. In some examples, in place of first electrode 112, device 104 includes a fixation element (not shown) of similar shape and mechanical, but without an electrically active region or electrode formed thereon or borne thereby; in such examples, electrically active region 216 can be positioned on a separate member and/or on the housing 202. In some examples, device 104 only includes first electrode 112 and electrode 218 and does not include any second electrodes 114.

[0054] Inflammation of patient tissue may result from interaction with device 104. For example, penetration of tissue by first electrode 112 and/or contact between tissue and second electrode 114 may result in inflammation of the tissue. Inflammation of patient tissue proximate to first and second electrodes 112 and 114 may result in higher thresholds for stimulation delivered to the tissue to activate, or capture, the tissue. Higher capture thresholds may, in turn, increase the consumption of a power source of device 104 associated with delivery of the stimulation.

[0055] In some examples device 104 includes one or more therapeutic substance dispensing devices 215, e.g., on face 212, within a recess defined by second electrode 114. The steroid may mitigate inflammation of patient tissue resulting from interaction with the IMD. Therapeutic substance dispensing devices 215 may be configured to elute one or more steroids to tissue in proximity to therapeutic substance dispensing devices 215 over time. In some examples, therapeutic substance dispensing devices 215 comprise one or more monolithic controlled release devices (MCRDs).

[0056] Ramp 214 may cause second electrode 114 to maintain consistent contact with the wall tissue, e.g., by raising second electrode 114 from face 212 by a fixed distance. Consistent contact between second electrode 114 and the wall tissue may improve electrical conductivity and the delivery of electrical signals from second electrode 114 to the wall tissue. Where device 104 is an implantable pacing device, the consistent contact between second electrode 114 and the wall tissue may reduce and/or maintain a pacing threshold for a chamber (e.g., the right atrium) of heart 102.

[0057] FIG. 2B is a perspective diagram illustrating a top-down view of the example device 104 of FIG. 2A. As illustrated in FIG. 2B, tissue retention features 220 may be distributed around the outer perimeter of distal end 204. First opening 222 A of each issue retetion feature 220 may define a curvature extending along a reference perimeter 224 (also referred to as a “reference arc 224”). Reference perimeter 224 may be defined by a predetermined diameter and may be disposed radially outwards of first electrode 112 and radially inwards of the outer perimeter of distal end 204. Reference perimeter 224 may be separated from the outer perimeter of distal end 204 by a fixed distance such that the material defining distal end 204 may fully enclose first opening 222A of tissue retention features 220 disposed along reference perimeter 224. In some examples, ramp 214 extends along reference perimeter 224, e.g., a centerline of ramp 214 extends at least partially along reference perimeter 224. In such examples, ramp 214 may extend to the outer perimeter of distal end 204, as illustrated in FIG. 2B, or may terminate before reaching the outer perimeter of distal end 204.

[0058] Each tissue retention feature 220 and/or ramp 214 may be disposed along a common reference perimeter 224, as illustrated in FIG. 2B, or may be disposed along the same reference perimeter 224 as at least one other tissue retention feature 220 and/or ramp 214, or may be disposed along a different reference perimeter 224. Placement of tissue retention features 220 along a different reference perimeter 224 may allow for the alteration of the dimensions of one or more of openings 222 and/or the channel connecting openings 222, thereby altering the amount of ingrown tissue each tissue retention feature 220 is configured to retain.

[0059] First openings 222A of tissue retention features 220 may define curved edges, e.g., to prevent pinching or inflammation of the tissue. Each first opening 222A may be completely enclosed or surrounded, e.g., to retain the ingrown tissue within the channel. During removal of device 104 from the tissue, the ingrown tissue may tear or otherwise separate and exit the channel via one or more of openings 222. In some examples, as illustrated in FIG. 2B, tissue retention features 220 are equally spaced around the outer perimeter of distal end 204, e.g., to provide evenly distributed fixation around the outer perimeter of distal end 204. In some examples, tissue retention feature 220 is disposed directly opposite a second electrode 114 around the outer perimeter of distal end 204 (e.g., a center of tissue retention feature 220 is disposed at a location 180 degrees around the outer perimeter of distal end 204 from second electrode 114). Placing tissue retention feature 220 and second electrode 114 directly opposite each other may increase stability of device 104 within the tissue and/or improve the consistency of contact between second electrode 114 and the tissue. In some examples, one or more of tissue retention features 220 are disposed directly circumferentially adjacent to second electrode 114, e.g., to improve the consistency of contact between second electrode 114 and the tissue.

Placement of ramp 214 and/or of second electrode 114 relative to first electrode 112 may be the same as those described in previously incorporated U.S. Provisional Patent Application No. 63/485,174.

[0060] FIG. 3A is a cross-section diagram illustrating a cross-section view of an example of device 104 of FIG. 2A, the cross-section being taken along line A-A of FIG. 2B and along a plane parallel to longitudinal axis 210 of device 104. FIG. 3B is a crosssection diagram illustrating a cross-section view of another example of device 104 of FIG. 2A, the cross-section being taken along line A-A of FIG. 2B. FIG. 3C is a cross-section diagram illustrating a cross-section view of another example of device 104 of FIG. 2A, the cross-section being taken along line A-A of FIG. 2B. [0061] As illustrated in FIGS. 3A-3C, a removable assembly (e.g., a removable header) may include distal end 204 of housing 202. A clinician or manufacturer may remove distal end 204 to access computing circuitry disposed within housing 202 or to switch to a distal end 204 with desired components. Each of first electrode 112 and second electrode 114 may be connected to computing circuitry within housing 202 via a corresponding feedthrough assembly. For example, as illustrated in FIG. 3A, first electrode 112 may be connected to the computing circuitry via first feedthrough assembly 302 and second electrode 114 may be connected to the computing circuitry via second feedthrough assembly 304. Other electrodes (e.g., another second electrode 114, electrode 218) may each be connected to the computing circuitry via a corresponding feedthrough assembly. Each feedthrough assembly may extend along longitudinal axis 210 or may be offset relative to longitudinal axis 210, e.g., to accommodate different positions and/or orientations of first electrodes 112, second electrode 114, and the computing circuitry.

[0062] In some examples, as illustrated in FIG. 3A, tissue retention feature 220 includes first opening 222A disposed on face 212 of distal end, second opening 222B disposed on a side of housing 202 and proximal to face 212, and channel 306 connecting first opening 222A to second opening 222B. Channel 306 may be defined by two interconnecting channels extending from each of openings 222. For example, channel 306 may be defined by a first channel extending proximally along longitudinal axis 210 from first opening 222A and a second channel extending radially inwards from second opening 222B towards longitudinal axis 210.

[0063] The first channel and the second channel may be orthogonal to each other. For example, a reference axis 308 of channel 306 may define a right angle at the intersection between the first channel and the second channel. In other examples, reference axis 308 may define a different angle at the intersection. Forming channel 306 from the first channel and the second channel may simplify the manufacturing process by allowing the manufacturer to form two relatively simpler channels in a pre-formed distal end 204 to form tissue retention feature 220.

[0064] Each of the first and second channel may define similar dimensions (e.g., length, width, depth) or may define different dimensions. Each of openings 222 may be chamfered around the outer edge, e.g., to mitigate inflammation of the tissue. In some examples, the edges within channel 306 (e.g., along each of the first and second channels, at the intersection between the first and second channels) are rounded or chamfered, e.g., to mitigate inflammation of the ingrown tissue. An antibacterial or other therapeutic substance may be disposed within channel 306, e.g., to mitigate or prevent infection and/or inflammation of the ingrown tissue.

[0065] In some examples, as illustrated in FIG. 3B, tissue retention feature 220 defines a channel 310 extending from first opening 222 A to second opening 222B. Channel 310 may define a continuous arc (e.g., may extend along a reference axis 312 defining a continuous arc). Forming channel 310 defining a continuous arc between openings 222 may reduce inflammation of the ingrown tissue. The edges of channel 310 may be rounded and chamfered and/or a therapeutic substance may be disposed within channel 306 (e.g., along the walls of channel 306) to further reduce inflammation of the ingrown tissue. [0066] In some examples, as illustrated in FIG. 3C, tissue retention features 220 defines a channel 314 extending from first opening 222 A to second opening 222B. Channel 314 may define a linear or substantially linear channel extending between openings 222 (e.g., extending along a linear reference axis 316). Forming a linear channel 314 may simplify the manufacturing process. Reference axis 316 may be offset from longitudinal axis 210 by an angle. The angle may be based on placement of each of openings 222, dimensions of channel 314, a desired volume of ingrown tissue within channel 314, and/or the like.

[0067] In some examples, each tissue retention feature 220 on distal end 204 defines the same type of channel (e.g., channel 306, 310, 314). In some examples, each tissue retention feature 220 defines a different type of channel than another tissue retention feature 220. Each first opening 222A of tissue retention features 220 may be disposed along a reference perimeter 224 around distal end 204. Each second opening 222B may be separated from face 212 by a fixed distance. For each distal end 204, second openings 222B may be separated from face 212 by the same fixed distance or by two or more different fixed distances. A manufacturer may determine the fixed distance and/or the diameter of reference perimeter 224 based at least in part on a desired volume of ingrown tissue within each tissue retention feature 220.

[0068] As illustrated in FIGS. 3A-3C, distal end 204 may include ramp 214 extending distally from face 212. In some examples, one or more tissue retention features 220 are be disposed on or along ramp 214. In such examples, each of the one or more tissue retention features 220 may include first opening 222A disposed on a distalmost surface of ramp 214 and/or a distal surface leading to the distalmost surface of ramp 214. Each tissue retention feature 220 may further include second opening 222B disposed on a side of ramp 214 and around an outer perimeter of ramp 214.

[0069] Although FIGS. 3A-3C illustrates three example channels of tissue retention features 220 (e.g., channel 306, 310, 314), tissue retention feature 220 may include channels defining any other path within distal end 204 from first opening 222A to second opening 222B .

[0070] FIG. 4A is a perspective diagram illustrating a top-down view of another example of device 104 of FIG. 1 with tissue retention features 402 having flexible pins 404. FIG. 4B is a cross-section diagram illustrating a cross-section view of device 104 of FIG. 4A, the cross-section being taken along line B-B of FIG. 4A and along a plane parallel to longitudinal axis 210 of device 104. Each tissue retention feature 402 may extend from a first opening 408A disposed on face 212 of distal end 204 to a second opening 408B (illustrated in FIG. 4B) disposed along a side of housing 202. Openings 408A, 408B (collectively referred to as “openings 408”) may be similar to openings 222 and may define similar dimensions and positions on device 104. For example, openings 408 may be disposed along one or more reference perimeters 224, e.g., as previously described herein.

[0071] Each tissue retention feature 402 may include a flexible pin 404 (also referred to herein as “pin 404”) extending along the outer perimeter of distal end 204. Each pin may extend from a fixed end 406A to a free end 406B . Fixed end 406A may be permanently affixed to distal end 204 of housing 202. Free end 406B may be configured to elastically deform, e.g., away from longitudinal axis 210. For example, pin 404 may be configured to transition between a relaxed or equilibrium configuration (e.g., where free end 406B is disposed along the outer perimeter of distal end 204) and an deformed configuration (e.g., where free end 406B is disposed radially outward of the outer perimeter of distal end 204). When pin 404 is in the relaxed configuration, pin 404 may at least partially define each of openings 408 such that openings 408 are connected by an enclosed channel. For each tissue retention feature 402, distal end 204 may define a recess along a portion of an outer distal edge of distal end 204. In the relaxed configuration, pin 404 may separate a first portion of the recess on face 212 from a second portion of the recess on the side of housing 202 such that the first portion of the recess and the second portion of the recess define openings 408A and 408B, respectively.

[0072] Each of openings 408 may be separated from the outer distal edge of distal end 204 by pin 404. Tissue may grow into the recess via one or more of openings 408 and pin 404 may prevent unintended movement of the ingrown tissue out of the recess (e.g., movement of the ingrown tissue radially away from longitudinal axis 210). Free end 406B may be configured to elastically flex away from longitudinal axis 210 such that during removal of device 104 (e.g., via rotation of device 104 by the clinician), the forces exerted on pin 404 by the clinician and/or the tissue surrounding pin 404 may cause free end 406B to elastically flex away from longitudinal axis 210 and cause pin 404 to transition to the deformed configuration. When pin 404 is in the deformed configuration, the ingrown tissue may exit tissue retention feature 402 while an opening between free end 406B and distal end 204 of housing 202.

[0073] Pin 404 may extend from fixed end 406A to free end 406B in a specific direction. In some examples, the direction is the same as a direction of winding of first electrode 112. In some examples, the direction is different from the direction of winding of first electrode 112. In some examples, where pin 404 extends from fixed end 406 A to free end 406B in a direction opposite to the winding of first electrode 112, the difference in direction further facilitates the elastic bending of pin 404 during removal of device 104 from the tissue by urging free end 406B away from longitudinal axis 210. The flexibility of pin 404 may allow a clinician to access a recess defining tissue retention feature 402 without separating or damaging portions of the ingrown tissue. The flexibility of pin 404 may reduce an amount of force required to remove device 104 from the tissue while inhibiting unintended rotation of device 104.

[0074] In some examples, as illustrated in FIG. 4B, pin 404 defines a circular cross section and in the relaxed configuration may define a channel 410 connecting openings 408. As illustrated in FIG. 4B, channel 410 may be similar to channel 306 of FIG. 3A. In some examples, pin 404 defines another cross section, e.g., a cross section having rectangular, quadrilateral, or other polygonal shapes. When pin 404 is in the relaxed configuration, channel 410 may be the same as or similar to channel 306, 310, 314, of the like. In some examples, channel 410 defines any other path between openings 408. [0075] FIG. 5 is a functional block diagram illustrating an example configuration of device 104. As illustrated in FIG. 5, device 104 include electrodes 112 and 114, which may be configured as described with respect to FIGS. 1-4B. For example, as described previously, first electrode 112 may be configured to extend from distal end 204 of housing 202 and may penetrate through the wall tissue of a first chamber (e.g., the RA) into wall tissue of a second chamber (e.g., the LV). Second electrode 114 extends from distal end 204 of housing 202 and may be configured to maintain contact with the wall tissue of the first chamber without penetration of the wall tissue of the first chamber by second electrode 114. Second electrode 114 may maintain contact in this manner by virtue of being disposed in and/or on ramp 214.

[0076] In the example shown in FIG. 5, device 104 includes switch circuitry 502, sensing circuitry 504, signal generation circuitry 506, sensor(s) 508, processing circuitry 510, telemetry circuitry 512, memory 514, and power source 516. The various circuitry may be, or include, programmable or fixed function circuitry configured to perform the functions attributed to respective circuitry. Memory 514 may store computer-readable instructions that, when executed by processing circuitry 510, cause device 104 to perform various functions. Memory 514 may be a storage device or other non-transitory medium. The components of device 104 illustrated in FIG. 5 may be housed within housing 202. [0077] Signal generation circuitry 506 generates electrical stimulation signals, e.g., cardiac pacing pulses. Switch circuitry 502 is coupled to electrodes 112, 114, and 218 and may include one or more switch arrays, one or more multiplexers, one or more switches (e.g., a switch matrix or other collection of switches), one or more transistors, or other electrical circuitry. Switch circuitry 502 is configured to direct stimulation signals from signal generation circuitry 506 to a selected combination of electrodes 112, 114, and 218, having selected polarities, e.g., to selectively deliver pacing pulses to the RA, ventricles, or interventricular septum of heart 102. For example, in order to pace one or both of the ventricles, switch circuitry 502 may couple first electrode 112, which has penetrated to wall tissue of a ventricle or the intraventricular septum, to signal generation circuitry 506 as a cathode, and one or both of second electrode 114 or electrode 218 to signal generation circuitry 506 as an anode. As another example, in order to pace the RA, switch circuitry 502 may couple second electrode 114, which maintains contact with the RA endocardium, to signal generation circuitry 506 as a cathode, and one or both of first electrode 112 or electrode 218 to signal generation circuitry 506 as an anode.

[0078] Each of electrodes 112, 114, 218 may be coupled to switch circuitry 502 via a corresponding feedthrough assembly. In some examples, each feedthrough assembly is substantially straight (e.g., along longitudinal axis 210). In some examples, such as when distal end 204 of housing 202 is removable from housing 202 (e.g., when distal end 204 is a removable header), the feedthrough assemblies are offset to allow for removal of distal end 204. For example, when a header defining distal end 204 is configured to be removably secured to housing 202 (e.g., via a turn-lock mechanism), the feedthrough assemblies are offset from longitudinal axis 210 to allow the header to turn relative to housing 202.

[0079] Switch circuitry 502 may also selectively couple sensing circuitry 504 to selected combinations of electrodes 112, 114, and 218, e.g., to selectively sense the electrical activity of either the RA or ventricles of heart 102. Sensing circuitry 504 may include filters, amplifiers, analog-to-digital converters, or other circuitry configured to sense cardiac electrical signals via electrodes 112, 114, and/or 218. For example, switch circuitry 502 may couple each of first electrode 112 and second electrode 114 (in combination with electrode 218) to respective sensing channels provided by sensing circuitry 504 to respectively sense either ventricular or atrial cardiac electrical signals. In some examples, sensing circuitry 504 is configured to detect events, e.g., depolarizations, within the cardiac electrical signals, and provide indications thereof to processing circuitry 510. In this manner, processing circuitry 510 may determine the timing of atrial and ventricular depolarizations, and control the delivery of cardiac pacing, e.g., AV synchronized cardiac pacing, based thereon. Processing circuitry 510 may include any one or more of a microprocessor, a controller, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), discrete logic circuitry, or any other processing circuitry configured to provide the functions attributed to processing circuitry 510 herein may be embodied as firmware, hardware, software or any combination thereof.

[0080] Sensor(s) 508 may include one or more sensing elements that transduce patient physiological activity to an electrical signal to sense values of a respective patient parameter. Sensor(s) 508 may include one or more accelerometers, optical sensors, chemical sensors, temperature sensors, pressure sensors, or any other types of sensors. Sensor(s) 508 may output patient parameter values that may be used as feedback to control sensing and delivery of therapy by device 104.

[0081] Telemetry circuitry 512 supports wireless communication between device 104 and an external programmer (not shown in FIG. 5) or another computing device under the control of processing circuitry 510. Processing circuitry 510 of device 104 may receive, as updates to operational parameters from the computing device, and provide collected data, e.g., sensed heart activity or other patient parameters, via telemetry circuitry 512. Telemetry circuitry 512 may accomplish communication by radiofrequency (RF) communication techniques, e.g., via an antenna (not shown).

[0082] Power source 516 delivers operating power to various components of device 104. Power source 516 may include a rechargeable or non-rechargeable battery and a power generation circuit to produce the operating power. Recharging may be accomplished through proximal inductive interaction between an external charger and an inductive charging coil within device 104.

[0083] While FIGS. 1-5 describe device 104 as configured to be implanted wholly within heart 102, the same structures and components described herein may be used to fix another implantable medical device within tissue of a patient. For example, an implantable medical device may include a fixation device similar to structure and/or function to helix and/or coil defined by first electrode 112 and tissue retention features (e.g., tissue retention features 220, tissue retention features 402) as described above. In such examples, the tissue retention features may prevent or inhibit unintended rotation of a fixation helix and/or coil extending from a distal end of the fixation device.

[0084] FIG. 6 is a flow diagram illustrating an example process for sensing a cardiac electrical signal and delivering cardiac pacing therapy to a heart of a patient via an device 104 of any of FIGS. 1-5. The technique of FIG. 6 will be described with concurrent reference to device 104 as illustrated in FIGS. 1-5, although a person having ordinary skill in the art will understand that the technique may be performed in reference to an implantable medical lead or other medical device.

[0085] A clinician may insert device 104 within a single first chamber of the heart 102 (602). The first chamber of heart 102 may be the right atrium, left atrium, the right ventricle, or the left ventricle. The clinician may insert device 104 into the first chamber via delivery tool connected to device 104 (e.g., connected to delivery tool interface member 208). The clinician may advance first electrode 112 extending distally from housing 202 of device 104 to penetrate through wall tissue of the first chamber and into wall tissue of a second chamber of heart 102 (604). In some examples, advancing first electrode 112 includes positioning a distal end of first electrode 112 (e.g., a first electrically active region 216) within a ventricular myocardium 108 of the patient. The clinician may advance first electrode 112 by rotating device 104 clockwise or counterclockwise within the first chamber, depending on how first electrode 112 is wound. [0086] The clinician may cause device 104 to maintain contact between second electrode 114 and the wall tissue of the first chamber, without penetrating the wall tissue of the first chamber (606). The clinician may advance device 104 into the wall tissue until the wall tissue contacts ramp 214 and/or face 212 of housing 202. In some examples, when second electrode 114 is disposed on ramp 214, ramp 214 extends second electrode 114 distally from face 212 (e.g., from distal end 204) and along longitudinal axis 210 by a fixed distance. Ramp 214 may cause second electrode 114 to be placed relatively deeper within wall tissue than face 212 without penetrating the wall tissue, thereby allowing the wall tissue to at least partially envelop a distal surface and/or sides of second electrode 114. In some examples, ramp 214 causes second electrode 114 to maintain contact with the wall tissue of the first chamber (e.g., the atrial endocardium of the patient). Ramp 214 may place second electrode 114 in consistent contact with the wall tissue of the first chamber, thereby increasing the consistency of the sensing and/or pacing functionalities of second electrode 114.

[0087] While device 104 is implanted within the cardiac tissue, device 104 may allow cardiac tissue to grow into channels of tissue retention feature 220 or 402 disposed on distal end 204 (e.g., channel 306, 310, 314, 410, or the like) of device 104 via one or more of openings 222 and/or openings 408 (608). Openings 222 and/or openings 408 may be disposed on face 212 and/or along a side of housing 202 at distal end 204. Once the cardiac tissue has at least partially occupied each tissue retention feature 220, the ingrown cardiac tissue may act against the walls of the channels of tissue retention features 220, e.g., to inhibit unintended rotation of device 104 within the cardiac tissue. The clinician may remove device 104 from the cardiac tissue by rotating device 104 (e.g., via delivery tool interface member 208). Rotation of device 104 by the clinician may cause the ingrown cardiac tissue to exit tissue retention features 220 (e.g., via separation of the ingrown cardiac tissue by an uncut portion of distal end 204 defining openings 222) and/or cause the ingrown cardiac tissue to exit tissue retention features 402 (e.g., via flexure of pins 404 away from longitudinal axis 210).

[0088] The clinician may deliver cardiac pacing from device 104 to the second chamber via first electrode 112 and to the first chamber via second electrode 114 (610). Device 104 may deliver cardiac pacing to the first chamber and/or the second chamber via first electrode 112, second electrode 114, and/or one or more other electrodes of device 104 (e.g., electrode 218).

[0089] It should be understood that various aspects disclosed herein may be combined in different combinations than the combinations specifically presented in the description and accompanying drawings. It should also be understood that, depending on the example, certain acts or events of any of the processes or methods described herein may be performed in a different sequence, may be added, merged, or left out altogether (e.g., all described acts or events may not be necessary to carry out the techniques). In addition, while certain aspects of this disclosure are described as being performed by a single module or unit for purposes of clarity, it should be understood that the techniques of this disclosure may be performed by a combination of units or modules associated with, for example, a medical device.

[0090] In one or more examples, the described techniques may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored as one or more instructions or code on a computer-readable medium and executed by a hardware -based processing unit. Computer-readable media may include non-transitory computer-readable media, which corresponds to a tangible medium such as data storage media (e.g., RAM, ROM, EEPROM, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer).

[0091] In addition, it should be noted that system described herein may not be limited to treatment of a human patient. In alternative examples, the system may be implemented in non-human patients, e.g., primates, canines, equines, pigs, and felines. These other animals may undergo clinical or research therapies that may benefit from the subject matter of this disclosure. [0092] Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Accordingly, the term “processor” as used herein may refer to any of the foregoing structure or any other physical structure suitable for implementation of the described techniques. Also, the techniques could be fully implemented in one or more circuits or logic elements.

[0093] This disclosure describes each of the following examples.

[0094] Example 1 : A fixation device comprising: an elongated body extending distally from a distal end of a housing of an implantable medical device (IMD), the elongated body comprising: a proximal end located at the distal end of the IMD; and a helix extending distally from the proximal end and defining one or more coils, wherein a distal end of the helix is configured to penetrate into tissue of a patient; and one or more tissue retention features defined by the distal end of the housing, each tissue retention feature comprising: a first opening disposed on the distal end of the housing; a second opening disposed on an outer surface of the housing, wherein the outer surface is proximal to the distal end of the housing and disposed along a perimeter of the housing; and a channel connecting the first opening and the second opening, wherein one or more openings of the first opening or the second opening is configured to allow tissue growth into the channel via the one or more openings.

[0095] Example 2: the fixation device of example 1, wherein the first opening is completely enclosed by the distal end of the housing, and wherein the second opening is completely enclosed by the outer surface of the housing.

[0096] Example 3: the fixation device of example 2, wherein the first opening and the second opening are separated from an outer edge of the housing by a flexible pin.

[0097] Example 4 : the fixation device of example 3, wherein the flexible pin is configured to deform radially away from a longitudinal axis of the IMD.

[0098] Example 5: the fixation device of any of examples 3 and 4, wherein the flexible pin extends along an outer perimeter of the housing of the IMD.

[0099] Example 6: the fixation device of any of examples 3-5, wherein the flexible pin at least partially defines the first opening and the second opening. [00100] Example 7 : the fixation device of any of examples 3-6, wherein the flexible pin extends from a fixed end to a free end, wherein the fixed end is connected to the housing of the IMD.

[0100] Example 8: the fixation device of example 7, wherein the helix is wound in a first direction, and wherein the flexible pin extends from the fixed end to the free end in the first direction.

[0101] Example 9 : the fixation device of example 8, wherein the first direction is in a counterclockwise direction around a longitudinal axis of the IMD.

[0102] Example 10: the fixation device of any of examples 1-9, wherein the one or more tissue retention features comprises a plurality of tissue retention features disposed around the perimeter of the housing.

[0103] Example 11: the fixation device of example 10, wherein the plurality of tissue retention features is equally spaced around the perimeter of the housing.

[0104] Example 12: the fixation device of any of examples 1-11, wherein for each tissue retention feature of the one or more tissue retention features, the channel comprises a fully enclosed channel extending from the first opening to the second opening.

[0105] Example 13: the fixation device of example 12, wherein for each tissue retention feature, the channel extends along a reference axis extending from the first opening to the second opening.

[0106] Example 14: the fixation device of example 13, wherein the reference axis is offset from a longitudinal axis of the housing by an angle.

[0107] Example 15: the fixation device of example 14, wherein the angle is about 29 degrees to about 44 degrees.

[0108] Example 16: the fixation device of example 12, wherein for each tissue retention feature, the channel extends along a reference arc extending from the first opening to the second opening.

[0109] Example 17: the fixation device of example 12, wherein for each tissue retention feature, the channel comprises: a first channel extending proximally from the first opening along a longitudinal axis of the housing; and a second channel extending radially inwards from the second opening towards the longitudinal axis of the housing, wherein the first channel is connected to the second channel. [0110] Example 18: the fixation device of any of examples 1-17, wherein each tissue retention feature of the one or more tissue retention features is configured to retain a fixed amount of ingrown tissue.

[0111] Example 19: a device comprising: an elongated housing extending from a proximal end to a distal end along a longitudinal axis, the elongated housing being configured to be implanted wholly within a chamber of a heart; a first electrode extending distally from the distal end of the elongated housing, the first electrode comprising an elongated body defining a helix, wherein a distal end of the helix is configured to penetrate wall tissue of the chamber; a second electrode extending distally from the distal end of the elongated housing, wherein the second electrode is configured to be placed in contact with the wall tissue of the chamber without penetrating the wall tissue; and one or more tissue retention features defined by the distal end of the elongated housing, each tissue retention feature comprising: a first opening disposed on the distal end of the elongated housing; a second opening disposed on an outer surface of the elongated housing between the proximal end and the distal end; and a channel connecting the first opening and the second opening, wherein one or more openings of the first opening or the second opening is configured to allow ingrowth of the wall tissue into the channel via the one or more openings.

[0112] Example 20: the device of example 19, wherein the first opening is completely enclosed by the distal end of the elongated housing, and wherein the second opening is completely enclosed by the outer surface of the elongated housing.

[0113] Example 21: the device of any of examples 19 and 20, wherein the first opening and the second opening are separated from an outer edge of the distal end of the elongated housing by a flexible pin.

[0114] Example 22: the device of example 21, wherein the flexible pin is configured to deform radially away from the longitudinal axis.

[0115] Example 23: the device of any of examples 21 and 22, wherein the flexible pin extends along an outer perimeter of the distal end of the elongated housing.

[0116] Example 24: the device of any of examples 21-23, wherein the flexible pin at least partially defines the first opening and the second opening. [0117] Example 25: the device of any of examples 21-24, wherein the flexible pin extends from a fixed end to a free end, and wherein the fixed end is connected to the elongated housing.

[0118] Example 26: the device of example 25, wherein the helix is wound in a first direction, and wherein the flexible pin extends from the fixed end to the free end in the first direction.

[0119] Example 27 : the device of example 26, wherein the first direction is in a counterclockwise direction around the longitudinal axis.

[0120] Example 28: the device of any of examples 19-27, wherein the one or more tissue retention features comprises a plurality of tissue retention features disposed on the distal end of the elongated housing and around a perimeter of the elongated housing.

[0121] Example 29: the device of example 28, wherein the plurality of tissue retention features is equally spaced around the perimeter of the housing.

[0122] Example 30: the device of example 28, wherein at least one tissue retention feature of the plurality of tissue retention features is circumferentially adjacent to the second electrode.

[0123] Example 31: the device of any of examples 28-30, wherein a tissue retention feature of the plurality of tissue retention features is separated from the second electrode by 180 degrees around the perimeter of the elongated housing.

[0124] Example 32: the device of any of examples 19-31, wherein for each tissue retention feature of the one or more tissue retention features, the channel comprises a fully enclosed channel extending from the first opening to the second opening.

[0125] Example 33: the device of example 32, wherein for each tissue retention feature, the channel extends along a reference axis extending from the first opening to the second opening, and wherein the reference axis is offset from the longitudinal axis by an angle.

[0126] Example 34: the device of example 33, wherein the angle is about 29 degrees to about 44 degrees.

[0127] Example 35: the device of example 32, wherein for each tissue retention feature, the channel extends along a reference arc extending from the first opening to the second opening. [0128] Example 36: the device of example 32, wherein for each tissue retention feature, the channel comprises: a first channel extending proximally from the first opening along the longitudinal axis; and a second channel extending radially inwards from the second opening towards the longitudinal axis, wherein the first channel is connected to the second channel.

[0129] Example 37: the device of any of examples 19-36, wherein the device further comprises a ramp extending distally from the distal end of the elongated housing, wherein the second electrode is disposed on a distalmost surface defined by the ramp, and wherein the ramp is configured to separate the second electrode from the distal end of the elongated housing by a fixed distance.

[0130] Example 38: the device of any of examples 19-37, wherein the second electrode extends distally from the distal end of the elongated housing and is separated from the distal end by a fixed distance.

[0131] Example 39: the device of any of examples 19-38, further comprising a therapeutic substance dispensing device disposed on the distal end of the elongated housing.

[0132] Example 40: the device of example 39, wherein the therapeutic substance dispensing device comprises a monolithic controlled release device.

[0133] Example 41: the device of any of examples 19-40, wherein the chamber of the heart comprises a first chamber of the heart, and wherein the helix is configured to penetrate into wall tissue of a second chamber of the heart that is separate from the first chamber of the heart.

[0134] Example 42: the device of any of examples 19-41, wherein the one or more tissue retention features are configured to inhibit unintended rotation of the elongated body within the wall tissue of the chamber.

[0135] Example 43: the device of any of examples 42, wherein the distal end of the elongated housing further comprises one or more additional features configured to inhibit unintended rotation of the elongated body within wall tissue of the second chamber.

[0136] Example 44: a method comprising: implanting a device within a first chamber of a heart of a patient, wherein the device comprises: an elongated housing extending from a proximal end to a distal end along a longitudinal axis, the elongated housing being configured to be implanted wholly within a first chamber of a heart; a first electrode extending distally from the distal end of the elongated housing, the first electrode comprising an elongated body defining a helix, wherein a distal end of the helix is configured to penetrate first wall tissue of the first chamber; a second electrode extending distally from the distal end of the elongated housing, wherein the second electrode is configured to be placed in contact with the first wall tissue of the first chamber without penetrating the first wall tissue; one or more tissue retention features defined by the distal end of the elongated housing, each tissue retention feature comprising: a first opening disposed on the distal end of the elongated housing; a second opening disposed on an outer surface of the elongated housing between the proximal end and the distal end; and a channel connecting the first opening and the second opening, wherein one or more openings of the first opening or the second opening is configured to allow ingrowth of the first wall tissue into the channel via the one or more openings; and signal generation circuitry within the elongated housing, the signal generation circuitry being coupled to the first electrode and the second electrode; delivering, by the signal generation circuitry, cardiac pacing to a second chamber of the heart via the first electrode, wherein the second chamber of the heart is separate from the first electrode; and delivering, by the signal generation circuitry, cardiac pacing to the first chamber of the heart via the second electrode.

[0137] Example 45: the method of example 44, wherein the device further comprises sensing circuitry disposed within the elongated housing, the sensing circuitry being coupled to the first electrode and the second electrode, and wherein the method further comprises: sensing, by the sensing circuitry and via the first electrode, cardiac signals from the second chamber of the heart; and sensing, by the sensing circuitry and via the second electrode, cardiac signals from the first chamber of the heart.

[0138] Example 46: the method of any of examples 44 and 45, wherein the first chamber of the heart comprises an atrium, and wherein the second chamber of the heart comprises a ventricle.

[0139] Example 47: the method of any of examples 44-46, wherein the first opening is completely enclosed by the distal end of the elongated housing, and wherein the second opening is completely enclosed by the outer surface of the elongated housing. [0140] Example 48: the method of any of examples 44-47, wherein the first opening and the second opening are separated from an outer edge of the distal end of the elongated housing by a flexible pin.

[0141] Example 49: the method of example 48, wherein the flexible pin is configured to deform radially away from the longitudinal axis.

[0142] Example 50: the method of any of examples 48 and 49, wherein the flexible pin extends along an outer perimeter of the distal end of the elongated housing.

[0143] Example 51: the method of any of examples 48-50, wherein the flexible pin at least partially defines the first opening and the second opening.

[0144] Example 52: the method of any of examples 48-51, wherein the flexible pin extends from a fixed end to a free end, and wherein the fixed end is connected to the elongated housing.

[0145] Example 53: the method of example 52, wherein the helix is wound in a first direction, and wherein the flexible pin extends from the fixed end to the free end in the first direction.

[0146] Example 54: the method of example 53, wherein the first direction is in a counterclockwise direction around the longitudinal axis.

[0147] Example 55: the method of any of examples 44-54, wherein the one or more tissue retention features comprises a plurality of tissue retention features disposed on the distal end of the elongated housing and around a perimeter of the elongated housing.

[0148] Example 56: the method of example 55, wherein the plurality of tissue retention features is equally spaced around the perimeter of the housing.

[0149] Example 57: the method of example 56, wherein at least one tissue retention feature of the plurality of tissue retention features is circumferentially adjacent to the second electrode.

[0150] Example 58: the method of any of examples 55-57, wherein a tissue retention feature of the plurality of tissue retention features is separated from the second electrode by 180 degrees around the perimeter of the elongated housing.

[0151] Example 59: the method of any of examples 44-58, wherein for each tissue retention feature of the one or more tissue retention features, the channel comprises a fully enclosed channel extending from the first opening to the second opening. [0152] Example 60: the method of example 59, wherein for each tissue retention feature, the channel extends along a reference axis extending from the first opening to the second opening, and wherein the reference axis is offset from the longitudinal axis by an angle.

[0153] Example 61: the method of example 60, wherein the angle is about 29 degrees to about 44 degrees.

[0154] Example 62: the method of example 59, wherein for each tissue retention feature, the channel extends along a reference arc extending from the first opening to the second opening.

[0155] Example 63: the method of example 59, wherein for each tissue retention feature, the channel comprises: a first channel extending proximally from the first opening along the longitudinal axis; and a second channel extending radially inwards from the second opening towards the longitudinal axis, wherein the first channel is connected to the second channel.

[0156] Various examples have been described. These and other examples are within the scope of the following claims.

Claims

WHAT IS CLAIMED IS:

1. A device comprising: an elongated housing extending from a proximal end to a distal end along a longitudinal axis, the elongated housing being configured to be implanted wholly within a chamber of a heart; a first electrode extending distally from the distal end of the elongated housing, the first electrode comprising an elongated body defining a helix, wherein a distal end of the helix is configured to penetrate wall tissue of the chamber; a second electrode extending distally from the distal end of the elongated housing, wherein the second electrode is configured to be placed in contact with the wall tissue of the chamber without penetrating the wall tissue; and one or more tissue retention features defined by the distal end of the elongated housing, each tissue retention feature comprising: a first opening disposed on the distal end of the elongated housing; a second opening disposed on an outer surface of the elongated housing between the proximal end and the distal end; and a channel connecting the first opening and the second opening, wherein one or more openings of the first opening or the second opening is configured to allow ingrowth of the wall tissue into the channel via the one or more openings.

2. The device of claim 1, wherein the first opening is completely enclosed by the distal end of the elongated housing, and wherein the second opening is completely enclosed by the outer surface of the elongated housing.

3. The device of any of claims 1 and 2, wherein the first opening and the second opening are separated from an outer edge of the distal end of the elongated housing by a flexible pin.

4. The device of claim 3, wherein the flexible pin is configured to deform radially away from the longitudinal axis.

5. The device of any of claims 3 and 4, wherein the flexible pin extends from a fixed end to a free end, and wherein the fixed end is connected to the elongated housing.

6. The device of any of claims 1-5, wherein the one or more tissue retention features comprises a plurality of tissue retention features disposed on the distal end of the elongated housing and around a perimeter of the elongated housing.

7. The device of claim 6, wherein at least one tissue retention feature of the plurality of tissue retention features is circumferentially adjacent to the second electrode.

8. The device of any of claims 6 and 7, wherein a tissue retention feature of the plurality of tissue retention features is separated from the second electrode by 180 degrees around the perimeter of the elongated housing.

9. The device of any of claims 1-8, wherein for each tissue retention feature of the one or more tissue retention features, the channel comprises a fully enclosed channel extending from the first opening to the second opening.

10. The device of claim 9, wherein for each tissue retention feature, the channel extends along a reference axis extending from the first opening to the second opening, and wherein the reference axis is offset from the longitudinal axis by an angle.

11. The device of claim 9, wherein for each tissue retention feature, the channel extends along a reference arc extending from the first opening to the second opening.

12. The device of claim 9, wherein for each tissue retention feature, the channel comprises: a first channel extending proximally from the first opening along the longitudinal axis; and a second channel extending radially inwards from the second opening towards the longitudinal axis, wherein the first channel is connected to the second channel.

13. The device of any of claims 1-12, wherein the device further comprises a ramp extending distally from the distal end of the elongated housing, wherein the second electrode is disposed on a distalmost surface defined by the ramp, and wherein the ramp is configured to separate the second electrode from the distal end of the elongated housing by a fixed distance.

14. The device of any of claims 1-13, wherein the chamber of the heart comprises a first chamber of the heart, and wherein the helix is configured to penetrate into wall tissue of a second chamber of the heart that is separate from the first chamber of the heart.

15. The device of any of claims 1-14, wherein the one or more tissue retention features are configured to inhibit unintended rotation of the elongated body within the wall tissue of the chamber.