Distal end fixation for implantable medical device

Abstract

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; an elongated body extending distally from the distal end of the elongated housing, wherein the elongated body defines a helix, the elongated body defining a first electrode; a second electrode disposed on the distal end the elongated housing; and two or more protrusions extending from the distal end of the elongated housing, the two or more protrusions being configured to interface with wall tissue of the chamber without penetrating the wall tissue; and a channel separating at least two protrusions of the two or more protrusions, a bottom of the channel being proximal to respective distal ends of the at least two protrusions.

Description

DISTAL END FIXATION FOR IMPLANTABLE MEDICAL DEVICE

[0001] This application claims the benefit of U.S. Provisional Patent Application Serial No. 63 / 664,518, filed June 26, 2024, the entire content of which is incorporated herein by reference.TECHNICAL FIELD

[0002] The disclosure relates to medical devices, and more particularly to configuration of electrodes 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 HMDs 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 HMDs 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. A single HMD may be implanted in one chamber of a heart of the patient and may be able to sense signals from 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.

[0006] 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. In some examples described herein, IMDs may have protrusions extending from a distal end of an elongated housing of the IMD. The protrusions may be separated by one or more channels. One or more pacing electrodes may be disposed within the one or more channels and / or at a center of the distal end of the IMD. The protrusions may provide an impediment to unintended rotation and / or dislodgement of the IMD from the tissue of the patient. Placement of pacing electrode(s) within the one or more channels may reduce compression and / or irritation of tissue around the pacing electrode(s), e.g., which may improve pacing capabilities of the pacing electrode(s).

[0007] In some examples described herein, IMDs may include distal ends defining a flat portion and a rounded portion connecting the flat portion to at least one side surface of the IMD. The combination of the flat and rounded portion may increase the possible implantation angles of the IMD relative to a tissue surface and may facilitate implantation of the IMD, e.g., at target locations where it is difficult for the clinician to align the IMD orthogonal to the tissue surface.

[0008] 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; an elongated body extending distally from the distal end of the elongated housing, wherein the elongated body defines a helix, the elongated body defining a first electrode; a second electrode disposed on the distal end the elongated housing; and two or more protrusions extending from the distal end of the elongated housing, the two or more protrusions being configured to interface with wall tissue of the chamber without penetrating the wall tissue; and a channel separating at least two protrusions of the two or more protrusions, a bottom of the channel being proximal of respective distal ends of the at least two protrusions.

[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; an elongated body extending distally from the distal end of the elongated housing, wherein the elongated body defines a helix, the elongated body defining a first electrode at or around a distal end of the elongated body; and a second electrode disposed on the distal end the elongated housing, wherein the distal end of the elongated housing defines a flat section and a rounded section, wherein the elongated body and the second electrode are disposed on the flat section, and wherein the rounded section is configured to enable the elongated body to puncture wall tissue of the chamber at an angle offset from orthogonal to a surface of the wall tissue.

[0010] In some examples, this disclosure is directed to a fixation device extending distally from a distal end of an implantable medical device, the fixation device comprising: a helix extending distally from the distal end of the elongated body along the longitudinal axis and defining one or more coils, wherein a distal end of the helix is configured to penetrate into tissue of a patient; two or more protrusions extending distally from the distal end of the implantable medical device, the two or more protrusions being configured to interface with the tissue without penetrating the tissue; and a channel separating first and second protrusions of the two or more protrusions, a bottom of the channel being disposed proximal of respective distal ends of the at least two protrusions.

[0011] In some examples, this disclosure is directed to a fixation device comprising: an elongated housing coupled to a distal end of an implantable medical device and extending distally from a proximal end to a distal end along a longitudinal axis, wherein the distal end of the elongated housing defines a flat section and a rounded section; and a helix extending distally from the distal end of the elongated housing along the longitudinal axis and defining one or more coils, wherein a distal end of the helix is configured to penetrate into tissue of a patient, wherein the rounded section of the distal end of the elongated housing is configured to enable the helix to penetrate the tissue at an angle offset from a surface of the tissue.

[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. l 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 number of protrusions on a distal end of the device.

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

[0017] FIG. 2C is a perspective diagram illustrating a side view of the distal end of the example device of FIG. 2 A.

[0018] FIG. 3 is a cross-sectional diagram illustrating a cross-sectional view of the distal end of the example device of FIG. 2A, the cross-section being taken along line A-A of FIG. 2B.

[0019] FIG. 4A is a perspective diagram illustrating another example of the device of FIG. 1 with a distal end including a flat portion and a rounded portion.

[0020] FIG. 4B is a perspective diagram illustrating a top view of the example device of FIG. 4 A.

[0021] FIG. 5 is a functional block diagram illustrating an example configuration of the IMD of FIGS. 1-4B, in accordance with one or more aspects of this disclosure.

[0022] FIG. 6 is a conceptual diagram of the device of FIGS. 4A-4B implanted at a target implant site.

[0023] FIG. 7 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. 1-6.DETAILED DESCRIPTION

[0024] In general, this disclosure is directed to configurations of electrodes of implantable medical devices (IMDs). More particularly, this disclosure is directed to HMDs having a plurality of electrodes configured to sense electrical signals from and to deliver electrical stimulation (e.g., cardiac pacing) to tissue of a patient. A physical arrangement of plurality of electrodes on the IMD may define a plurality of reference axes defining a three-dimensional (3D) coordinate system.

[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 into and / or 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 distalend 110 (e.g., within a channel between protrusions on 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] In some examples, where second electrode 114 is disposed within a channel between protrusions extending from distal end 110, second electrode 114 may be configured to contact the wall tissue without compressing the wall tissue. The lack of compression of the wall tissue may reduce irritation and / or inflammation of the wall tissue and improve pacing capabilities of second electrode 114 (e.g., may reduce pacing thresholds for second electrode 114).

[0028] As illustrated in FIG. 1, target implant region 106 within heart 102 may be shaped such that at least a portion of the surface of the wall tissue within target implant region 106 may be curved, may define an irregular shape, or may otherwise not define a flat surface. In some examples, distal end 110 of device 104 may define a flat portion and a rounded portion. The rounded portion of distal end 110 of device 104 may allow for device 104 to be implanted at target implant region 106 at angle(s) offset from the surface of the wall tissue (e.g., when device 104 is not orthogonal to the surface of the wall tissue). In such examples, the rounded portion of distal end 110 may increase a number of possible target implant regions 106 within heart 102 and reduce a complexity and / or difficulty of implantation of device 104 into target implant region 106 by the clinician.

[0029] 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 multi-chamber pacing (e.g., DDD pacing) and / or 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 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 such as a leadless pacemaker, or an implantable lead, having an electrode and / or distal end configuration in accordance with the examples of this disclosure (e.g., as shown in FIGS. 2-4B and FIG. 6) may be implanted at any of a variety of locations within a patient for sensing and / or delivery of therapy to other patient tissue. Such locations include any of the chambers of the heart, in the right atrium at the triangle of Koch or elsewhere therein, in the right ventricle at or near the apex thereof, or in the interventricular septum in the right ventricle, e.g. with the device implanted in the septum so as to enable conduction system pacing (CSP) such as left bundle branch area pacing (LBBAP) with first electrode 112 selectively or non- selectively capturing the left bundle branch (LBB). In some examples first electrode 112 may extend into the tissue of heart 102 at region 106 and affix device 104 to the tissue of heart 102.

[0030] The 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 electrical activity 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 protrusions separated by channels at a distal end and / or a distal end with flat and rounded portions.

[0031] 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.

[0032] Housing 202 extends between distal end 204 and proximal end 206 along longitudinal axis 210. In some examples, housing can be cylindrical or substantiallycylindrical 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 205 of housing 202. Face 205 may define a distal end major surface. Face 205 may be orthogonal to longitudinal axis 210. In some examples, face 205 may be slanted, e.g., face 205 may define a reference plane that is not orthogonal to longitudinal axis 210.

[0033] Device 104 may include two or more protrusions 214 disposed on face 205. Protrusions 214 may be arranged around a circumference of distal end 204 of device 104 (e.g., around longitudinal axis 210). In some examples, as illustrated in FIG. 2A, protrusions 214 may be disposed between an outer perimeter of distal end 204 and first electrode 112. For example, each of protrusions 214 may be disposed radially inwards of the outer perimeter of distal end 204 and radially outwards of an outer perimeter of first electrode 112. Each protrusion 214 may protrude from face 205 and may define a distal surface longitudinally and distally offset from face 205. Protrusions 214 may be evenly angularly distributed around longitudinal axis 210 or may be concentrated in a one or more portions of the circumference of distal end 204.

[0034] When device 104 is implanted within target implant region 106 of heart 104, wall tissue may contact the distal surfaces (and possibly the sides) of protrusions 214. Protrusions 214 may interface with the wall tissue to inhibit unintended rotation of first electrode 112 within the wall tissue and maintain fixation of first electrode 112 within the wall tissue. Protrusions 214 may be formed from a biocompatible polymer (e.g., PEEK). In some examples, protrusions 214 are formed from a biocompatible metal alloy and coated with an electrically insulating material. Protrusions 214 may be electrically inactive and / or electrically isolated from electrodes 112, 114.

[0035] Circumferentially adjacent protrusions 214 may be separated by gaps or channels 216. In some examples, as illustrated in FIG. 2A, the bottom surfaces of channels 216 may define or be formed by face 205. In some examples, the bottom surfaces of channel 216 may be proximal to the distal surfaces of protrusions 214 and distal to face 205. In some examples, channels 216 may be recessed into face 205 (and thereby longitudinally proximally offset from face 205) or project distally beyond face 205 (and therefore be longitudinally distally offset from face 205). Each channel 216 may extendfrom at or near the outer perimeter of distal end 204 of device 104 towards and / or to a center of face 205 (e.g., radially inward of first electrode 112). The bottom surfaces of channels 216 may be longitudinally offset from the distal surfaces of protrusions 214, e.g., to reduce compression of wall tissue within channels 216 when device 104 is implanted into target implant region 106 of heart 102.

[0036] One or more second electrodes 114 may be disposed on face 205. In some examples, as illustrated in FIG. 2A, second electrode 114 may be disposed at a center of face 205 (e.g., radially inwards of first electrode 112). In some examples, one or more second electrodes 114 may be disposed within one or more of channels 216 on face 205. For example, each channel 216 may contain one of second electrodes 114. Second electrodes 114 may be flush with face 205 (e.g., may be flush with a bottom surface of channel 216) or may be proud of (e.g., longitudinally distal of) face 205. In examples where second electrode 114 is proud of face 205, protrusions 214 may be longitudinally distal of the distal end of second electrode 114.

[0037] First electrode 112 may include one or more coatings (e.g., electrically insulative coating(s)) configured to define a first electrically active region 212, or first electrode 112 may otherwise define first electrically active region 212. In some examples, first electrically active region 212 may be more proximate to the second, e.g., distal, end of first electrode 112. In the example of FIG. 2A, first electrically active region 212 includes the distal end (e.g., distal tip) of electrode 112. Second electrode 114 may include one or more coatings configured to define a second electrically active region 213 on an outer surface or distal surface of second electrode 114. Second electrode 114 may include, but is not limited to, may be a button electrode, a spring electrode, or any other suitable type or shape of electrode.

[0038] 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 212 and 213. Defining first and second electrically active regions 212 and 213 by covering portions with an insulating coating may increase the electrical impedance of first andsecond 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.

[0039] In some examples, first and second electrodes 112 and 114 may have an electrically conducting material coating on first and second electrically active regions 212 and 213 to define the active regions. For example, first and second electrically active regions 212 and 213 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.

[0040] In the example of FIG. 2 A, 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 205 from a proximal end to a distal end, e.g., defining first electrically active region 212. The proximal end may be a location along first electrode 112 where first electrode 112 extends distally past distal end 204 and / or face 205 of device 104.

[0041] In some examples, first electrode 112 may include 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 protrusions 214 and / or within channels 216. The one or more antirotation 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., protrusions 214).

[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 212 and 213. 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 may have 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 213.

[0043] In some examples, where device 104 includes two or more second electrodes 114, the clinician may select, e.g., based on a position and / or orientation of device 104 within target implant region 106, one or more second electrodes 114 for delivery of pacing signals. The inclusion of multiple second electrodes 114 may thereby reduce reliance on a specific implanted orientation of device 104 within target implant region 106 for efficacious delivery of pacing signals to heart 104. In some examples, device 104 is configured to deliver pacing signals to heart 102 via two or more second electrodes 114. In such examples, the surface areas of each second electrically active region 213 may be less than the surface area of second electrically active region 213 of an otherwise identical device 104 with a single second electrode 114. In such examples, the combined total surface area of the second electrically active regions 213 of the two or more second electrodes 114 may be substantially equal to the surface area of second electrically active region 213 of an otherwise identical device 104 with the single second electrode 114.

[0044] 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 nature or type of tissue into which the electrodes are implanted or contact, as well as how long device 104 is intended to be implanted.

[0045] 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. In some examples, 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 lateraldisplacement of the distal end of first electrode 112 and undesired tissue trauma. In some examples, first electrode 112 may have 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 may vary 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.

[0046] The outer dimensions of first electrode 112 can be substantially straight and cylindrical, with first electrode 112 being rigid in some examples. 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 212 and housing distal end 204.

[0047] Distal end of first electrode 112 can pierce through one or more tissue layers to position first electrically active region 212 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 longitudinalaxis (substantially similar to or coincident with longitudinal axis 210), first electrode 112 retains a straight, linear configuration as shown.

[0048] 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 can circumscribe 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. 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 may be disposed on face 205 (e.g., on or within protrusions 214 and / or channels 216).

[0049] 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.

[0050] 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.

[0051] In some examples, electrode 218 may be 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.

[0052] In some examples, second electrode 114 or electrode 218 may be paired with first electrode 112 for sensing ventricular signals and delivering ventricular pacing pulses. In some examples, second electrode 114 may be paired with electrode 218 or first electrode 112 for sensing atrial signals and delivering pacing pulses to atrial tissue (e.g., tothe atrial myocardium) in target implant region 106. In other words, electrode 218 may be paired, at different times, with first electrode 112 and / or second electrode 114 for either ventricular or atrial functionality, respectively, in some examples. In some examples, first and second electrodes 112 and 114 may be paired with each other, with different polarities, for atrial and ventricular functionality.

[0053] In some examples, second electrode 114 may be 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.

[0054] A distal end of first electrode 112 can be configured to rest within a ventricular myocardium of the patient, and second electrode 114, protrusions 214, and channels 216 can be configured to contact an atrial endocardium of the patient. In such examples, second electrode 114 may contact the atrial endocardium without substantially compressing the atrial endocardium. Device 104 may include more or fewer electrodes than two electrodes. 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 may include 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, first electrically active region 212 can be positioned on a separate member and / or on the housing 202.

[0055] 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 capturethresholds may, in turn, increase the consumption of a power source of device 104 associated with delivery of the stimulation.

[0056] In some examples device 104 includes one or more therapeutic substance dispensing devices (not pictured in FIG. 2A), e.g., on protrusions 214, within a recess defined by second electrode 114, within channels 216, or the like. The steroid may mitigate inflammation of patient tissue resulting from interaction with the IMD. Therapeutic substance dispensing devices may be configured to elute one or more steroids to tissue in proximity to the therapeutic substance dispensing devices over time. In some examples, the therapeutic substance dispensing device may include one or more monolithic controlled release devices (MCRDs).

[0057] FIG. 2B is a perspective diagram illustrating a top-down view of the example device of FIG. 2A. FIG. 2C is a perspective diagram illustrating a side view of the distal end of the example device of FIG. 2A. As illustrated in FIGS. 2B and 2C, protrusions 214 may be disposed around the outer perimeter housing 202 and may be separated by channels 216. Each of protrusions 214 may be disposed radially outwards of first electrode 114 and radially inwards of or aligned with the outer perimeter of housing 202.Protrusions 214 may extend distally from face 205 and the bottom surfaces of channels 216 may define (e.g., be formed by) face 205 of device 104 or be located distal of face 205 but less distal than the distal surfaces of protrusions 214. As another alternative, the bottom surfaces of channels 216 may be recessed into (e.g., be situated proximal of) face 205. While device 104 as illustrated in FIGS. 2A-2B includes three protrusions 214 separated by three channels 216, in other examples, device 104 may include two or four or more protrusions 214 separated by two or four or more channels 216, respectively. A radially outer surface of each protrusion 214 may be flush with an outer perimeter of housing 202 or may be radially inwards of the outer perimeter of housing 202, e.g., as illustrated in FIG. 2B.

[0058] FIG. 3 is a cross-sectional diagram illustrating a cross-sectional view of the distal end of the example device of FIG. 2A, the cross-section being taken along line A-A of FIG. 2B. As illustrated in FIG. 3, each of protrusions 214 may define a distal surface 302 and sides 304 (e.g., sides 304A, 304B, collectively referred to herein as “sides 304”) connecting distal surface 302 to face 205.

[0059] Distal surface 302 may be parallel to face 205, e.g., as illustrated in FIG. 3. In some examples, distal surface 302 may be offset from (e.g., not parallel to) face 205 and may define a slope. The slope may extend distally and towards longitudinal axis 210 or proximally and towards longitudinal axis 210. Each side 304 may extend at non- orthogonal angle(s) from face 205 to distal surface 302 or may extend orthogonally from face 205 to distal surface 302. For example, as illustrated in FIG. 3, a radially inner side 304A may define a slope extending proximally towards longitudinal axis 210 from distal surface 302 to face 205. The sloped surface of sides 204 may reduce compression of wall tissue, e.g., between protrusions 214 and first electrode 112, while inhibiting unintended rotation of first electrode 112 within the wall tissue.

[0060] For each protrusion 214, sides 304 may be connected to distal surface 302 along a plurality of edges. Each edge may define a sharp edge, a filleted edge, rounded edge, or a chamfered edge. For example, as illustrated in FIG. 3, each protrusion 214 may define a rounded edge between distal surface 302 and side 304B. A filleted or chamfered edge may reduce tissue irritation and / or inflammation at or around the edges of protrusion 214. Side 304B may be radially inwards of, radially outwards of, or flush with the outer perimeter of housing 202.

[0061] The plurality of protrusions 214 on device 104 may be of uniform configuration or may be irregularly configured. For example, one protrusion 214 may define different dimensions and / or proportions than another of protrusions 214. The irregularity between protrusions 214 may facilitate implantation of device 104 within target implant location 106 at specific orientation(s) and / or may reduce tissue compression, inflammation, and / or irritation around specific portions of device 104 when device 104 is implanted within target implant location 106. For example, distal surfaces 302 of protrusions 214 may be longitudinally offset, e.g. disposed at different longitudinal distances from face 205 relative to each other, to facilitate implantation of device 104 at a non-orthogonal angle to the surface of the wall tissue at target implant location 106.

[0062] FIG. 4A is a perspective diagram illustrating another example of device 104 of FIG. 1 with a distal portion 402 including a flat portion 406 and a rounded portion 408. FIG. 4B is a perspective diagram illustrating a top view of device 104 of FIG. 4 A.

[0063] As illustrated in FIGS 4 A and 4B, device 104 may include a face 404 defining a distal end of device 104 (e.g., a distal end of distal portion 402 of device 104). Distalsurfaces of flat portion 406 and rounded portion 408 may collectively define face 404. First electrode 112 may extend from face 404 from proximal end 410 of first electrode 112 to a distal end. Second electrode 114 may be disposed on face 404.

[0064] Housing 202 may define an elongated cylindrical body extending along longitudinal axis 210. Flat portion 406 of distal portion 402 may define at least a portion of face 205. The distal surface of flat portion 406 may define a reference plane orthogonal to longitudinal axis 210. Rounded portion 408 may connect flat portion 406 to outer perimeter of housing 202, e.g., to enclose distal portion 402 of device 104. Rounded portion 408 may define a continuous curvature extending from an edge of flat portion 406 to an edge of housing 202.

[0065] The distal surface of flat portion 406 may be substantially similar to face 205, e.g., as previously described herein. Flat portion 406 may encompass at least 50% of the surface area of face 404 of distal portion 402. Device 104 may include one or more elements disposed on the distal surface of flat portion 406 including, but are not limited to, first electrode 112, second electrode(s) 114, anti-rotation and / or fixation features (e.g., protrusions 114, tines, barbs, recesses, ramps), or the like. For example, as illustrated in FIG. 4B, proximal end 410 of first electrode 112 may extend distally past face 404 from a location on the distal surface of flat portion 406. Second electrode 114 may be disposed on the distal surface of flat portion 406 and may be flush with the distal surface or may be proud of (e.g., protruding distally beyond) the distal surface (e.g., as illustrated in FIG.4A). Flat portion 406 may be orthogonal to a cylindrical portion of housing 202. Flat portion 406 may extend at least 180 degrees around longitudinal axis 210.

[0066] Rounded portion 408 may connect flat portion 406 to housing 202. Rounded portion 408 may define a curved distal surface extending form the distal surface of flat portion 406 to the outer surface of housing 202, e.g., to enclose the inner volume of housing 202. Rounded portion 408 may define a radius of curvature defining the distal surface. The radius of curvature may be up to 3.81 centimeters (cm) (e.g., up to 0.15 inches (in)). For example, the radius of curvature may be up to 1.91 cm (e.g., up to 0.075 in). In some examples, one or more elements are disposed on the distal surface of rounded portion 408 including, but are not limited to, anti-rotation and / or fixation features, second electrode 114, or the like.

[0067] Rounded portion 408 may allow for contact between face 404 of device 104 with tissue when device 104 is not orthogonal to the surface of the tissue, e.g., when longitudinal axis 210 is not orthogonal to the surface of the tissue. Rounded portion 408 may increase a number of possible angles and / or orientations to affix device to tissue and maintain a threshold amount of contact between device 104 and the tissue surface.

[0068] FIG. 5 is a functional block diagram illustrating an example configuration of device 104 of FIGS. 1-4B, in accordance with one or more aspects of this disclosure. 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 with respect to FIGS. 1-4B, 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 may be disposed on or within face 205 of device 104 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. In some examples, second electrode 114 is configured to contact the wall tissue of the first chamber without penetrating or compressing the wall tissue. Second electrode 114 may maintain contact in this manner by virtue of being disposed at a center of face 208 and / or within one of channels 216, as previously described herein.

[0069] 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.

[0070] Signal generation circuitry 506 generates electrical stimulation signals, e.g., cardiac pacing pulses. Switch circuitry 502 is coupled to electrodes 112, 114, and 218, 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.

[0071] Each of electrodes 112, 114, 218 may be coupled to switch circuitry 502 via a corresponding feedthrough assembly. In some examples, each feedthrough assembly may be 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 may be 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 may be offset from longitudinal axis 210 to allow the header to turn relative to housing 202.

[0072] 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, anal og-to-digi tai 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 applicationspecific 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.

[0073] 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.

[0074] 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).

[0075] 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.

[0076] FIG. 6 is a conceptual diagram of the device of FIGS. 4A-4B implanted at one example of a target implant location 106. First electrode 112 may be inserted (e.g., in a manner similar to rotating and advancing a threaded screw) such that tissue becomes engaged with the helix of first electrode 112. As first electrode 112 becomes engaged with tissue, first electrode 112 pierces into the tissue at target implant region 106 and advances through atrial myocardium 610 and central fibrous body 606 to position first electrically active region 212 in ventricular myocardium 108 as shown in FIG. 6. In some examples, first electrode 112 penetrates into the interventricular septum. In some examples, first electrode 112 does not perforate either of the ventricular endocardial or epicardial surface. While FIG. 6 is primarily described with reference to device 104 illustrated in FIGS. 4A-4B, the techniques described below may be used to implant device 104 illustrated in any of FIGS. 1-5 within tissue.

[0077] In some examples, manual pressure applied to the housing proximal end 206, e.g., via an advancement tool, provides the longitudinal force to pierce the cardiac tissue at target implant region 106. In some examples, actuation of an advancement tool rotates device 104 and first electrode 112 configured as a helix about longitudinal axis 210. The rotation of the helix about the longitudinal axis 210 advances first electrode 112 through atrial myocardium 610 and central fibrous body 606 to position first electrically active region 212 in ventricular myocardium 108 as shown in FIG. 4.

[0078] As first electrode 112 advances into the tissue, the distance between second electrode 114 on a distal end of device 104 (e.g., on distal portion 402 of device 104) and atrial endocardium 608 decreases until second electrode 114 and a distal end of device 104 (e.g., face 205, face 404 of device 104) contact and / or may press against, the surface of atrial endocardium 608. In some examples, such as with device 104 illustrated in FIGS. 1- 3, protrusions 214 (not pictured in FIG. 6) may contact and / or compress atrial endocardium 608 while portions of atrial endocardium 608 within channels 216 (not pictured in FIG. 6) are not compressed, e.g., thereby allowing second electrode 114 to contact atrial endocardium 608 without compressing atrial endocardium 608. Protrusions 214 increase friction between device 104 and the wall tissue and prevent or inhibit rotation of device 104 due to movement of tissue of heart 102 (e.g., movement of ventricular myocardium 108, atrial myocardium 610, central fibrous body 606, or the like) or blood flow during cardiac function.

[0079] In some examples, as illustrated in FIGS. 4A-4B and FIG. 6, distal portion 402 of device 104 may include flat portion 406 and rounded portion 408. In the example illustrated in FIG. 6, device 104 may be implanted at target implant location 106 at an orientation that is not orthogonal to a surface of atrial endocardium 608. Device 104 may be implanted at an angle relative to the surface of atrial endocardium 608 such that longitudinal axis 210 is offset from a reference axis 602 orthogonal to the surface of atrial endocardium 608 by angle 604. When device 104 is implanted at angle 604, rounded portion 408 may maintain contact with the surface of atrial endocardium 608, e.g., to increase stability of device 104 within target implant location 106 and / or increase fixation of device 104 at target implant location 106. The ability of rounded portion 408 tomaintain contact with the surface of atrial endocardium 608 while device 104 is at angle 604 may increase a number of possible target implant locations 106 within heart 102, e.g., by enabling implantation of device 104 at locations where there is insufficient space for the clinician to implant device 104 into tissue in an orthogonal orientation.

[0080] Target implant region 106 in some pacing applications is along atrial endocardium 404, substantially inferior to the AV node and bundle of His. First electrode 112 can have a length that penetrates through atrial endocardium 608 in target implant region 106, through the central fibrous body 606 and into ventricular myocardium 108 without perforating through the ventricular endocardial surface. In some examples, when the full length of first electrode 112 is fully advanced into target implant region 106, first electrically active region 212 rests within ventricular myocardium 108 and second electrode 114 is positioned in intimate contact with atrial endocardium 608. First electrode 112 may extend from housing distal end 204 approximately 3 mm to 12 mm in various examples. In some examples, first electrode 112 may extend a distance from distal end 204 by at least 3 mm, at least 3 mm but less than 20 mm, less than 15 mm, less than 10 mm, or less than 8 mm in various examples. The diameter of an elongated body defining first electrode 112 may be 2 mm or less, e.g., may be 1 mm or less, may be 0.6 mm or less. An outer diameter of the helix or coil defined by first electrode 112 may be 4 mm or less.

[0081] FIG. 7 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 device 104 of any of FIGS. 1-6. The technique of FIG. 7 will be primarily described with concurrent reference to device 104 as illustrated in FIGS. 1-3, although a person having ordinary skill in the art will understand that the technique may be performed in reference to another implantable medical lead or other medical device.

[0082] A clinician may insert device 104 within a single first chamber of the heart 102 (702). 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., 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 (704). In some examples, advancing first electrode 112 includes positioning a distal end of first electrode 112 (e.g., a first electrically activeregion 212) 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.

[0083] The clinician may orient device 104 to be orthogonal to the surface of the wall tissue prior to causing first electrode 112 to penetrate the wall tissue. In some examples, where distal portion 402 of device 104 includes flat portion 406 and rounded portion 408, the clinician may orient device 104 to be offset from a reference axis orthogonal to the surface by up to angle 604. The offset by angle 604 may allow the clinician to affix device 104 to wall tissue at locations where there is insufficient space to implant device 104 orthogonal to the surface of the wall tissue. In such examples, the clinician may advance first electrode 112 into the wall tissue until first electrode 112 is at a specified depth within the wall tissue and device 104 is in a specified orientation within target implant region 106. As first electrode 112 is advanced into wall tissue (e.g., via rotation of device 104), flat portion 406 and rounded portion 408 may impart different torques on the delivery tool coupled to device 104. The different torque values imparted by flat portion 406 and rounded portion 408 may define a substantially sinusoidal pattern over time. The clinician may rotate device 104 until first electrode 112 is at a sufficient depth and device 104 is imparting a reduced torque value on the delivery tool, which may indicate that rounded portion 408 (e.g., and flat portion 406 in some examples) are contacting the surface of the wall tissue. Contact between the surface of the wall tissue and rounded portion 408 may improve stability of device 104 within heart 102 and may inhibit unintended rotation of first electrode 112 within the wall tissue.

[0084] 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 (706). The clinician may advance device 104 into the wall tissue until the wall tissue contacts face 205. For example, the clinician may advance device 104 into the wall tissue until the wall tissue flows around protrusions 214 on face 205 and into channels 216 separating protrusions 214. The portion of the wall tissue around a center of device 104 and / or within channels 216 may not be compressed, e.g., due to the longitudinal offset between distal surfaces 302 of protrusions 214 and the bottom surfaces of channels 216 defining face 205 of device 104. Second electrode 114 may be disposed at a center of device 104 and / or within channels 216. Second electrode 114 may contact thewall tissue within the center of device 104 and / or within channels 216 without compression of the wall tissue. In some examples, where second electrode 114 is proud of face 205, second electrode 114 may contact the wall tissue without substantially compressing the wall tissue. The reduced compression of the wall tissue may reduce pacing thresholds required for second electrode 114 to deliver efficacious stimulation to the wall tissue of the first chamber.

[0085] While device 104 is implanted within the cardiac tissue, one or more antirotation features disposed on device 104 may resist rotation of device 104 due to movement of the cardiac tissue and blood flow. The one or more anti-rotation features may prevent inhibit movement of first electrode 112 away from wall tissue of the second chamber of heart 102 (e.g., ventricular myocardium 108 of the patient). The one or more anti -rotation features may also prevent inhibit dislodgement of device 104 from within wall tissue of the first chamber of heart 102. The one or more anti -rotation features may include protrusions 214 disposed on distal end 204 of device 104 and any other antirotation features previously described herein. Ramp 212 may increase compression of the wall tissue which causes device 104 to resist rotation due to movement of the wall tissue. The anti-rotation features may include one or more additional features (e.g., hooks, barbs, recesses, textured surfaces) disposed on one or more of first electrode 112, ramp 212, and / or face 205 of device 104.

[0086] 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 (708). 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).

[0087] 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 thisdisclosure may be performed by a combination of units or modules associated with, for example, a medical device.

[0088] 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).

[0089] 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.

[0090] 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.

[0091] This disclosure describes each of the following examples.

[0092] Example 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; an elongated body extending distally from the distal end of the elongated housing, wherein the elongated body defines a helix, the elongated body defining a first electrode; a second electrode disposed on the distal end the elongated housing; and two or more protrusions extending from the distal end of the elongated housing, the two or more protrusions being configured to interface with wall tissue of the chamber without penetrating the wall tissue; and achannel separating at least two protrusions of the two or more protrusions, a bottom of the channel being proximal of respective distal ends of the at least two protrusions.

[0093] Example 2: the device of example 1, wherein the channel extends from a center of the distal end of the elongated housing towards an outer perimeter of the distal end of the elongated housing.

[0094] Example 3 : the device of any of examples 1 or 2, wherein the second electrode is disposed within the channel.

[0095] Example 4: the device of example 3, wherein the channel comprises a plurality of channels, each channel of the plurality of channels separating two circumferentially adjacent protrusions of the two or more protrusions, wherein the second electrode comprises two or more second electrodes, each second electrode of the two or more second electrodes being disposed within a corresponding channel of the plurality of channels, and wherein the two or more second electrodes are evenly circumferentially distributed about the longitudinal axis.

[0096] Example 5: the device of any of examples 1-4, wherein the second electrode is disposed at a center of the distal end of the elongated housing.

[0097] Example 6: the device of any of examples 1-5, wherein a bottom of the channel is longitudinally offset from a distal surface of a protrusion of the two or more protrusions.

[0098] Example 7: the device of any of examples 1-6, wherein the two or more protrusions are disposed radially outwards of the elongated body.

[0099] Example 8: the device of any of examples 1-7, wherein the elongated body is configured to penetrate the wall tissue, and wherein the two or more protrusions are configured to interface with the wall tissue to inhibit rotation of the elongated body within the wall tissue.

[0100] Example 9: the device of any of examples 1-8, wherein the second electrode is configured to contact the wall tissue of the chamber without penetrating or compressing the wall tissue.

[0101] Example 10: the device of any of examples 1-9, 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 separated from the first chamber of the heart.

[0102] Example 11 : the device of example 10, wherein the first chamber comprises an atrium of the heart, and wherein the second chamber comprises a ventricle of the heart.

[0103] Example 12: the device of any of examples 1-11, wherein a distal surface of the second electrode is flush with a distal end of the elongated housing.

[0104] Example 13: the device of any of examples 1-12, wherein the bottom of the channel defines a distal end of the elongated housing.

[0105] Example 14: 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; an elongated body extending distally from the distal end of the elongated housing, wherein the elongated body defines a helix, the elongated body defining a first electrode at or around a distal end of the elongated body; and a second electrode disposed on the distal end the elongated housing, wherein the distal end of the elongated housing defines a flat section and a rounded section, wherein the elongated body and the second electrode are disposed on the flat section, and wherein the rounded section is configured to enable the elongated body to puncture wall tissue of the chamber at an angle offset from orthogonal to a surface of the wall tissue.

[0106] Example 15: the device of example 14, wherein the flat section defines a reference plane orthogonal to the longitudinal axis.

[0107] Example 16: the device of any of examples 14 or 15, wherein the elongated body extends distally from the distal end of the elongated housing from a proximal end of the elongated body to the distal end of the elongated body, and wherein the proximal end of the elongated body contacts the distal end of the elongated housing within the flat section.

[0108] Example 17: the device of any of examples 14-16, wherein the rounded section extends from an edge of the flat section of the elongated housing towards a side surface of the elongated housing.

[0109] Example 18: the device of any of examples 14-17, wherein the rounded section extends up to 180 degrees around an outer perimeter of the distal end of the elongated housing.

[0110] Example 19: the device of any of examples 14-18, wherein the distal end of the elongated housing is asymmetrical about the longitudinal axis of the elongated housing.

[0111] Example 20: the device of any of examples 14-19, wherein the second electrode is configured to contact the wall tissue of the chamber without penetrating or compressing the wall tissue.

[0112] Example 21 : the device of any of examples 14-20, 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 separated from the first chamber of the heart.

[0113] Example 22: the device of example 21, wherein the first chamber comprises an atrium of the heart, and wherein the second chamber comprises a ventricle of the heart.

[0114] Example 23: a fixation device extending distally from a distal end of an implantable medical device, the fixation device comprising: a helix extending distally from the distal end of the elongated body along the longitudinal axis and defining one or more coils, wherein a distal end of the helix is configured to penetrate into tissue of a patient; two or more protrusions extending distally from the distal end of the implantable medical device, the two or more protrusions being configured to interface with the tissue without penetrating the tissue; and a channel separating first and second protrusions of the two or more protrusions, a bottom of the channel being disposed proximal of respective distal ends of the at least two protrusions.

[0115] Example 24: the fixation device of example 23, wherein the IMD comprises one or more of: a pacing lead; or a leadless pacemaker.

[0116] Example 25: the fixation device of any of examples 23 or 24, wherein the channel extends from a center of the distal end of the elongated body towards an outer perimeter of the distal end of the elongated housing.

[0117] Example 26: the device of any of examples 23-25, wherein the channel comprises a plurality of channels, each channel of the plurality of channels separating two circumferentially adjacent protrusions of the two or more protrusions.

[0118] Example 27: the device of example 26, wherein the plurality of channels are evenly circumferentially distributed about the longitudinal axis.

[0119] Example 28: the device of any of examples 23-27, wherein the bottom of the channel is longitudinally offset from a distal surface of a protrusion of the two or more protrusions.

[0120] Example 29: the fixation device of any of examples 23-28, wherein the two or more protrusions are radially outwards of the elongated body.

[0121] Example 30: the device of any of examples 23-29, wherein the two or more protrusions are configured to interface with the tissue to inhibit rotation of the helix within the tissue.

[0122] Example 31 : the device of any of examples 23-30, wherein the bottom of the channel defines a distal end of the elongated housing.

[0123] Example 32: a fixation device comprising: an elongated housing coupled to a distal end of an implantable medical device and extending distally from a proximal end to a distal end along a longitudinal axis, wherein the distal end of the elongated housing defines a flat section and a rounded section; and a helix extending distally from the distal end of the elongated housing along the longitudinal axis and defining one or more coils, wherein a distal end of the helix is configured to penetrate into tissue of a patient, wherein the rounded section of the distal end of the elongated housing is configured to enable the helix to penetrate the tissue at an angle offset from a surface of the tissue.

[0124] Example 33: the device of example 32, wherein the flat section defines a reference plane orthogonal to the longitudinal axis.

[0125] Example 34: the device of any of examples 32 or 33, wherein the helix extends distally from the distal end of the elongated housing from a proximal end of the helix, and wherein the proximal end of the helix contacts the distal end of the elongated housing within the flat section.

[0126] Example 35: the device of any of examples 32-34, wherein the rounded section extends from an edge of the flat section of the elongated housing towards a side surface of the elongated housing.

[0127] Example 36: the device of any of examples 32-35, wherein the rounded section extends up to 180 degrees around an outer perimeter of the distal end of the elongated housing.

[0128] Example 37: the device of any of examples 32-36, wherein the distal end of the elongated housing is circumferentially asymmetrical about the longitudinal axis.

[0129] 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; an elongated body extending distally from the distal end of the elongated housing, wherein the elongated body defines a helix, the elongated body defining a first electrode; a second electrode disposed on the distal end the elongated housing; and two or more protrusions extending from the distal end of the elongated housing, the two or more protrusions being configured to interface with wall tissue of the chamber without penetrating the wall tissue; and a channel separating at least two protrusions of the two or more protrusions, a bottom of the channel being proximal of respective distal ends of the at least two protrusions.

2. The device of claim 1, wherein the channel extends from a center of the distal end of the elongated housing towards an outer perimeter of the distal end of the elongated housing.

3. The device of any of claims 1 or 2, wherein the second electrode is disposed within the channel.

4. The device of claim 3, wherein the channel comprises a plurality of channels, each channel of the plurality of channels separating two circumferentially adjacent protrusions of the two or more protrusions, wherein the second electrode comprises two or more second electrodes, each second electrode of the two or more second electrodes being disposed within a corresponding channel of the plurality of channels, and wherein the two or more second electrodes are evenly circumferentially distributed about the longitudinal axis.

5. The device of any of claims 1-4, wherein the second electrode is disposed at a center of the distal end of the elongated housing.

6. The device of any of claims 1-5, wherein a bottom of the channel is longitudinally offset from a distal surface of a protrusion of the two or more protrusions.

7. The device of any of claims 1-6, wherein the two or more protrusions are disposed radially outwards of the elongated body.

8. The device of any of claims 1-7, wherein the elongated body is configured to penetrate the wall tissue, and wherein the two or more protrusions are configured to interface with the wall tissue to inhibit rotation of the elongated body within the wall tissue.

9. The device of any of claims 1-8, wherein the second electrode is configured to contact the wall tissue of the chamber without penetrating or compressing the wall tissue.

10. The device of any of claims 1-9, 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 separated from the first chamber of the heart.

11. The device of claim 10, wherein the first chamber comprises an atrium of the heart, and wherein the second chamber comprises a ventricle of the heart.

12. The device of any of claims 1-11, wherein a distal surface of the second electrode is flush with a distal end of the elongated housing.

13. The device of any of claims 1-12, wherein the bottom of the channel defines a distal end of the elongated housing.

14. 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; an elongated body extending distally from the distal end of the elongated housing, wherein the elongated body defines a helix, the elongated body defining a first electrode at or around a distal end of the elongated body; and a second electrode disposed on the distal end the elongated housing, wherein the distal end of the elongated housing defines a flat section and a rounded section, wherein the elongated body and the second electrode are disposed on the flat section, and wherein the rounded section is configured to enable the elongated body to puncture wall tissue of the chamber at an angle offset from orthogonal to a surface of the wall tissue.

15. The device of claim 14, wherein the distal end of the elongated housing is asymmetrical about the longitudinal axis of the elongated housing.

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