Fixation for electrode of an implantable medical device

Abstract

A device including: 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, wherein the elongated housing defines a recess extending from the distal end towards the proximal end; and an electrode assembly comprising an electrode, the electrode comprising: an elongated body defining a helix, wherein a proximal end of the electrode assembly is configured to be retained within the recess of the elongated housing to secure the electrode to the elongated housing, and wherein when the electrode is secured to the elongated housing, the electrode extends distally past the distal end of the elongated housing.

Description

FIXATION FOR ELECTRODE OF AN IMPLANTABLE MEDICAL DEVICE

[0001] This application claims the benefit of U.S. Provisional Patent Application Serial No. 63 / 559,367, filed February 29, 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 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.

[0005] 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 multichamber functionality by being implanted in respective chambers. In some examples, a cardiac pacemaker sized for implantation in a heart chamber may be configured with electrodes that enable multi-chamber functionality.SUMMARY

[0006] 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. More particularly, this disclosure is directed to IMDs with one or more features configured to secure an electrode (e.g., a helical electrode) to an elongated housing of the IMD.

[0007] An example IMD described herein may include one or more electrodes extending away from an elongated housing of the IMD and configured to puncture tissue of a patient, e.g., to affix the IMD to the tissue, sense signals from the tissue, and / or deliver stimulation signals to the tissue. Movement of the tissue and / or fluids around the IMD and / or applied forces on the IMD (e.g., during implantation of the IMD) may lead to an unintended application of forces on the one or more electrodes. The application of forces on the one or more electrodes may lead to an unintended separation of the one or more electrodes from the rest of the IMD, deformation and / or damage to one or more components of the IMD, and / or electrical separation of the one or more electrodes from one or more computing components disposed within the IMD.

[0008] This disclosure describes IMDs with example electrode assemblies configured to interface with recesses in elongated housings of IMDs to affix the electrode assemblies to the elongated housings of the IMDs. The electrode assembly may be inserted into the recess in an unlocked orientation and subsequently rotated into a locked orientation within the recess to secure the electrode assembly to the elongated housing. When the electrode assembly is in the locked orientation within the elongated housing, portions of the elongated housing may interface with portions of the electrode assembly to inhibit unintended movement of the electrode assembly relative to the elongated housing along up to all six degrees of movement of the electrode assembly. For example, tabs of an assembly body (e.g., a bushing) of the electrode assembly may interface with sidewalls of openings and / or undercuts of the recess to inhibit unintended movement of the electrode assembly out of the recess and / or unintended rotation of the electrode assembly within the recess.

[0009] The IMD may include a compressible element disposed within the recess. The compressible element may be at least partially compressed to facilitate transition of the electrode assembly between the locked orientation and unlocked orientation. When the electrode assembly is in the locked orientation within the recess of the electrode assembly, the compressible element may at least partially expand towards an uncompressed state, e.g., to apply a force on the electrode assembly (e.g., on the one or more tabs) and further inhibit unintended movement of the electrode assembly within the recess of the elongated housing.

[0010] In some examples, this disclosure describes 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, wherein the elongated housing defines a recess extending from the distal end towards the proximal end; and an electrode assembly comprising an electrode, the electrode comprising: an elongated body defining a helix, wherein a proximal end of the electrode assembly is configured to be retained within the recess of the elongated housing to secure the electrode to the elongated housing, and wherein when the electrode is secured to the elongated housing, the electrode extends distally past the distal end of the elongated housing.

[0011] In some examples, this disclosure describes a method comprising: delivering cardiac pacing from a device to a heart, 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 chamber of a heart, wherein the elongated housing defines a recess extending from the distal end towards the proximal end; and an electrode assembly comprising an electrode, the electrode comprising: an elongated body defining a helix, wherein a proximal end of the electrode assembly is configured to be retained within the recess of the elongated housing to secure the electrode to the elongated housing, and wherein when the electrode is secured to the elongated housing, the electrode extends distally past the distal end of the elongated housing.

[0012] In some examples, this disclosure describes a method comprising attaching a tool to an assembly body of an electrode assembly of a device, wherein the electrode assembly comprises: the assembly body; and an electrode connected to the assembly body, the electrode comprising an elongated body defining a helix, and wherein the device further 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 chamber of a heart; inserting, via the tool, the electrode assembly along a longitudinal axis and into a recess of an elongated housing of the device; rotating, via the tool, the electrode assembly about the longitudinal axis to secure the electrode assembly within the recess; and releasing the tool from the bushing of the electrode assembly to cause the recess to interface with the electrode assembly to inhibit unintended movement of the electrode assembly relative to the elongated housing.

[0013] In some examples, this disclosure describes 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, wherein the elongated housing defines a recess extending from the distal end towards the proximal end; and a fixation assembly comprising a fixation member, wherein a proximal end of the fixation assembly is configured to be retained within the recess of the elongated housing to secure the fixation member to the elongated housing, and wherein when the fixation member is secured to the elongated housing, the fixation member extends distally past the distal end of the elongated housing.

[0014] In some examples, this disclosure describes a method comprising: delivering cardiac pacing from a device to a heart, 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 chamber of a heart, wherein the elongated housing defines a recess extending from the distal end towards the proximal end; and a fixation assembly comprising a fixation member, wherein a proximal end of the fixation assembly is configured to be retained within the recess of the elongated housing to secure the fixation member to the elongated housing, and wherein when the fixation member is secured to the elongated housing, the fixation member extends distally past the distal end of the elongated housing.

[0015] In some examples, this disclosure describes a method comprising: attaching a tool to an assembly body of an fixation assembly of a device, wherein the fixation assembly comprises: the assembly body; and a fixation member connected to the assembly body, and wherein the device further 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 chamber of a heart; inserting, via the tool, the fixation assembly along a longitudinal axis and into a recess of an elongated housing of the device; rotating, via the tool, the fixation assembly about the longitudinal axis to secure the fixation assembly within the recess, wherein when the fixation assembly is secured within the recess, the fixation member extends distally past the distal end of the elongated housing; and releasing the tool from the assembly body of the fixation assembly to cause the recess to interface with the electrode assembly to inhibit unintended movement of the electrode assembly relative to the elongated housing.

[0016] 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

[0017] 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.

[0018] 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.

[0019] FIG. 2A is a perspective diagram illustrating an example of the implantable medical device (IMD) of FIG. 1.

[0020] FIG. 2B is a perspective diagram illustrating another example of the IMD of FIG. 1.

[0021] FIG. 3 is a functional block diagram illustrating an example configuration of the IMD of FIGS. 1-2B, in accordance with one or more aspects of this disclosure.

[0022] FIG. 4 is a conceptual diagram of the IMD of FIGS. 1-3 implanted at a target implant site.

[0023] FIG. 5 is a perspective diagram illustrating a partially exploded view of the IMD of FIG. 2 A.

[0024] FIG. 6A is a perspective diagram illustrating a side view of an example of the electrode assembly of FIG. 5.

[0025] FIG. 6B is a perspective diagram illustrating a top view of the example electrode assembly of FIG. 6 A.

[0026] FIG. 7A is a perspective diagram illustrating a side view of a distal portion of an example of the elongated housing of FIG. 5.

[0027] FIG. 7B is a cross-sectional diagram illustrating a cross-section view of the distal portion of the elongated housing of FIG. 7A, the cross-section being taken parallel to a longitudinal axis of the elongated housing and along line A-A of FIG. 7A.

[0028] FIG. 7C is a cross-sectional diagram illustrating a cross-section view of the distal portion of the elongated housing of FIG. 7A, the cross-section being taken along a reference plane orthogonal to the longitudinal axis of the elongated housing and along line B-B of FIG. 7 A.

[0029] FIG. 7D is a cross-sectional diagram illustrating a cross-section view of the distal portion of the elongated housing of FIG. 7A, the cross-section being taken along areference plane orthogonal to the longitudinal axis of the elongated housing and along line C-C of FIG. 7 A.

[0030] FIG. 8 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 IMD of any of FIGS. 1-7D.

[0031] FIG. 9 is a flow diagram illustrating an example process for assembling an example IMD of any of FIGS. 1-7D.DETAILED DESCRIPTION

[0032] In general, this disclosure is directed to configurations of electrodes of implantable medical devices (IMDs). More particularly, this disclosure is directed to IMDs 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.

[0033] 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.

[0034] 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 chamberby 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.

[0035] 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 may extend into the tissue of heart 102 at region 106 and affix device 104 to the tissue of heart 102.

[0036] First electrode 112 may be disposed on an electrode assembly (e.g., attached to an assembly body of an electrode assembly). The electrode assembly may be removably attached to an elongated housing of device 104 to secure first electrode 112 to device 104. For example, the elongated housing of device 104 may define a recess configured to receive at least a portion (e.g., a proximal portion) of the electrode assembly. Once the electrode assembly is disposed within the recess, the electrode assembly may interface with the elongated housing (e.g., via rotation of the electrode assembly within the recess) to inhibit unintended movement of the electrode assembly, and by extension first electrode 112, relative to the elongated housing of device 104.

[0037] The interface between the electrode assembly and the elongated housing may constrain movement of first electrode 112 relative to the elongated housing in all six degrees of movement and inhibit unintended separation of first electrode 112 from the elongated housing when device 104 is affixed to the tissue of heart 102 at region 106. The six degrees of movement includes movement of first electrode 112 along an x-axis ofdevice 104, movement of first electrode 112 along a y-axis of device 104, movement of first electrode 112 along a z-axis of device 104, rotation of first electrode 112 about the x- axis of device 104, rotation of first electrode 112 about the y-axis of device 104, and rotation of first electrode 112 about the z-axis of device 104.

[0038] While the examples of device 104 described herein are described primarily with reference to an electrode assembly including first electrode 112, other example devices may include a fixation assembly instead of and or in addition to an electrode assembly. In such examples, the fixation assembly may include one or more fixation members including one or more tines, a fixation helix, first electrode 112, and / or one or more other fixation mechanisms. In such examples, the fixation assembly may be inserted into and / or secured to device 104 via any of the example techniques described below. For example, the fixation assembly may include a fixation member, wherein a proximal end of the fixation assembly is configured to be retained within a recess of an elongated housing of device 104 to secure the fixation member to the elongated housing, and wherein when the fixation member is secured to the elongated housing, the fixation member extends distally past the distal end of the elongated housing.

[0039] 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.

[0040] Housing 202 extends between distal end 204 and proximal end 206 along longitudinal axis 210. In some examples, housing can 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 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.

[0041] Device 104 may include a ramp 212. Ramp 212 extends from a first end 214A that is fixedly attached to housing 202 at or near distal end 204 (e.g., attached to face 205), to a second end 214B that is more distal to first end 214A. Ramp 212 may be disposed radially outwards of first electrode 112 relative to longitudinal axis 210. Ramp 212 may extend around at least a portion of a perimeter of housing 202. Ramp 212 may extend up to 180 degrees around longitudinal axis 210 and along the perimeter of housing 202. Ramp 212 may be integrally formed as a part of the manufacturing of at least a portion of housing 202 (e.g., as a part of the manufacturing of a header defining distal end 204 and face 205 of housing 202). Ramp 212 may be formed via a molding process, via additive manufacturing, or the like. In some examples ramp 212 is formed separately and affixed to face 205 of housing 202 afterwards. Ramp 212 may define a partial helix, e.g., wound in a same direction and / or in different directions as a helix and / or coil defined by first electrode 112.

[0042] Ramp 212 may be an anti -rotation feature. Ramp 212 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 212 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) 212 on face 205, presence of additional antirotation feature(s), or the like.

[0043] Second end 214B may define a distal surface orthogonal to longitudinal axis 210. Second electrode 114 may be disposed on the distal surface of second end 214B. In some examples, second electrode 114 may be disposed partially along ramp 212, e.g., between first end 214A and second end 214B.

[0044] 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 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 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 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. 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.

[0045] 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.

[0046] In some examples, first and second electrodes 112 and 114 may have 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.

[0047] 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 proximal end 220 to a distal end, e.g., defining first electricallyactive region 216. Proximal end 220 may be a location along first electrode 112 where first electrode 112 extends distally past distal end 204 of device 104.

[0048] Device 104 may include an electrode assembly including first electrode 112. In some examples, first electrode 112 (e.g., a proximal portion of first electrode 112) may be affixed to an assembly body of the electrode assembly. The electrode assembly may interface with a recess within housing 202 to secure first electrode 112 to housing 202, e.g., such that at least a portion of first electrode 112 extends distally away from face 205 of housing 202.

[0049] A manufacturing assembly and / or manufacturer may affix and / or detach first electrode 112 from housing 202 via manipulation of the electrode assembly, e.g., within the recess of housing 202. In some examples, the manufacturing assembly affixes first electrode 112 to housing 202 by inserting the electrode assembly into the recess of housing 202 and subsequently rotating first electrode 112 about longitudinal axis 210 within the recess, e.g., to secure first electrode 112 to housing 202. In some examples, the manufacturing assembly performs the reverse procedure to separate and remove first electrode 112 from housing 202. When the electrode assembly is retained within the recess of housing 202, sidewalls of housing 202 defining the recess may interface with the electrode assembly, e.g., interface with tabs extending radially away from an assembly body of the electrode assembly to inhibit movement of the electrode assembly within the recess, e.g., in up to six degrees of movement.

[0050] Housing 202 may include a compressible element disposed within the recess. When the manufacturing assembly inserts the electrode assembly into the recess, the electrode assembly may at least partially compress the compressible element, e.g., to allow for rotation of fist electrode 112 about longitudinal axis 210 within the recess. Once first electrode 112 is disposed within the recess (e.g., after rotation of first electrode 112), the compressible element may at least partially expand towards an uncompressed configuration and apply forces on the electrode assembly, e.g., to inhibit unintended movement and / or rotation of first electrode 112 within housing 202.

[0051] 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 may have a plurality of second electrodes 114 (e.g., two or more second electrodes 114) disposed on distal end 204 of housing 202. The plurality ofsecond 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 212). In some examples, each of the plurality of second electrodes 114 may be disposed on ramps. Each ramp 212 may include a single second electrode 114 or two or more second electrodes 114. In some examples, second electrode 114 may be disposed at a predetermined angle away from first end of first electrode 112.

[0052] 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 ramp 212 and / or of face 205. 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 212).

[0053] As illustrated in FIG. 2A, first electrode 112 may be a helix extending distally from face 205 and revolving around longitudinal axis 210 in a counter-clockwise direction (i.e., “wound” in a counter-clockwise direction, and ramp 212 may define partial helix extending distally from face 205 and revolving around longitudinal axis 210 in a clockwise direction, although in other examples the first electrode 112 and ramp 212 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 212 revolves around longitudinal axis 210 in a counter-clockwise direction) or first electrode 112 and ramp 212 may revolve around longitudinal axis 210 in a same direction. The helix may extend from a proximal end along and around longitudinal axis 210 towards a distal end. The distal end of the helix may define first electrically active region of first electrode 112. The proximal end of the helix may be retained or otherwise affixed to an assembly body ofthe electrode assembly, e.g., around a protrusion of the assembly body to affix first electrode 112 to the assembly body. The helix may define an inner diameter sized to facilitate insertion of an installation tool into an inner channel defined by the helix. The inner diameter may at least about 2.946 millimeters (mm) (e.g., about 0.116 inches (in)).

[0054] 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 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 217.

[0055] 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.

[0056] 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 lateral displacement 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 such examples, the distal end of first electrode 112 may define an inner diameter of at least about 2.946 mm. 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.

[0057] 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 216 and housing distal end 204.

[0058] 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.

[0059] 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 or on another ramp 212 disposed on face 205. For example, electrode 114 may be disposed on a first ramp 212 and electrode 218 may be disposed on a second ramp 212.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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., to the 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.

[0064] 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 pacingpulses delivered using first electrode 112 as a cathode and electrode 218 as the return anode.

[0065] A distal end of first electrode 112 can be configured to rest within a ventricular myocardium of the patient, and second electrode 114 and ramp 212 can be configured to contact an atrial endocardium of the patient. Device 104 may include more or fewer electrodes than two electrodes. In some examples, device 104 may include 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 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, electrically active region 216 can be positioned on a separate member and / or on the housing 202.

[0066] 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.

[0067] In some examples device 104 includes one or more therapeutic substance dispensing devices 215, e.g., on face 205, within a recess defined by second electrode 114, on ramp 212. 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, steroid eluting elements 215 comprise one or more monolithic controlled release devices (MCRDs).

[0068] In some examples, device 104 includes one or more therapeutic substance dispensing devices 215 configured to elute one or more steroids to tissue proximate to first electrode 112. Therapeutic substance dispensing devices 215 may be disposed within a recess defined by second electrode 114. In some examples, therapeutic substance dispensing devices 215 may be disposed at a center of face 205, e.g., within recess defined by housing 202, and / or on ramp 212, e.g., between first end 214A and second end 214B.

[0069] Ramp 212 may cause second electrode 114 to maintain consistent contact with the wall tissue, e.g., by raising second electrode 114 from face 205 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. In some examples, 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.

[0070] FIG. 2B is a perspective diagram illustrating another example of IMD 104 of FIG. 1. In the example illustrated in FIG. 2B, second electrode 114 is disposed directly on face 205 and separate from ramp 212. In such examples, second electrode 114 may be a button electrode, a wire electrode, or any other type of electrode. Second electrode 114 may extend distally away from face 205 or may be flush with face 205. In the example illustrated in FIG. 2B, ramp 212 may interface with tissue at target implant region 106 to inhibit unintended rotation of device 104 relative to the tissue. Examples of second electrode 114 are described in commonly-owned U.S. provisional application no. 63 / 625,461 filed January 26, 2024 and entitled “DISTAL END FIXATION FOR IMPLANTABLE MEDICAL DEVICE”, the entirety of each of which is incorporated herein by reference.

[0071] FIG. 3 is a functional block diagram illustrating an example configuration of device 104. As illustrated in FIG. 3, device 104 include electrodes 112 and 114, which may be configured as described with respect to FIGS. 1 and 2. For example, as described with respect to FIGS. 1 and 2, 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 chamberby second electrode 114. Second electrode 114 may maintain contact in this manner by virtue of being disposed in and / or on ramp 212 or another ramp as described herein. Ramp 212 may position second electrode 114 at a distance (e.g., distance 226) away from face 205, thereby causing second electrode 114 to maintain consistent contact with the wall tissue when first electrode 112 is secured within the wall tissue.

[0072] In the example shown in FIG. 3, device 104 includes switch circuitry 302, sensing circuitry 304, signal generation circuitry 306, sensor(s) 308, processing circuitry 310, telemetry circuitry 312, memory 314, and power source 316. The various circuitry may be, or include, programmable or fixed function circuitry configured to perform the functions attributed to respective circuitry. Memory 314 may store computer-readable instructions that, when executed by processing circuitry 310, cause device 104 to perform various functions. Memory 314 may be a storage device or other non-transitory medium. The components of device 104 illustrated in FIG. 3 may be housed within housing 202.

[0073] Signal generation circuitry 306 generates electrical stimulation signals, e.g., cardiac pacing pulses. Switch circuitry 302 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 302 is configured to direct stimulation signals from signal generation circuitry 306 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 302 may couple first electrode 112, which has penetrated to wall tissue of a ventricle or the intraventricular septum, to signal generation circuitry 306 as a cathode, and one or both of second electrode 114 or electrode 218 to signal generation circuitry 306 as an anode. As another example, in order to pace the RA, switch circuitry 302 may couple second electrode 114, which maintains contact with the RA endocardium, to signal generation circuitry 306 as a cathode, and one or both of first electrode 112 or electrode 218 to signal generation circuitry 306 as an anode.

[0074] Each of electrodes 112, 114, 218 may be coupled to switch circuitry 302 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 end204 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.

[0075] Switch circuitry 302 may also selectively couple sensing circuitry 304 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 304 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 302 may couple each of first electrode 112 and second electrode 114 (in combination with electrode 218) to respective sensing channels provided by sensing circuitry 304 to respectively sense either ventricular or atrial cardiac electrical signals. In some examples, sensing circuitry 304 is configured to detect events, e.g., depolarizations, within the cardiac electrical signals, and provide indications thereof to processing circuitry 310. In this manner, processing circuitry 310 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 310 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 310 herein may be embodied as firmware, hardware, software or any combination thereof.

[0076] Sensor(s) 308 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) 308 may include one or more accelerometers, optical sensors, chemical sensors, temperature sensors, pressure sensors, or any other types of sensors. Sensor(s) 308 may output patient parameter values that may be used as feedback to control sensing and delivery of therapy by device 104.

[0077] Telemetry circuitry 312 supports wireless communication between device 104 and an external programmer (not shown in FIG. 3) or another computing device under the control of processing circuitry 310. Processing circuitry 310 of device 104 may receive, asupdates to operational parameters from the computing device, and provide collected data, e.g., sensed heart activity or other patient parameters, via telemetry circuitry 312. Telemetry circuitry 312 may accomplish communication by radiofrequency (RF) communication techniques, e.g., via an antenna (not shown).

[0078] Power source 316 delivers operating power to various components of device 104. Power source 316 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.

[0079] FIG. 4 is a conceptual diagram of device 104 implanted at target implant region 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 406 and central fibrous body 402 to position first electrically active region 216 in ventricular myocardium 108 as shown in FIG. 4. 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.

[0080] 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 406 and central fibrous body 402 to position first electrically active region 216 in ventricular myocardium 108 as shown in FIG. 4.

[0081] As first electrode 112 advances into the tissue, the distance between second electrode 114 (e.g., on ramp 212) and atrial endocardium 404 decreases until second electrode 114 and ramp 212 contact, and may press against, the surface of atrial endocardium 404. Second electrode 114 and ramp 212 may press against the surface of atrial endocardium 404 and compress the wall tissue. The compression of the wall tissue may increase friction between ramp 212 and the wall tissue and prevent or inhibit rotation of device 104 due to movement of tissue of heart 102 (e.g., movement of ventricularmyocardium 108, atrial myocardium 406, central fibrous body 402, or the like) or blood flow during cardiac function. Ramp 212 pressing against heart tissue may cause heart tissue to become engaged with second electrically active region 217 of second electrode 114 disposed on ramp 212. Second electrode 114 is held in contact with atrial endocardium 404 by first electrode 112 and ramp 212. Retraction of second electrode 114 from the surface of atrial endocardium 404 may be prevented or inhibited by first electrode 112 and ramp 212.

[0082] Ramp 212 can be the sole anti-rotation feature of device 104 in some examples. In some examples, device 104 may have one or more additional anti-rotation features, e.g., defined and / or disposed on first electrode 112, on face 205, and / or on ramp 212. The distance by which first electrode 112 extends from housing 202 can be selected so first electrically active region 216 reaches an appropriate depth in the tissue layers to reach the targeted pacing and sensing site, in this case in ventricular myocardium 108, without puncturing all the way through into an adjacent cardiac chamber.

[0083] 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 404 in target implant region 106, through the central fibrous body 402 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 216 rests within ventricular myocardium 108 and second electrode 114 is positioned in intimate contact with atrial endocardium 404. 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.

[0084] FIG. 5 is a perspective diagram illustrating a partially-exploded view of device 104 of FIG. 2A. While IMD 104 is primarily described with reference to FIG. 2A, device 104 may be any IMD described and illustrated herein, e.g., in FIG. 2B. Device 104 mayinclude electrode assembly 502 and housing 202. Electrode assembly 502 may be configured to be inserted and retained within recess 512 of housing 202.

[0085] Electrode assembly 502 may include an assembly body 504 and first electrode 112 coupled to assembly body 504. Assembly body 504 may include, but is not limited to, a bushing. In some examples, as illustrated in FIG. 5, a proximal end of first electrode 112 may be affixed to assembly body 504. Assembly body 504 may include one or more extensions 508 (e.g., tabs) extending radially away from a center point of assembly body 504. In some examples, assembly body 504 defines a tool interface 506 disposed radially inwards of first electrode 112. Tool interface 506 may be configured to removably couple electrode assembly 502 to an installation tool, e.g., to facilitate the transmission of linear force (e.g., along a direction parallel to longitudinal axis 210) and / or rotary force (e.g., about longitudinal axis 210) from a manufacturing assembly to electrode assembly 502.

[0086] Housing 202 may include a distal portion 510 (alternatively referred to herein as “header 510”). Distal portion 510 may be a separate component from a remainder of housing 202 and may be affixed to one or more other components defining housing 202 to seal an inner volume of housing 202. Header 510 may be formed from a same or different material as one or more other components of housing 202. Header 510 may define distal end 204 of housing 202 and face 205. Header 510 may define recess 512, which may extend from face 205 towards proximal end 206 of housing 202 in a direction parallel to longitudinal axis 210. When electrode assembly 502 is affixed to housing 202, a portion of electrode assembly 502 longitudinally overlapping with housing 202 may be disposed entirely within header 510 of housing 202.

[0087] Header 510 may define one or more channels 514 around the inner surface of recess 512. Each channel 514 may extend from face 205 to a proximal end of recess 512 along a same direction as recess 512. In some examples, as illustrated in FIG. 5, each channel 514 extends along a direction parallel to longitudinal axis 514. Each channel 514 may be sized to retain a corresponding extension 508. For example, when electrode assembly 502 is circumferentially and radially aligned with recess 512, a first linear distance from a radially-outward-most point on each extension 508 to a center point of assembly body 504 may be less than or equal to a second linear distance from a radially- outward-most point within a corresponding channel 514 to a center point of recess 512. In some examples, extension(s) 508 may be uniform and channel(s) 514 may be uniform,e.g., such that each of extension(s) 508 may enter any of channel(s) 514. In some examples, extension(s) 508 may be nonuniform, channel(s) 514 may be nonuniform, and / or the spacing between extension(s) 508 and / or between channel(s) 514 are nonuniform, e.g., to permit entry of electrode assembly 502 into recess 510 only when electrode assembly 502 is in one or more specific orientations relative to recess 510. For example, electrode assembly 502 may only enter recess 510 in a specific orientation, e.g., to control the orientation of first electrode 112 relative to one or more other features (e.g., ramp 212, second electrode 114) when electrode assembly 502 is secured within recess 510.

[0088] The manufacturing assembly may insert electrode assembly 502 into recess 512 until electrode assembly 502 reaches a proximal-most position within recess 512. Extension(s) 508 may travel in a direction parallel to longitudinal axis 210 within channel(s) 514 to facilitate travel of electrode assembly 502 within recess 512. When electrode assembly 502 is at the proximal most position, electrode assembly 502 may at least partially compress a compressible element on one or more of extension(s) 508 and / or within recess 512, which may permit access to one or more undercuts within recess 512 from one or more of extensions 508. The manufacturing assembly may rotate electrode assembly 502 about longitudinal axis 210 to transition extension(s) 508 from channel(s) 514 into the undercuts. When extension(s) 508 are in the undercut(s), the sidewalls of the undercut(s) may interface with surfaces on extension(s) 508 to inhibit movement of extension(s) 508 along a direction parallel to longitudinal axis 210.

[0089] When the manufacturing assembly releases electrode assembly 502, the compressible element may at least partially expand. The expansion of the compressible element may apply a compressive force on extension(s) 508 to inhibit rotation of electrode assembly 502 within recess 510. Thus, the applied forces on extension(s) 508 and on assembly body 504 inhibits unintentional movement and / or rotation of electrode assembly 502 within recess 510, thereby securing electrode assembly 502 to housing 202. A reverse procedure may be applied to remove electrode assembly 502 from within recess 510.

[0090] FIG. 6A is a perspective diagram illustrating a side view of an example of electrode assembly 502 of FIG. 5. FIG. 6B is a perspective diagram illustrating a top view of example electrode assembly 502 of FIG. 6A. As illustrated in FIGS. 6A, and 6B, assembly body 504 of electrode assembly 502 may include a base section 604, aprotrusion 602 extending distally from base section 604, and one or more extensions 508 extending radially away from base section 604.

[0091] Protrusion 602 may extend distally from base section 604 and along longitudinal axis 210. First electrode 112 may be affixed around an outer perimeter of protrusion 602. In some examples, first electrode 112 is electrically coupled to feedthrough interface in base section 604 (not pictured) via an electrically conductive portion of base section 604 and / or of protrusion 602. Protrusion 602 may define tool interface 506 radially inwards of first electrode 112. Tool interface 506 may include a cavity 605 within protrusion 602, e.g., as illustrated in FIG. 6B which receives a distal end of an installation tool. The installation tool may interface with tool interface 506 (e.g., may interface with sidewalls of protrusion 602 defining cavity 605, may interface with the sidewalls of column 606 within cavity 605) to transmit linear and / or rotary forces from a manufacturing assembly to electrode assembly 502. In some examples, as illustrated in FIG. 6B, cavity 605 defines a rectangular shape and column 606 within cavity 605 defines a cylindrical shape. In some examples, one or more of cavity 605 or column 606 may define a cylindrical, triangular, rectangular, quadrilateral, pentagonal, hexagonal, octagonal, cross, or any other polygonal shape. Cavity 605 may extend from a distal end of protrusion 602 towards base section 604 (e.g., up to base section 604). In some examples, depending on the shape of the distal end of the installation tool, column 606 is not present within cavity 605.

[0092] Assembly body 502 may include one or more extensions 508 extending radially away from base section 604. Assembly body 502 may include one, two, three, or four more extensions 508 arranged around the outer perimeter of base section 604. Extension(s) 508 may be equally distributed or unequally distributed around the outer perimeter of base section 604. Extension(s) 508 may be unequally distributed to restrict electrode assembly 502 to being able to be inserted into recess 512 of housing 202 only in specific orientations. Each extension 508 may define a thickness less than, equals to, or greater than a thickness of base section 604. Extension(s) 508 may define uniform or different shapes and / or dimensions. Extension(s) 508 may define an oval, circular, semicircular, rectangular, triangular, or other shape. In some examples, extension(s) 508 may include a compressible element (e.g., a compressible material, a compressible spring) disposed on one or more surfaces of extension(s) 508. In such examples, the compressibleelement may be at least partially compressed to reduce a thickness of each of extension(s) 508, e.g., which may facilitate the insertion of extension(s) 508 into the undercut(s) of recess 510.

[0093] Base section 604 may include a feedthrough interface disposed on a proximal surface of base section 604. The feedthrough interface may be configured to receive a distal end of a feedthrough assembly disposed within recess 510 to electrically couple first electrode 112 to one or more components within housing 202 (e.g., to switch circuitry 302, to sensing circuitry 304, to signal generation circuitry 306).

[0094] FIG. 7A is a perspective diagram illustrating a side view of a distal portion of an example of elongated housing 202 of FIG. 5. FIG. 7B is a cross-sectional diagram illustrating a cross-section view of the distal portion 510 of the elongated housing 202 of FIG. 7A, the cross-section being taken parallel to longitudinal axis 210 of elongated housing 202 and along line A-A of FIG. 7A. FIG. 7C is a cross-sectional diagram illustrating a cross-section view of the distal portion 510 of the elongated housing 202 of FIG. 7A, the cross-section being taken along a reference plane orthogonal to longitudinal axis 210 of elongated housing 202 and along line B-B of FIG. 7A. FIG. 7D is a cross- sectional diagram illustrating a cross-section view of distal portion 510 of elongated housing 202 of FIG. 7 A, the cross-section being taken along a reference plane orthogonal to longitudinal axis 210 of elongated housing 202 and along line C-C of FIG. 7A. While FIGS. 7A-7D are primarily described herein with respect to device 104 as illustrated in FIGS. 2A and 5, the example structure of distal portion 510 described herein may be included in any other examples of device 104 and / or of housing 202 described herein.

[0095] As illustrated in FIGS. 7A and 7B, recess 512 extends in a direction parallel to longitudinal axis 210 from face 205 towards a proximal end of header 510. Recess 512 may include one or more channels 514 extending from face 205 towards the proximal end of header 510. Channel(s) 514 may extend in the same direction as recess 512 and may extend for less than, more than, or the same linear distance as recess 512. For example, as illustrated in FIGS. 7A and 7B, a proximal end of recess 512 may be flush as the proximal ends of channel (s) 514.

[0096] Each channel 514 may be connected to a corresponding undercut 702. Each undercut 702 may be radially and circumferentially overlapping with a more distal portion of header 510, e.g., such that the more distal portion of header 510 inhibit direct access toundercut 702 along a direction parallel to longitudinal axis 210. Each undercut 702 may be sized to retain a corresponding extension 508 on electrode assembly 502. For example, each undercut 702 may define a length, width, and height greater than equal to a length, width, and thickness of a corresponding extension 508, respectively. Each channel 514 may be connected to the corresponding undercut 702 via an entrance 703. Entrance 703 may be disposed at or around a proximal end of channel 514.

[0097] Recess 512 may include a compressible element 704 disposed at a proximal end of recess 512 (e.g., along a proximal surface of recess 512). Compressible element 704 may be configured to compress in response to receiving a compressive force along a direction parallel to longitudinal axis 210. Compressible element 704 may be a single continuous element or multiple discrete elements. Compressible element 704 may be formed by one or more materials including, but is not limited to, silicon. In some examples, compressible element 704 includes a compressible spring. Compressible element 704 may be electrically insulated and / or coated with an electrically insulated material, e.g., to inhibit unintended transmission of an electric current through compressible element 704.

[0098] Compressible element 704 may be at least partially disposed within channel(s) 514, entrance(s) 703, and / or undercut(s) 702. When uncompressed, compressible element 704 may restrict access to undercuts 702. For example, compressible element 704, when uncompressed, may reduce a height of each of entrance(s) 703, as measured along a direction parallel to longitudinal axis 210, to less than a height a corresponding extension 508 of electrode assembly 502. In such examples, compressible element 704 may, when uncompressed, inhibit movement of each extension 508 from a corresponding channel 514 into a corresponding undercut 702 through the corresponding entrance 703. In such examples, compressible element 704 may also, when uncompressed, inhibit movement of each extension 508 from within the corresponding undercut 702 into the corresponding channel 514 through the corresponding entrance 703. When compressible element 704 is at least partially compressed (e.g., by electrode assembly 502), compressible element 704 may un-restrict entrance(s) 703, thereby allowing each extension 508 to transition between the corresponding channel 514 and the corresponding undercut 702 through the corresponding entrance 703.

[0099] While FIGS. 7A and 7B illustrate compressible element 704 as being disposed within recess 512, in some examples, one or more compressible elements may be disposed on extension(s) 508 of electrode assembly 502 (e.g., on each extension 508 of electrode assembly 502). The one or more compressible elements may, when uncompressed, increase a thickness of extension(s) 508 such that the thickness of one or more extension(s) 508 is greater than the height of one or more corresponding entrance(s) 703. In such examples, the increased thickness of extension(s) 508 inhibit travel of extension(s) 508 between channel(s) 514 and undercut(s) 702 through entrance(s) 703. The one or more compressible elements may be at least partially compressed (e.g., in response to a compressive force applied by the manufacturing assembly on electrode assembly 502) to reduce the thickness of extension(s) 708 to less than or equal to the heights of corresponding entrance(s) 703, thereby allowing for the travel of extension(s) 508 between channel(s) 514 and undercut(s) 702 through entrance(s) 703.

[0100] As illustrated in FIG. 7B, a feedthrough assembly 708 may extend from within an inner volume of housing 202 into header 210 and into recess 512. When electrode assembly 502 is secured within recess 512, feedthrough assembly 708 may contact a feedthrough interface on electrode assembly 502, e.g., to electrically couple first electrode 112 to one or more components within housing 202.

[0101] At one or more positions along longitudinal axis 210 between face 205 and a proximal end of recess 512, portion(s) of header 510 radially and circumferentially overlaps with and radially and circumferentially occludes undercut(s) 702. In such examples, when extension(s) 508 are disposed within undercut(s) 702, the portion(s) of header 510 radially and circumferentially occluding undercut(s) 702 inhibit movement of extension(s) 508 from within undercut(s) 702 along a direction parallel to longitudinal axis 210. In such examples, when extension(s) 508 are disposed within undercut(s) 702, header 510 interfaces with extension(s) 508 to inhibit unintended movement of electrode assembly 502 out of recess 512.

[0102] As illustrated in FIGS. 7B and 7D, channel(s) 514 may be connected to corresponding undercut(s) 702 via entrance(s) 703. When extension(s) 508 are disposed within channel(s) 514 and positioned at or around proximal end(s) of channel(s) 514, the manufacturing assembly may apply a force along a direction parallel to longitudinal axis 210 to at least partially compress compressible element 704 and allow access fromchannel(s) 514 to undercut(s) 702. The manufacturing assembly may subsequently apply a rotary force about longitudinal axis 210 to rotate extension(s) 508 from channel(s) 514 into undercut(s) 702. When the manufacturing assembly releases electrode assembly 502 (e.g., when extension(s) 508 are disposed within undercut(s) 702), compressible element 704 may expand to an uncompressed configuration, thereby securing extension(s) 508 within undercut(s) 702.

[0103] FIG. 8 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 IMD of any of FIGS. 1-7D. The technique of FIG. 8 will be described with concurrent reference to device 104 as illustrated in FIG. 2 A, 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.

[0104] A clinician may insert device 104 within a single first chamber of the heart 102 (802). 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 (804). 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.

[0105] 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 (806). The clinician may advance device 104 into the wall tissue until the wall tissue contacts ramp 212 and / or face 205 of housing 202. In some examples, when second electrode is disposed on ramp 212, ramp 212 may extend second electrode 114 distally from face 205 (e.g., from distal end 204) and along longitudinal axis 210 by distance 226. Ramp 212 may cause second electrode 114 to be placed relatively deeper within wall tissue than face 205 without penetrating the wall tissue, thereby allowing the wall tissue to at least partially envelop a distal surface and / or sides of second electrode114. In some examples, ramp 212 causes second electrode 114 to maintain contact with the wall tissue of the first chamber (e.g., atrial endocardium 404 of the patient). Ramp 212 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.

[0106] While device 104 is implanted within the cardiac tissue, the one or more antirotation features defined 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 ramp 212 maintaining contact with the wall tissue of the first chamber. 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.

[0107] 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 (808). 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).

[0108] FIG. 9 is a flow diagram illustrating an example process for assembling an example device 104 of any of FIGS. 1-7D. The technique of FIG. 9 will be described with concurrent reference to device 104 as illustrated in FIGS. 5-7D, 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 described herein. In some examples, the example process described below with respect to FIG. 9 may be performed in reverse to remove electrode assembly 502 from within housing 202 of device 104.

[0109] A manufacturing assembly may insert a tool (e.g., an installation tool) into tool interface 506 of electrode assembly 502 (902). Tool interface 506 may be defined by a protrusion 602 of assembly body 504 of electrode assembly 502. Tool interface 506 maydefine a cavity 605 sized and shaped to receive and interface with a distal end of the tool. Tool interface 506 may define a column 606 extending parallel to a longitudinal axis of electrode assembly 502 within cavity 605. The sidewalls of tool interface 506 defining cavity 605 and / or column 606 may interface with corresponding surfaces on the distal end of the tool to receive forces from the tool. For example, once the distal end of the tool is retained within tool interface 506, electrode assembly 502 may be advanced in a specific direction (e.g., along longitudinal axis 210) in response to application of a linear force on the tool (e.g., on a proximal end of the tool) and / or may be rotated about a specific axis (e.g., about longitudinal axis 210) in response to the application of a rotary force or torque on the tool. The tool may apply any forces directly to assembly body 504 of electrode assembly 502, e.g., without applying any forces on or otherwise contacting first electrode 112 of electrode assembly 502.

[0110] The manufacturing assembly may insert electrode assembly 502 into recess 512 of elongated housing 202 via the tool (904). Recess 512 may include one or more channels 514 disposed on the inner surface of recess 512 and extending away from the longitudinal axis of housing 202. The manufacturing assembly may, via the tool, align electrode assembly 502 relative to recess 512 of housing 202, e.g., such that electrode assembly 502 is radially and circumferentially aligned with recess 512 (e.g., the longitudinal axis of electrode assembly 502 is aligned with the longitudinal axis of housing 202 to define longitudinal axis 210). In such examples, the manufacturing assembly may radially and circumferentially align extension(s) 508 on assembly body 504 of electrode assembly 502 with channel(s) 514 in recess 512.[oni] In some examples, where all extensions 508 are uniform and all channels 514 are uniform, the manufacturing assembly aligns each extension 508 with any of channels 514. In some examples, where extensions 508 are non-uniform and / or where channels 514 are non-uniform, the manufacturing assembly may align each extension 508 to a corresponding channel 514 (e.g., a channel 514 sized and shaped to fully retain extension 508 when the longitudinal axis of electrode assembly 502 is aligned with the longitudinal axis of housing 202 to define longitudinal axis 210).

[0112] Once the manufacturing assembly aligns electrode assembly 502 with recess 512, the manufacturing assembly may apply a linear force along a direction parallel to longitudinal axis 210 and towards proximal end 206 of device 102 to insert electrodeassembly 502 into recess 512. As electrode assembly 502 enter recess 512, each extension 508 on assembly body 504 enters and travels within a corresponding channel 514, e.g., to facilitate the travel of electrode assembly 502 within recess 512. The manufacturing assembly may contain to advance electrode assembly 502 within recess 512 until electrode assembly 502 reaches an end of travel within recess 512 (e.g., until base section 604 of electrode assembly 502 contacts a proximal end of recess 512, until base section 604 contacts and / or compresses compressible element 704 within recess 512).

[0113] The manufacturing assembly may rotate electrode assembly 502 within recess 512 of elongated housing 202 via the tool (906). The manufacturing assembly may apply a linear force along a direction parallel to longitudinal axis 210 and towards proximal end 206 to assembly body 504 of electrode assembly cause assembly body 504 to compress one or more compressible elements. The compressible elements may be disposed on a surface of one or more of extension(s) 508 and / or within recess 512 (e.g., as compressible element 704). In response to the applied force on assembly body 504, the compressible elements may at least partially compress, thereby decreasing a thickness of the compressible elements. The decreased thickness of the compressible elements may reduce an overall thickness of the one or more extensions 508 and / or increase a height of one or more entrances 703 connecting channel(s) 514 to undercut(s) 702. The decreased thickness of extension(s) 508 and / or increased height of entrance(s) 703 may allow for access from channel(s) 514 into corresponding undercut(s) 702 by extension(s) 508, e.g., as the compression of the compressible elements causes the thickness of extension(s) 508 to be less than or equal to the height of undercut(s) 702.

[0114] The manufacturing assembly may apply a rotary force or torque on electrode assembly 502 to cause electrode assembly 502 to rotate about longitudinal axis 210. Rotation of electrode assembly 502 about longitudinal axis 210 may cause extension(s) 508 to rotate from within channel(s) 514 into undercut(s) 702 through the connecting entrance(s) 703. The manufacturing assembly may apply the rotary force while applying the linear force on electrode assembly 502 to keep the compressible elements at least partially compressed while electrode assembly 502 is rotated within recess 512.

[0115] The applied rotary force or torque maybe in a same direction as a direction of winding of first electrode 112. For example, first electrode 112 may be wound in a counterclockwise direction and the manufacturing assembly may apply the torque to rotateelectrode assembly in the counterclockwise direction to cause extension(s) 508 to enter undercut(s) 702. In some examples, the applied rotary force or torque may be in an opposite direction as a direction of winding of first electrode 112. . For example, first electrode 112 may be wound in a counterclockwise direction and the manufacturing assembly may apply the torque to rotate electrode assembly in a clockwise direction to cause extension(s) 508 to enter undercut(s) 702.

[0116] Once extension(s) 508 are disposed within undercut(s) 702, the sidewalls defining undercut(s) 702 may interface with surfaces of extension(s) 708 (e.g., with distal surfaces of extension(s) 708) to inhibit travel of electrode assembly 502 relative to housing 202 along longitudinal axis 210. When extension(s) 708 are within channel(s) 514, electrode assembly 502 may be referred to as being in an “unlocked configuration” relative to housing 202. When extension(s) 708 are within undercut(s) 702 and not within channel(s) 514, electrode assembly 502 may be referred to as being in a “locked configuration.” Electrode assembly 502 may transition from the unlocked orientation to the locked orientation in response to receiving, from the tool, a rotary force or torque in a first direction. Electrode assembly 502 may transition from the locked orientation to the unlocked orientation in response to receiving, from the tool, a rotary force or torque in a second direction opposite the first direction.

[0117] The manufacturing assembly may release the tool from tool interface 506 of electrode assembly 502 (908). The manufacturing assembly may secure the tool to tool interface 506 via one or more locking elements (e.g., locking surfaces, locking extensions, locking pins, locking protrusions, locking bearings, or the like). The one or more locking elements may interface with one or more elements of tool interface 506 (e.g., with column 606) to secure electrode assembly 502 to the tool. The manufacturing assembly may manipulate the tool to cause the one or more locking elements of the tool to be released from the one or more elements of tool interface 506. In some examples, the manufacturing assembly may retract the tool away from electrode assembly 502 to release the tool from tool interface 506.

[0118] Once the tool is released from tool interface 506 of electrode assembly 502, the manufacturing assembly ceases the transmission of any forces to electrode assembly 502. In some examples, the manufacturing assembly ceases the transmission of forces to electrode assembly 502 prior to release of the tool from tool interface 506. In response tothe termination of the application of forces on electrode assembly 502, the compressible elements may at least partially expand towards the corresponding uncompressed configurations. For example, compressible element 704 may at least partially expand along longitudinal axis 210 and towards a distal end 204 of device 104. The expansion of the compressible elements may apply a compressive force on extension(s) 708 of electrode assembly 502, which may inhibit rotation of extension(s) 708 within undercut(s) 702 (e.g., towards channel(s) 514). The inhibition of rotation of extension(s) 708 may inhibit unintended rotation of electrode assembly 502 within recess 512 (e.g., from the locked orientation towards the unlocked orientation). In conjunction, the sidewalls of undercut(s) 702 and the compressible elements may inhibit movement of electrode assembly 502 in any combination of up to all six degrees of movement within recess 512.

[0119] 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.

[0120] 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).

[0121] 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 otheranimals may undergo clinical or research therapies that may benefit from the subject matter of this disclosure.

[0122] 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.

[0123] This disclosure describes each of the following examples.

[0124] 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, wherein the elongated housing defines a recess extending from the distal end towards the proximal end; and an electrode assembly comprising an electrode, the electrode comprising: an elongated body defining a helix, wherein a proximal end of the electrode assembly is configured to be retained within the recess of the elongated housing to secure the electrode to the elongated housing, and wherein when the electrode is secured to the elongated housing, the electrode extends distally past the distal end of the elongated housing.

[0125] Example 2: the device of example 1, wherein the electrode comprises a first electrode, and wherein the device comprises a second electrode disposed on the distal end of the housing, wherein the second electrode is configured to contact the wall tissue of the chamber without penetrating the wall tissue when the device is implanted within the chamber.

[0126] Example 3: the device of example 2, wherein the second electrode comprises one or more of: a button electrode; or a wire electrode.

[0127] Example 4: the device of any of examples 1-3, wherein the electrode assembly comprises: an assembly body affixed to a proximal end of the electrode, and one or more tabs extending radially away from an outer perimeter of the assembly body, wherein the recess comprises one or more channels extending from the distal end of the elongated housing, and wherein each tab of the one or more tabs is configured to interface with acorresponding channel of the one or more channels to facilitate travel of the electrode assembly into the recess.

[0128] Example 5: the device of example 4, wherein the assembly body comprises a bushing.

[0129] Example 6: the device of any of examples 4 or 5, wherein when the electrode assembly is disposed within the recess, the electrode assembly is configured to rotate about the longitudinal axis to transition between a locked configuration and an unlocked configuration, wherein when the electrode assembly is in the locked configuration, each tab of the one or more tabs is circumferentially offset from the corresponding channel of the one or more channels, and wherein when the electrode assembly is in the unlocked configuration, each tab of the one or more tabs is circumferentially overlapping with the corresponding channel of the one or more channels.

[0130] Example 7: the device of any of examples 4-6, wherein the elongated housing comprises: a compressible element disposed at a proximal end of the recess, wherein the recess comprises: one or more undercuts, each undercut of the one or more undercuts being connected to a corresponding channel of the one or more channels and sized to retain a corresponding tab of the one or more tabs, wherein the compressible element is configured to be compressed along the longitudinal axis to allow access from each channel of the one or more channels into a corresponding undercut of the one or more undercuts.

[0131] Example 8: the device of example 7, wherein the electrode assembly is configured to: in response to receiving a force acting proximally along the longitudinal axis, enter the recess and compress the compressible element; in response to receiving a torque about the longitudinal axis, rotate within the recess such that the one or more tabs transition from within the one or more channels into the one or more undercuts, and wherein when the one or more tabs of the electrode assembly are disposed within the one or more undercuts and the electrode assembly ceases to receive the force and the torque, the compressible element and the elongated housing apply a compressible force on the one or more tabs of the electrode assembly to inhibit unintended movement of the electrode assembly relative to the elongated housing.

[0132] Example 9: the device of any of examples 7 or 8, wherein the compressible element comprises one or more of: a compressible spacer; or a spring.

[0133] Example 10: the device of any of examples 7-9, wherein the compressible element is at least partially disposed within the one or more channels.

[0134] Example 11 : the device of any of examples 4-6, wherein each tab of the one or more tabs comprises a compressible element disposed along a surface of the tab, wherein the recess comprises: one or more undercuts, each undercut of the one or more undercuts being connected to a corresponding channel of the one or more channels and sized to retain a corresponding tab of the one or more tabs, wherein the compressible element is configured to be compressed along the longitudinal axis to allow entry of each tab of the one or more tabs from the corresponding channel into a corresponding undercut of the one or more undercuts.

[0135] Example 12: the device of any of examples 4-11, wherein the assembly body is configured to interface with a tool disposed radially inwards of the electrode, and wherein the electrode assembly is configured to enter and interface with the recess of the elongated housing to affix the electrode assembly to the elongated housing in response to receiving a force from the tool.

[0136] Example 13: the device of any of examples 4-12, wherein the recess is sized to fully retain the assembly body.

[0137] Example 14: the device of any of examples 1-13, further comprising: a feedthrough assembly extending distally from a proximal end of the recess towards the distal end of the elongated housing, wherein the feedthrough assembly is configured to electrically interface with the electrode assembly to electrically couple the electrode to one or more computing components disposed within the elongated housing.

[0138] Example 15: the device of any of examples 1-14, further comprising a ramp extending distally from the distal end of the elongated housing, wherein the ramp is configured to, without penetration of wall tissue of the chamber, inhibit unintended rotation of the elongated body within the wall tissue.

[0139] Example 16: the device of any of examples 1-15, further comprising a therapeutic substance dispensing device disposed on the distal end.

[0140] Example 17: the device of example 16, wherein the therapeutic substance dispensing device comprises a monolithic controlled release device.

[0141] Example 18: the device of any of examples 1-17, wherein the chamber of the heart comprises a first chamber of the heart, and wherein the helix is configured topenetrate into wall tissue of a second chamber of the heart that is separated from the first chamber of the heart.

[0142] Example 19: the device of any of examples 1-18, wherein the distal end of the elongated housing further comprises one or more features configured to inhibit unintended rotation of the elongated body with the wall tissue of the second chamber.

[0143] Example 20: a method comprising: delivering cardiac pacing from a device to a heart, 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 chamber of a heart, wherein the elongated housing defines a recess extending from the distal end towards the proximal end; and an electrode assembly comprising an electrode, the electrode comprising: an elongated body defining a helix, wherein a proximal end of the electrode assembly is configured to be retained within the recess of the elongated housing to secure the electrode to the elongated housing, and wherein when the electrode is secured to the elongated housing, the electrode extends distally past the distal end of the elongated housing.

[0144] Example 21 : the method of example 20, wherein the electrode comprises a first electrode, wherein the chamber of the heart comprises a first chamber of the heart, wherein the device comprises a second electrode disposed on the distal end of the housing, wherein the second electrode is configured to contact the wall tissue of the first chamber without penetrating the wall tissue when the device is implanted within the first chamber, and wherein delivering the cardiac pacing comprises: delivering cardiac pacing to a second chamber of the heart via the first electrode; and delivering cardiac pacing to the first chamber of the heart via the second electrode.

[0145] Example 22: the method of example 21, wherein the first chamber of the heart comprises an atrium of the heart, and wherein the second chamber of the heart comprises a ventricle of the heart.

[0146] Example 23: the method of any of examples 20-22, wherein the electrode assembly comprises: an assembly body affixed to a proximal end of the electrode, and one or more tabs extending radially away from an outer perimeter of the assembly body, wherein the recess comprises one or more channels extending from the distal end of the elongated housing, and wherein each tab of the one or more tabs is configured to interfacewith a corresponding channel of the one or more channels to facilitate travel of the electrode assembly into the recess.

[0147] Example 24: the method of example 23, wherein the assembly body comprises a bushing.

[0148] Example 25: the method of any of examples 23 or 24, wherein when the electrode assembly is disposed within the recess, the electrode assembly is configured to rotate about the longitudinal axis to transition between a locked configuration and an unlocked configuration, wherein when the electrode assembly is in the locked configuration, each tab of the one or more tabs is circumferentially offset from the corresponding channel of the one or more channels, and wherein when the electrode assembly is in the unlocked configuration, each tab of the one or more tabs is circumferentially overlapping with the corresponding channel of the one or more channels.

[0149] Example 26: the method of any of examples 23-25, wherein the elongated housing comprises: a compressible element disposed at a proximal end of the recess, wherein the recess comprises: one or more undercuts, each undercut of the one or more undercuts being connected to a corresponding channel of the one or more channels and sized to retain a corresponding tab of the one or more tabs, wherein the compressible element is configured to be compressed along the longitudinal axis to allow access from each channel of the one or more channels into a corresponding undercut of the one or more undercuts.

[0150] Example 27: the method of example 26, wherein the compressible element comprises one or more of: a compressible spacer; or a spring.

[0151] Example 28: the method of any of examples 26 or 27, wherein the compressible element is at least partially disposed within the one or more channels.

[0152] Example 29: the method of any of examples 23-28, wherein each tab of the one or more tabs comprises a compressible element disposed along a surface of the tab, wherein the recess comprises: one or more undercuts, each undercut of the one or more undercuts being connected to a corresponding channel of the one or more channels and sized to retain a corresponding tab of the one or more tabs, wherein the compressible element is configured to be compressed along the longitudinal axis to allow entry of each tab of the one or more tabs from the corresponding channel into a corresponding undercut of the one or more undercuts.

[0153] Example 30: the method of any of examples 23-29, wherein the assembly body is configured to interface with a tool disposed radially inwards of the electrode, and wherein the electrode assembly is configured to enter and interface with the recess of the elongated housing to affix the electrode assembly to the elongated housing in response to receiving a force from the tool.

[0154] Example 31 : the method of any of examples 23-30, wherein the recess is sized to fully retain the assembly body.

[0155] Example 32: the method of any of examples 21-31, further comprising: a feedthrough assembly extending distally from a proximal end of the recess towards the distal end of the elongated housing, wherein the feedthrough assembly is configured to electrically interface with the electrode assembly to electrically couple the electrode to one or more computing components disposed within the elongated housing.

[0156] Example 33: the method of any of examples 20-32, further comprising a ramp extending distally from the distal end of the elongated housing, wherein the ramp is configured to, without penetration of wall tissue of the chamber, inhibit unintended rotation of the elongated body within the wall tissue.

[0157] Example 34: the method of any of examples 20-33, further comprising a therapeutic substance dispensing device disposed on the distal end.

[0158] Example 35: the method of example 34, wherein the therapeutic substance dispensing device comprises a monolithic controlled release device.

[0159] Example 36: a method comprising attaching a tool to an assembly body of an electrode assembly of a device, wherein the electrode assembly comprises: the assembly body; and an electrode connected to the assembly body, the electrode comprising an elongated body defining a helix, and wherein the device further 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 chamber of a heart; inserting, via the tool, the electrode assembly along a longitudinal axis and into a recess of an elongated housing of the device; rotating, via the tool, the electrode assembly about the longitudinal axis to secure the electrode assembly within the recess; and releasing the tool from the bushing of the electrode assembly to cause the recess to interface with the electrode assembly to inhibit unintended movement of the electrode assembly relative to the elongated housing.

[0160] Example 37: the method of example 36, wherein the assembly body comprises a bushing.

[0161] Example 38: the method of any of examples 36 or 37, wherein the electrode assembly comprises one or more tabs extending radially away from an outer perimeter of the assembly body, wherein the recess comprises one or more channels extending from the distal end of the elongated housing, wherein inserting the electrode assembly into the recess comprises: inserting, via the tool, the electrode assembly into the recess by inserting the one or more tabs of the electrode assembly into the one or more channels of the recess.

[0162] Example 39: the method of example 38, wherein the elongated housing comprises a compressible element disposed at a proximal end of the recess, wherein the recess comprises one or more undercuts, each undercut of the one or more undercuts being connected to a corresponding channel of the one or more channels and sized to retain a corresponding tab of the one or more tabs of the electrode assembly, wherein inserting the electrode assembly into the recess comprises: applying, by the tool and via the electrode assembly, a force on the compressible element to at least partially compress the compressible element, wherein when the compressible element is at least partially compressed, the compressible element is configured to allow access to the one or more undercuts from the one or more channels, and wherein rotating the electrode assembly about the longitudinal axis to secure the electrode assembly within the recess comprises: rotating, by the tool, the electrode assembly about the longitudinal axis to rotate the one or more tabs from the one or more channels into the one or more undercuts.

[0163] Example 40: the method of example 39, wherein releasing the tool from the bushing of the electrode assembly to cause the recess to interface with the electrode assembly to inhibit unintended movement of the electrode assembly relative to the elongated housing comprises: releasing the tool from the bushing of the electrode assembly when the one or more tabs are disposed within the one or more undercuts, wherein when the tool is released from the bushing of the electrode assembly, the compressible element and the elongated housing are configured to apply a compressive force on the one or more tabs to affix the electrode assembly to the elongated housing.

[0164] Example 41 : the method of any of examples 39 or 40, wherein the compressible element comprises one or more of: a compressible spacer; or a spring.

[0165] Example 42: the method of any of examples 39-41, wherein the compressible element is at least partially disposed within the one or more channels.

[0166] Example 43: the method of any of examples 36-42, wherein the assembly body defines a tool interface disposed radially inwards of the first electrode.

[0167] Example 44: the method of any of examples 36-43, further comprising: electrically coupling the electrode to a feedthrough assembly disposed within the recess of the elongated housing to couple the electrode to one or more computing components disposed within the elongated housing.

[0168] Example 45: the method of any of examples 36-44, further comprising a ramp extending distally from the distal end of the elongated housing, wherein the ramp is configured to, without penetration of wall tissue of the chamber, inhibit unintended rotation of the elongated body within the wall tissue.

[0169] Example 46: the method of any of examples 36-45, 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.

[0170] Example 47: the method of any of examples 36-46, wherein the distal end of the elongated housing further comprises one or more features configured to inhibit unintended rotation of the elongated body with the wall tissue of the second chamber.

[0171] Example 48: 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, wherein the elongated housing defines a recess extending from the distal end towards the proximal end; and a fixation assembly comprising a fixation member, wherein a proximal end of the fixation assembly is configured to be retained within the recess of the elongated housing to secure the fixation member to the elongated housing, and wherein when the fixation member is secured to the elongated housing, the fixation member extends distally past the distal end of the elongated housing.

[0172] Example 49: the device of example 48, wherein the fixation member comprises one or more of: one or more tines, a fixation helix, or an electrode.

[0173] Example 50: the device of any of examples 48 or 49, wherein the device may be combined in any combination with the device described in any of examples 2-19.

[0174] Example 51 : a method comprising: delivering cardiac pacing from a device to a heart, 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 chamber of a heart, wherein the elongated housing defines a recess extending from the distal end towards the proximal end; and a fixation assembly comprising a fixation member, wherein a proximal end of the fixation assembly is configured to be retained within the recess of the elongated housing to secure the fixation member to the elongated housing, and wherein when the fixation member is secured to the elongated housing, the fixation member extends distally past the distal end of the elongated housing.

[0175] Example 52: the method of example 51, wherein the fixation member comprises one or more of: one or more tines, a fixation helix, or an electrode.

[0176] Example 53: the method of any of examples 51 or 52, wherein the device may be combined in any combination with the device described in any of examples 21-34.

[0177] Example 54: a method comprising: attaching a tool to an assembly body of an fixation assembly of a device, wherein the fixation assembly comprises: the assembly body; and a fixation member connected to the assembly body, and wherein the device further 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 chamber of a heart; inserting, via the tool, the fixation assembly along a longitudinal axis and into a recess of an elongated housing of the device; rotating, via the tool, the fixation assembly about the longitudinal axis to secure the fixation assembly within the recess, wherein when the fixation assembly is secured within the recess, the fixation member extends distally past the distal end of the elongated housing; and releasing the tool from the assembly body of the fixation assembly to cause the recess to interface with the electrode assembly to inhibit unintended movement of the electrode assembly relative to the elongated housing.

[0178] Example 55: the method of example 54, wherein the fixation member comprises one or more of: one or more tines, a fixation helix, or an electrode.

[0179] Example 56: the method of any of examples 54 or 55, wherein the device may be combined in any combination with the device described in any of examples 37-47.

[0180] 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, wherein the elongated housing defines a recess extending from the distal end towards the proximal end; and an electrode assembly comprising an electrode, the electrode comprising: an elongated body defining a helix, wherein a proximal end of the electrode assembly is configured to be retained within the recess of the elongated housing to secure the electrode to the elongated housing, and wherein when the electrode is secured to the elongated housing, the electrode extends distally past the distal end of the elongated housing.

2. The device of claim 1, wherein the electrode comprises a first electrode, and wherein the device comprises a second electrode disposed on the distal end of the housing, wherein the second electrode is configured to contact the wall tissue of the chamber without penetrating the wall tissue when the device is implanted within the chamber.

3. The device of claim 2, wherein the second electrode comprises one or more of: a button electrode; or a wire electrode.

4. The device of any of claims 1-3, wherein the electrode assembly comprises: an assembly body affixed to a proximal end of the electrode, and one or more tabs extending radially away from an outer perimeter of the assembly body, wherein the recess comprises one or more channels extending from the distal end of the elongated housing, and wherein each tab of the one or more tabs is configured to interface with a corresponding channel of the one or more channels to facilitate travel of the electrode assembly into the recess.

5. The device of claim 4, wherein when the electrode assembly is disposed within the recess, the electrode assembly is configured to rotate about the longitudinal axis to transition between a locked configuration and an unlocked configuration, wherein when the electrode assembly is in the locked configuration, each tab of the one or more tabs is circumferentially offset from the corresponding channel of the one or more channels, and wherein when the electrode assembly is in the unlocked configuration, each tab of the one or more tabs is circumferentially overlapping with the corresponding channel of the one or more channels.

6. The device of any of claims 4 or 5, wherein the elongated housing comprises: a compressible element disposed at a proximal end of the recess, wherein the recess comprises: one or more undercuts, each undercut of the one or more undercuts being connected to a corresponding channel of the one or more channels and sized to retain a corresponding tab of the one or more tabs, wherein the compressible element is configured to be compressed along the longitudinal axis to allow access from each channel of the one or more channels into a corresponding undercut of the one or more undercuts.

7. The device of claim 6, wherein the electrode assembly is configured to: in response to receiving a force acting proximally along the longitudinal axis, enter the recess and compress the compressible element; in response to receiving a torque about the longitudinal axis, rotate within the recess such that the one or more tabs transition from within the one or more channels into the one or more undercuts, and wherein when the one or more tabs of the electrode assembly are disposed within the one or more undercuts and the electrode assembly ceases to receive the force and the torque, the compressible element and the elongated housing apply a compressible force onthe one or more tabs of the electrode assembly to inhibit unintended movement of the electrode assembly relative to the elongated housing.

8. The device of any of claims 6 or 7, wherein the compressible element comprises one or more of: a compressible spacer; or a spring.

9. The device of any of claims 6-8, wherein the compressible element is at least partially disposed within the one or more channels.

10. The device of any of claims 4-9, wherein each tab of the one or more tabs comprises a compressible element disposed along a surface of the tab, wherein the recess comprises: one or more undercuts, each undercut of the one or more undercuts being connected to a corresponding channel of the one or more channels and sized to retain a corresponding tab of the one or more tabs, wherein the compressible element is configured to be compressed along the longitudinal axis to allow entry of each tab of the one or more tabs from the corresponding channel into a corresponding undercut of the one or more undercuts.

11. The device of any of claims 4-10, wherein the assembly body is configured to interface with a tool disposed radially inwards of the electrode, and wherein the electrode assembly is configured to enter and interface with the recess of the elongated housing to affix the electrode assembly to the elongated housing in response to receiving a force from the tool.

12. The device of any of claims 1-11, further comprising: a feedthrough assembly extending distally from a proximal end of the recess towards the distal end of the elongated housing,wherein the feedthrough assembly is configured to electrically interface with the electrode assembly to electrically couple the electrode to one or more computing components disposed within the elongated housing.

13. The device of any of claims 1-12, further comprising a ramp extending distally from the distal end of the elongated housing, wherein the ramp is configured to, without penetration of wall tissue of the chamber, inhibit unintended rotation of the elongated body within the wall tissue.

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 separated from the first chamber of the heart.

15. The device of any of claims 1-14, wherein the distal end of the elongated housing further comprises one or more features configured to inhibit unintended rotation of the elongated body with the wall tissue of the second chamber.

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