Patent Description:
Cardiac pacing by an artificial pacemaker provides an electrical stimulation of the heart when its own natural pacemaker and/or conduction system fails to provide synchronized atrial and ventricular contractions at rates and intervals sufficient for a patient's health. Such antibradycardial pacing provides relief from symptoms and even life support for hundreds of thousands of patients. Cardiac pacing may also provide electrical overdrive stimulation to suppress or convert tachyarrhythmias, again supplying relief from symptoms and preventing or terminating arrhythmias that could lead to sudden cardiac death.

Leadless cardiac pacemakers incorporate electronic circuitry at the pacing site and eliminate leads, thereby avoiding shortcomings associated with conventional cardiac pacing systems. Leadless cardiac pacemakers can be anchored at the pacing site, e.g., in a right ventricle and, for dual-chamber pacing, in a right atrium, by an anchor. A delivery system can be used to deliver the leadless cardiac pacemakers to the target anatomy.

Cardiac pacing of the His-bundle is clinically effective and advantageous by providing a narrow QRS affecting synchronous contraction of the ventricles. His-bundle pacing in or near a membranous septum of a heart, however, has some drawbacks. The procedure is often long in duration and requires significant fluoroscopic exposure. Furthermore, successful His-bundle pacing cannot always be achieved. Pacing thresholds are often high, sensing is challenging, and success rates can be low.

Pacing at the left bundle branch (LBB) is an alternative to His-bundle pacing. Pacing at the LBB involves pacing past the His-bundle toward the right ventricle apex. More particularly, a pacing site for LBB pacing is typically below the His-bundle, on the interventricular septal wall near the tricuspid valve and pulmonary artery outflow track.

<CIT> discloses a hinged anchor for a medical device electrode. The hinged anchor has a hinged portion and an anchor portion. The hinged portion can have a first configuration forming a first angle and a second configuration forming a second angle. The second angle can be a sharper angle than the first angle, and the hinged portion can be predisposed to assume the second configuration. The hinged anchor can be disposed on a control module of a leadless microstimulator device.

<CIT> discloses an intra-cardiac implantable medical device (IIMD) system including a housing and an intra-cardiac (IC) device extension. The housing may be configured to be implanted entirely within a local chamber of the heart. The housing includes a base configured to be secured to the local chamber. The IC device extension may include a proximal end, a distal end, and an extension body extending there between. The proximal end may be coupled to the housing and configured to be located in the local chamber. The extension body may include an IIMD-to-electrode (IE) orientation segment connected to a chamber transition segment that is sufficient in length to extend from the local chamber into an adjacent chamber. The IE orientation segment is configured to be lodged within the adjacent chamber in order to stabilize the system within heart.

<CIT> discloses an implantable pacemaker system including a housing having a proximal end and a distal end. A control electronics subassembly defines the housing proximal end, and a battery subassembly defines the housing distal end. A distal fixation member extends from the housing distal end for fixing the housing distal end at an implant site. A pacing extension extends from the housing proximal end and carries a pacing cathode electrode. The pacing extension extends the pacing cathode electrode to a pacing site that is spaced apart from the implant site when the pacemaker is deployed in a patient's body.

Existing leadless pacemakers may not fit, or may interfere with heart structures, when placed at the pacing site for left bundle branch (LBB) pacing. More particularly, existing leadless pacemakers having bodies that are long and rigid and, when implanted at the interventricular septal wall, could extend into contact with the cardiac tissue of a ventricular free wall or the tricuspid valve. The long and rigid body of existing leadless pacemakers could also become tangled within chordae tendinae. Furthermore, a proximal end of the existing leadless pacemakers may flail within the heart chamber as the heart beats, causing cyclical contact with adjacent heart structures. Such contact could interfere with heart function. Thus, there is a need for a leadless biostimulator that can be engaged to the interventricular septal wall to pace the LBB without interfering with adjacent structures of the heart.

The present invention is defined in the independent claim. Further embodiments of the invention are defined in the dependent claims.

A biostimulator is described. The biostimulator includes a pacing electrode and a housing. The pacing electrode includes a helical electrode. The housing has an electronics compartment containing pacing circuitry that is electrically connected to the pacing electrode to deliver pacing impulses through the pacing electrode to a target tissue. The pacing electrode and the housing have respective axes, e.g., a pacing electrode axis and a housing axis. The biostimulator includes an articulable extension extending between a distal end of the housing and the pacing electrode and includes an articulation to provide movement between the pacing electrode and the housing (or an anchor). The articulation can be between the pacing electrode and the housing (or between the pacing electrode and an anchor) such that when the pacing electrode is affixed to an interventricular septal wall and the housing (or the anchor) is located at a ventricular apex, the electrode axis and the housing axis (or an anchor axis) extend in different directions. Accordingly, the pacing electrode can engage target tissue on an upper portion of the interventricular septal wall while the housing can be directed toward the ventricular apex without interfering with adjacent structures of the heart. The biostimulator further comprises a strain relief between the distal end of the housing and the articulable extension. A stiffness of the strain relief decreases in a distal direction from the housing distal end.

The biostimulator may include an anchor. The anchor can be mounted on the housing, e.g., on an attachment feature of the housing. Alternatively, the anchor may be mounted on a tether that extends proximally from the housing. The anchor can include several flexible tines arranged about the anchor axis. As described above, the anchor can be located at the ventricular apex when the pacing electrode is engaged to the septal wall tissue. Accordingly, the anchor can engage heart structures near the ventricular apex to secure and stabilize the housing in the downward direction, out of the way of the heart wall opposite to the septal wall and/or the heart valve leaflets.

The articulation can be a portion of the biostimulator that deforms, deflects, rotates, etc. For example, the biostimulator may include a flexible extension interconnecting the housing to the pacing electrode, and the articulation may be a flexible portion of the extension, e.g., a segment of the flexible extension. Alternatively or additionally, the articulation may include a hinge that connects the housing to a header assembly having the pacing electrode, and the hinge may rotate to provide relative movement between the housing and the pacing electrode. The biostimulator may include a tether that, like the flexible extension, includes a flexible segment to provide the articulation and relative movement between the pacing electrode and the housing or anchor. Accordingly, the articulation may be integrated in the biostimulator to join and provide relative movement between biostimulator structures such as the pacing electrode and the housing.

A biostimulator system is described. In an embodiment, the biostimulator system includes a biostimulator transport system. The biostimulator can be mounted on the biostimulator transport system to carry the biostimulator to or from the target anatomy.

The above summary does not include an exhaustive list of all aspects of the present invention. It is contemplated that the invention includes all systems that can be practiced from all suitable combinations of the various aspects summarized above, as well as those disclosed in the Detailed Description below and particularly pointed out in the claims filed with the application. Such combinations have particular advantages not specifically recited in the above summary.

A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings.

Embodiments describe a biostimulator and a biostimulator system for septal pacing. The biostimulator may, however, be used in other applications, such as deep brain stimulation. Thus, reference to the biostimulator as being a cardiac pacemaker for septal pacing is not limiting.

In various embodiments, description is made with reference to the figures. However, certain embodiments may be practiced without one or more of these specific details, or in combination with other known methods and configurations. In the following description, numerous specific details are set forth, such as specific configurations, dimensions, and processes, in order to provide a thorough understanding of the embodiments. In other instances, well-known processes and manufacturing techniques have not been described in particular detail in order to not unnecessarily obscure the description. Reference throughout this specification to "one embodiment," "an embodiment," or the like, means that a particular feature, structure, configuration, or characteristic described is included in at least one embodiment. Thus, the appearance of the phrase "one embodiment," "an embodiment," or the like, in various places throughout this specification are not necessarily referring to the same embodiment. Furthermore, the particular features, structures, configurations, or characteristics may be combined in any suitable manner in one or more embodiments.

The use of relative terms throughout the description may denote a relative position or direction. For example, "distal" may indicate a first direction along a longitudinal axis of a biostimulator. Similarly, "proximal" may indicate a second direction opposite to the first direction. Such terms are provided to establish relative frames of reference, however, and are not intended to limit the use or orientation of a biostimulator to a specific configuration described in the various embodiments below.

In an aspect, a biostimulator includes an articulation to allow an electrode axis of a pacing electrode to be directed differently than a housing axis of a housing. For example, the pacing electrode can be a helical electrode that affixes to an interventricular septal wall and the electrode axis can extend normal to the septal wall, while the housing can be located in a ventricular apex and the housing axis can be normal to an apex wall. Accordingly, when the fixation element is anchored in a septal wall of a heart, the housing can be located in the ventricular apex without interfering with a heart valve or an outer heart wall opposite to the septal wall. The biostimulator therefore fits well within the limited space of the target heart chamber. A biostimulator system is described that can transport the biostimulator to or from a pacing site at the septal wall.

Referring to <FIG>, a diagrammatic cross section of a patient heart illustrating an example implantation of a biostimulator in a target anatomy is shown in accordance with an embodiment. A leadless biostimulator system, e.g., a cardiac pacing system, includes one or more biostimulators <NUM>. The biostimulators <NUM> can be implanted in a patient heart <NUM>, and can be leadless (and thus, may be leadless cardiac pacemakers). Each biostimulator <NUM> can be placed in a cardiac chamber, such as a right atrium and/or right ventricle of the heart <NUM>, or attached to an inside or outside of the cardiac chamber. For example, the biostimulator <NUM> can be attached to one or more of an interventricular septal wall <NUM> or a ventricular apex <NUM> of the heart <NUM>. More particularly, the biostimulator <NUM> can be delivered to the septum, and one or more elements, such as a pacing electrode <NUM>, can pierce the interventricular septal wall <NUM> of the septum to engage and anchor the biostimulator <NUM> to the tissue. Similarly, a housing <NUM> and/or an anchor <NUM> can be delivered into the ventricular apex <NUM>.

The pacing electrode <NUM> can have an electrode axis <NUM>, which is directed toward, e.g., normal to, the septal wall when the pacing electrode <NUM> is affixed to the septal wall. Similarly, the housing <NUM> can have a housing axis <NUM>, which is directed toward, e.g., oblique to, an apex wall of the ventricular apex <NUM> when the housing <NUM> is located therein. When the pacing electrode <NUM> is affixed to the interventricular septal wall <NUM>, and the housing <NUM> is located at the ventricular apex <NUM>, the electrode axis <NUM> can extend in a different direction than the housing axis <NUM>. For example, the electrode axis <NUM> can extend in a direction that is transverse or oblique to a direction of the housing axis <NUM>. Accordingly, the pacing electrode <NUM> can be located to effectively probe and pace the left bundle branch <NUM>, while the housing <NUM> can be placed in a safe and non-obstructive location within the heart chamber.

The non-coaxial relationship of the electrode axis <NUM> and the housing axis <NUM>, which allows for safe and non-obstructive placement of the pacing electrode <NUM> and the housing <NUM>, may be provided by an articulation <NUM> of the biostimulator <NUM>. The articulation <NUM> can be located between the pacing electrode <NUM> and the housing <NUM>. For example, as described below, the articulation <NUM> may be a flexible portion of the lead extension, a hinge, or any other mechanism that acts as a joint or juncture between a distal portion and a proximal portion of the biostimulator. More particularly, the articulation <NUM> may provide a movable joint between the portions to allow the biostimulator to articulate and conform to the target anatomy.

Leadless pacemakers or other leadless biostimulators <NUM> can be delivered to or retrieved from a patient using delivery or retrieval systems. The leadless biostimulator system can include delivery or retrieval systems, which may be catheter-based systems used to carry a leadless biostimulator <NUM> intravenously to or from a patient anatomy. The delivery or retrieval systems may be referred to collectively as transport systems, or biostimulator transport systems. Examples of transport systems are described below. In some implementations of biostimulator systems, a leadless pacemaker is attached, connected to, or otherwise mounted on a distal end of a catheter of the biostimulator transport system. The leadless pacemaker is thereby advanced intravenously into or out of the heart <NUM>. The transport system can include features to engage the leadless pacemaker to allow fixation of the leadless pacemaker to tissue. For example, in implementations where the leadless pacemaker includes an active engaging mechanism, such as a helical fixation element, the transport system can include a docking cap or key at a distal end of the catheter, and the docking cap or key may be configured to engage the leadless pacemaker and apply torque to screw the active engaging mechanism into or out of the tissue. In other implementations, the transport system includes clips designed to match the shape of a feature on the leadless pacemaker and apply torque to screw the active engaging mechanism into or out of the tissue.

When the biostimulator <NUM> is delivered to and screwed into the septum of the heart <NUM>, the pacing electrode <NUM> may be positioned for deep septal pacing at a target bundle branch <NUM> in the septum. For example, an active electrode of the pacing element can be positioned at the left bundle branch <NUM> in the septum. The biostimulator <NUM> may deliver pacing impulses through the pacing electrode <NUM> to the bundle branch(es).

Referring to <FIG>, a side view of a biostimulator having an articulable extension is shown in accordance with an embodiment. The biostimulator <NUM> can be a leadless cardiac pacemaker that can perform cardiac pacing and that has many of the advantages of conventional cardiac pacemakers while extending performance, functionality, and operating characteristics. In a particular embodiment, the biostimulator <NUM> can use two or more electrodes located on or within a housing <NUM> of the biostimulator <NUM> for pacing the cardiac chamber upon receiving a triggering signal from at least one other device within the body. The biostimulator <NUM> can have two or more electrodes, e.g., a portion of the pacing electrode <NUM> that acts as an active electrode and/or a portion of the housing <NUM> that acts as an active electrode. The electrodes can deliver pacing pulses to bundle branches <NUM> within the septum of the heart <NUM> to perform deep septal pacing, and optionally, can sense electrical activity from the muscle. The electrodes may also communicate bidirectionally with at least one other device within or outside the body.

In an embodiment, a leadless pacing system includes the biostimulator <NUM> having a flexible extended electrode. The flexible extended electrode includes the articulation <NUM>, which allows the pacing electrode <NUM> to be located at the pacing site at a location on the septal wall nearer to the heart valve than the housing <NUM> while the housing <NUM> is located at the ventricular apex <NUM> for maximum stability.

The biostimulator <NUM> includes the housing <NUM> having a longitudinal axis, e.g., the housing axis <NUM>. The housing <NUM> can contain a primary battery to provide power for pacing, sensing, and communication, which may include, for example, bidirectional communication. The housing <NUM> can optionally contain an electronics compartment <NUM> (shown by hidden lines) to hold circuitry adapted for different functionality. For example, the electronics compartment <NUM> can contain pacing circuitry for sensing cardiac activity from the electrodes, for receiving information from at least one other device via the electrodes, for generating pacing pulses for delivery to tissue via the pacing electrode <NUM>, or other circuitry. The electronics compartment <NUM> may contain circuits for transmitting information to at least one other device via the electrodes and can optionally contain circuits for monitoring device health. The circuitry of the biostimulator <NUM> can control these operations in a predetermined manner. In some implementations of a cardiac pacing system, cardiac pacing is provided without a pulse generator located in the pectoral region or abdomen, without an electrode-lead separate from the pulse generator, without a communication coil or antenna, and without an additional requirement of battery power for transmitted communication.

Leadless pacemakers or other leadless biostimulators <NUM> can be fixed to an intracardial implant site, e.g., at the septal wall, by one or more actively engaging mechanism or fixation mechanism. For example, the fixation mechanism can include a screw or helical member that screws into the myocardium. In an embodiment, the pacing electrode <NUM> includes the fixation element. The pacing element can be coupled to the housing <NUM> by an extension <NUM>. More particularly, the extension <NUM> extends between a housing distal end <NUM>, at a distal end of the housing <NUM>, and the pacing electrode <NUM>.

In an embodiment, the extension <NUM> includes a flexible portion <NUM>. The flexible portion <NUM> of the extension <NUM> can be the articulation <NUM> that allows for relative movement between the electrode axis <NUM> and the housing axis <NUM>. More particularly, the axes <NUM>, <NUM> may be coaxial in <FIG> when the flexible portion <NUM> is not bent, however, when the extension <NUM> is bent about the articulation <NUM> of the flexible portion <NUM> (<FIG>) the axes of the pacing electrode <NUM> and the housing <NUM> become non-coaxial.

The articulation <NUM> may be any feature along the biostimulator <NUM> that allows for relative angular movement between the pacing electrode <NUM> and the housing <NUM> (or the anchor <NUM>). As described below, the articulation <NUM> may include a mechanism, such as a hinge. In the case of a flexible portion of the biostimulator <NUM>, however, such as the extension <NUM> or a tether (<FIG>) the articulation can be a segment of material that deforms, deflects, or otherwise allows movement between a first boundary of the segment and a second boundary of the segment. For example, in the case of the flexible extension <NUM>, a polymer jacket may extend longitudinally over the extension length. The polymer jacket may be flexible in that strain input during delivery can cause the polymer jacket to bend. More particularly, forces applied to the polymer jacket can cause strain and deflection of the flexible extension <NUM>. A location of the deformation may be considered to be the articulation <NUM>. Accordingly, the extension <NUM> can have one or more articulations when it is bent at one or more locations.

The extension <NUM> may include a structure that provides good torque transfer. For example, the flexible extension <NUM> can include fibers and/or cables that are woven, cross-wound, interlaced, or otherwise configured to provide good transfer of torque from the housing distal end <NUM> to the pacing electrode <NUM> through the extension <NUM>. Accordingly, torque can be transferred from a proximal end of the extension <NUM> to a distal end of the extension <NUM> at the pacing electrode <NUM> during device implantation. More particularly, torque may be applied at the housing <NUM> to screw the pacing electrode <NUM> into the myocardium. Alternatively, the flexible section of the extension <NUM> may he designed to turn independently of the housing <NUM> to facilitate engagement of the pacing electrode <NUM> to the myocardium after the housing <NUM> is located at the apex.

The biostimulator <NUM> may include a strain relief <NUM> between the housing distal end <NUM> and the extension <NUM>. The strain relief <NUM> may be a separate component, or integrated with the extension <NUM>. As described below, the strain relief <NUM> can be a tapered section that provides a transition to ease delivery by a transport system. More particularly, the strain relief <NUM> can effectively transfer torque and bending forces applied to the housing <NUM> by the transport system, to the extension <NUM>.

In an embodiment, the biostimulator <NUM> includes an attachment feature <NUM>. The attachment feature <NUM> can be mounted on a proximal housing end <NUM> of the housing <NUM>. More particularly, the attachment feature <NUM> can be mounted on an opposite end of the housing <NUM> from the extension <NUM> and the pacing electrode <NUM>, which as described above, can be coupled to the distal housing end <NUM> of the housing <NUM>. The attachment feature <NUM> can facilitate precise delivery or retrieval of the biostimulator <NUM>. For example, the attachment feature <NUM> can be formed from a rigid material to allow a delivery or retrieval system to engage the attachment feature <NUM> and transmit torque through the housing <NUM> and extension <NUM> to screw the pacing electrode <NUM> into the target tissue.

The biostimulator <NUM> may include the anchor <NUM> to affix or maintain the housing <NUM> at the apex. The anchor <NUM> may include, for example, several flexible tines <NUM> arranged about an anchor axis <NUM>. As described further below, the flexible tines <NUM> can have a structure to facilitate interference between the tines <NUM> and heart structures that maintain the housing <NUM> in the apex region of the heart chamber.

Optionally, an anode <NUM> may be on the extension <NUM>. More particularly, the anode <NUM> can be an anode ring, such as an annular band of metal, mounted on an outer surface of the extension <NUM>. The anode <NUM> may be spaced proximally apart from the pacing electrode <NUM>. More particularly, the anode ring can be at a predetermined distance from the electrode to provide for adequate electrical isolation between the pacing electrode <NUM> and the anode <NUM>.

Referring to <FIG>, a side view of a pacing electrode of a biostimulator is shown in accordance with an embodiment. The biostimulator <NUM> can include the pacing electrode <NUM> coupled to the housing <NUM>. The pacing electrode <NUM> can extend along, e.g., axially along or helically about, the longitudinal axis of the extension <NUM>. For example, the pacing electrode <NUM> can include a helical electrode <NUM> extending about the electrode axis <NUM>. The helical electrode <NUM> can include a wire or filament extending helically about the electrode axis <NUM>. The helical electrode <NUM> can extend from an extension distal end <NUM> of the extension <NUM> to an electrode tip <NUM>. Over its length, the helical electrode <NUM> can revolve about electrode axis <NUM>. The helical pacing electrode <NUM> can screw into a target tissue. When the pacing electrode <NUM> engages the target tissue, the housing <NUM> can be advanced and/or rotated to cause the helical electrode <NUM> to anchor the biostimulator <NUM>. Accordingly, the pacing electrode <NUM> may both pace the septal wall as well as affix the biostimulator <NUM> to the septal wall.

As described below, the pacing electrode <NUM> may alternatively be a prong electrode (<FIG>) having a linear or conical element to pierce into the target tissue. Other electrode configurations are also contemplated. For example, the pacing electrode <NUM> may be a passive electrode or a tined electrode. Accordingly, the electrode structures described herein are provided by way of example and not limitation.

Referring to <FIG>, a side view of a strain relief of a biostimulator is shown in accordance with an embodiment. The strain relief <NUM> coupled to the housing distal end <NUM> can have a conical profile. More particularly, an outer dimension of the strain relief <NUM> at the housing distal end <NUM> may be greater than an outer dimension of the strain relief <NUM> at a transition into the extension <NUM>. A stiffness of the strain relief <NUM> may reduce in a distal direction from the housing distal end <NUM>. More particularly, a material or geometry of the strain relief <NUM> is such that flexibility of the strain relief <NUM> increases in a direction from the housing distal end <NUM> to the extension <NUM>. Accordingly, the strain relief <NUM> can provide a gradual transition of stiffness between the housing <NUM> and the extension <NUM> to allow for effective torque transfer and pushability of the biostimulator <NUM>.

Referring to <FIG>, a side view of an anchor of a biostimulator is shown in accordance with an embodiment. The anchor <NUM> of the biostimulator <NUM> may be mounted on the housing <NUM>. For example, the anchor <NUM> may include a collar <NUM>, e.g., an annular element, coaxial with and mounted on a stem of the attachment feature <NUM>. The stem can be a reduced diameter section of the attachment feature <NUM> between a proximal portion that connects to the transport system and a distal portion that mounts on the housing proximal end <NUM>. Accordingly, the collar <NUM> can fit between the proximal portion and the distal portion to secure the anchor <NUM> to the attachment feature <NUM> and/or housing <NUM>. The anchor <NUM> can have the anchor axis <NUM>, e.g., coaxial with the collar <NUM>, and the anchor axis <NUM> may be coaxial with the housing axis <NUM>.

In an embodiment, the anchor <NUM> includes several flexible tines <NUM> arranged about the anchor axis <NUM>. Each tine <NUM> may extend radially outward from the collar <NUM>. For example, two or more tines <NUM> may extend in an outward direction from the anchor axis <NUM> to respective tine tips <NUM> at a radially outward location. The tine tips may be distal to or proximal to a base of the tines <NUM>. For example, the tine tips <NUM> may be distal to the collar <NUM>, as shown in <FIG>. Alternatively, the tines <NUM> may extend proximally to tine tips <NUM> that are proximal to the collar <NUM> and/or the attachment feature <NUM>.

The tines <NUM> may be flexible to allow the tines <NUM> to deflect during delivery and/or implantation. For example, the tines <NUM> may flex backward during delivery to fit within a lumen of the transport system. Upon delivery, e.g., when the biostimulator <NUM> is advanced out of the transport system, the tines <NUM> can recover to a predetermined shape. For example, the tines <NUM> can spring forward to the distally directed shape shown in <FIG>. During recovery, the tines <NUM> can entangle with and/or otherwise grip an anatomical structure, e.g., trabeculae carneae, within the heart <NUM> chamber. Accordingly, the flexible tines <NUM> can interact with inner surface structures of the ventricle to anchor and stabilize the housing <NUM> within the heart chamber.

Flexibility of the tines <NUM> may be provided by the material and/or structure of the tine <NUM>. More particularly, at least a portion of the tines <NUM> may be formed from a flexible material such as a soft, molded silicone. Alternatively, the flexible tines <NUM> may be formed from a shape memory material, such as super elastic nickel titanium. The tines <NUM> may have a hybrid construction as well. For example, the flexible tines <NUM> could include a core material, such as metal wires, that are overmolded with or coated by an implantable polymer, such as an elastomer material. Accordingly, the tines <NUM> may be flexible enough to bend into the transport system and stiff enough to hold the housing <NUM> in place within the heart chamber.

Referring to <FIG>, a side view of an anchor of a biostimulator is shown in accordance with an embodiment. The tines <NUM> may extend outward from a structure other than the collar <NUM>. In an embodiment, the anchor <NUM> includes an anchor post <NUM> extending proximally from the housing proximal end <NUM>. For example, the anchor post <NUM> can extend along the anchor axis <NUM> in the longitudinal direction. Each of the flexible tines <NUM> can extend radially outward, either distally or proximally, from the anchor post <NUM>. Accordingly, the flexible tines <NUM> of the anchor <NUM> structure can reach out to interfere with and grip anatomical structures within the heart <NUM> chamber to anchor <NUM> the housing <NUM> therein.

The flexible tines <NUM> can have an outer dimension that is less than or greater than an outer dimension of the housing <NUM>. For example, referring again to <FIG>, the flexible tines <NUM> extend radially outward from an outer dimension of the housing wall, and thus, the outer dimension of the tines <NUM> is greater than the outer dimension of the housing <NUM>. By contrast, referring to <FIG>, an anchor outer dimension <NUM> is equal to or less than a housing outer dimension <NUM>. The anchor outer dimension <NUM> can balance the advantages of loading the biostimulator <NUM> into the transport system with a likelihood of gripping anatomical structures when deployed from the transport system. More particularly, when the anchor outer dimension <NUM> is equal to or less than the housing outer dimension <NUM>, the anchor <NUM> may be more easily loaded into the transport system. When the anchor outer dimension <NUM> is greater than the housing outer dimension <NUM>, however, the anchor <NUM> may be more likely to engage trabeculae carneae within the heart chamber.

Referring to <FIG>, a side view of a stabilizer of a biostimulator is shown in accordance with an embodiment. Stabilizing the pacing electrode <NUM> within the target tissue can the beneficial for several reasons. First, it may be advantageous to hold the pacing electrode <NUM> in a position such that the electrode axis <NUM> extends normal or perpendicular to the heart wall. The electrode may be more likely to reach and effectively pace the bundle branch <NUM> under such circumstances. Additionally, stabilizing the pacing electrode <NUM> within the heart tissue can reduce the likelihood that the electrode will back out of the tissue and lose effective contact with the bundle branch <NUM>. In an embodiment, the biostimulator <NUM> includes a stabilizer <NUM> to engage the heart wall such that the pacing electrode <NUM> is oriented and maintained in an effective pacing position.

The stabilizer <NUM> may be mounted on the flexible extension <NUM> of the biostimulator <NUM>. The stabilizer <NUM> can include one or more stabilizing elements <NUM> that extend radially outward from the extension <NUM>. For example, the stabilizing elements <NUM> can extend in a distal direction and radially outward relative to the electrode axis <NUM> from a stabilizer mount <NUM>. The stabilizer mount <NUM> can be positioned on an outer surface of the extension <NUM>. The stabilizing elements <NUM> can extend to distal ends that directly contact the target tissue, or alternatively, the distal ends may connect to a stabilizer loop <NUM> that interconnects the distal ends and presses against the septal wall during implantation.

A profile of the stabilizer <NUM>, as defined by the stabilizer elements <NUM> and the stabilizer loop <NUM>, may be cupped or conical. More particularly, the profile can be concave in the distal direction. Accordingly, stabilizer <NUM> may include a cup structure, e.g., molded from silicone or an elastomeric material, rather than the framework structure, e.g., a shape memory wire structure, shown in <FIG>. At least a portion of the stabilizer <NUM> may be radiopaque. For example, radiopaque marker bands may be located on the stabilizer loop <NUM>.

In an embodiment, stabilizer <NUM> is movable along the flexible extension <NUM>. For example, the stabilizer mount <NUM> may move longitudinally along the extension <NUM>. Movement may be provided by a friction fit between the stabilizer mount <NUM> and an outer surface of the extension <NUM>. For example, an axial load applied during implantation may be sufficient to cause the stabilizer <NUM> to slide along the extension <NUM>. By contrast, the axial load applied to the stabilizer <NUM> after implantation by the beating heart <NUM> may be insufficient to cause relative motion between the stabilizer mount <NUM> and the extension <NUM>.

Referring to <FIG>, a pictorial view of a biostimulator having a stabilizer engaged to a target anatomy is shown in accordance with an embodiment. When the biostimulator <NUM> is engaged to the septal wall, pacing electrode <NUM> can extend into the heart tissue to contact the target bundle branch <NUM>. During implantation, the stabilizer <NUM> can slide or move along the extension <NUM> to allow the pacing electrode <NUM> to be deployed to a desired depth within the target tissue. After implantation, the stabilizer <NUM> can press against the heart wall. Such pressure can maintain the orientation of the pacing electrode <NUM> in a generally perpendicular direction relative to the heart wall. More particularly, rather than the extension <NUM> weighing on and deflecting the pacing electrode <NUM> into a non-perpendicular orientation, the stabilizer <NUM> supports the pacing electrode <NUM> and relieves strain to maintain the pacing electrode position. Furthermore, the stabilizer <NUM> can apply some back pressure that pre-loads the pacing electrode <NUM> within the heart tissue to limit excessive movement of the pacing electrode <NUM> within the septal wall as the heart beats.

Referring to <FIG>, a diagrammatic cross section of a patient heart illustrating an example implantation of a biostimulator in a target anatomy is shown in accordance with an embodiment. The articulation <NUM> of the biostimulator <NUM> may be provided by alternative structures. In an embodiment, the articulation <NUM> includes a hinge <NUM>. As described below, the hinge <NUM> allows relative movement between a distal portion of the biostimulator <NUM> and the housing <NUM>. Accordingly, the pacing electrode <NUM> can extend into the target tissue, e.g., perpendicular to the heart wall, and the housing <NUM> may be hinged downward and directed toward the apex of the heart <NUM> to take advantage of the space within the heart chamber without interfering with the opposite heart wall or heart valve.

Referring to <FIG>, a side view of a biostimulator having an articulable hinge is shown in accordance with an embodiment. The hinge <NUM> can interconnect a body of the biostimulator <NUM> and the distal portion of the biostimulator <NUM>, including the pacing electrode <NUM>. The biostimulator <NUM> can include a header assembly <NUM> that includes the hinge <NUM>. More particularly, the header assembly <NUM> can be coupled to the housing <NUM>, e.g., at the housing distal end <NUM>. The hinge <NUM> can allow a distal portion of the header assembly <NUM> having the pacing electrode <NUM> to pivot or move with respect to a proximal portion of the header assembly <NUM> that connects to the housing <NUM>. Accordingly, the pacing electrode <NUM> of the header assembly <NUM> can be directed toward the bundle branch <NUM> and the housing <NUM> can be directed toward the ventricular apex <NUM>. More particularly, the hinge <NUM> can be articulated such that the electrode axis <NUM> can be directed differently, e.g., orthogonal to, the housing axis <NUM>.

Referring to <FIG>, a front perspective view of a distal portion of a biostimulator having an articulable hinge is shown in accordance with an embodiment. The articulable hinge <NUM> of the biostimulator <NUM> may be any of several known hinge configurations. For example, the hinge <NUM> can include a barrel hinge having a pin connecting the distal portion of the header assembly <NUM> to the proximal portion of the header assembly <NUM>. The hinge <NUM> can allow the portions to pivot relative to each other about a pin axis. Alternatively, the articulation <NUM> can include a universal joint. More particularly, the articulation <NUM> can include a pair of hinges connected by a cross shaft. The universal joint can allow the distal portion of the header assembly <NUM> to move with respect to the proximal portion of the header assembly <NUM> within several degrees of freedom. For example, the distal portion may pivot about two different planes or axes, in contrast to the single axis of rotation of the barrel hinge <NUM>. Alternative hinge <NUM> configurations may be incorporated to allow the pacing electrode <NUM> to engage the septal wall when the housing <NUM> is directed downward toward the apex of the heart <NUM>.

The hinge <NUM> may provide movement between portions of the biostimulator <NUM> during implantation, and can resist relative movement of the portions after implantation. For example, the hinge <NUM> may have sufficient friction, e.g., between the pin and the header assembly portions, to allow the hinge <NUM> to resist movement and lock into place when the biostimulator <NUM> is implanted within heart chamber. The friction may be insufficient, however, to resist implantation forces applied by the transport system, and thus, the biostimulator <NUM> may be articulated to fit within the heart chamber in an orientation that is maintained by the hinge <NUM> thereafter.

The portion of the header assembly <NUM> distal to the hinge <NUM> can include a helix mount <NUM>. The helix mount <NUM> can support a fixation helix <NUM>. More particularly, the fixation helix <NUM> can include a helical wire mounted on an outer surface of the helix mount <NUM>. For example, the helical wire can extend through a helical groove formed in an outer surface of the helix mount <NUM>. The fixation helix <NUM> may extend and/or revolve about electrode axis <NUM>, similar to the helical pacing electrode <NUM>. Accordingly, like the pacing electrode <NUM>, the fixation helix <NUM> may be screwed into the target tissue to anchor the header assembly <NUM> to the ventricular wall.

The pacing electrode <NUM> may be radially inward from the fixation helix <NUM>. In an embodiment, the pacing electrode <NUM> is independently movable relative to the fixation helix <NUM>. For example, the pacing electrode <NUM> may be rotatable relative to the fixation helix <NUM>. The header assembly <NUM> can include an electrode support <NUM>. Electrode support <NUM> can be a post extending along the electrode axis <NUM> through the helix mount <NUM>. The post can have an outer surface, e.g., a threaded surface, on which the pacing electrode <NUM> is located. For example, a distal portion of the post can extend through a center of the pacing electrode <NUM> such that the helical electrode <NUM> extends along and grips the outer surface of the electrode support <NUM>. Accordingly, the pacing electrode <NUM> can be mounted on the electrode support <NUM>.

An external threaded surface of the electrode support <NUM> may engage in internal threaded surface of the header assembly <NUM>. For example, the electrode support <NUM> can include external square threads that engage corresponding threads of the helix mount <NUM>. Rotation of electrode support <NUM> can cause the threads to interact such that the distal portion of the post moves longitudinally relative to the helix mount <NUM>. It will be appreciated that, when the pacing electrode <NUM> is mounted on the electrode support <NUM>, rotation of the electrode support <NUM> can cause a distal tip of the pacing electrode <NUM> to move longitudinally relative to a distal tip of fixation helix <NUM>. Similarly, rotation of the electrode support <NUM> relative to the helix mount <NUM> causes the pacing electrode <NUM> to rotate relative to the fixation helix <NUM>. Thus, rotation of electrode support <NUM> relative to the helix mount <NUM> when the helices are engaged with the target tissue can drive the distal tip of the pacing electrode <NUM> to a different depth than a depth of the fixation helix <NUM>. Furthermore, a distance between the distal tips of the fixation helix <NUM> and the pacing electrode <NUM> can be varied. Accordingly, pacing electrode <NUM> can be driven to any depth needed to engage the target bundle branch <NUM>.

Referring to <FIG>, a rear perspective view of a distal portion of a biostimulator having an articulable hinge is shown in accordance with an embodiment. As described above, the pacing electrode <NUM> can be rotatable relative to other components of the header assembly <NUM>, e.g., the helix mount <NUM>. Rotation of the pacing electrode <NUM> relative to the helix mount <NUM> may be affected through a drive mechanism. In an embodiment, the drive mechanism includes a drive socket <NUM>. For example, the header assembly <NUM> can include the drive socket <NUM> to receive torque to rotate the pacing electrode <NUM> relative to the fixation helix <NUM>. The drive socket <NUM> may include a hex socket within which a wrench may be placed to transmit the torque to electrode support <NUM>. Accordingly, rotation of the drive socket <NUM> by a tool can rotate the pacing electrode <NUM> to a desired depth, independently of the fixation helix <NUM>.

Referring to <FIG>, a rear perspective view of a distal portion of a biostimulator having an articulable hinge is shown in accordance with an embodiment. The drive mechanism may incorporate an alternative coupling to transmit torque from a drive tool to the electrode support <NUM>. For example, the header assembly <NUM> can include a drive loop <NUM> to receive torque to rotate the pacing electrode <NUM> relative to the fixation helix <NUM>. The drive loop <NUM> can include a curved bar extending and/or looping back to a distal face of electrode support <NUM>. The loop can be engaged by a wrench, prong, or another mating structure of a tool to receive torque. More particularly, rotation of the drive loop <NUM> about the electrode axis <NUM> can transmit rotation to the electrode support <NUM> and thus to the pacing electrode <NUM>.

Referring to <FIG>, a rear view of a distal portion of a biostimulator having an articulable hinge is shown in accordance with an embodiment. Pacing impulses can be delivered from the pacing circuitry within the electronics compartment <NUM> to the pacing electrode <NUM> through the header assembly <NUM>. In an embodiment, the header assembly <NUM> includes an electrical feedthrough <NUM> electrically connected to the pacing electrode <NUM> and to the pacing circuitry. Accordingly, pacing and/or sensing impulses can be transmitted through the electrical feedthrough <NUM> from the pacing circuitry to the pacing electrode <NUM>, or vice versa.

In an embodiment, the header assembly <NUM> includes an electrical interconnect <NUM> between the electronics compartment <NUM> and the pacing electrode <NUM>. For example, the electrical interconnect <NUM> can include a ball plunger <NUM> that conducts electrical signals between the pacing circuitry and the pacing electrode <NUM>. For example, the ball plunger <NUM> may include a metal ball that receives the pacing impulse. The metal ball may be in contact with a proximal end of the electrode support <NUM>. For example, the ball of the ball plunger <NUM> can contact the drive mechanism of the electrode support <NUM>. Similarly, the electrode support <NUM> can be in electrical contact with the pacing electrode <NUM>, as described above. Thus, the pacing impulse may be delivered from the ball plunger <NUM> to the pacing electrode <NUM> through the electrode support <NUM>.

Referring to <FIG>, a sectional view of a distal portion of a biostimulator having an articulable hinge is shown in accordance with an embodiment. In cross-section, the electrical conductivity of the ball plunger <NUM> may be understood. The ball plunger <NUM> can include the ball <NUM> in electrical contact with a spring <NUM>. The spring <NUM> can bias the ball <NUM> upward into contact with the electrode support <NUM>, as shown in <FIG>. The spring <NUM> may extend through a vertical channel within the header assembly <NUM> to a proximal end below the ball <NUM>. The proximal end of the spring <NUM> may electrically connect to pacing circuitry contained within the housing <NUM>. For example, an electrical lead may interconnect the pacing circuitry to the proximal end of the spring <NUM>. Accordingly, the ball <NUM> can deflect as required, when the helix mount <NUM> rotates about the hinge <NUM>, to provide resilient and consistent electrical contact tween the pacing circuitry and the pacing electrode <NUM>.

Referring to <FIG>, a rear perspective view of a distal portion of a biostimulator having an articulable hinge is shown in accordance with an embodiment. The electrical interconnect <NUM> connecting the pacing circuitry to the pacing electrode <NUM> may be alternatively configured. In an embodiment, the electrical interconnect <NUM> includes an electrical lead <NUM>, e.g., a wire or cable, extending between electronics compartment <NUM> and the pacing electrode <NUM>. For example, the electrical lead <NUM> can extend through a proximal portion of the header assembly <NUM> into the housing cavity at a proximal end, and may extend through or into contact with the electrode support <NUM> at a distal end. The electrical lead <NUM> may therefore conduct pacing impulses from the pacing circuitry contained within the housing <NUM> to electrode support <NUM> and/or the pacing electrode <NUM>. Electrical lead <NUM>, like the ball plunger <NUM>, allows for relative movement between the header assembly <NUM> portions at the hinge <NUM> while maintaining electrical conductivity between the pacing circuitry and the pacing electrode <NUM>.

As described above, the pacing electrode <NUM> may be electrically active to pace the target tissue after implantation. It will be appreciated, however, that the fixation helix <NUM> may be electrically active instead of or in addition to the pacing electrode <NUM>. For example, an electrical lead <NUM> can interconnect the pacing circuitry to the fixation helix <NUM>. The fixation helix <NUM> may therefore deliver the pacing impulse to tissue when it is implanted within the septal wall. By way of example, fixation helix <NUM> may be screwed into the tissue near the right bundle branch and the pacing electrode <NUM> may be screwed into the tissue by the left bundle branch. Accordingly, each helix may pace a different bundle branch <NUM> or a different region of the target tissue.

Referring to <FIG>, a diagrammatic cross section of a patient heart illustrating an example implantation of a biostimulator in a target anatomy is shown in accordance with an embodiment. The articulation <NUM> of the biostimulator <NUM> may be located distal or proximal to the housing <NUM>. In embodiment, the articulation <NUM> includes a tether <NUM> extending from the housing <NUM>. For example, the tether <NUM> can extend proximately from the attachment feature <NUM>. The anchor <NUM> may be mounted on the tether <NUM>, rather than being mounted on the housing <NUM> or the attachment feature <NUM>, as described above. Accordingly, when the housing <NUM> is affixed to the septal wall, e.g., by the pacing electrode <NUM> and/or the fixation helix <NUM>, the anchor <NUM> may be affixed to anatomical structures at the apex of the heart <NUM>. The tether <NUM> extending between the anchor <NUM> and the housing <NUM> may therefore restrain the housing <NUM> or bias the housing <NUM> in a downward direction away from an opposite heart wall and/or heart valve. More particularly, the tether <NUM> can limit movement of the leadless pacemaker housing <NUM> to reduce the likelihood that the housing <NUM> will flip up into engagement with a chamber wall or valve leaflets.

Referring to <FIG>, a side view of a biostimulator having an articulable tether is shown in accordance with an embodiment. The body of the leadless pacemaker may have structure similar to that described above. Biostimulator <NUM> can include the housing <NUM> containing pacing circuitry and the attachment feature <NUM> to engage the transport system during delivery or retrieval. Biostimulator <NUM> may include the header assembly <NUM> mounted on the distal end of the housing <NUM>. In an embodiment, the header assembly <NUM> includes the fixation helix <NUM>. The fixation helix <NUM> can screw into the target tissue to anchor the housing <NUM> to the septal wall. Furthermore, the pacing electrode <NUM> may be integrated with the header assembly <NUM> to deliver the pacing impulse from pacing circuitry to the target tissue. The pacing electrode <NUM> may include a helical electrode, as described above, a prong electrode or any other electrode shape that engages the septal wall and/or the bundle branch <NUM> during implantation.

In an embodiment, the tether <NUM> is a flexible leash. For example, the tether <NUM> can include a cable, e.g., an MP35N or nickel-titanium cable, or wire that is pliable and extends over a length from a distal end at the attachment feature <NUM> to a proximal end at the anchor <NUM>. Alternatively, the tether <NUM> may include a polymer structure, e.g., a polymer cord, filament, wire, or cable. In any case, the tether <NUM> can deflect easily at one or more articulations <NUM> along its length. In the case of a flexible cable, essentially the entire length of the tether can articulate.

A length of the tether <NUM> may be selected to allow the tether <NUM> to extend from the body of the biostimulator <NUM>, when the biostimulator <NUM> is affixed to an upper region of the septal wall, into the apex region of the heart chamber. For example, a length of the tether <NUM> may be greater than a length of the housing <NUM>. Accordingly, the tether <NUM> can interconnect the body of the biostimulator <NUM> to the anchor <NUM> affixed at the apex.

The anchor <NUM> may be attached to the proximal end of the tether <NUM>. The anchor <NUM> can have a structure similar to that described above. For example, the anchor <NUM> may include a central body coupled to the tether <NUM>, and several tines that extend radially outward from the tether body. The tines <NUM> may be formed from a soft flexible material such as silicone. Alternatively, the tines <NUM> may be metallic. In any case, the tines <NUM> may be resiliently deformed to be loaded into the transport system, and may recover to a larger dimension to entangle within the anatomical structures of the heart <NUM>. When the anchor <NUM> is entangled within the anatomical structures, it can pull on the tether <NUM> to restrain upward movement of the housing <NUM> and to reduce a likelihood of contact between the body of the biostimulator <NUM> and the lateral heart wall or the heart valve leaflets.

Referring to <FIG>, a side view of a biostimulator having an independently rotatable pacing electrode is shown in accordance with an embodiment. For bundle branch pacing, e.g., left bundle branch pacing, the depth at which the pacing electrode <NUM> penetrates the septal wall may be important to effective treatment. More particularly, the pacing electrode <NUM> may adequately engage the tissue around the target bundle branch <NUM> to ensure effective pacing. In an embodiment, the biostimulator <NUM> includes several fixation elements. More particularly, the biostimulator <NUM> may include the helical electrode <NUM> and the fixation helix <NUM>. As described above, the fixation helix <NUM> may be used to affix the housing <NUM> to the septal wall and the helical electrode <NUM> may deliver the pacing impulse to the target tissue. Given that each of the helical structures is screwed into the heart tissue, a number of rotations that each of the helices requires to engage the tissue may not match. For example, five rotations of the pacing electrode <NUM> may optimally locate the electrode tip <NUM> at the left bundle branch <NUM>, however, only two rotations of the fixation helix <NUM> may be needed to optimally affix the housing <NUM> to the target tissue. Accordingly, the ability to rotate the fixation helix <NUM> separately from and to a different depth than the pacing electrode <NUM> may be advantageous.

In an embodiment, the biostimulator <NUM> includes one or more torque transfer features <NUM>. The torque transfer features <NUM> can include a prong, a protrusion, a nub, or another feature that can be engaged by a tool to transmit torque to the biostimulator body. More particularly, rotation of the torque transfer features <NUM> can transmit torque to the housing <NUM> and the fixation helix <NUM>. Thus, the torque transfer features <NUM> can receive and transmit torque to allow the fixation helix <NUM> to be screwed to an appropriate depth within the target tissue.

The pacing electrode <NUM> may be rotated independently of the fixation helix <NUM>. In an embodiment, the pacing electrode <NUM> includes a rotation rod <NUM> extending through the biostimulator <NUM> from the pacing electrode <NUM>. More particularly, the rotation rod <NUM> can have a proximal end located proximal to the attachment feature <NUM> of the biostimulator <NUM>. The proximal end of the rotation rod <NUM> can be gripped and rotated by a tool to transmit torque to the pacing electrode <NUM>. Accordingly, pacing electrode <NUM> can be rotated independently from the fixation helix <NUM>. The pacing electrode <NUM> may therefore be screwed to an appropriate depth within the target tissue to effectively pace the target bundle branch <NUM>.

Referring to <FIG>, a sectional view of a biostimulator having an independently rotatable pacing electrode is shown in accordance with an embodiment. The rotation rod <NUM> may reside within a hermetically sealed lumen that extends through a center of the biostimulator <NUM>. More particularly, a passage can extend through the attachment feature <NUM>, the housing <NUM> (including a battery <NUM> and the electronics compartment <NUM>), and the header assembly <NUM>. The rotation rod <NUM> can extend through the passage to the pacing electrode <NUM>. Rotation of the rod when the pacing electrode <NUM> is engaged to the tissue can cause the pacing electrode <NUM> to screw deeper into the tissue. As the pacing electrode <NUM> screws into the tissue, the rotation rod <NUM> can move axially relative to the body of the biostimulator <NUM>. The fixation helix <NUM> may be mounted on the body of the biostimulator <NUM>, and thus, rotation of the rotation rod <NUM> causes axial movement of the pacing electrode <NUM> relative to fixation helix <NUM>. Accordingly, the pacing electrode <NUM> and the fixation helix <NUM> may be independently set to respective depths within the target tissue.

Referring to <FIG>, a side view of a biostimulator having a post electrode is shown in accordance with an embodiment. A depth of pacing within the septal wall may be controlled by electrode selection, rather than by varying a depth of a specific electrode. In an embodiment, the pacing electrode <NUM> includes a post electrode <NUM> extending along the electrode axis <NUM>. The post electrode <NUM> can include an elongated prong extending longitudinally along the electrode axis <NUM> to a piercing tip. For example, the piercing tip may be a conical or sharpened tip configured to pierce the septal wall when the biostimulator <NUM> is delivered. The elongated prong can have a length such that, when the fixation helix <NUM> mounted on the header assembly <NUM> of the biostimulator <NUM> is screwed into the target tissue, the piercing tip can extend at least as far as the target bundle branch <NUM>. The piercing tip may extend beyond the target bundle branch <NUM> after fixation.

In an embodiment, the prong electrode includes one or more electrode bands <NUM> mounted on an outer surface of the elongated prong between the helix mount <NUM> and the piercing tip. For example, the pacing electrode <NUM> can include several electrode bands <NUM> distributed along the prong length. When the elongated prong is implanted within the target tissue, and the piercing tip extends at least as far as the target bundle branch <NUM>, at least one of the electrode bands may be located near the target bundle branch <NUM>. Accordingly, the optimally located electrode band <NUM> may be selected and activated to pace the target bundle branch <NUM>.

The electrode bands <NUM> may be independently registrable by circuitry of the biostimulator <NUM>. For example, each electrode band <NUM> may be connected to a respective conductor running through the post electrode <NUM> and the header assembly <NUM> into the electronics compartment <NUM>. The independent conductors can conduct the pacing impulse from the pacing circuitry to the respective electrode band <NUM>. In an embodiment, multiplexing chips can be used to switch the electrode bands <NUM>, or portions of the post electrode <NUM>, on or off. Accordingly, each of the electrode bands <NUM> may be controlled by a same chip. Alternatively, each electrode band <NUM> may be controlled by a respective chip. Accordingly, the chip(s) can operate to select the electrode band(s) <NUM> that are placed in proximity to the target bundle branch <NUM>, and to deliver the pacing impulse to those band(s) through electrical conductors of the header assembly <NUM>.

Referring to <FIG>, a side view of a biostimulator including a housing in wireless communication with a pacing electrode is shown in accordance with an embodiment. The pacing and sensing signals of the biostimulator <NUM> may be transferred wirelessly from the pacing circuitry to the pacing electrode <NUM>. In an embodiment, the biostimulator <NUM> includes a distal module <NUM> and a proximal module <NUM>. The modules may resemble portions of the biostimulator <NUM> described above. For example, the distal module <NUM> can include a distal module housing <NUM> having a profile similar to the extension <NUM>. Furthermore, the distal module <NUM> can include the pacing electrode <NUM>, e.g., the helical electrode <NUM>. The distal module housing <NUM> can contain circuitry to receive wireless signals from the proximal module <NUM>. The circuitry may transform the wireless signals into the pacing impulse that is then delivered through the pacing electrode <NUM> to the target bundle branch <NUM>. In an embodiment, the distal module <NUM> includes the anode <NUM>. The anode <NUM> may be mounted at a proximal end of the distal module <NUM>, spaced apart from the pacing electrode <NUM> at the distal end of the module.

The proximal module <NUM> may include a proximal module housing <NUM>. The proximal module housing <NUM> may be similar to the body of the biostimulator <NUM> described above. More particularly, the proximal module housing <NUM> can contain the electronics compartment <NUM> and the pacing circuitry. Furthermore, the housing <NUM> can contain the battery <NUM> of the biostimulator <NUM>. Similar to the biostimulator <NUM> embodiments described above, the proximal module <NUM> may include the anchor <NUM> and/or the attachment feature <NUM>. Accordingly, the proximal module <NUM> may be delivered and anchored within the heart chamber in a manner similar to that used for the biostimulator embodiments described above. The distal module <NUM> and the proximal module <NUM> may operate to deliver the pacing impulse to the target tissue. Unlike biostimulator embodiments described above, however, rather than delivering the pacing impulse through conductors of the extension <NUM> or the header assembly <NUM>, pacing impulse is wirelessly transmitted and generated for delivery through the pacing electrode <NUM>.

Referring to <FIG>, a side view of a biostimulator including a housing having a helical anchor is shown in accordance with an embodiment. The proximal module <NUM> may include alternative anchoring structures to affix the housing <NUM> to the heart wall. In an embodiment, the anchor <NUM> includes a proximal fixation helix <NUM> that may be screwed into the heart tissue to secure the housing <NUM>. More particularly, the proximal fixation helix <NUM> may be a helical wire mounted on and extending from the housing proximal end <NUM>. The proximal fixation helix <NUM> can actively engage tissue of the ventricular apex <NUM> to stabilize and anchor the proximal module <NUM> within the heart <NUM>. By contrast, the distal module <NUM> may be delivered to an engaged with the septal wall. Accordingly, the proximal module <NUM> near the apex can wirelessly transmit the pacing signal to the distal module <NUM> on the septal wall to perform bundle branch pacing.

Referring to <FIG>, a perspective view of a biostimulator system is shown in accordance with an embodiment. The biostimulator system <NUM> can include a biostimulator transport system <NUM>. The biostimulator transport system <NUM> can include a handle <NUM> to control movement and operations of the transport system from outside of a patient anatomy. One or more elongated members extend distally from the handle <NUM>. For example, an outer member <NUM> and an inner member <NUM> extend distally from the handle <NUM>. The inner member <NUM> can extend through a lumen of the outer member <NUM> to a distal end of the transport system. In an embodiment, the biostimulator <NUM> is mounted on the biostimulator transport system <NUM>, e.g., at the distal end of one of the elongated members.

The transport system can include a protective sheath <NUM> to cover the biostimulator <NUM> during delivery and implantation. The protective sheath <NUM> can extend over, and be longitudinally movable relative to, the elongated members. The transport system may also include an introducer sheath <NUM> that can extend over, and be longitudinally movable relative to, the protective sheath <NUM>. The introducer sheath <NUM> can cover a distal end of the protective sheath <NUM>, the elongated members, and the biostimulator <NUM> as those components are passed through an access device into the patient anatomy.

Several components of the biostimulator transport system <NUM> are described above by way of example. It will be appreciated, however, that the biostimulator transport system <NUM> may be configured to include additional or alternate components. More particularly, the biostimulator transport system <NUM> may be configured to deliver and/or retrieve the biostimulator <NUM> to or from the target anatomy.

Referring to <FIG>, a flowchart of a method of implanting a biostimulator for septal pacing is shown. During the implantation procedure, the biostimulator transport system <NUM> can carry the biostimulator <NUM> into the target heart chamber. When implantation is to be within the right ventricle, the biostimulator transport system <NUM> can be tracked through the inferior vena cava into the right atrium and across the tricuspid valve into the right ventricle. The distal end of the transport system can be steered toward a desired location of the septal wall. For example, the target area may be in an upper region of the interventricular septal wall <NUM>.

At operation <NUM>, the pacing electrode <NUM> may be affixed to the interventricular septum. When a distal end of the biostimulator <NUM> is in contact with the septal wall, torque can be transferred from the biostimulator transport system <NUM> to the biostimulator <NUM>, e.g., via the attachment feature <NUM>. Rotation of the biostimulator <NUM> can drive the pacing electrode <NUM> and/or the fixation helix <NUM> into the septal tissue. Alternatively, the electrode support <NUM> may be rotated via the drive mechanism in some embodiments to cause the pacing electrode <NUM> to screw into the target tissue. More particularly, the pacing electrode <NUM> and/or the fixation helix <NUM> can be screwed into the tissue to a desired depth by rotating the helices into the target tissue. The pacing electrode <NUM> may engage the tissue at a depth that allows effective pacing of the target bundle branch <NUM>.

At operation <NUM>, the biostimulator <NUM> may be articulated at the articulation <NUM>. For example, the biostimulator transport system <NUM> can be placed in a tether mode that allows the attachment feature <NUM> to interconnect to the elongated members by flexible cables, without requiring the biostimulator <NUM> to be directly engaged to the protective sheath <NUM> or the elongated members. In the tether mode, the proximal portion of the biostimulator <NUM> can be deflected downward toward the ventricular apex <NUM>. More particularly, the extension <NUM> of the biostimulator <NUM> can be bent, the hinge <NUM> may be pivoted, or any other articulation <NUM> may be actuated to direct the housing <NUM> of the biostimulator <NUM> toward the ventricular apex <NUM>.

At operation <NUM>, optionally, an anchor <NUM> of the biostimulator <NUM> may be affixed at the ventricular apex <NUM>. More particularly, the anchor <NUM> can engage with trabeculae carneae on an internal surface of the myocardium, or another heart structure. The anchor <NUM> may include flexible tines <NUM> arranged about an anchor axis <NUM>, as described above, and the tines <NUM> may engage the heart structure. Accordingly, the anchor <NUM> can achieve fixation and stabilization of the housing <NUM> to reduce a likelihood that the housing <NUM> will interfere with the heart wall or the heart valve while the pacing electrode <NUM> paces the target bundle branch <NUM>.

It will be appreciated that the operations described above may be performed in any order. For example, the order described above may be a forward implant procedure in which the pacing electrode <NUM> is engaged to the septal wall before directing the housing <NUM> toward the apex. In an alternative embodiment a backward implant procedure may be used. In the backward implant procedure, the housing <NUM> of the biostimulator <NUM> may first be placed at the apex. The articulation <NUM> may then be articulated to direct the pacing electrode <NUM> toward the septal wall. The pacing electrode <NUM> and/or the fixation helix <NUM> may then be screwed into the septal wall to engage the target tissue.

Claim 1:
A biostimulator (<NUM>), comprising:
a helical pacing electrode (<NUM>) extending about an electrode axis (<NUM>);
a housing (<NUM>) having an electronics compartment (<NUM>) containing pacing circuitry electrically connected to the helical pacing electrode (<NUM>), wherein the housing (<NUM>) has a housing distal end (<NUM>) and a housing proximal end (<NUM>) along a housing axis (<NUM>);
an articulable extension (<NUM>) extending between the housing distal end (<NUM>) and the helical pacing electrode (<NUM>), wherein the articulable extension (<NUM>) includes an articulation (<NUM>) such that, when the helical pacing electrode (<NUM>) is affixed to an interventricular septal wall and the housing (<NUM>) is located at a ventricular apex, the electrode axis (<NUM>) and the housing axis (<NUM>) extend in different directions; and
a strain relief (<NUM>) between the housing distal end (<NUM>) and the articulable extension (<NUM>), characterized in that a stiffness of the strain relief (<NUM>) decreases in a distal direction from the housing distal end (<NUM>).