阅读说明：本技术 具有低极化电极的生物刺激器 (Biostimulator with low polarization electrodes ) 是由 G.A.博恩辛 W.阿尔曼 T.J.斯特朗 K.维克托林 N.库珀 于 2021-04-01 设计创作，主要内容包括：描述了一种生物刺激器,比如无引线起搏器,其具有涂覆有低极化涂层的电极。可以在阳极上设置包括氮化钛的低极化涂层,并且可以在阴极上设置包括第一氮化钛层和第二铂黑层的低极化涂层。阳极可以是用于将扭矩传递至生物刺激器的附接特征。阴极可以是用于将生物刺激器固定到目标组织的固定元件。低极化涂层将低极化赋予电极,以使心房诱发反应能够被检测到并用于实现生物刺激器的自动输出调节。还描述并要求保护其他实施例。(A biostimulator, such as a leadless pacemaker, having electrodes coated with a low-polarization coating is described. A low-polarization coating comprising titanium nitride may be disposed on the anode, and a low-polarization coating comprising a first titanium nitride layer and a second platinum black layer may be disposed on the cathode. The anode may be an attachment feature for transmitting torque to the biostimulator. The cathode may be a fixation element for securing the biostimulator to the target tissue. The low polarization coating imparts a low polarization to the electrodes so that atrial evoked responses can be detected and used to effect automatic output regulation of the biostimulator. Other embodiments are described and claimed.)

1. A biostimulator, comprising:

a battery assembly including a single cell case containing an electrolyte;

an attachment feature coupled to the battery assembly, wherein the attachment feature comprises a rod having an annular rod wall extending between a base and a button; and

a low polarization coating on an exterior surface of the attachment feature.

2. The biostimulator of claim 1, wherein the low-polarization coating comprises one or more of titanium nitride or iridium oxide.

3. The biostimulator of claim 2, wherein the low-polarization coating covers the entire exterior surface.

4. The biostimulator of claim 3, wherein the attachment feature comprises an interior surface surrounding an interior cavity, and wherein the low-polarization coating covers only a portion of the interior surface.

5. The biostimulator of claim 1, wherein the attachment feature is coupled to the battery assembly by a weld extending circumferentially around the base and cell box.

6. The biostimulator of claim 1, further comprising an insulating coating on the single battery compartment.

7. The biostimulator of claim 1, wherein the attachment feature is integrally formed from a rigid material, and wherein the rod is a single post having an annular transverse profile.

8. The biostimulator of claim 1, wherein the attachment feature is an anode of the biostimulator.

9. A biostimulator system, comprising:

a delivery system comprising a catheter having a distal end; and

the biostimulator of any of claims 1-8 coupled to the distal end.

10. A method, comprising:

providing a low-polarization coating on an exterior surface of an attachment feature, wherein the attachment feature comprises a stem having an annular stem wall extending between a base and a button; and is

After the low-polarization coating is disposed on the exterior surface, the attachment feature is mounted on a battery assembly, wherein the battery assembly includes a cell case containing an electrolyte.

11. The method of claim 10, wherein the low-polarization coating comprises one or more of titanium nitride or iridium oxide.

12. The method of claim 11, wherein the low-polarization coating covers the entire exterior surface.

13. The method of claim 12, wherein the attachment feature comprises an interior surface surrounding an interior cavity, and wherein the low-polarization coating covers only a portion of the interior surface.

14. The method of claim 10, further comprising welding the attachment feature to the battery assembly circumferentially around the base and cell box.

15. The method of claim 10, further comprising disposing an insulating coating on the cell casing.

Technical Field

The present disclosure relates to biostimulators. More particularly, the present disclosure relates to leadless biostimulators.

Background

Cardiac pacing by an artificial pacemaker provides electrical stimulation to the heart when the heart's natural pacemaker and/or conduction system fails to provide synchronized atrial and ventricular contractions at a rate and interval sufficient to make the patient healthy. Cardiac pacing with conventional pacemakers is typically performed by a pulse generator subcutaneously or submuscularly implanted in or near the thoracic cavity region of a patient, which delivers electrical pulses to the heart through elongated electrical leads implanted therein. Conventional pacemakers present well-known difficulties, such as complex lead connectors and/or the risk of mechanical failure of the leads. As a result, leadless cardiac pacemakers have been developed.

Leadless cardiac pacemakers are self-contained and sustainable biostimulators that can be attached to tissue within a dynamic environment. For example, a leadless cardiac pacemaker may be implanted in a chamber of a heart to deliver pacing pulses to target tissue in an atrium or ventricle of the heart. Leadless cardiac pacemakers include batteries to provide the energy for pacing pulses. The capacity of the battery is limited by the size of the leadless cardiac pacemaker. In addition, a small size leadless pacemaker is required to allow the leadless pacemaker to be delivered intravenously and reside within the ventricle.

Disclosure of Invention

The limitations imposed by device size requirements on the battery capacity of leadless cardiac pacemakers indicate that the power consumption of leadless cardiac pacemakers should be minimized to maximize the pacemaker's useful life. Existing leadless cardiac pacemakers may implement "auto-capture" to minimize power consumption. When the device determines that the pacing output captured by the target chamber (e.g., the atrium) is lost, automatic capture is performed by the leadless cardiac pacemaker, and then the stimulation amplitude is set to the threshold plus a safety margin. Automatic capture allows for efficient pacing with minimal battery current drain, thereby extending the useful life of the pacemaker. However, a prerequisite for successful implementation of automatic capture is that the leadless pacemaker can determine the capture threshold by detecting the chamber evoked response, which is consistent with chamber capture. Therefore, a leadless cardiac pacemaker must be able to accurately detect ventricular evoked responses in order to successfully achieve automatic capture.

Detection of chamber-induced reactions can be complicated by the small amplitude of the chamber-induced reactions. More particularly, polarization of the pacemaker electrodes during pacing may cause decaying polarization potentials that are superimposed on and mask the ventricular evoked responses. Although the pacemaker electrodes are polarized, complex signal discrimination techniques such as frequently performed correlations can be used to improve the detection of chamber evoked responses. However, this technique requires a large amount of processing power and is itself a burden on battery current consumption. As a result, existing leadless pacemakers that experience pacemaker electrode polarization may not reliably perform automatic capture, particularly in target chambers with low chamber evoked responses (such as the atria).

Biostimulators, such as leadless cardiac pacemakers, having electrodes coated with a low-polarization coating are described below. In one embodiment, the biostimulator has a battery assembly that includes a single battery compartment containing an electrolyte, and the attachment feature is connected to the battery assembly. The attachment feature may be used to transfer torque to the biostimulator. Thus, the attachment feature includes a rod having an annular rod wall extending between a base connected to the battery assembly and a button that receives torque. A low-polarization coating is disposed on an exterior surface of the attachment feature to impart low polarization to the attachment feature, which may be an anode of the biostimulator. Thus, the coated attachment feature may enable atrial evoked responses to be detected and used to enable automatic output adjustment of the biostimulator.

The low polarization coating may include titanium nitride and/or iridium oxide. In an embodiment, the low-polarization coating covers the entire exterior surface of the attachment feature. The attachment feature may have an interior surface, and the low-polarization coating may cover only a portion of the interior surface.

The biostimulator component can have other significant features. The attachment features may be coupled to the battery assembly by welds that extend circumferentially around the base and the cell box. The battery may also be at least partially covered by an insulating coating. The attachment feature may be integrally formed of a rigid material, and the rod may be a single post having an annular transverse profile. These features and others described below may help the biostimulator to be able to detect atrial evoked responses and use them to effect automatic output adjustment.

A biostimulator system including a biostimulator is also described. For example, the biostimulator system may include a delivery system including a catheter having a distal end, and the biostimulator may be connected to the distal end.

Methods of making the biostimulators are also described. In an embodiment, a low-polarization coating is disposed on an exterior surface of the attachment feature, and the attachment feature is mounted on the battery assembly.

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 and methods that can be practiced from all suitable combinations of the various aspects summarized above, as well as all suitable combinations of those disclosed in the following detailed description and particularly pointed out in the claims filed with the application. Such combinations have particular advantages not specifically recited in the above summary.

Drawings

The novel features of the invention are set forth with particularity in the appended claims. 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 of which:

FIG. 1 is a diagram of atrial evoked response and electrode polarization waveforms according to one embodiment.

FIG. 2 is a diagram of an atrial evoked response waveform superimposed on an electrode polarization waveform according to one embodiment.

Fig. 3 is a schematic medial-lateral cross-section of a patient's heart showing an exemplary implantation of a biostimulator in the patient's heart, according to an embodiment.

Fig. 4A-4B are perspective views of a biostimulator delivery system according to an embodiment.

Fig. 5A-5B are perspective views of a biostimulator retrieval system according to an embodiment.

Fig. 6A-6B are side and end views, respectively, of a biostimulator having a low-polarization coating on an electrode according to an embodiment.

Fig. 7-8 are side views of an attachment feature according to an embodiment.

Fig. 9 is a proximal view of the attachment feature of fig. 7-8 according to an embodiment.

Figure 10 is a cross-sectional view of the attachment feature of figures 7-8 taken about section line 10-10 of figure 9 according to an embodiment.

Fig. 11 is a flow diagram of a method of manufacturing a biostimulator with a low-polarization coating on the attachment features according to an embodiment.

Fig. 12 is a perspective view of a distal portion of a biostimulator having a coaxial fixation element according to an embodiment.

Fig. 13 is a flow diagram of a method of manufacturing a biostimulator with a low-polarization coating on the internal fixation elements and attachment features according to an embodiment.

FIG. 14 is a diagram of atrial evoked response waveforms and electrode polarization waveforms through a broadband filter according to an embodiment.

FIG. 15 is a diagram of an atrial evoked response waveform and an electrode polarization waveform after low pass filtering and differentiation, according to one embodiment.

FIG. 16 is a diagram of atrial evoked response waveforms and electrode polarization waveforms with a high pass filter and integration according to one embodiment.

Detailed Description

Embodiments describe a biostimulator having electrodes coated with a low-polarization coating. The biostimulator may be a leadless biostimulator, such as a leadless cardiac pacemaker for pacing cardiac tissue. However, the biostimulator may be used for other applications, such as deep brain stimulation. Thus, the reference to a biostimulator as a cardiac pacemaker is not limiting. Furthermore, the reference to the biostimulator as being used to detect atrial evoked responses does not limit the application of the biostimulator, as the biostimulator may be used to detect other tissue or ventricular evoked responses, such as ventricular evoked responses. More particularly, the biostimulator may be implanted in an atrium, a ventricle, or another body tissue of the heart.

In various embodiments, reference is made to the accompanying drawings. 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 appearances of the phrases "one embodiment," "an embodiment," and the like in various places throughout this specification are not necessarily all 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 specification may refer to relative positions or orientations. For example, "distal" may indicate a first direction along a longitudinal axis of the biostimulator. Similarly, "proximal" may indicate a second direction opposite the first direction. These terms are provided to establish a relative frame of reference, however, are not intended to limit the use or orientation of the biostimulator to the particular configuration described in the various embodiments below.

In one aspect, the biostimulator includes a coating on the anode to impart a low polarization to the anode. The low polarization coating may be, for example, a titanium nitride or iridium oxide coating. In one embodiment, the anode is an attachment feature of the biostimulator for capturing and transferring torque to the biostimulator. A low polarization anode may improve atrial evoked response sensing for atrial auto-capture. More particularly, the coated anode enables atrial evoked response sensing to enable automatic output regulation of the biostimulator.

In one aspect, the biostimulator includes a coating on the cathode to impart low polarization to the cathode. The low polarization coating may be a two layer coating comprising a first layer comprising titanium nitride and a second layer comprising platinum black. For example, the first layer may be a base layer of titanium nitride and the second layer may be formed by platinizing the base layer. In one embodiment, the cathode is a fixation element of the biostimulator for attaching the biostimulator to the target tissue. A coated and platinized cathode may be used in combination with a low polarization anode. For example, a low polarization coating may be applied to the anode of the biostimulator, as described above. Low polarization cathodes and/or anodes may improve atrial evoked response sensing for atrial auto-capture. More particularly, the coated electrodes are capable of eliciting an atrial evoked response to achieve automatic output modulation by the biostimulator.

Figures 1-2 show how polarization of the electrodes can negatively impact the ability of the biostimulator to detect the chamber evoked response. Referring to FIG. 1, a diagram of atrial evoked response and electrode polarization waveforms is shown, according to one embodiment. A ventricular evoked response, such as the atrial evoked response 102 in this case, occurs in response to pacing from the biostimulator. For example, the biostimulator may deliver a pacing pulse between 0.5 to 1.5 volts over a period of 0.4ms to capture the atrium. When the biostimulator delivers pacing pulses to the atrium, a burst of excitation waves traverses the atrium, during which the tissue has a latency period and then depolarizes before contracting. The negative depolarization of the cell is an atrial evoked response 102 with an amplitude of a few millivolts and a duration of, for example, about 50ms or less.

During pacing, when current passes through the cathode of the biostimulator to the anode of the biostimulator, the electrode-electrolyte interface behaves like a capacitor and charges to tens or hundreds of millivolts. There is a time delay of 8ms after delivery of the atrial pacing pulse during which the biostimulator will perform blanking sensing while the pacing pulse is delivered and the pacing capacitor is charging. Charging occurs over a period of about 7ms and drives current through the electrode system (e.g., the cathode and anode of the biostimulator) in a direction that cancels some of the polarization that accumulates at the electrode interface. The blanking and charging periods have a short duration to avoid negative transitions affecting the atrial evoked response 102 that peak after about 20ms, and thus, residual charge may remain at the electrodes. An example of this phenomenon is represented in the form of electrode polarization 104, which shows that current passing through an electrode causes an initial polarization of about-5 mV, after which the polarization decays exponentially with a time constant of about 100 ms. Thus, the decay of the polarization on the electrodes may last longer than the atrial evoked response 102.

Referring to FIG. 2, a diagram of an atrial evoked response waveform superimposed on an electrode polarization waveform is shown, according to one embodiment. Electrode polarization 104 challenges the detection of atrial evoked responses 102. The detection of depolarization (atrial evoked response) of the cells occurs at the electrodes with residual polarization. Thus, the detection signal 206 may include residual charge on the cathode and anode superimposed on the atrial evoked response 102. However, the electrode polarization 104 may be so large that the atrial evoked response 102 is covered by the polarization potential. This is illustrated in fig. 2, which shows that the combined detection signal 206 is in the same order of magnitude as the polarization potential. As a result, simple signal filtering may make it difficult to select an atrial evoked response 102 from the sensed signal 206, which is determined by the electrode polarization 104.

With the findings of fig. 1-2 as background, it should be appreciated that reducing residual polarization on the anode and/or cathode may allow simple signal filtering (e.g., band-pass filtering or signal crossing) to be used to select the atrial evoked response 102 from the sensed signal 206. By reducing the electrode polarization 104, the detection signal 206 may be on the same order of magnitude as the atrial evoked response 102. The reduction of electrode polarization 104 may be achieved by a biostimulator configured as described below.

Referring to fig. 3, a schematic medial-lateral cross-section of a patient's heart illustrating an exemplary implantation of a biostimulator in the patient's heart is shown, according to an embodiment. The cardiac pacing system includes one or more biostimulators 300. The biostimulator 300 may be implanted at various target sites of a patient. For example, the biostimulator 300 may be implanted within a target tissue 302 in a patient's heart 304.

Biostimulator 300 may be a leadless biostimulator, such as a leadless cardiac pacemaker. Each biostimulator 300 may be placed in a ventricle, such as the right atrium and/or right ventricle of a patient's heart 304, or attached to the inside or outside of the ventricle. Attachment of the biostimulator 300 to the target tissue 302 may be accomplished by one or more fixation elements 306 (e.g., helical anchors). In particular embodiments, a leadless pacemaker may use two or more electrodes located on or within a housing or body of the leadless pacemaker to pace the ventricle when receiving a trigger signal from internal circuitry and/or from at least one other device within the body.

Referring to fig. 4A, a perspective view of a biostimulator delivery system is shown according to one embodiment. The biostimulator system may include a biostimulator delivery system 400 for delivering or retrieving a biostimulator 300 (e.g., a leadless pacemaker) into or from a patient. For example, biostimulator delivery system 400 can be biostimulator delivery system 402 for delivering biostimulator 300 into a patient.

The biostimulator delivery system 400 can include a handle 404 and an elongated catheter 406 extending distally from the handle 404 to a distal catheter end 408. Handle 404 may include multiple portions, such as a distal handle portion 410 and a proximal handle portion 412, as well as features that allow a user to provide input at the proximal end of the system that is converted into output at the distal end of the system. For example, the elongated catheter 406 may be a deflectable catheter, and the operator may use the handle 404 to manipulate the distal catheter end 408 within the patient.

In one embodiment, the handle 404 includes a deflection lever 414 that can be used to deflect the distal catheter end 408. By pivoting the deflection lever 414 toward the distal handle portion 410 of the handle 404, an operator may cause a pull ring assembly extending within the elongated catheter 406 to apply off-axis compression to the elongated catheter 406, resulting in lateral deflection of the distal catheter end 408.

The handle 404 may be used to apply torque to a docking cap 416 at the distal catheter end 408 of the system. In an embodiment, the proximal handle portion 412 may rotate and/or move longitudinally relative to the distal handle portion 410. For example, the distal handle portion 410 may be coupled to the elongate catheter 406 and the proximal handle portion 412 may be coupled to a torque shaft (not shown) extending within the elongate catheter 406. The docking cap 416 may be mounted on the torque shaft. Thus, the operator may rotate the proximal handle portion 412 relative to the distal handle portion 410 to apply torque to the torque shaft. The torque may cause the docking cap 416, which is rotationally coupled to the proximal handle portion 412 via a torque shaft, to rotate relative to the elongate catheter 406, which is rotationally coupled to the distal handle portion 410.

In one embodiment, the biostimulator delivery system 400 includes a protective sheath 418 mounted on the elongate catheter 406. The protective sheath 418 may be slidably disposed over the elongate catheter 406. The protective sheath 418 may include an atraumatic end 420, such as a soft, funnel-shaped distal portion that may slide distally over the elongate catheter 406 and/or the distal catheter end 408 of the biostimulator 300 (not shown). The atraumatic end 420 may have an outer dimension that may be larger than a proximal portion of the protective sheath 418. For example, the atraumatic end 420 may flare in a distal direction to a funnel opening that may be advanced over the docking cap 416 of the biostimulator delivery system 400. The outer dimension of the atraumatic end 420 may be larger than the area of the protective sheath 418 that supports the valve bypass tool 422.

The valve bypass tool 422 can be slidably disposed on the protective sheath 418 such that a distal portion of the valve bypass tool 422 can slide distally over the distal catheter end 408 of the elongate catheter 406 and/or the atraumatic end 420 of the protective sheath 418. More specifically, the valve bypass tool 422 can be inserted into an introducer (not shown) to access the patient vasculature, and after access is established, a distal portion of the protective sheath 418 and/or a distal end of the elongate catheter 406 can be advanced into the patient through the valve bypass tool 422.

Referring to fig. 4B, a distal perspective view of a biostimulator delivery system having a docking cap to receive a biostimulator is shown according to one embodiment. The distal catheter end 408 of the elongated catheter 406 may be selectively connected to the biostimulator 300. More specifically, the biostimulator 300 may be mounted on and/or coupled to the distal catheter end 408 of the elongated catheter 406. In an embodiment, the biostimulator 300 includes an attachment feature 450 that interfaces within or on the docking cap 416. The attachment feature 450 may include a channel (not shown) shaped and sized to receive one or more tethers 452. The tether 452 may comprise a wire, shaft, tube, string, rope, lace, or other similar structure that may extend throughout the catheter shaft. For example, the tether 452 may extend through a shaft lumen of the torque shaft assembly. In some embodiments, tether 452 comprises a shape memory material, such as nickel titanium. In other embodiments, tether 452 comprises a stainless steel wire or braid. The tether 452 may be inserted and locked into the attachment feature 450 to connect the biostimulator 300 to the biostimulator delivery system 400.

When the tether 452 is locked within the attachment feature 450, the tether may retract to pull the biostimulator 300 toward the docking cap 416. The docking cap 416 may include a docking cavity 454 shaped and dimensioned to receive the attachment feature 450 of the biostimulator 300. When the biostimulator 300 is moved toward the docking cap 416, the attachment feature 450 may be inserted into the docking cavity 454. Accordingly, the docking cavity 454 may receive the attachment feature 450 to dock the biostimulator 300 to the biostimulator delivery system 402 for delivery to the patient.

When the attachment feature 450 is received in the docking cap 416, torque may be transferred from the docking cap 416 to the biostimulator 300 via the torque shaft. More specifically, the torque shaft may be rotated in a first direction (e.g., clockwise) to transmit torque to the attachment feature 450 through the docking cap 416 and cause the fixation element 306 to engage and thread into the target tissue 302.

During delivery and/or retrieval of the biostimulator 300 from the patient, the biostimulator 300 may be protected by the atraumatic end 420 of the protective sheath 418. The atraumatic end 420 may have a braided or woven tubular construction. Thus, where the outer dimension of the biostimulator is greater than the inner diameter of the atraumatic end, the atraumatic end 420 may be advanced over the biostimulator 300 and may expand radially over the biostimulator. Accordingly, the atraumatic end 420 may cover the biostimulator 300 to protect the biostimulator during advancement into the patient.

Referring to fig. 5A, a perspective view of a biostimulator retrieval system is shown according to one embodiment. The biostimulator delivery system 400 can be a biostimulator retrieval system 502. Biostimulator retrieval system 502 may be used to remove one or more biostimulators 300 from an atrium and/or ventricle of patient's heart 304. Removal and retrieval of the biostimulator 300 may be accomplished on the endocardium. For example, the torque shaft of the elongate catheter 406 may be rotated in a second direction, e.g., counterclockwise, to disengage the biostimulator 300 from the target tissue 302. Thus, the structure of the biostimulator retrieval system 502 shown in fig. 5A may be similar to the structure shown and described with respect to the biostimulator delivery system 402 of fig. 4A to retrieve the biostimulator 300 from the target anatomy. For the sake of brevity, similarly numbered components of the biostimulator retrieval system 502 will not be repeated herein.

Referring to fig. 5B, a perspective view of a biostimulator retrieval system is shown according to one embodiment. The distal portion of the biostimulator retrieval system 502 can include features that engage the biostimulator 300 to facilitate capturing and unscrewing the biostimulator 300 from the target tissue 302. More specifically, the biostimulator retrieval system 502 may include a snare 504 extending through the elongate catheter 406 to grasp the biostimulator 300 or other medical device. The snare 504 may include at least one snare loop, such as a wire loop, extending from the elongate catheter 406. In some embodiments, as shown in fig. 5B, snare 504 may comprise multiple loops, for example three loops. However, any number of rings may be used as long as the elongated conduit 406 contains a volume sufficient to accommodate the rings.

When snare 504 is removed distally from the docking cap 416 from the biostimulator retrieval system 502, the loop may expand in size to assist the user in positioning the snare 504 around or near the biostimulator 300 to be retrieved. For example, a ring may be positioned around or near the attachment feature 450.

The distal portion of the retrieval catheter may include a docking cap 416 configured to allow the leadless pacemaker to dock with the biostimulator retrieval system 502 after engaging the pacemaker with the snare 504. A user may transmit torque through the torque shaft via the handle 404 to rotate the docking cap 416 relative to the elongate catheter 406. More specifically, the torque shaft may extend through the length of the catheter to a handle 404, such as a proximal handle portion 412, coupled to the torque shaft. Rotation or actuation of the handle 404 rotates the torque shaft, thereby rotating the docking cap 416 at the end of catheter retrieval. A protective sheath 418 may be positioned along the elongate catheter 406 and may be advanced or retracted to cover or uncover the docking cap 416 and leadless pacemaker through the use of an atraumatic tip 420.

During retrieval, the biostimulator retrieval system 502 can be navigated through the patient to the implantation site. The snare 504 may be placed on the attachment feature 450 and the loop of the snare 504 may be reduced in size to grip or lock onto the attachment feature 450 of the pacemaker. After capturing and locking snare 504 with the leadless pacemaker, biostimulator 300 may be docked within docking cap 416. More specifically, the attachment feature 450 of the biostimulator 300 can be pulled into the docking cavity 454 of the docking cap 416. In some embodiments, the docking cap 416 may include a key or interference feature configured to mate and engage with a corresponding key or feature on the biostimulator 300. In some embodiments, a key or slot on docking cap 416 may match a unique shape or feature of an accessory feature 450 of the pacemaker. Because a key or slot on or in docking cap 416 may mate with and engage attachment feature 450 of the pacemaker, the retrieval catheter may be configured to apply torque to the pacemaker to unscrew and remove the pacemaker from the tissue.

Referring to fig. 6A, a side view of a biostimulator having a low-polarization coating on an electrode is shown according to one embodiment. Biostimulator 300 may be a leadless pacemaker that may perform cardiac pacing and have many of the advantages of conventional cardiac pacemakers while extending performance, functionality, and operational characteristics. The biostimulator 300 may have two or more electrodes, such as a proximal electrode or anode 602 and a distal electrode or cathode 604, located within, on, or near the housing or body of the biostimulator 300. The distal electrode may be a dome-shaped electrode centrally located along the longitudinal axis 610. In an embodiment, one or more fixation elements 306 form at least a portion of the distal electrode. For example, the internal fixation element 606 may serve as an electrode, such as the cathode 604. In certain embodiments, the internal fixation element 606 is the only distal electrode. For example, the dome-shaped electrode may be omitted and/or may be a smooth distal surface of the biostimulator 300 that has no electrical function. The electrodes may deliver pacing pulses to the muscles of the ventricle. Alternatively, the electrodes may sense electrical activity from the muscle. For example, electrodes may be used to sense chamber-induced reactions to achieve auto-capture.

In an embodiment, the housing or body of the biostimulator 300 may include a housing 608. The housing 608 may have a longitudinal axis 610, and the distal electrode may be a distal pacing electrode mounted or coupled to the housing 608 along the longitudinal axis 610. The housing 608 may include a housing wall 612 containing an electronics compartment 614 (shown by hidden lines) to house circuitry suitable for different functions. For example, the electronics compartment 614 may contain: circuitry for sensing cardiac activity, such as atrial evoked response 102, from the electrodes; circuitry for receiving information from at least one other device via the electrodes; circuitry for generating pacing pulses for delivery to tissue through the electrodes; or other circuitry. The electronics compartment 614 may contain circuitry for transmitting information to at least one other device via the electrodes, and may optionally contain circuitry for monitoring the health of the device. The circuitry of biostimulator 300 may control these operations in a predetermined manner. In some embodiments of the cardiac pacing system, cardiac pacing is provided without a pulse generator located in the chest region or abdomen, without electrode leads separate from the pulse generator, without a communication coil or antenna, and without additional battery power to transmit communications.

The housing or body of the biostimulator 300 may include a battery assembly 616. Battery assembly 616 may be a primary battery to provide power for pacing, sensing, and communicating, which may include, for example, bi-directional communication with at least one other device. In one embodiment, battery assembly 616 includes a single battery compartment 618. A single battery compartment 618 may be coupled to housing 608. For example, housing 608 may be mounted at the distal end of single battery compartment 618. The battery compartment 618 contains electrolytes and provides power for pacing and sensing to the electronics within the electronics compartment 614 through feedthroughs. More specifically, the battery assembly 616 may include a spacer, which may be a pouch containing electrolyte, and the spacer may be housed within the cell case 618. In one embodiment, the cell cartridges 618 are in direct contact with the spacers. For example, the single battery compartment 618 may include an annular wall having an outer surface facing the ambient environment and an inner surface in contact with the spacer.

The annular wall of battery compartment 618 extends along a longitudinal axis 610. More specifically, the annular wall may extend longitudinally from the distal battery end to the proximal battery end. The battery assembly 616 may include positive and negative terminals at a distal end (not shown). The terminals may be electrically coupled to the electrolyte to transmit power from the battery assembly 616 to the internal electronics within the electronics compartment 614.

A leadless pacemaker or other leadless biostimulator may be secured to the intracardiac implant site by one or more active engagement mechanisms or securing mechanisms, such as screws or helical members threaded into the myocardium. In an embodiment, biostimulator 300 includes a plurality of fixation elements 306 coupled to housing 608. More specifically, biostimulator 300 may include a head assembly 620 mounted on the distal end of housing 608. An outer fixation element 622 may be mounted on the head assembly 620 and thus coupled to the housing 608.

The outer fixation element 622 may be a helical element that is threaded into the target tissue 302. More specifically, the outer fixation element 622 may extend helically from the flange of the biostimulator 300 mounted on the housing 608 to the distal end at the distal tip of the helix. Thus, the outer fixation element 622 may comprise an outer helix. Similarly, the internal fixation element 606 may be coupled to the housing 608 by a head assembly 620. More specifically, the internal fixation element 606 may extend helically from the flange to a distal end at the distal tip of the helix. Accordingly, the internal fixation element 606 may comprise an internal screw. In one embodiment, the inner and outer spirals rotate about a longitudinal axis 610. The inner fixation element 606 may be arranged coaxially with the outer fixation element 622 (fig. 6B). More specifically, the inner spiral may be radially inward of the outer spiral, e.g., radially between the outer spiral and the longitudinal axis 610. When the biostimulator 300 contacts the target tissue 302, the distal tip of the inner fixation element 606 and the outer fixation element 622 can pierce the tissue and the housing 608 can be rotated to thread the outer fixation element 622 into the target tissue 302 to pull the distal electrode 604 into contact with the tissue.

Biostimulator 300 may include attachment feature 450 coupled to battery assembly 616. More specifically, attachment feature 450 may be mounted and/or attached to a proximal end of cell compartment 618. In an embodiment, attachment feature 450 is coupled to cell assembly 616 by weld 624 (e.g., laser weld). For example, the weld 624 may extend circumferentially around the cell case 618 and a proximal lip of the attachment feature 450, as described below. As described above, the attachment feature 450 may be captured by the tether 452 or snare 504 of the biostimulator delivery system 400 and used to transmit torque from the docking cap 416 to the housing or body of the biostimulator 300. Thus, the attachment feature 450 allows torque to be transmitted to the fixation element 306 to screw the biostimulator 300 into the target tissue 302. However, both the fixation element 306 (e.g., the internal fixation element 606) and the attachment feature 450 may also provide electrical functionality. More specifically, the attachment feature 450 may be the anode 602 of the biostimulator 300, and the internal fixation element 606 may be the cathode 604 of the biostimulator 300.

To facilitate the electrical function of the anode 602 (e.g., attachment feature 450) and cathode 604 (e.g., internal fixation element 606), these elements may be coated in respective low polarization coatings. Such a coating can reduce the polarization of the electrode by effectively increasing the surface area of the electrode, thereby increasing the overall capacitance of the surface (which in turn reduces the polarization of the surface).

Examples may help illustrate the substantial effect of a low polarization coating on the exterior surface 626 of the attachment feature 450 and/or the exterior surface 628 of the inner fixation element 606 on element polarization. It has been found that for an attachment feature 450 having the structure described below and formed of titanium, under standard testing (described below), a polarization of 800mV was produced on the anode surface. This polarization will mask the atrial evoked response 102 (fig. 2). However, when treated with a low polarization coating described below, only 10mV polarization was produced on the anode surface. Also, it has been found that for an internal fixation element 606 having the structure described below and formed of platinum iridium, a polarization of 1000mV on the cathode surface is produced under standard testing. This polarization will mask the atrial evoked response 102. However, when treated with a low polarization coating described below, only 10-20mV of polarization is produced on the cathode surface. These examples represent a significant reduction in electrode polarization 104, which may allow biostimulator 300 to detect atrial evoked responses 102 using simple signal processing techniques.

For reference, the standard test described above involves a 10 milliamp constant current pulse of 1ms duration applied in a 0.9% sodium chloride solution between the electrode (e.g., internal fixation element 606 or attachment feature 450) and the large area titanium nitride plate. During the pulse, the potential between the electrodes increases as the polarization establishes the capacitive double layer. The polarization potential is a measure of the polarizability of the electrode and can be measured by the electronic system from the beginning to the end of the constant current pulse to determine electrode polarization 104.

In one embodiment, biostimulator 300 includes an insulating coating 630 on the single cell cartridge 618. The insulating coating 630 may be, for example, a parylene coating. Insulative coating 630 may provide insulation from surrounding tissue to limit or prevent current flow through cell cartridge 618 and direct current flow through attachment features 450. Thus, the entire outer surface of battery case 618 may be covered by insulative coating 630, for example, from welds 624 attaching attachment features 450 to battery case 618 to welds attaching battery case 618 to housing 608. Similarly, the outer surface of the housing 608 and/or the flange of the header assembly 620 may be coated with an insulating coating 630. Thus, in an embodiment, current may only flow through the inner fixation element 606 and the attachment feature 450. The chamber-induced reaction can be broadened by separating the anode 602 and cathode 604 as much as possible, for example by forming an insulator between the electrodes using an insulating coating 630. Wider evoked responses may be easier to detect because less bandwidth is required to detect such responses. Thus, when combined with the low-polarization coated electrodes described herein, the insulating coating 630 on the cell 618 can facilitate detection of chamber-induced reactions using simple signal processing techniques.

For completeness, it is noted that battery assembly 616 may also be coated with a non-polarizable coating. That is, a low-polarization coating used on attachment features 450 or internal fixation elements 606 may also be applied to the outer surface of cell case 618. Such a coating may increase the anode surface area and thereby reduce the polarization of the anode 602 at the expense of reducing the spacing between the electrodes.

In an embodiment, the low-polarization coating on the exterior surface 626 of the attachment feature 450 includes one or more non-polarized materials. For example, the low polarization coating on the attachment feature 450 may include one or more of titanium nitride, iridium oxide, or platinum black. The exterior surface 626 may be an outwardly facing surface of the attachment feature 450, which may be made of titanium, for example.

In one embodiment, the low polarization coating on the outer surface 628 of the inner fixation element 606 is a double layer coating. More specifically, the dual layer coating may include a first or base layer applied to the outer surface 628 of the inner fixation element 606. A second layer may then be applied over the first layer. In one embodiment, the first layer comprises titanium nitride sputtered on the outer surface 628 of the inner stationary element 606. The second layer may include platinum black. More particularly, the second layer may be a platinum-plated electrode deposition layer that covers the first layer and the outer surface 628 of the internal fixation element 606. Thus, the first layer may be between the second layer and the outer surface 628 of the inner fixation element 606.

The advantage of applying a two-layer coating to the internal fixation elements 606 has been demonstrated through testing. Applying a single titanium nitride coating to the internal fixation elements 606 provided a polarization of 73mV using standard testing. In contrast, when standard testing was used for the internal fixation element 606 having a dual layer coating including a first titanium nitride layer and a second platinum black layer, the polarization was reduced to 41 mV. The additional platinization reduces polarization even further. For example, platinizing at 800 microamps for 30 minutes produces 41mV electrode polarization 104, while platinizing at 800 microamps for 1 hour produces 18mV electrode polarization 104.

Low polarization coatings on the anode 602 and cathode 604 can effectively provide a larger electrode surface area. In the case of the anode 602, the geometric surface area (regardless of surface morphology) of the exterior surface 626 of the attachment features 450 described below may be at least 150mm²E.g. 177mm². In the case of the cathode 604, the geometric surface area of the outer surface 628 of the geometry of the internal fixation element 606 described below may be less than 20mm²E.g. 8mm². Therefore, it may be necessary to effectively increase the surface area of the cathode 604 to be larger than the surface area of the anode 602 to achieve a sufficient reduction in the polarization of both electrodes. In consideration of the surface morphology, the surface area can be effectively enlarged by increasing the surface area.

In one embodiment, the low polarization coating on the anode 602 includes a morphology having a microstructure on the order of 500 nm. It is contemplated that the bilayer coating on the cathode 604 can comprise a morphology having a smaller microstructure than the microstructure on the anode 602, such as a microstructure smaller than 500 nm. Smaller microstructures can provide a greater effective surface area (morphology considered) per geometric surface area (morphology not considered) than larger microstructures. The effective surface area may take into account morphology, such as surface roughness, as compared to a geometric surface area that does not take into account morphology. Thus, while the internal fixation element 606 may have a smaller geometric surface area than the attachment features 450, the ratio of the geometric surface area of the internal fixation element 606 to the geometric surface area of the attachment features 450 may be less than the ratio of the effective surface area of the internal fixation element 606 to the effective surface area of the attachment features 450. The platinization process of the electrowinning platinum creates a further sub-micron surface structure on the internal fixation element 606 that achieves the necessary real surface area, thereby reducing the electrode polarization 104.

Referring to fig. 7-8, a side view of the attachment feature 450 is shown. In an embodiment, the attachment feature 450 may include a base 702, a button 704, and a stem 706. The attachment feature 450 may have a one-piece construction. For example, the attachment feature 450 may be integrally formed from a rigid material such as titanium such that the base 702, the button 704, and the stem 706 are all part of a single structure. The structure may have a stem 706 that includes a single post interconnecting the base 702 and the button 704, making the integral attachment feature 450 strong and stiff. Thus, the rigid attachment feature 450 may effectively transfer torque from the delivery or retrieval system to the leadless pacemaker.

In an embodiment, base 702 includes a distal flange 708. The distal flange 708 may be a tubular portion of the attachment feature 450. For example, the distal flange 708 may have a cylindrical outer surface and may include a flange port 710 of the outer surface. The flange port 710 may extend in a longitudinal direction through the attachment feature 450 about a longitudinal axis 610. For example, the distal flange 708 may have an inner surface extending about the longitudinal axis 610 that defines a flange port 710.

The button 704 may be disposed along the longitudinal axis 610. For example, the button 704 may have a proximal button face 712 extending orthogonal to the longitudinal axis 610. In one embodiment, the proximal button face 712 has a face port about the longitudinal axis 610 (fig. 9-10). For example, the button 704 may have an inner surface extending about the longitudinal axis 610 that defines a face port.

The rod 706 may be disposed between the base 702 and the button 704 along the longitudinal axis 610. In an embodiment, the stem 706 has an annular stem wall (fig. 10) that extends from a distal end at the base 702 to a proximal end at the button 704. The stem may be continuous with the base 702 and the button portion of the attachment feature 450. The transition between the portions may be made in various ways. In at least one side view, the rod 706 can have a transverse dimension that is smaller than the base 702 and the button 704. For example, in the side view of fig. 7, the lateral dimension of the rod 706 may be the smallest lateral dimension of the attachment feature 450. Conversely, in the side view of fig. 8, the lateral dimensions of the button 704 and the rod 706 may be equal and are the smallest lateral dimension of the attachment feature 450.

One or more of the base portion or the button portion of the attachment feature 450 may smoothly transition into the stem 706. For example, the base 702 can include a taper that tapers radially inward from the distal flange 708 toward the stem 706. In an embodiment, the distal flange 708 has a circular transverse profile taken about a plane extending through the flange orthogonal to the longitudinal axis 610, and the stem 706 has a rectangular transverse profile. The diameter of the circular transverse profile may be larger than the length of the sides of the rectangular transverse profile. Thus, the base 702 may have a smaller and smaller circular transverse profile diameter at each point between the distal flange 708 and the outer proximal end of the base 702.

In at least one side view (fig. 7), the exterior surface 626 of the attachment feature 450 may transition abruptly inward from the taper to the stem 706 along a lateral surface at the outer proximal end. Conversely, in another side view (fig. 8), the taper may gradually transition to the stem 706 at the outer proximal end (without interruption).

In an embodiment, the distal button face 714 tapers radially inward from the proximal surface of the button 704 toward the stem 706. For example, the distal button face 714 can include an angled plane extending from a lateral perimeter of the button 704 toward the button 704. A distal button face 714 extending along an angled plane oblique to the longitudinal axis 610 can transition from the transverse perimeter toward the stem 706. The transverse perimeter may be a contour taken along a transverse plane through the button 704 that is orthogonal to the longitudinal axis 610. In one embodiment, the lateral perimeter is taken at an outermost point along the outer surface of the button 704. Thus, the lateral perimeter may represent the largest perimeter in any cross-section taken through the button 704.

In one embodiment, the transverse profile of the rod 706 extends about the longitudinal axis 610. For example, the rod 706 may be a single elongated rectangular column having a rectangular cross-section lofted along the longitudinal axis 610. Alternatively, the rod 706 may be a single elongated cylindrical post having a circular cross-section extending along the longitudinal axis 610. Similar monolithic pillar structures may have triangular, elliptical, etc. transverse profiles. The transverse profile of the rod 706 may be defined in part by a long rod axis and a short rod axis, which may be of equal (in the case of a square cross-section) or different (in the case of a rectangular cross-section) dimensions.

Referring to fig. 9, a proximal view of the attachment feature of fig. 7-8 is shown. The transverse perimeter of the button 704 may have an oval shape. For example, the transverse perimeter may have a major axis 904 and a minor axis 906 that are different to define an oval shape. The oval shape may be symmetric about one or more of the major axis 904 and the minor axis 906. As shown in fig. 9, the oval may be an ellipse that is symmetric about two axes. The transverse perimeter may be egg-shaped and thus may be symmetrical about only one axis. The ellipse may include a curved segment having a curved length, and the curved segment may be a portion of the ellipse that intersects the major axis 904. In an embodiment, the ellipse includes a straight segment having a straight length, and the straight segment intersects the minor axis 906. In another embodiment, the portion of the oval that intersects the major axis 904 may be straight, while the portion that intersects the minor axis 906 may be curved.

Referring to FIG. 10, a cross-sectional view of the attachment feature of FIGS. 7-8 taken about section line 10-10 of FIG. 9 is shown. In an embodiment, the attachment feature 450 includes an internal cavity 1002 that is laterally surrounded by the base 702, the button 704, and the stem 706. For example, the internal cavity 1002 may extend along the longitudinal axis 610 from the face port 902 to the flange port 710. The internal cavity 1002 may extend in a longitudinal direction through the base 702, button 704, and rod 706 from a proximal end of the attachment feature 450 to a distal end. Thus, the internal cavity 1002 provides an opening to receive a tether 452 of a delivery or retrieval system for docking and undocking, as described above.

An internal cavity 1002 extending longitudinally through the rod 706 may create an annular transverse profile. Rod 706 may be a tubular structure rather than a solid post. The tubular stem 706 may have an outer surface provided by the outer surface 626 of the attachment feature 450. An interior surface 1004 of attachment feature 450 may extend around interior cavity 1002 and may be an interior surface of tubular rod 706. More specifically, the exterior surface 626 and the interior surface 1004 may be continuous and define an annular shaft wall 1006 about the longitudinal axis 610. Thus, the stem 706 may have an internal lumen extending longitudinally between the base 702 and the button 704.

In terms of cavity portions, an interior cavity 1002 may be further defined that extends longitudinally through the attachment feature 450 and is surrounded in a transverse direction by an interior surface of the attachment feature 450. For example, the mounting cavity of the inner cavity 1002 may extend from the distal end of the distal flange 708 to the inner proximal face 1006 of the base 702. The mounting cavity may be a region of the internal cavity 1002 that receives a portion of the battery cell 618 (e.g., an end boss of the battery cell 618), as described below. Inner proximal surface 1006 may extend orthogonal to longitudinal axis 610. The inner surface of the attachment feature 450 surrounding the mounting cavity may have a similar form as the outer surface 626 of the attachment feature 450 surrounding the inner surface. For example, the region of the mounting cavity within the distal flange 708 may be cylindrical, while the region of the mounting cavity within the taper may be frustoconical.

The internal cavity 1002 may include a captive cavity proximate to the mounting cavity. The tethered cavity can be a region of the internal cavity 1002 that receives the tether 452 of the delivery or retrieval system during docking or undocking of the leadless pacemaker, as described above. More particularly, the width of the captive cavity may be greater than the combined width of the two captive distal features. The captive cavity may extend proximally from an inner proximal face 1006 of the base 702 to an inner distal face 1008 of the button 704. The inner distal face 1008 may extend orthogonal to the longitudinal axis 610. The inner surface of the attachment feature 450 (a portion of which is the inner surface 1004) surrounding the captive cavity may be cylindrical.

The internal cavity 1002 may include a passage cavity proximate to a captive cavity. The passage cavity may be a region of the internal cavity 1002 that receives the tether 452 of the delivery or retrieval system during docking or undocking of the leadless pacemaker, as described above. More particularly, the width of the channel cavity may be less than the combined width of the two tether distal features. The channel cavity may extend proximally from the inner distal face 1008 to the face port 902. The inner surface of the attachment feature 450 surrounding the channel cavity may be, for example, cylindrical.

All or a portion of the surface of the attachment feature 450 described above may be coated with a low-polarization coating. In one embodiment, the low-polarization coating covers the entire exterior surface 626. Exterior surfaces 626 include those surfaces visible in fig. 7-9. In contrast, the low-polarization coating may cover only a portion of the interior surface 1004. For example, only portions of interior surface 1004 that are susceptible to overspray during titanium nitride sputtering may be coated. Such portions may include regions of the interior surface 1004 near the proximal end (e.g., near the face port 902) and the distal end (e.g., near the flange port 710) of the interior cavity 1002. Thus, the low-polarization coating may reduce the polarization of the attachment features 450 by increasing only the true surface area of the exterior surface 626.

Referring to fig. 11, a flow diagram of a method of manufacturing a biostimulator with a low-polarization coating on the attachment features is shown, according to an embodiment. Biostimulator 300 may have a low-polarization coating on attachment feature 450 and may or may not have a low-polarization coating on inner fixation element 606. The process of manufacturing biostimulator 300 to include coated attachment feature 450 coupled to battery assembly 616 may begin at operation 1102, where a low-polarization coating is disposed on exterior surface 626 of attachment feature 450. Disposing a low-polarization coating on the attachment feature 450 may include sputtering one or more of titanium nitride or iridium oxide onto the outer surface 626. The low-polarization coating may cover the entire exterior surface 626 of the attachment feature 450 and all or some of the interior surface 1004 of the attachment feature 450. When the attachment feature 450 has not been coupled to the battery assembly 616, a sputtering process may be performed. More specifically, attachment features 450 may be coated with a low polarization coating prior to assembly of biostimulator 300.

At operation 1104, an insulative coating 630 may optionally be disposed on the cell cartridges 618 of the battery assembly 616. The insulating coating 630 may extend from the distal cell end to the proximal cell end on the annular wall of the cell case 618. Similar to the coating of attachment features 450, the insulation of cell compartments 618 may be applied when cell assembly 616 is at the sub-component level. More specifically, the cell cassettes 618 may be insulated prior to assembly of the biostimulator 300.

At operation 1106, the attachment feature 450 is mounted on the battery assembly 616. Mounting the distal flange 708 of the attachment feature 450 onto the battery proximal end can be performed after disposing the low-polarization coating on the exterior surface 626 of the attachment feature 450. Doing so provides a convenient and robust manufacturing process, as it has been found more difficult to cover accessory feature 450 with a low-polarization coating after coupling accessory feature 450 to battery assembly 616.

At operation 1108, the attachment features 450 are welded to the battery assembly 616 to secure the components to one another. More specifically, the attachment features 450 may be welded circumferentially to the battery assembly 616 around the base 702 and the cell case 618. Laser welding may be used to form weld 624 around the proximal cell end of cell cartridge 618 and distal flange 708 of attachment feature 450. The circumferential weld may be narrow and thus may have minimal impact on the integrity of the insulating coating 630 and the low polarization coating. Thus, a biostimulator 300 having an anode 602 that exhibits low electrode polarization 104 may be provided.

Referring to fig. 12, a perspective view of a distal portion of a biostimulator having a coaxial fixation element is shown according to one embodiment. The biostimulator 300 may include an inner fixation element 606 nested within an outer fixation element 622. More specifically, the inner fixation element 606 can include an inner helix 1202 that is radially inward from an outer helix 1204 of the outer fixation element 622. The spirals may extend or rotate about the longitudinal axis 610 and the fixation element 306 may extend along the respective spiral. The helical radius of the outer fixation element 622 may be larger than the helical radius of the inner fixation element 606. As described below, the spirals can have opposing configurations that facilitate tissue penetration.

In one embodiment, the spirals have the same clock relative to the longitudinal axis 610. More specifically, the inner and outer spirals 1202, 1204 can rotate in the same direction about the longitudinal axis 610. For example, both helices of fixation element 306 may extend in a counterclockwise (e.g., right-handed) direction about longitudinal axis 610 to the respective distal tips. Similar timing of the helix may cause the fixation elements 306 to simultaneously advance or retract from the target tissue 302 as the biostimulator 300 rotates. Alternatively, the helix may rotate in different directions along the longitudinal axis 610.

The relative orientation characteristics of the fixation elements 306 may be predetermined. For example, the distal tip of fixation element 306 may terminate in a different radial direction than longitudinal axis 610, and the angular spacing between the termination points may be controlled. It is contemplated that a greater angular distance between the distal tips of the fixation elements 306 may help the fixation elements achieve greater purchase in the target tissue 302. The maximum spacing may make it easier to screw fixation elements 306 into tissue, and there is less chance that the tunnels formed by advanced fixation elements 306 will intersect within the tissue as fixation elements 306 are screwed into the tissue. Thus, the distance and angular separation between the distal tips can be maximized to enhance tissue engagement.

The head assembly 620 of the biostimulator 300 may include a screw mount 1203 that may be mounted on the housing 608. For example, the screw mount 1203 may have internal threads that are mounted on external threads of the flange 1205 by a threaded connection. Biostimulator 300 may include a cup 1206. In one embodiment, the inner fixation element 606 is mounted on the cup 1206 radially inward from the outer fixation element 622 mounted on the screw mount 1203. Pacing pulses may be delivered to the internal fixation element 606 through the cup 1206 to pace the target tissue 302.

The cup 1206 may contain a filler (not shown). The filler may be referred to as a controlled release device (MCRD) overall, and may include a therapeutic material. The therapeutic agent can include corticosteroids such as dexamethasone sodium phosphate, dexamethasone acetate, and the like. In addition, the therapeutic agent may be loaded in a silicone matrix. Thus, the filler can deliver a prescribed dose of a therapeutic agent, such as a corticosteroid, into the target tissue 302. When target tissue 302 is drawn into cup 1206 through coaxial fixation element 306, a therapeutic agent can be effectively delivered into the tissue after biostimulator 300 is implanted in a patient as biostimulator 300 is screwed into the tissue. Thus, inflammation or damage to the captured tissue may be reduced.

All or a portion of the surface of the internal fixation element 606 may be covered by a low-polarization coating. In one embodiment, the low-polarization coating covers the entire outer surface 628 of the inner fixation element 606. The outer surface 628 comprises the surface of the inner fixation element 606 that is visible in fig. 12. As described above, the low polarization coating on the outer surface 628 may comprise a two-layer coating having a titanium nitride base layer covered by a platinized top layer. Thus, the low polarization coating may reduce the polarization of the inner fixation element 606 by increasing the true surface area of the outer surface 628.

Referring to fig. 13, a flow diagram of a method of manufacturing a biostimulator with a low-polarization coating on the internal fixation elements and attachment features is shown, according to one embodiment. Similar to the fabrication of attachment feature 450, a low-polarization coating may be applied to inner fixation element 606 prior to integrating the sub-components into biostimulator 300. In operation 1302, a low-polarization coating, which may be the first low-polarization coating in the manufacturing process, may be disposed on the cathode 604. The cathode 604 may be the inner stationary element 606 and thus a low polarization coating may be applied to the outer surface 628 of the inner stationary element 606. However, it should be understood that the cathode 604 may be in the shape of a spherical or dome-shaped electrode. More specifically, a low-polarization coating may be applied to any portion of the biostimulator 300 that serves as a cathode 604 to deliver pacing pulses to the target tissue 302.

Applying a low polarization coating to the cathode 604 may include a number of sub-operations. A first sub-operation may include sputtering a low polarization material such as titanium nitride onto outer surface 628 which is a base layer. The second sub-operation may include platinizing the base layer to form the top layer. The electrodes may be platinized by driving the electrodes with a cathodic current in an aqueous solution. For example, the aqueous solution may be a 0.072 molar solution of chloroplatinic acid with about 0.00013 molar lead acetate. This may be an aqueous solution of about 2.92% chloroplatinic acid and about 0.044% lead acetate. The counter electrode or anode used in the platinizing process may be platinum. The applied current may be in the range of 10 milliamps per square centimeter for a total of 330 milliamp-seconds per square centimeter. However, the described process is provided by way of example only, and other processes may be used to provide platinization, resulting in advantageous performance of the cathode 604. More specifically, a low polarization coating on the cathode 604 may be formed by one or more sub-operations to make the true surface area of the cathode 604 large enough to reduce the electrode polarization 104.

At operation 1304, the internal fixation element 606 is mounted to the housing 608 or another portion of the housing or shell of the biostimulator 300. The mounting operation may be performed after the low-polarization coating is disposed on the outer surface 628. Performing the installation at this stage is convenient because it may be difficult to coat the internal fixation element 606 after it is integrated into the biostimulator 300. As described above, the internal fixation element 606 may be coupled to the cup 1206 attached to the screw mount 1203. The screw mount 1203, in turn, may be screwed onto the flange 1205 of the head assembly 620, and the head assembly 620 may then be mounted on the distal end of the housing 608 and welded thereto. Thus, at operation 1304, the internal fixation element 606 may be indirectly mounted to the housing 608.

At operation 1306, the outer fixation element 622 is mounted on the housing 608. Similar to the inner fixation element 606, an outer fixation element 622 may be indirectly mounted on the housing 608. For example, the outer fixation element 622 may be threaded onto the screw mount 1203, which is coupled to the housing 608 through the flange 1205 of the head assembly 620. The flange 1205 may be secured to the distal end of the housing 608 by a weld (e.g., a laser weld) extending circumferentially around the housing 608 and the flange 1205. Thus, after operation 1306, the distal portion of the biostimulator 300 including the housing 608 and the head assembly 620 can be assembled.

At operation 1308, formation of a proximal portion of biostimulator 300 may be initiated by providing a second low-polarization coating on exterior surface 626 of attachment feature 450. Operation 1308 may be identical to operation 1102 described above. For example, the low polarization coating may be a titanium nitride coating applied to the attachment feature 450 at the sub-component level.

At operation 1310, after applying the low-polarization coating to the exterior surface 626, the attachment feature 450 may be mounted on the proximal end of the battery cell 618. The attachment feature 450 may be secured to the cell case 618 via the weld 624, as described above. Thus, after operation 1310, the proximal portion of the biostimulator 300 including the attachment feature 450 and the battery assembly 616 may be assembled.

At operation 1312, housing 608 may be mounted on the distal end of single battery compartment 618. The proximal end of the housing 608 may mate with the distal end of the cell cartridge 618 and a weld may be formed circumferentially around the housing 608 and the cell cartridge 618 to secure the components. When housing 608 is mounted on battery compartment 618, the feedthrough pins of battery assembly 616 may connect to corresponding connectors of the electronic device within electronic device compartment 614. Thus, assembly of the biostimulator 300 can be completed with a battery assembly 616 that can provide power to the electronics to deliver pacing pulses to the target tissue 302 through the internal fixation element 606.

The biostimulator 300 having the above-described features may be used to pace the target tissue 302. After pacing, the biostimulator sensing circuit may perform capture verification by sensing atrial evoked response potentials between the cathode 604 and the anode 602. The low polarization electrodes of biostimulator 300 allow atrial automatic capture based on the sensed evoked response. More particularly, the sensing system may use a differentiating device to differentiate the atrial evoked response 102. The differentiation of the atrial evoked response 102 may be performed by using a simple analog or digital algorithm of the detected atrial evoked response, a simple digital derivative of the atrial evoked response, or a simple digital integral of the atrial evoked response. More specifically, the detection signal 206, a first derivative of the detection signal, or an integral of the detection signal may be compared to a threshold to distinguish whether the atrium has been captured.

Referring to FIG. 14, a diagram of an atrial evoked response waveform and an electrode polarization waveform through a broadband filter is shown, according to one embodiment. The filtered detection signal 1402 may be detected by a sensing system between the cathode 604 and the anode 602. The filtered detection signal 1402 represents the combined atrial evoked response 102 and electrode polarization 104 signals, such as the detection signal 206, that have passed through the broadband filter. For example, the wideband filter may have a bandpass of 1 to 50 Hz. The polarization of the electrode is reduced by the above structure. For example, the anode 602 and cathode 604 may be treated with respective low polarization coatings to reduce the electrode polarization 104 by an order of magnitude from 5mV to 0.5 mV. Thus, the basic shape of the atrial evoked response 102 is retained in the filtered sensed signal 1402. The filtered detection signal 1402 can be compared to a threshold 1404 by one or more processors of the biostimulator 300 executing a simple threshold detector algorithm. For example, if the filtered detection signal 1402 falls below the threshold 1404 of-0.7 mV, the processor may determine that atrial capture has occurred.

Referring to FIG. 15, a diagram of an atrial evoked response waveform and an electrode polarization waveform after low pass filtering and differentiation is shown, according to one embodiment. The processor of the biostimulator 300 may implement a simple integral to distinguish the atrial evoked response 102. The detection signal 206 combining the atrial evoked response 102 and the electrode polarization 104 may be passed through a low pass filter having a high frequency cut-off and a predetermined gain to produce a filtered detection signal 1402. For example, the high frequency cutoff may be 1Hz and the predetermined gain may be 30 x. Using the biostimulator 300 with low polarization electrodes as described above, the biostimulator 300 can detect the integrated evoked response 1502. The integrated evoked response 1502 may be determined by the processor of the biostimulator 300 using a simple analog or digital algorithm to integrate the filtered detection signal 1402. The processor may compare the integrated evoked response 1502 to a threshold 1404 to confirm atrial capture. For example, if the integrated evoked response 1502 falls below the threshold 1404 of-0.7 mV, the processor may determine that an atrial capture has occurred. Alternatively, the biostimulator 300 may use an analog-to-digital converter to digitize the detected signal 206 and sum the points of the digitized signal. Assuming that the atrial evoked response 102 is sampled at 256Hz, this may require very few, e.g., 13 summations and thus may be performed with low processing power.

Referring to FIG. 16, a diagram of an atrial evoked response waveform and an electrode polarization waveform with a high pass filter and integration is shown, according to one embodiment. The processor of the biostimulator 300 may implement a simple differentiation to differentiate the atrial evoked response 102. The detection signal 206 combining the atrial evoked response 102 and the electrode polarization 104 may be passed through a high pass filter having a predetermined low frequency roll-off to produce a filtered detection signal 1402. For example, the low frequency cutoff may be 1Hz, and the predetermined low frequency roll wave may be 18 Hz. Using the biostimulator 300 with low polarization electrodes as described above, the biostimulator 300 can detect the differentiated evoked response 1602. The differentiated evoked response 1602 may be determined by the processor of the biostimulator 300 using a simple analog or digital algorithm to differentiate the filtered detection signal 1402. The processor may compare the differentiated evoked response 1602 to a threshold 1404 to confirm atrial capture. For example, if the differentiated evoked response 1602 exceeds the threshold 1404 of 0.2mV, the processor may determine that an atrial capture has occurred. Alternatively, the biostimulator 300 may use an analog-to-digital converter to digitize the detection signal 206 and obtain the difference between the pair of points. Assuming that the atrial evoked response 102 is sampled at 256Hz, this may require very few, e.g., 13 subtractions, and thus may be performed with low processing power. A negative detection threshold 1404 may be used for comparison with the differentiated evoked response 1602, however it is expected that positive derivative detection may be more reliable.

Based on the above data, it has been shown that a low-polarization coating on the electrodes of biostimulator 300 can reduce electrode polarization, such that simple signal processing techniques (including direct signal comparison, differentiation and comparison, or integration and comparison) can be used to reliably detect atrial evoked responses (or another ventricular or tissue evoked response). Accordingly, the biostimulator 300 having the above-described structure and configuration can perform automatic capture without increasing the battery capacity. Thus, the described biostimulator 300 may reliably pace the heart over an extended period of time.

In one embodiment, the biostimulator includes a battery assembly including a single battery compartment containing an electrolyte. The biostimulator includes an attachment feature connected to the battery assembly. The attachment feature includes a stem having an annular stem wall extending between a base and a button. The biostimulator includes a low-polarization coating on the exterior surface of the attachment feature.

In an embodiment, the low polarization coating comprises one or more of titanium nitride or iridium oxide.

In one embodiment, the low-polarization coating covers the entire exterior surface.

In an embodiment, the attachment feature includes an interior surface surrounding the interior cavity, and the low-polarization coating covers only a portion of the interior surface.

In an embodiment, the attachment feature is coupled to the battery assembly by a weld extending circumferentially around the base and the cell box.

In one embodiment, the biostimulator includes an insulating coating on the single cell cartridge.

In an embodiment, the attachment feature is integrally formed of a rigid material and the rod is a single post having an annular transverse profile.

In one embodiment, the attachment feature is an anode of the biostimulator.

In one embodiment, a biostimulator system includes a delivery system including a catheter having a distal end. The biostimulator system includes a biostimulator coupled to the distal end. The biostimulator includes a battery assembly including a single battery compartment containing an electrolyte. The biostimulator includes an attachment feature coupled to the battery assembly. The attachment feature includes: a stem having an annular stem wall extending between a base and a button; and a low polarization coating on an exterior surface of the attachment feature.

In an embodiment, the low polarization coating comprises one or more of titanium nitride or iridium oxide.

In one embodiment, the low-polarization coating covers the entire exterior surface.

In an embodiment, the attachment feature includes an interior surface surrounding the interior cavity. The low-polarization coating covers only a portion of the interior surface.

In an embodiment, the attachment feature is coupled to the battery assembly by a weld extending circumferentially around the base and the cell box.

In one embodiment, the attachment feature is an anode of the biostimulator.

In an embodiment, a method includes providing a low-polarization coating on an outer surface of an attachment feature. The attachment feature includes a stem having an annular stem wall extending between a base and a button. The method includes mounting the attachment feature on the battery assembly after disposing the low-polarization coating on the exterior surface. The battery assembly includes a single case containing an electrolyte.

In an embodiment, the low polarization coating comprises one or more of titanium nitride or iridium oxide.

In one embodiment, the low-polarization coating covers the entire exterior surface.

In an embodiment, the attachment feature includes an interior surface surrounding the interior cavity. The low-polarization coating covers only a portion of the interior surface.

In an embodiment, the method includes welding the attachment feature to the battery assembly circumferentially around the base and the cell case.

In one embodiment, the method includes providing an insulating coating on the cell case.

In one embodiment, a biostimulator includes a housing including a housing wall having an electronics compartment. The biostimulator includes an outer fixation element coupled to the housing. The external fixation element comprises an external thread. The biostimulator includes an internal fixation element coupled to the housing. The inner fixation element includes an inner helix radially inward of the outer helix. The biostimulator includes a first low-polarization coating on the outer surface of the inner fixation element.

In an embodiment, the first low-polarization coating includes a first layer having titanium nitride and a second layer having platinum black.

In one embodiment, the first layer is between the second layer and the outer surface.

In one embodiment, the first low-polarization coating covers the entire outer surface.

In one embodiment, the biostimulator includes a battery assembly including a single battery compartment containing an electrolyte. The housing is mounted on the distal end of the single battery compartment. The biostimulator includes an attachment feature mounted on the proximal end of the single battery compartment. The attachment feature includes a stem having an annular stem wall extending between a base and a button. The biostimulator includes a second low-polarization coating on the exterior surface of the attachment feature.

In an embodiment, the second low polarization coating comprises one or more of titanium nitride or iridium oxide.

In an embodiment, the first low-polarization coating has more microstructures than the second low-polarization coating.

In one embodiment, the internal fixation element is a cathode of the biostimulator and the attachment feature is an anode of the biostimulator.

In one embodiment, a biostimulator system includes a delivery system including a catheter having a distal end. The biostimulator system includes a biostimulator coupled to the distal end. The biostimulator includes a housing including a housing wall having an electronics compartment. The biostimulator includes an outer fixation element coupled to the housing. The external fixation element comprises an external thread. The biostimulator includes an internal fixation element coupled to the housing. The inner fixation element includes an inner helix radially inward of the outer helix. The biostimulator includes a first low-polarization coating on the outer surface of the inner fixation element.

In an embodiment, the first low-polarization coating includes a first layer having titanium nitride and a second layer having platinum black.

In one embodiment, the first layer is between the second layer and the outer surface.

In one embodiment, the biostimulator system includes a battery assembly including a single battery compartment containing an electrolyte. The housing is mounted on the distal end of the single battery compartment. The biostimulator system includes an attachment feature mounted on the proximal end of the battery cell cartridge. The attachment feature includes a stem having an annular stem wall extending between a base and a button. The biostimulator system includes a second low-polarization coating on the exterior surface of the attachment feature.

In an embodiment, the second low polarization coating comprises one or more of titanium nitride or iridium oxide.

In an embodiment, the first low-polarization coating has more microstructures than the second low-polarization coating.

In one embodiment, the internal fixation element is a cathode of the biostimulator. The attachment feature is an anode of the biostimulator.

In one embodiment, a method includes providing a first low-polarization coating on an outer surface of an inner fixation element. The internal fixation element includes an internal screw. The method includes mounting the inner fixation element on a housing comprising a housing wall containing the electronics compartment after disposing the first low-polarization coating on the outer surface. The method includes mounting an outer fixation element to the housing. The outer fixation element includes an outer helix radially outward of the inner helix.

In an embodiment, the first low-polarization coating includes a first layer having titanium nitride and a second layer having platinum black.

In one embodiment, the first layer is between the second layer and the outer surface.

In an embodiment, the method includes providing a second low-polarization coating on an exterior surface of the attachment feature. The attachment feature includes a stem having an annular stem wall extending between a base and a button. The method includes mounting an attachment feature on a proximal end of a cell casing of the battery assembly after disposing a second low-polarization coating on the exterior surface. The single cell cartridge contains an electrolyte. The method includes mounting the housing on the distal end of the single battery compartment.

In an embodiment, the first low-polarization coating has more microstructures than the second low-polarization coating.

In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will be evident that various modifications may be made thereto without departing from the broader spirit and scope of the invention as set forth in the following claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.