Patent Publication Number: US-2021187310-A1

Title: Biostimulator header assembly having integrated antenna

Description:
This application claims the benefit of priority to U.S. Provisional Patent Application No. 62/949,996 entitled “BIOSTIMULATOR HEADER ASSEMBLY HAVING INTEGRATED ANTENNA” filed on Dec. 18, 2019, and that patent application is incorporated herein in its entirety. 
    
    
     BACKGROUND 
     Field 
     The present disclosure relates to biostimulators. More specifically, the present disclosure relates to leadless biostimulators having header assemblies. 
     Background Information 
     Cardiac pacing by an artificial pacemaker provides an electrical stimulation to 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&#39;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. 
     Cardiac pacing by currently available or conventional pacemakers is usually performed by a pulse generator implanted subcutaneously or sub-muscularly in or near a patient&#39;s pectoral region. Pulse generator parameters are usually interrogated and modified by a programming device outside the body, via a loosely-coupled transformer with one inductance within the body and another outside, or via electromagnetic radiation with one antenna within the body and another outside. The generator usually connects to the proximal end of one or more implanted leads, the distal end of which contains one or more electrodes for positioning adjacent to the inside or outside wall of a cardiac chamber. The leads have an insulated electrical conductor or conductors for connecting the pulse generator to electrodes in the heart. 
     Conventional pacemakers have several drawbacks, including complex connections between the leads and the pulse generator, and a risk of infection and morbidity due to the separate leads and pulse generator components. Self-contained and self-sustainable biostimulators, or so-called leadless biostimulators, have been developed to address such drawbacks. A leadless biostimulator has no connections between the pulse generator and a lead. Furthermore, the leadless biostimulator can be attached to tissue within a dynamic environment, e.g., within a chamber of a beating heart, with reduced likelihood of infection. Accordingly, leadless biostimulator technology represents the latest advancement in pacemaker technology. The leadless biostimulator can interact with the tissue using a header assembly, which typically includes a fixation mechanism to attach to the tissue and an electrical feedthrough to deliver electrical impulses from the pulse generator to the tissue. 
     SUMMARY 
     Existing leadless biostimulators could benefit from the ability to communicate data, such as performance information, from the implanted biostimulator to a device external to the patient. To enable such communication, an antenna can be integrated into the leadless biostimulator. It may be undesirable, however, to integrate the antenna if it requires an increase in a size of the biostimulator. For example, the antenna may require an increase to the size of a biostimulator housing, which may negatively impact device implantation and/or performance. Compactness of implantable devices is paramount, and thus, there is a need to integrate the antenna within the biostimulator without changing the form factor of the biostimulator. 
     A biostimulator having an antenna to wirelessly communicate signals is provided. The antenna is integrated into an insulator of a header assembly, and thus, does not require enlargement of the biostimulator form factor. The insulator can include, for example, a ceramic material, and the antenna can be a monopole antenna embedded within the ceramic material. 
     The biostimulator can include a housing having an electronics compartment, and the header assembly can be mounted on the housing. More particularly, the header assembly can include a flange, and the flange can be mounted on the housing to enclose the electronics compartment. Electronic circuitry, such as communication circuitry, can be located within the electronics compartment. In an embodiment, the antenna has an antenna lead that connects to the electronic circuitry. The antenna can be embedded within the insulator of the header assembly, and thus, the antenna lead can extend from the electronic circuitry contained within the electronics compartment through the insulator to one or more antenna loops. 
     In an embodiment, the insulator includes an insulator wall extending around an insulator cavity. The insulator cavity extends along a longitudinal axis from an insulator distal end of the insulator wall to an insulator proximal end of the insulator wall. An electrode of the header assembly can be disposed within the insulator cavity. The antenna has one or more antenna loops embedded in the insulator wall between the insulator distal end and the insulator proximal end. Thus, the antenna loop(s) can extend around the electrode. The antenna loop(s) can include one or more open loops. For example, the one or more open loops can include several open loops extending around the longitudinal axis. In an embodiment, one or more of the antenna loop(s) are located distal to the flange of the header assembly, and thus, the flange does not interfere with communication by the antenna loop(s). 
     In an embodiment, the header assembly includes a helix mount mounted on the flange. The header assembly can also include a gasket. The gasket can have an annular body extending around the electrode. The annular body may be resiliently compressed between the helix mount and one of the flange or the insulator. In an embodiment, the gasket is resiliently compressed between the helix mount and the flange. In an embodiment, the gasket is resiliently compressed between the helix mount and the insulator. The gasket prevents liquid ingress that could interfere with device function. 
     In an embodiment, a distal section of the insulator wall of the insulator has a first transverse width larger than a second transverse width of a proximal section of the insulator wall. The antenna loop(s) can be embedded within the distal section, which can be located distal to the flange. The antenna lead can run through the proximal section, which can be located radially inward from the flange. Accordingly, the antenna lead can carry signals through the proximal section to the antenna loop(s) in the distal section for transmission. 
     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 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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features of the invention are set forth with particularity in the claims that follow. 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 perspective view of a biostimulator, in accordance with an embodiment. 
         FIG. 2  is an exploded view of a biostimulator, in accordance with an embodiment. 
         FIG. 3  is a perspective view of a feedthrough subassembly of a header assembly of a biostimulator, in accordance with an embodiment. 
         FIG. 4  is an exploded view of a feedthrough subassembly of a header assembly of a biostimulator, in accordance with an embodiment. 
         FIG. 5  is a cross-sectional view of a header assembly of a biostimulator, in accordance with an embodiment. 
         FIG. 6  is a perspective view of an insulator for a header assembly of a biostimulator, in accordance with an embodiment. 
         FIG. 7  is a cross-sectional view of a header assembly of a biostimulator, in accordance with an embodiment. 
         FIG. 8  is a perspective view of an insulator for a header assembly of a biostimulator, in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments describe a biostimulator, e.g., a leadless pacemaker, having a header assembly that includes an antenna. The biostimulator may be used to pace cardiac tissue. Alternatively, the biostimulator may be used in other applications, such as deep brain stimulation. Thus, reference to the biostimulator as being a leadless cardiac pacemaker 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 such as a leadless cardiac pacemaker is provided. The biostimulator includes an antenna integrated into a header assembly. More particularly, the antenna can be integrated into a feedthrough subassembly of the header assembly, e.g., by embedding the antenna within an insulator of the subassembly. Embedding the antenna within a ceramic material of the insulator allows integration of the antenna without increasing a form factor of the biostimulator. The insulator can separate a flange of the biostimulator from an electrode of the biostimulator, and at least a portion of the insulator can extend distal to the flange. Accordingly, the antenna can include one or more loops, e.g., open loops, embedded within the insulator distal to the flange. Positioning the one or more loops distal to the flange can reduce signal interference from the flange, which may increase a communication range of the antenna. The header assembly may include a gasket to prevent ingress of fluid into an internal volume of the biostimulator, and the gasket may be located outside of or inside of the insulator. 
     Referring to  FIG. 1 , a perspective view of a biostimulator is shown in accordance with an embodiment. A biostimulator  100  can be a leadless biostimulator, e.g., a leadless cardiac pacemaker. The biostimulator  100  can include an electrode  104  at a distal end of the device, and a proximal electrode  106  proximal to the electrode  104 . The electrodes can be integral to a housing  102 , or connected to the housing, e.g., at a distance of less than several centimeters from the housing  102 . The housing  102  can contain an energy source to provide power to the pacing electrodes. The energy source can be a battery, such as a lithium carbon monofluoride (CFx) cell, or a hybrid battery, such as a combined CFx and silver vanadium oxide (SVO/CFx) mixed-chemistry cell. Similarly, the energy source can be an ultracapacitor. In an embodiment, the energy source can be an energy harvesting device, such as a piezoelectric device that converts mechanical strain into electrical current or voltage. The energy source can also be an ultrasound transmitter that uses ultrasound technology to transfer energy from an ultrasound subcutaneous pulse generator to a receiver-electrode implanted on an endocardial wall. 
     The biostimulator  100  can have a longitudinal axis  108 . The longitudinal axis  108  can be an axis of symmetry, along which several biostimulator components are disposed. For example, a header assembly  110  can be mounted on a distal end of the housing  102  along the longitudinal axis  108 . The header assembly  110  can include an electrical feedthrough subassembly including an electrical feedthrough (not shown) and the electrode  104 , e.g., a pacing tip. The header assembly  110  can also include a fixation subassembly. The fixation subassembly can include a helix mount  112 . The helix mount  112  can be mounted on the electrical feedthrough subassembly around the longitudinal axis  108 . In an embodiment, the fixation subassembly includes a fixation element  114  mounted on the helix mount  112  along the longitudinal axis  108 . The assembled components of the biostimulator  100  can provide a distal region that attaches to a target tissue, e.g., via engagement of the fixation element  114  with the target tissue. The distal region can deliver a pacing impulse to the target tissue, e.g., via the distal electrode  104  that is held against the target tissue. 
     Referring to  FIG. 2 , an exploded view of a biostimulator is shown in accordance with an embodiment. The housing  102  can contain an electronics compartment  116 . More particularly, the housing  102  can have a housing wall, e.g., a cylindrical wall, laterally surrounding the electronics compartment  116 . In an embodiment, the housing wall has an inner surface  118  extending around the electronics compartment  116  on the longitudinal axis  108 . The housing wall can include a conductive, biocompatible, inert, and anodically safe material such as titanium, 316L stainless steel, or other similar materials, to laterally enclose the electronics compartment  116 . The electronics compartment  116  can be axially enclosed at a proximal end by the battery  202 . More particularly, a distal surface or face of the battery  202  can define the proximal end of the electronics compartment  116 . The electronics component  116  can be axially enclosed at a distal end by the header assembly  110 . More particularly, a proximal surface of a feedthrough subassembly  204  of the header assembly  110  can define the distal end of the electronics compartment  116 . The housing  102  can be attached, e.g., welded, to the header assembly  110  and the battery  202 . Accordingly, the electronics compartment  116  can be contained between the battery  202 , the inner surface  118  of the housing  102 , and the header assembly  110 . 
     In an embodiment, electronic circuitry  206  is contained within the electronics compartment  116 . The electronic circuitry  206  can include a flexible circuit assembly having a flexible substrate. One or more electronic components may be mounted on the flexible substrate. For example, the electronic circuitry  206  can include one or more passive electronic components, e.g., capacitors, and one or more active electronic components, e.g., processors. The electronic components can be interconnected by electrical traces, vias, or other electrical connectors. In an embodiment, the electronics assembly includes one or more electrical connectors, e.g., socket and pin connectors or metallized contact pads, to connect to the battery  202  and the electrical feedthrough subassembly  204 . For example, a socket connector or a metallized pad can receive and/or connect to an electrode pin, a terminal pin, or an antenna lead, as described below. 
     To reduce the likelihood that the electrical connectors of the electronic circuitry  206  might accidentally short-circuit to other conductive components of the biostimulator  100 , such as the housing  102  or battery  202 , the biostimulator  100  may incorporate components to electrically insulate and/or protect the electronic components from short-circuiting. For example, the biostimulator  100  can include an end insulator  208 . The end insulator  208  can include a planar structure formed from insulating material and sized to separate the electronic circuitry  206  from the energy source  202 . The biostimulator  100  may also include a wall insulator  210 . The wall insulator  210  can be a cylindrical sleeve formed from insulating material and sized to separate the electronic circuitry  206  from the inner surface  118  of the housing  102 . Accordingly, the end insulator  208  and the wall insulator  210  can shroud the electronic circuitry  206  to reduce the likelihood of short circuiting between the electronic components and surrounding structures. It will be appreciated that the flexible substrate of the electronic circuitry  206  may provide insulation and separation from the housing  102  and/or the battery  202 . For example, a distal end of the electronic circuitry  206  may be a fold that is entirely formed from insulating material, and thus, short circuiting between the distal end and the feedthrough subassembly  204  can be avoided. 
     The biostimulator components can form a hermetic enclosure around the electronic circuitry  206 . For example, the battery  202 , housing  102 , and feedthrough subassembly  204  can be welded along mating seams at the proximal and distal ends of the housing  102  to hermetically seal the electronics compartment  116 . The feedthrough subassembly  204  can provide an isolated electrical path from the electronic circuitry  206 , which is hermetically sealed within the electronics compartment  116 , to the electrode  104 . More particularly, in an embodiment, the feedthrough subassembly  204  transmits afferent and efferent signals between the electronic circuitry  206  and a target tissue. 
     Referring to  FIG. 3 , a perspective view of a feedthrough subassembly of a header assembly of a biostimulator is shown in accordance with an embodiment. The electrical feedthrough subassembly  204  of the header assembly  110  can be a multifunction component. Unlike a traditional pacemaker where the electrical feedthrough is separated from the pacing site by a lead and functions solely to transfer power to the lead, the distal electrode  104  of the electrical feedthrough subassembly  204  of the biostimulator  100  may be in direct contact with the stimulation site and used to deliver impulses to the tissue. Additionally, the electrical feedthrough subassembly  204  can not only serve as the electrical pass-through from a hermetic package to a surrounding environment, but may also serve other functions, such as providing a housing for a steroid or other filler, or providing direct tissue interaction. 
     The feedthrough subassembly  204  can include several components having respective functions. A flange  302  of the subassembly can be connected to a case of the biostimulator  100 . For example, the flange  302  can be mounted on and bonded to the housing  102  as described above. The subassembly can include an insulator  304  to electrically isolate the flange  302  from electrical components passing from the hermetic enclosure of the biostimulator  100  to the surrounding environment. For example, the insulator  304  can include and/or be formed from a ceramic material that insulates the flange  302  from the electrode  104 . The electrode  104  can connect a pulse generator of the electronic circuitry  206  to a pacing tip. The flange  302 , the insulator  304 , and the electrode  104  can be connected by a brazed joint that hermetically seals the components and isolates the pacing tip on a distal end of the subassembly from a proximal end of the subassembly that connects to the electronic circuitry  206 . 
     In certain implementations, the electrical feedthrough subassembly  204  can be an unfiltered assembly. More particularly, the configuration of the electrical feedthrough subassembly  204  can include an active component, e.g., the distal electrode  104 , isolated from a ground component (e.g., the flange  302 ) by the insulator  304 . The electrode  104  may include the pacing tip, which can include an electrode body  306  and/or an electrode tip  308 . In implementations of the present disclosure, the electrode tip  308  may be mounted on the electrode body  306 , e.g., on a distal end of the electrode body  306 , as illustrated in  FIG. 3 . The electrode body  306  and electrode tip  308  can be welded together. 
     The insulator  304  can surround a portion of the electrode body  306 . More particularly, the insulator  304  can contain and separate the conductive electrode body  306  from a mounting wall  310  of the flange  302 . Both the electrode body  306  and the mounting wall  310  can be conductive. By contrast, the insulator  304  can be formed from an alumina ceramic or other insulating material. Accordingly, the insulator  304  can be located between the electrode body  306  and the mounting wall  310  to electrically insulate the distal electrode  104  from the flange  302 . The mounting wall  310  can include a thread, e.g., an external thread on an outer surface, which may form a threaded connection between the electrical feedthrough subassembly  204  and a fixation subassembly of the header assembly  110 . The fixation subassembly can include the helix mount  112  and the fixation element  114  mounted on the helix mount  112  ( FIG. 1 ). In implementations in which the electrical feedthrough subassembly  204  is bonded, press-fit, or otherwise coupled to the helix mount  212 , the thread may be omitted or the mounting wall  310  may include other surface features adapted for coupling the feedthrough subassembly  204  to the fixation subassembly to form the header assembly  110 . 
     Referring to  FIG. 4 , an exploded view of a feedthrough subassembly of a header assembly of a biostimulator is shown in accordance with an embodiment. The flange  302  can include a mounting lip  402  to engage a distal end of the housing  102  ( FIG. 1 ). A hermetic weld can be formed around the mounting lip  402  to seal the electronics compartment  116  between the flange  302  and the housing  102 . In one implementation, the flange  302  includes a mounting hole  404  that, when the biostimulator  100  is assembled, extends distally from the electronics compartment  116  along the longitudinal axis  108  and through a distal surface of the flange  302  to a surrounding environment. More particularly, the mounting hole  404  provides a channel between the electronics compartment  116  and the surrounding environment. 
     The mounting wall  310  of the flange  302  can extend around the mounting hole  404 . In an embodiment, the mounting wall  310  extends around a flange cavity  406  (a distal portion of the mounting hole  404 ). For example, an interior surface  408  of the mounting wall  310  can define the flange cavity  406 . The flange cavity  406  can extend through the flange  302  from a flange shoulder  410  to a flange distal end  412  of the mounting wall  310 . 
     In one implementation and as further illustrated in  FIG. 4 , the insulator  304  for the header assembly  110  of the biostimulator  100  has an insulator wall  420  extending around an insulator cavity  422 . The insulator wall  420  can extend longitudinally from an insulator distal end  430  to an insulator proximal end  432 . In one implementation, the insulator wall  420  can be cylindrical, having an outer diameter and an inner diameter; however, other insulator shapes may be used in other implementations of the present disclosure. The outer diameter of the insulator wall  420  can be sized to fit within the mounting hole  404  of the flange  208 . More particularly, the insulator  304  can be disposed within, and can fill, the flange cavity  406  in the assembled state. 
     In certain implementations, the insulator  304  includes an insulator base  424  extending laterally within the insulator cavity  422  at a location between the insulator distal end  430  and the insulator proximal end  432 . The insulator base  424  can be a transverse wall extending across the interior of the insulator  304 , orthogonal to the longitudinal axis  108 . More particularly, the insulator base  424  can be a transverse wall separating the insulator cavity  422  of the insulator  304  from a proximal cavity  426  of the insulator  304 . The cavities  422 ,  426  may be radially inward from the insulator wall  420 . In one implementation, an insulator hole  428  extends through the insulator base  424  along the longitudinal axis  108 . The insulator hole  428  can interconnect the cavities  422 ,  426 , and the interconnected hole and cavities can provide the insulator cavity  422  that extends along the longitudinal axis  108  from the insulator distal end  430  to the insulator proximal end  432 . Accordingly, when the insulator  304  is mounted within the flange cavity  406  of the flange  208 , and sealed to the flange  208  by a brazed joint, the insulator cavity  422  provides a channel between the electronics compartment  116  and the surrounding environment. 
     In an embodiment, the insulator  304  includes an antenna  434 . The antenna  434  can be at least partly embedded within the insulator wall  420 , as described below. The antenna  434  can be electrically connected to communication circuitry of the electronic circuitry  206 , and thus, provides wireless communication from the biostimulator  100  to an external communication device. The antenna  434  configuration is described further below. 
     The electrode  104  of the feedthrough subassembly  204  in accordance with the present disclosure may include a monolithic electrode body  306 . For example, the monolithic electrode body  306  can have several distinct portions that are integrally formed with each other. In one implementation, the electrode body  306  includes a cup  440  and a pin  442  that are integrally formed such that the electrode body  306  is monolithic, or, in other words, has a unitary or single-piece construction. 
     The electrode  104  can be sized to fit within the insulator cavity  422 . For example, the pin  442  can be sized to fit through the insulator hole  428  of the insulator  304 , and the cup  440  can be sized to fit within the insulator cavity  422  of the insulator  304  ( FIG. 5 ). It will be appreciated that, when the electrode  104  is disposed within the insulator cavity  422 , the antenna  434  embedded within the insulator wall  420  can extend around the electrode  104 . For example, loops of the antenna  434  can extend circumferentially around the cup  440 . When the electrode  104  is disposed within the insulator  304  and the flange  302 , and sealed to the insulator  304  by a brazed joint, the monolithic electrode body  306  provides an electrical pathway from the electronics compartment  116  to the surrounding environment. Electrical impulses can be transmitted from the electronic circuitry  206  proximal to the insulator base  424  to the cup  440  distal to the insulator base  424 . More particularly, the cup  440  and the pin  442  can serve as the electrically active path from the electronic circuitry  206  within the electronics compartment  116  to the patient-contacting pacing electrode tip  308 . 
     The biostimulator  100 , and more particularly the electrical feedthrough subassembly  204 , can include a filler  450 , such as a monolithic controlled release device (MCRD). By way of introduction and without limitation, the filler  450  may include a therapeutic material, and can be loaded into the cup  440 . Accordingly, the filler  450  can deliver a specified dose of a therapeutic agent, e.g., a corticosteroid, into target tissue at an implantation site of the biostimulator  100  within a patient. In an embodiment, the filler  450  is retained at a proximal location within an interior cavity of the cup  440  by a retention spring  451 . The retention spring  451  can press against a distal end of the filler  450  and a proximal end of the electrode tip  308  to urge the filler  450  away from the electrode tip  308  and reduce the likelihood of the filler  450  clogging a tip hole  452  of the electrode tip  308 . 
     The electrode tip  308  can be mounted on the electrode body  306  after the filler  450  is loaded into the cup  440 . In one implementation, the electrode tip  308  includes the tip hole  452  extending through the electrode tip  308  along the longitudinal axis  108 . The tip hole  452  may provide a channel between the interior cavity of the cup  440  and the surrounding environment. Accordingly, therapeutic agent eluted by the filler  450  can pass through the retention spring  451  and the tip hole  452  to the target tissue at the implantation site of the biostimulator  100 . In other implementations, the electrode tip  308  and/or the electrode body  306  may include other openings or ports through which fluid may enter and exit the cup  440 . The electrode tip  308  can be conductive, and electrically in contact with the electrode body  306 , such that pacing impulses transmitted through the electrode body  306  from the electronic circuitry  206  can travel through the electrode tip  308  to the target tissue. 
     In certain implementations, each of the components of the electrical feedthrough subassembly  204  may be symmetrically formed about the longitudinal axis  108 . For example, the cross-sectional area of the insulator  304  illustrated in  FIG. 4  can be swept about the longitudinal axis  108  such that the insulator wall  420  has a hollow cylindrical shape and the insulator base  424  has an annular disc shape. In other implementations, the profiles of the one or more of the components of the electrical feedthrough subassembly  204  may be non-symmetrical. For example, a cross-section of the electrode body  306  taken about a transverse plane extending orthogonal to the longitudinal axis  108  may reveal an outer surface of the pin  442  and/or the cup  440  that is square, pentagonal, elliptical, etc., or any other suitable shape. Accordingly, the particular shapes illustrated in the figures are provided by way of example only and not necessarily by way of limitation. 
     Referring to  FIG. 5 , a cross-sectional view of a header assembly of a biostimulator is shown in accordance with an embodiment. As described above, the housing  102  and a portion of the header assembly  110 , e.g., the flange  302 , can define the electronics compartment  116 . The electronic circuitry  206  can be mounted in the electronics compartment  202 , and may be in electrical communication with the feedthrough subassembly  204 , e.g., the pin  442 , through a socket connector  501  or another electrical connection. 
     The header assembly  110  includes the fixation subassembly mounted on the feedthrough subassembly  204 . More particularly, the helix mount  112  can be mounted on the mounting wall  310  of the flange  302  to connect the subassemblies and form the header assembly  110 . In one implementation, the fixation element  114  includes a helix mounted on the helix mount  112 . The fixation element  114  can be suitable for attaching the biostimulator  100  to tissue, such as heart tissue. The helix can extend distally from the helix mount  112  about the longitudinal axis  108 . For example, the helix can revolve about the longitudinal axis  108 . The helix can include a spiral wire, formed by coiling or cut from a wall of a length of tubing, which extends in a rotational direction around the longitudinal axis  108 . For example, the helix can revolve in a right-handed direction about the longitudinal axis  108 . In the case of a right-handed spiral direction, the biostimulator  100  can be advanced into contact with a target tissue, and the biostimulator  100  can then be rotated in the right-handed direction to screw the helix into the tissue. The fixation element  114  may alternatively have a left-handed spiral direction to enable the biostimulator  100  to be screwed into the target tissue via left-handed rotation. 
     In an embodiment, the helix mount  112  may be positioned between the fixation element  114  and the flange  302 . The helix mount  112  can electrically isolate the fixation element  114  from the feedthrough subassembly  204 . For example, the helix mount  112  can be formed from an insulating material, such as polyetheretherketone (PEEK) to reduce the likelihood of electrical shorting between the helix  114  and the electrode  104  or the flange  302 . The insulating material of the helix mount  112  may also be rigid to mechanically support the fixation element  114  during advancement into the target tissue. 
     The biostimulator  100  can be implanted in a body region having fluids, e.g., within the blood of a heart chamber, and thus, portions of the biostimulator  100  can be sealed and/or protected against fluid ingress that may compromise functionality of the biostimulator  100 . For example, portions of the electrical feedthrough subassembly  204 , such as the flange  302 , may be coated with a protective coating to prevent short circuiting of the distal electrode  104  and the proximal electrode  106 . In one implementation, the distal electrode  104  is spatially near the flange  302 , which can be a portion of the proximal electrode  106 . Thus, if blood were allowed to fill the gap between the distal electrode  104  and the flange  302 , the electrodes  104 ,  106  could be electrically shorted and pacing impulses may not properly pace the cardiac tissue. Accordingly, a barrier can be included in the biostimulator  100  to prevent blood from filling a cavity within the biostimulator between the distal electrode  104  and the proximal electrode  106 . 
     In one implementation, the barrier is provided by a gasket  502 . The gasket  502  can be resiliently compressed between the helix mount  112  and one of the flange  302  ( FIG. 5 ) or the insulator  304  ( FIG. 7 ). More particularly, the gasket  502  can have an annular body, e.g., an o-ring shape, and the annular body can be resiliently compressed between the helix mount  112  and either the flange  302  or the insulator  304 . The annular body of the gasket  502  can extend around the electrode  104 . For example, the annular body can extend circumferentially about the cup  440 . Accordingly, the gasket  502  can fill a gap between a proximal surface of the helix mount  112  and a distal face or surface of the electrical feedthrough subassembly  204 . The compressed gasket  502  can form a seal against the compressing surfaces to fill the gap between the distal electrode  104  and the proximal electrode  106  (e.g., the flange  302 ). Therefore, the gasket  502  can separate and protect the conductive surfaces of the biostimulator  100  from short circuiting. 
     Still referring to  FIG. 5 , in an embodiment, the gasket  502  is resiliently compressed between the helix mount  112  and the flange  302 , and the gasket  502  extends around the insulator wall  420 . A radially inward surface of the annular body can press against the insulator wall  420  to form a seal around the insulator  304 . Accordingly, ingress of fluid from a gap between the helix mount  112  and the electrode tip  308  toward the flange  302  may be prevented. 
     The antenna  434  can be embedded in the insulator wall  420  as described above. The antenna  434  may have one or more antenna loops  504  located within the insulator wall  420  between the insulator distal end  430  and the insulator proximal end  432 . The dielectric constant of the ceramic material surrounding the metallic antenna loops  504  can allow the antenna  434  to be much smaller than the typical ribbon antennas used in conventional pacemakers. Accordingly, the antenna  434  can occupy minimal space, and does not require an increase in the overall device size. 
     In an embodiment, the antenna loop(s) extend around the longitudinal axis  108 . For example, the one or more loops may include several loops extending circumferentially around the electrode  104  disposed within the insulator cavity  422 . In any case, the loops may have a circular pattern within respective transverse planes oriented perpendicular to the longitudinal axis  108 . 
     The one or more antenna loops  504  can be embedded in the insulator wall  420  distal to the flange distal end  412 . More particularly, the insulator distal end  430  can be distal to the flange distal end  412 , and the antenna loops  504  can be located longitudinally between the insulator distal end  430  and the flange distal end  412 . It will be appreciated that locating the antenna loops  504  distal to, e.g., vertically above, the flange distal end  412  can reduce interference from the metallic mounting wall  310 , and accordingly, may optimize a communication range of the antenna  434 . 
     The antenna  434  can include an antenna lead  506  extending longitudinally from the antenna loops  504 . In an embodiment, the antenna lead  506  is connected to a lower antenna loop at a distal end and extends from the lower antenna loop along a lead axis  508 . The lead axis  508  can extend longitudinally, e.g., parallel to the longitudinal axis  108 . Accordingly, the antenna lead  506  can extend through the insulator wall  420  and outward from the insulator proximal end  432 . In an embodiment, the antenna lead  506  extends into the electronics compartment  116  and electrically connects to electronic circuitry  206  contained within the electronics compartment  116 . Accordingly, communication circuitry can use the antenna  434  to communicate wirelessly with an external communication device. 
     In addition to the antenna lead  506 , the antenna  434  can include electrical connectors to interconnect the various antenna components. For example, the lower antenna loop can be connected to an adjacent (or an upper) antenna loop through an antenna via  510 . The antenna via  510  can extend vertically to interconnect the stacked loops. Alternative electrical connectors to interconnect the various antenna components can include lateral traces ( FIG. 7 ). 
     Referring to  FIG. 6 , a perspective view of an insulator for a header assembly of a biostimulator is shown in accordance with an embodiment. The insulator  304  is shown in dashed lines to improve visibility of the embedded antenna  434 . The antenna  434  may be a monopole antenna. More particularly, the one or more antenna loops  504  can include one or more open loops  602 . The open loops  602  can be c-shaped and extend from respective first ends  604  to respective second ends  606 . The first ends can be connected to the antenna lead  506  (or to the antenna via  510 ). By contrast, the second ends  606  can be free ends. The c-shaped profile of the open loops  602  may have a width dimension that is greater than a width of the insulator cavity  422  and less than a width of the insulator wall  420 . More particularly, the open loops  602  may be fully embedded within the insulator wall  420 . Alternatively, a portion of the antenna loops  504  may be exposed from the insulator wall  420 . For example, the first ends  604  may be exposed and the second ends  606  may be embedded. 
     The first end  604  and the second end  606  of each loop  504  can be within a same transverse plane. More particularly, the loops may be horizontally configured and vertically stacked. The horizontal orientation of the antenna loop  504  provides for the loop profile to be perpendicular to the lead axis  508 . Accordingly, the antenna lead  506  can intersect and extend perpendicular to the antenna loops  504 . The antenna lead  506  can be coaxial with, or laterally offset from, the antenna via  510 . The lead and the via may be embedded or exposed from the insulator wall  420 . As shown, the lead  506  can extend from the loops to a free end  610  that is exposed below the insulator wall  420 . More particularly, the free end  610  may be proximal to the insulator proximal end  432 . The free end  610  can connect to the electronic circuitry  206 . 
     Referring to  FIG. 7 , a cross-sectional view of a header assembly of a biostimulator is shown in accordance with an embodiment. The header assembly  110  of  FIG. 7  can have similar or identical components and features to the header assembly  110  of  FIG. 5 . In an embodiment, however, rather than being located external to the insulator  304 , the gasket  502  can be located internal to the insulator  304 . The gasket  502  can therefore be resiliently compressed between the helix mount  112  and the insulator  304  to seal against the ingress of fluid toward the flange  302 . Furthermore, the gasket  502  may extend around the electrode  104 , and thus, the gasket  502  may be resiliently compressed between the helix mount  112  and the electrode  104 . 
     In an embodiment, the insulator cavity  422  includes a counterbore  702 . For example, the insulator  304  can have a distal section  704  and a proximal section  706 , and the counterbore  702  can be in the distal section  704 . The counterbore  702  can be a flat-bottomed hole, and the bottom of the counterbore  702  can be a top surface of the insulator wall  420  extending over the proximal section  706 . The gasket  502  may be disposed within the counterbore  702 . The gasket  502  can be compressed vertically between a bottom surface of the helix mount  112  and the top surface of the proximal section  706  of the insulator wall  420 . The compressed gasket  502  within the counterbore  702  ensures electrical isolation between the tip electrode  104  and the flange  302 . 
     The antenna  434  can be embedded within the distal section  704  of the insulator wall  420 . As described above, the distal section  704  containing the antenna  434  can protrude out of the flange  302  such that the antenna loops  504  are positioned for optimal communication range. Furthermore, since the distal section  704  can extend radially outward from the proximal section  706 , the antenna loops  504  may be vertically above the mounting wall  310 . Accordingly, the antenna loops  504  of the embodiment illustrated in  FIG. 7  may be wider than the antenna loops  504  of the embodiment illustrated in  FIG. 5 . 
     Whereas the antenna loops  504  may be embedded within the wider distal section  704  of the insulator wall  420 , the antenna lead  506  may be embedded within the narrower proximal section  706  of the insulator wall  420 . As such, the antenna lead  506  may be radially inward from the antenna loops  504 , and accordingly, the lead axis  508  can extend longitudinally through (radially inward of) the one or more loops. For example, the lead axis  508  can extend perpendicular to the transverse planes containing the antenna loops  504  and through the areas contained by the antenna loops  504  within the transverse planes. The antenna lead  506  can extend through a length of the insulator  304  to the electronic circuitry  206  contained within the electronics compartment  116 . 
     The antenna loops  504  can include several stacked loops, as described above, and the loops can be interconnected by the antenna via  510 . Similarly, the lower antenna loop  504  can be connected to a distal end of the antenna lead  506  by a lateral trace  708 . More particularly, the lateral trace  708  can extend transversely inward from the lower antenna loop  504  to the antenna lead  506 . 
     Referring to  FIG. 8 , a perspective view of an insulator for a header assembly of a biostimulator is shown in accordance with an embodiment. As described above, the insulator wall  420  includes the distal section  704  having a first transverse width  802  larger than a second transverse width  804  of the proximal section  706  of the insulator wall  420 . The antenna loops  504  embedded in the wider distal section  704  can be open loops  602  to provide a monopole antenna  434 . The open loops  602  can be connected to the antenna lead  506 , which is embedded within the narrower proximal section  706 . A lateral trace  708  can extend laterally from the loops to the lead to interconnect the components. Thus, the antenna loops  504  can be mounted above the mounting wall  310 , and the antenna lead  506  can extend through the flange cavity  406  parallel to the pin  442  that carries electrical impulses to and from the electronic circuitry  206 . Accordingly, communication signals and pacing impulses can be simultaneously transmitted from the electronic circuitry  206  to locations distal to the flange  302  through the electrical feedthrough subassembly  204 . 
     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 sense rather than a restrictive sense.