Implantable heart monitors having capacitors with endcap headers

[0002] This application is related to commonly assigned application Ser. No. 09/706,447 , filed on even date herewith, entitled FLAT CAPACITOR FOR AN IMPLANTABLE MEDICAL DEVICE, which is incorporated herein by reference in its entirety.

[0003] The present invention concerns capacitors, particularly wet-electrolytic capacitors used in implantable medical devices, such as implantable defibrillators, cardioverters, and pacemakers.

[0004] The present invention concerns implantable heart monitors, such as defibrillators and cardioverters, particularly structures and methods for capacitors in such devices.

[0005] Since the early 1980s, thousands of patients prone to irregular and sometimes life-threatening heart rhythms have had miniature heart monitors, particularly defibrillators and cardioverters, implanted in their bodies. These devices detect onset of abnormal heart rhythms and automatically apply corrective electrical therapy, specifically one or more bursts of electric current, to hearts. When the bursts of electric current are properly sized and timed, they restore normal heart function without human intervention, sparing patients considerable discomfort and often saving their lives.

[0006] The typical defibrillator or cardioverter includes a set of electrical leads, which extend from a sealed housing into the walls of a heart after implantation. Within the housing are a battery for supplying power, monitoring circuitry for detecting abnormal heart rhythms, and a capacitor for delivering bursts of electric current through the leads to the heart.

[0007] The capacitor is often times a cylindrical aluminum wet electrolytic capacitor. This type capacitor usually includes stacked strips of aluminum foil and paper rolled, or wound, to form a cylindrical structure which is housed in a round tubular aluminum can. The can has an integral aluminum bottom end and an open top end sealed with a non-conductive flat circular lid, known as a header. Two terminals extend from the header, each connected to one of the rolled aluminum foils.

[0008] One problem the inventors recognized with these cylindrical capacitors is the overall height of the capacitor, measured from the bottom of the tubular aluminum can to the top of the terminals extending from the header. In particular, the terminals are rigid metal structures that generally require clearance space to avoid contacting other components within the housing of the implantable devices. Providing this clearance space ultimately increases the size of implantable devices beyond that otherwise necessary. Another related problem is that the diameter of the header has a practical minimum of about twelve millimeters and thus restricts how small capacitors and thus implantable devices can be made. Accordingly, the inventors identified a need to develop space-efficient techniques and structures for providing terminals on electrolytic capacitors.

[0009] To address this and other needs, the inventors devised wet electrolytic capacitors with unique connection structures. One exemplary capacitor includes two conductive endcaps at opposite ends of its capacitive element, instead of two upright terminals at one end, thereby allowing reduction in the height or volume of the capacitor and/or increases in the dimensions of other components, such as aluminum foils. Another exemplary capacitor includes two feedthrough assemblies at opposite ends of the wound capacitive element to also facilitate reduction in the height or volume of the capacitor or increasing its energy-storage density.

[0010] Other aspects of the invention include an implantable heart monitor, such as a pacemaker, defibrillator, congestive-heart-failure (CHF) device, or cardioverter defibrillator, that incorporates one or more capacitors with the unique connection structures.

[0011] FIG. 1 is a perspective view of an exemplary cylindrical wet electrolytic capacitor 100 embodying teachings of the present invention.

[0012] FIG. 2 is a cross-sectional view of capacitor 100 in FIG. 1 taken along line 2—2.

[0013] FIG. 3 is a perspective view of an exemplary cylindrical wet electrolytic capacitor 300 embodying teachings of the present invention.

[0014] FIG. 4 is a cross-sectional view of capacitor 300 taken along line 4—4 in FIG. 3.

[0015] FIG. 5 is a block diagram of an exemplary implantable heart monitor 500 which includes one or more electrolytic capacitors 532 embodying teachings of the present invention.

[0016] The following detailed description, which references and incorporates FIGS. 1-5, describes and illustrates one or more specific embodiments of the invention. These embodiments, offered not to limit but only to exemplify and teach, are shown and described in sufficient detail to enable those skilled in the art to implement or practice the invention. Thus, where appropriate to avoid obscuring the invention, the description may omit certain information known to those of skill in the art.

[0017] FIG. 1 shows a perspective view of an exemplary cylindrical wet electrolytic capacitor 100 which embodies teachings of the present invention. And,

[0018] FIG. 2 shows a cross-section of capacitor 100 taken along line 2-2.

[0019] In particular, capacitor 100 includes a cylindrical or tubular section 102, cylindrical endcaps 104 and 106, a cylindrical capacitive element 108, anode tab 110, and cathode tab 112. Tubular section 102, which comprises a non-conductive material, such as a ceramic, a polymer, or a plastic, in the exemplary embodiment, at least partially encloses a central portion of wound or rolled capacitive element 108. To fully enclose capacitive element 108, section 102 has two opposing ends 102aand 102bthat mate respectively with conductive end caps 104 and 106.

[0020] Endcaps 104 and 106, which are exemplarily formed of diecast (deep drawn) or machined aluminum or other conductive metal compatible with the capacitive element, are generally hemispherical or concave (cup-like) in structure, comprising respective planar end portions 104aand 106aand respective annular or tubular portions 104band 106b. Tubular portions 104band 106bhave respective interior annular shoulders 104cand 106c, which abut respective ends 102aand 102bof tubular section 102, and also allow portions 104band 106bto overlap corresponding portions of section 102. Thus, in this exemplary embodiment portions 104band 106bmate with section 102 via a compound butt and lap joint. However, other embodiments omit annular shoulders 104cand 106c, and include threads on the interior of portions 104band 106band on the exterior of corresponding portions section 102. Other embodiments use other complementary joint structures and/or adhesives, epoxies, or other sealing compounds.

[0021] Endcap 104 is coupled via anode tab 110 to one or more anodic layers within capacitive element 108, and endcap 106 is coupled via cathode tab 112 to a second conductive layer within the capacitive element. More particularly, anode tab 110 contacts an interior surface 104dof endcap 104, and cathode tab 112 contacts an interior surface 106dof endcap 106. Interior surfaces 104dand 106dare separated by respective distances 107 and 109 from capacitive element 108 to prevent the tabs from shorting with other parts of the capacitive element.

[0022] In the exemplary embodiment, tabs 110 and 112 are welded respectively to surfaces 104dand 106d, and distances 107 and 109 are both approximately 0.02 inches (0.508 millimeters.) Some embodiments attach the tabs using conductive adhesives. Other embodiments reduce one or both of distances 107 and 109 by increasing the end margins of separators in capacitive element 108 and/or placing one or more insulative inserts between surface 104dand the capacitive element or between surface 106dand the capacitive element.

[0023] Capacitive element 108 includes an anode, a cathode, one or more inner separators, and two or more outer separators. The one or more inner separators are sandwiched between the anode and the cathode, and the resulting anode-separator-cathode sandwich is itself sandwiched between the outer separators. In the exemplary embodiment, the anode comprises three etched foils; the cathode comprises a single etched foil; and the separators comprise electrolyte-impregnated kraft paper. Exemplary foil materials include aluminum, tantalum, hafnium, niobium, titanium, zirconium, and combinations of these metals, and exemplary foil structures include core-etched, tunnel-etched, and perforated-core-etched foils. FIGS. 3 and 4 show an exemplary capacitor 300, which also embodies teachings of the present invention. Specifically, FIG. 3 shows a perspective view of capacitor 300, and FIG. 4 shows a cross-section of the capacitor taken along line 4—4.

[0024] In particular, capacitor 300, which is similar in many respects to capacitor 100 in FIGS. 1 and 2, includes cylindrical endcaps 104 and 106, cylindrical capacitive element 108, anode tab 110, and cathode tab 112. For sake of brevity, these aspects of capacitor 300 will be redescribed only where appropriate to highlight certain differences between the two exemplary embodiments.

[0025] Unlike capacitor 100, capacitor 300 omits tubular section 102, by forming a conductive interface 402 between endcaps 104 and 106. Endcaps 104 and 106 include respective planar end portions 104aand 106aand respective annular or tubular portions 104band 106b. Tubular portions 104binclude an interior annular shoulder 104cwhich mates with a complementary exterior annular shoulder 106cof tubular portion 106b, forming interface 402.

[0026] The exemplary embodiment seals an exterior portion 402aof the interface with an adhesive, such as an epoxy, or with a circumferential weld. Other embodiments, however, form middle portion 402bof the interface with threads on corresponding portions of tubular portions 104band 106b. Still other embodiments omit annular shoulders 104cand 106c, welding, gluing, and or screwing tubular portions 104band 106btogether. Embodiments that omit shoulders 104cand 106clack portions 402aand 402bof interface 402.

[0027] Planar end portions 104aand 106ainclude respective holes 104hand 106hfor respective feedthrough assemblies 410 and 420. (Assemblies 410 and 420 are substantially identical in the exemplary embodiment, only assembly 410 is described here. However, some embodiments vary the assemblies appreciably still in keeping with one or more teachings of the invention.) Feedthrough assembly 410 includes a generally cylindrical insulative member 412 and a feedthrough conductor 414. Insulative member 412 includes an exterior face 412a, an interior face 412b, and a hole 412hwhich extends from face 412ato face 412b. Insulative member 412 has an exterior diameter (or more generally dimension) 412dfor establishing an interference fit with hole 104h. In embodiments that construct insulative member 412 from glass or ceramic, the insulative member is secured in place by brazing the insulative member to the perimeter of hole 104h. (Some other embodiments weld a short metallic collar or sleeve to the case around the hole, insert the insulative member into the sleeve, and braze the insulative member to the sleeve and/or the feedthrough conductor. The sleeve can be made of aluminum or other metal compatible with the capacitor.)

[0028] Extending through hole 104his a longitudinal shank portion 414aof feedthrough conductor 414. Shank portion 414ahas a diameter or dimension 414d. Conductor 414aalso has an integral disk-shaped head portion 414bwhich abuts interior face 412bof insulative member 412. An opposite side of head portion 414bis welded to anode tab 110, electrically coupling the feedthrough conductor to one or more anodes in capacitive element 108.

[0029] The exemplary embodiments forms insulative member 412 from glass, plastic, epoxy, or rubber and feedthrough conductor 414 from aluminum or other conductive material compatible with capacitive element 108. Additionally, it may be possible to size hole 104h, insulative member 412, hole 412h, and feedthrough conductor diameter 414dto cooperate with each other in establishing the interference fit between hole 104hand insulative member 412. Other embodiments epoxy the insulative member in place. Other embodiments mount the insulative member within hole 104hand apply an epoxy or other adhesive to secure and seal it in place. Still other embodiments mount the insulative member in a separate annular ring or collar having a flange, mount the annular ring into hole 104hand weld or braze the flange to planar portion 104aof the endcap.

[0030] FIG. 5 shows further details of the remaining portions of implantable heart monitor 500. Specifically, monitor 500 includes a lead system 510, which after implantation electrically contact strategic portions of a patient's heart, a monitoring circuit 520 for monitoring heart activity through one or more of the leads of lead system 510, and a therapy circuit 530 which includes one or more capacitors 532, each of which incorporates one or more teachings of capacitor 100 and/or 300. Monitor 500 operates according to well known and understood principles to perform defibrillation, cardioversion, pacing, and/or other therapeutic functions.

[0031] In addition to implantable defibrillators, congestive-heart-failure devices, and other cardiac rhythm management devices, such as pacemakers, the innovations of capacitor 100 can be incorporated into photographic flash equipment. Indeed, these innovations are pertinent to any application where compact, high-energy capacitors are desirable.

[0032] In furtherance of the art, the inventors have devised unique wet electrolytic capacitors for use in implantable heart monitors. One exemplary capacitor includes two conductive endcaps at opposite ends of its capacitive elements, instead of two upright terminals at one end, thereby allowing reduction in the height or volume of the capacitor and/or increases in the dimensions of other components, such as aluminum foils. Another exemplary capacitor includes two feedthrough assemblies at opposite ends of the wound capacitive element to also facilitate reduction in the height or volume of the capacitor or increase in its energy-storage density.

[0033] The embodiments described above are intended only to illustrate and teach one or more ways of practicing or implementing the present invention, not to restrict its breadth or scope. The actual scope of the invention, which embraces all ways of practicing or implementing the teachings of the invention, is defined only by the following claims and their equivalents.