Abstract:
Implantable heart-monitoring devices, such as defibrillators, pacemakers, and cardioverters, detect abnormal heart rhythms and automatically apply corrective electrical therapy, specifically one or more bursts of electric charge, to abnormally beating hearts. Critical parts in these devices include the capacitors that store and deliver the bursts of electric charge. Some devices use cylindrical aluminum electrolytic capacitors which include terminals that extend from one end of the case, making the capacitor longer and generally necessitating use of larger device housings. Accordingly, the inventors devised capacitor connection structures that allow size reduction. 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. Other aspects of the invention include heart-monitoring devices that incorporate these capacitors.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
   This application is a division of U.S. patent application Ser. No. 09/706,515, filed on Nov. 3, 2000 now U.S. Pat. No. 6,684,102, the specification of which is incorporated herein by reference. 
   This application is related to commonly assigned application Ser. No. 09/706,447, filed on Nov. 3, 2000, entitled FLAT CAPACITOR FOR AN IMPLANTABLE MEDICAL DEVICE, which is incorporated herein by reference in its entirety. 

   FIELD OF THE INVENTION  
   The present invention concerns capacitors, particularly wet-electrolytic capacitors used in implantable medical devices, such as implantable defibrillators, cardioverters, and pacemakers. 
   The present invention concerns implantable heart monitors, such as defibrillators and cardioverters, particularly structures and methods for capacitors in such devices. 
   BACKGROUND  
   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. 
   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. 
   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. 
   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. 
   SUMMARY OF THE INVENTION  
   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. 
   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. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a perspective view of an exemplary cylindrical wet electrolytic capacitor  100  embodying teachings of the present invention. 
       FIG. 2  is a cross-sectional view of capacitor  100  in  FIG. 1  taken along line  2 — 2 . 
       FIG. 3  is a perspective view of an exemplary cylindrical wet electrolytic capacitor  300  embodying teachings of the present invention. 
       FIG. 4  is a cross-sectional view of capacitor  300  taken along line  4 — 4  in  FIG. 3 . 
       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. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS  
   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. 
     FIG. 1  shows a perspective view of an exemplary cylindrical wet electrolytic capacitor  100  which embodies teachings of the present invention. And,  FIG. 2  shows a cross-section of capacitor  100  taken along line  2 — 2 . 
   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  102   a  and  102   b  that mate respectively with conductive end caps  104  and  106 . 
   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  104   a  and  106   a  and respective annular or tubular portions  104   b  and  106   b . Tubular portions  104   b  and  106   b  have respective interior annular shoulders  104   c  and  106   c , which abut respective ends  102   a  and  102   b  of tubular section  102 , and also allow portions  104   b  and  106   b  to overlap corresponding portions of section  102 . Thus, in this exemplary embodiment portions  104   b  and  106   b  mate with section  102  via a compound butt and lap joint. However, other embodiments omit annular shoulders  104   c  and  106   c , and include threads on the interior of portions  104   b  and  106   b  and on the exterior of corresponding portions section  102 . Other embodiments use other complementary joint structures and/or adhesives, epoxies, or other sealing compounds. 
   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  104   d  of endcap  104 , and cathode tab  112  contacts an interior surface  106   d  of endcap  106 . Interior surfaces  104   d  and  106   d  are separated by respective distances  107  and  109  from capacitive element  108  to prevent the tabs from shorting with other parts of the capacitive element. 
   In the exemplary embodiment, tabs  110  and  112  are welded respectively to surfaces  104   d  and  106   d , 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  104   d  and the capacitive element or between surface  106   d  and the capacitive element. 
   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 . 
   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. 
   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  104   a  and  106   a  and respective annular or tubular portions  104   b  and  106   b . Tubular portions  104   b  include an interior annular shoulder  104   c  which mates with a complementary exterior annular shoulder  106   c  of tubular portion  106   b , forming interface  402 . 
   The exemplary embodiment seals an exterior portion  402   a  of the interface with an adhesive, such as an epoxy, or with a circumferential weld. Other embodiments, however, form middle portion  402   b  of the interface with threads on corresponding portions of tubular portions  104   b  and  106   b . Still other embodiments omit annular shoulders  104   c  and  106   c , welding, gluing, and or screwing tubular portions  104   b  and  106   b  together. Embodiments that omit shoulders  104   c  and  106   c  lack portions  402   a  and  402   b  of interface  402 . 
   Planar end portions  104   a  and  106   a  include respective holes  104   h  and  106   h  for 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  412   a , an interior face  412   b , and a hole  412   h  which extends from face  412   a  to face  412   b . Insulative member  412  has an exterior diameter (or more generally dimension)  412   d  for establishing an interference fit with hole  104   h . 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  104   h . (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.) 
   Extending through hole  104   h  is a longitudinal shank portion  414   a  of feedthrough conductor  414 . Shank portion  414   a  has a diameter or dimension  414   d . Conductor  414   a  also has an integral disk-shaped head portion  414   b  which abuts interior face  412   b  of insulative member  412 . An opposite side of head portion  414   b  is welded to anode tab  110 , electrically coupling the feedthrough conductor to one or more anodes in capacitive element  108 . 
   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  104   h , insulative member  412 , hole  412   h , and feedthrough conductor diameter  414   d  to cooperate with each other in establishing the interference fit between hole  104   h  and insulative member  412 . Other embodiments epoxy the insulative member in place. Other embodiments mount the insulative member within hole  104   h  and 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  104   h  and weld or braze the flange to planar portion  104   a  of the endcap. 
     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&#39;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. 
   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. 
   CONCLUSION 
   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. 
   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.