Patent Publication Number: US-8541131-B2

Title: Elongate battery for implantable medical device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/182,337, filed on May 29, 2009. The entire disclosure of the above application is incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to an implantable medical device, such as a cardiac pacemaker device, and in particular, an implantable medical device with an elongate battery. 
     INTRODUCTION 
     Several medical devices have been designed to be implanted within the human body. Implantable medical devices (IMDs), such as implantable pulse generators (IPGs), often include an elongate, flexible lead having one end operatively coupled to cardiac tissue and an opposite end operatively coupled to a generator (e.g., a pulse generator). The generator can include a power source, a sensing amplifier which processes electrical manifestations of naturally occurring heart beats as sensed by the lead, computer logic, and output circuitry, which delivers the pacing impulse to the cardiac tissue via the lead. Other IMDs, such as implantable cardioverter-defibrillators (ICDs), include similar components; however, these devices generate and deliver a defibrillation signal to the cardiac tissue via the respective lead. 
     The following discussion discloses a generator for an IMD that is very compact, such that generator can be readily implanted in small spaces within the patient&#39;s anatomy, and such that the generator is less likely to cause patient discomfort. Also, the generator can have a relatively high energy capacity to prolong the useful life of the device. Additionally, manufacturing of the IMD can be facilitated due to several features, which will be described in greater detail below. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     A battery assembly for a medical device is disclosed that includes an elongate cathode, an elongate anode, an electrolyte, and an elongate housing assembly encapsulating the cathode, the anode, and the electrolyte. The battery assembly also includes a first electrode that is exposed from and electrically insulated from the housing assembly. One of the anode and the cathode is electrically coupled to the first electrode, and the other of the anode and the cathode is electrically coupled to the housing assembly. One of the cathode and the anode includes a first portion and a second portion disposed in spaced relationship from the first portion. The other of the cathode and the anode is disposed between the first and second portions. 
     In another aspect, a method of operatively coupling a medical device to a patient is disclosed. The method includes operatively coupling a lead of the medical device to cardiac tissue of the patient and implanting a control assembly and a battery assembly of the medical device within the patient. The battery assembly includes a cathode, an anode, an electrolyte, a housing assembly encapsulating the cathode, the anode, and the electrolyte, and a first electrode exposed from and electrically insulated from the housing assembly. One of the anode and the cathode is electrically coupled to the first electrode, and the other of the anode and the cathode is electrically coupled to the housing assembly. One of the cathode and the anode includes a first portion and a second portion disposed in spaced relationship from the first portion. Also, the other of the cathode and the anode is disposed between the first and second portions. The method also includes supplying power from the battery assembly to the control assembly and controlling electrical signal transmission through the lead. 
     In still another aspect, a battery assembly for an implantable cardiac device is disclosed that is implantable in a biological tissue. The battery assembly includes a cathode, an anode, an electrolyte, and a substantially cylindrical housing assembly encapsulating the cathode, the anode, and the electrolyte. An axis of the battery assembly is substantially parallel with respective axes of the cathode, the anode, and the housing. Also, the battery assembly includes a first electrode exposed from and electrically insulated from the housing assembly. One of the anode and the cathode is electrically coupled to the first electrode. The other of the anode and the cathode is electrically coupled to the housing assembly. One of the cathode and the anode includes a first portion and a second portion disposed in spaced relationship from the first portion. The other of the cathode and the anode is disposed between the first and second portions. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  is a perspective view of a medical device according to various teachings of the present disclosure; 
         FIG. 2  is a schematic view of the medical device of  FIG. 1  shown implanted within a patient; 
         FIG. 3  is a partial section view of the medical device of  FIG. 1 ; 
         FIG. 4  is an exploded view of a battery assembly of the medical device of  FIG. 1 ; 
         FIG. 5  is a perspective view of a portion of the battery assembly of  FIG. 4 ; 
         FIG. 6  is a section view of another exemplary embodiment of the battery assembly of the medical device; 
         FIG. 7  is a section view of the battery assembly of  FIG. 6  taken along the line  7 - 7 ; 
         FIG. 8  is a perspective view of a portion of another exemplary embodiment of the battery assembly of the medical device; 
         FIG. 9  is a perspective view of a portion of another exemplary embodiment of the battery assembly of the medical device; 
         FIG. 10  is a section view of a portion of another exemplary embodiment of the battery assembly of the medical device; 
         FIG. 11  is a section view of the battery assembly of  FIG. 10  taken along the line  11 - 11 ; 
         FIG. 12  is a section view of a portion of another exemplary embodiment of the battery assembly of the medical device; 
         FIG. 13  is a section view of the battery assembly of  FIG. 12  taken along the line  13 - 13 ; 
         FIG. 14  is a section view of a portion of another exemplary embodiment of the battery assembly of the medical device; 
         FIG. 15  is a section view of the battery assembly of  FIG. 14  taken along the line  15 - 15 ; 
         FIG. 16  is an exploded view of the medical device of  FIG. 1 ; 
         FIG. 17  is a section view of the medical device of  FIG. 16 ; 
         FIG. 18  is a section view of the medical device taken along the line  18 - 18  of  FIG. 17 ; 
         FIG. 19  is a section view of the medical device taken along the line  19 - 19  of  FIG. 17 ; 
         FIG. 20  is an exploded view of the medical device according to various other exemplary embodiments of the present disclosure; and 
         FIG. 21  is a section view of the medical device of  FIG. 20 . 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     Exemplary embodiments will now be described more fully with reference to the accompanying drawings. 
     Referring initially to  FIGS. 1 ,  2 , and  3 , an implantable medical device  10  (IMD) is illustrated according to various teachings of the present disclosure. The medical device  10  can be of any suitable type, and in some embodiments, the medical device  10  can be a cardiac pacemaker device  12  (i.e., an implantable pulse generator). The cardiac pacemaker device  12  can be an electronic device for providing an electrical cardiac signal to stimulate cardiac tissue and to thereby maintain a predetermined heart beat as described in greater detail below. It will be appreciated, however, that the medical device  10  can be of any other suitable type, such as an implantable cardioverter-defibrillator (ICD), without departing from the scope of the present disclosure. In other embodiments, the medical device  10  can be a neural device for providing electrical signals to a nerve or for any other suitable neural application. In still other embodiments, the medical device  10  can be a pressure sensor (e.g., for measuring blood pressure). Furthermore, it will be appreciated that the medical device  10  can include any suitable component(s) disclosed in U.S. Patent Publication Nos. 2007/0179552, 2007/0179550, and 2007/0179581, each to Dennis et al., each filed on Jan. 30, 2006, and each of which is incorporated herein by reference in its entirety. 
     As shown in  FIG. 1 , the pacemaker device  12  can include a generator  18  (e.g., a pulse generator) and a lead  20  (e.g., a pacing lead). The lead  20  can include a proximal end  22  and a distal end  24 . The lead  20  can be flexible and can include an electrically conductive material (e.g., one or more wires) for transmitting electrical signals. As shown in  FIG. 2 , the distal end  24  of the lead  20  can be operatively (i.e., electrically and mechanically) coupled to cardiac tissue  26  of a patient  14 , and the proximal end  22  of the lead  20  can be operatively (i.e., electrically and mechanically) coupled to the generator  18 . Thus, the generator  18  can receive signals via the lead  20  relating to the natural heart beat of the patient  14 , and the generator  18  can transmit controlled electrical signals via the lead  20  to the cardiac tissue  26  such that the cardiac tissue  26  maintains a predetermined heart beat. It will be appreciated that the lead  20  can be electrically connected to any other biological tissue, such as a neural tissue, without departing from the scope of the present disclosure. 
     Also, the generator  18  can be implanted within a blood vessel  16  of the patient  14 , and the lead  20  can extend through the blood vessel  16  to the cardiac tissue  26 . The shape and compact nature of the generator  18  allows the generator  18  to be implanted within the blood vessel  16 . In other embodiments, the generator  18  can be implanted subcutaneously, outside the blood vessel  16 , and the lead  20  can extend into the blood vessel  16  to operatively couple to the cardiac tissue  26 . It will be appreciated that the pacemaker device  12  can be implanted in any suitable location and be exposed to any suitable biological tissue (e.g., blood, blood vessel, fatty tissue, etc.) of the patient  14 . As will be discussed in greater detail, the pacemaker device  12  can be relatively small, compact, inconspicuous, and yet, the device  12  can have a relatively long operating life. 
     As shown in  FIG. 1 , the generator  18  can generally include a control assembly  28 , an energy storage device  29 , and a lead connector  35 . The energy storage device  29  can supply power to the control assembly  28  as will be discussed in greater detail below. The lead connector  35  can operatively couple the lead  20  to the control assembly  28  to transmit electrical signals between the cardiac tissue  26  and the control assembly  28 . 
     The control assembly  28 , energy storage device  29 , and lead connector  35  can be disposed end-to-end with the control assembly  28  arranged between the energy storage device  29  and the lead connector  35 . As such, the lead connector  35 , the control assembly  28 , and the energy storage device  29  can extend along different portions of a common, major axis X. Also, the control assembly  28 , the energy storage device  29 , and the lead connector  35  can each be cylindrical in shape and centered about the axis X. As shown in  FIG. 1 , the control assembly  28 , the energy storage device  29 , and the lead connector  35  can have a substantially constant width W along substantially the entire axis X of the generator  18 . The generator  18  can be relatively small to facilitate implantation within the patient  14 . For instance, in some embodiments, the generator  18  can have a volume of about 1.5 cubic centimeters (cc). 
     The energy storage device  29  can be of any suitable type, such as a battery assembly  30 . As shown in  FIG. 3 , the battery assembly  30  can generally include an anode  36 , a cathode  38 , a current collector  39 , a separator  40 , an insulator disk  27 , an insulator layer  31 , and other internal components. The anode  36  can be hollow and cylindrical and can enclose the cathode  38 . The cathode  38  can be solid and cylindrical. The current collector  39  can be partially embedded within and can partially extend out of the cathode  38 . The separator  40  can be hollow and tubular and can be disposed between the anode  36  and the cathode  38 . The insulator disk  27  and the insulator layer  31  can provide electrical insulation as will be discussed in greater detail. It will be appreciated that the battery assembly  30  can also contain an electrolyte (not specifically shown), such as a liquid electrolyte, for facilitating ionic transport and forming a conductive pathway between the anode  36  and the cathode  38 . 
     The battery assembly  30  can also include a housing assembly  41  that encloses and substantially hermetically seals the anode  36 , cathode  38 , current collector  39 , and separator  40 . The housing assembly  41  can include an outer battery case  42  and a header assembly  44 . 
     The battery case  42  can be hollow and cylindrical and can include an outer surface  46 . The outer surface  46  can be circular, elliptical, ovate, or any other suitable shape in a cross section taken perpendicular to the axis X. Furthermore, the battery case  42  can include a closed end  48  that is rounded outward ( FIGS. 3 and 4 ). The battery case  42  can also include an open end  50  through which the axis X extends. The battery case  42  can be made out of any suitable material, such as titanium. It will be appreciated that the battery case  42  can be the outermost surface of the battery assembly  30  so that patient  14  is directly exposed to (in direct contact with) the battery case  42 . As such, the battery case  42  is not covered by any covering layer so that the patient  14  is directly exposed to the battery case  42 . 
     Also, as shown in  FIG. 3 , the header assembly  44  can include a cover  59 . The cover  59  can be thin and disc-shaped. The cover  59  can cover the open end  50  of the battery case  42  and can hermetically seal the open end  50 . For instance, the cover  59  can be welded (e.g., via laser welding) to the open end  50  of the battery case  42 . The header assembly  44  can also include a pin  60  (i.e., first electrode). The pin  60  can be substantially axially straight and can be centered on the axis X. The pin  60  can be electrically connected to the current collector  39  within the battery case  42  and can extend through the cover  59  to an area outside the battery case  42  ( FIGS. 3 and 16 ). The cover  59  can be made out of any suitable material, such as an electrically-conductive material (e.g., titanium). Moreover, the insulator layer  31  can be disposed between the cover  59  and the pin  60  to provide electrical insulation between the cover  59  and the pin  60  and to substantially hermetically seal the pin  60 . The insulator layer  31  can be made out of any suitable insulator, such as a glass material. The insulator disk  27  can be disposed between the current collector  39  and the cover  59  to provide electrical insulation between the cover  59  and the current collector  39 . In addition, the header assembly  44  can include a fill port  64  ( FIG. 3 ) that extends through the cover  59  in a direction substantially parallel to the axis X and spaced from the axis X. The fill port  64  can be a sealed through-hole extending through the cover  59 . 
     To manufacture the battery assembly  30 , the anode  36 , cathode  38 , and separator  40  can be assembled and received within the battery case  42  through the open end  50  such that the battery case  42  substantially encloses those components. Then, the header assembly  44  can be fixed to the open end  50  of the battery case  42  (e.g., by a continuous, ring-shaped welded joint that extends about the axis X). Next, electrolyte material can be introduced into the battery case  42  through the fill port  64 , and then the fill port  64  can be sealed (e.g., by a weld, by a separate plug, or by both). It will be appreciated that the battery assembly  30  can be manufactured independently from other components of the pacemaker device  12 . As such, manufacturing of the pacemaker device  12  can be completed in a more efficient manner. 
     Referring now to FIGS.  1  and  16 - 19 , the control assembly  28  will be discussed in greater detail. As shown, the control assembly  28  can include a plurality of electrical control components, generally indicated at  32 . The control components  32  can include one or more integrated circuits having one or more amplifiers, capacitors, diodes, wiring, microprocessors, memory, and the like, for processing and controlling electrical signal transmissions via the lead  20  of the pacemaker device  12 . The control components  32  can be mounted to and supported by a circuit board  33  ( FIGS. 16-19 ). 
     As shown in  FIGS. 16 and 17 , the control assembly  28  can also include a first spacer  43   a  and a second spacer  43   b . The first and second spacers  43   a ,  43   b  can be substantially identical and can be flat, round discs with a plurality of projections  49  radiating outward therefrom. The first and second spacers  43   a ,  43   b  can also each include a respective inner face  51   a ,  51   b  and a respective outer face  53   a ,  53   b . The first and second spacers  43   a ,  43   b  can be disposed on opposite ends of the circuit board  33  such that the respective inner faces  51   a ,  51   b  face the circuit board and such that the spacers  43   a ,  43   b  are centered about the axis X. Also, the inner faces  51   a ,  51   b  can each include a rectangular inner recess  55   a ,  55   b  that receives the respective end of the circuit board  33 . In some exemplary embodiments, the inner recess can be approximately 0.005 inches deep. It will be appreciated that the recesses  55   a ,  55   b  can ensure proper orientation of the spacers  43   a ,  43   b  with respect to the circuit board  33 , and the recesses  55   a ,  55   b  can allow the control assembly  28  to be more compact. 
     Furthermore, the spacers  43   a ,  43   b  can each include a respective central opening  57   a ,  57   b . The openings  57   a ,  57   b  can be centered along the axis. The spacers  43   a ,  43   b  can each further include one or more respective lead openings  61   a ,  61   b  ( FIG. 16 ). The lead openings  61   a ,  61   b  can extend parallel to the axis X and can be disposed on a single side of the circuit board  33 . Additionally, the spacers  43   a ,  43   b  can each include respective recesses  93   a ,  93   b  ( FIG. 16 ) on the respective outer face  53   a ,  53   b  thereof. The recesses  93   a ,  93   b  can be oblong and can be disposed over the respective lead openings  61   a ,  61   b.    
     Moreover, the control assembly  28  can include an insulator sheet  63 . As shown in  FIG. 16 , the insulator sheet  63  can be a flat, rectangular, thin sheet of material. The insulator sheet  63  can be made out of any suitable electrically insulating material, such as polyimide. As shown in  FIG. 17 , the insulator sheet  63  can be wrapped in a tube to enclose the control components  32  and the circuit board  33 , between the spacers  43   a ,  43   b . For instance, the insulator sheet  63  can include a strip of pressure sensitive adhesive  65  ( FIG. 16 ) that extends along one edge substantially parallel to the axis X. The opposite edge  95  ( FIG. 16 ) can be wrapped around the control components  32  and the circuit board  33  to affix to the adhesive  65 . As such, the insulator sheet  63  can provide electrical insulation for the control components  32  as will be discussed in greater detail below. 
     Additionally, the control assembly  28  can include a first adhesive tape  66   a  and a second adhesive tape  66   b . The tapes  66   a ,  66   b  can be substantially identical, and can be in the shape of an incomplete annular ring. The first tape  66   a  can be adhesively affixed to the outer face  53   a  of the first spacer  43   a , and the second tape  66   b  can be adhesively affixed to the outer face  53   b  of the second spacer  43   b . The first tape  66   a  can be oriented about the axis X so as to cover one of the lead openings  61   a  of the first spacer  43   a  and to leave the other lead opening  61   a  uncovered. Likewise, the second tape  66   b  can be oriented about the axis X so as to cover one of the lead openings  61   b  of the second spacer  43   b  and to leave the other lead opening  61   b  uncovered. 
     Furthermore, the control assembly  28  can include an outer control housing  34  (shown in phantom in  FIG. 1  and shown in solid lines in  FIGS. 16 and 17 ). The control housing  34  can be made out of any suitable material, such as titanium or other electrically conductive material. The control housing  34  can be hollow, cylindrical, and open at both ends. The control housing  34  can at least partially enclose the control components  32 , the circuit board  33 , the insulator sheet  63 , the spacers  43   a ,  43   b , and the tapes  66   a ,  66   b . The projections  49  of the spacers  43   a ,  43   b  can abut against the control housing  34  as shown in  FIG. 17 . As such, the spacers  43   a ,  43   b  can maintain the circuit board  33  in a substantially fixed position within the control housing  34 . As will be discussed in greater detail below, the control housing  34  can be coupled to the housing assembly  41  of the energy storage device  29 . For instance, the control housing  34  can be mechanically coupled to the housing assembly  41  via any suitable method (e.g., laser welding). Also, the control housing  34  can be electrically coupled to the housing assembly  41  such that the control housing  34  can be electrically charged. 
     It will be appreciated that the insulator sheet  63  can be disposed between control housing  34  and the control components  32  ( FIG. 17 ) to thereby electrically insulate the housing  34  from the control components  32 . Also, it will be appreciated that the control housing  34  can be the outermost surface of the control assembly  28  so that the patient  14  is directly exposed to (in direct contact with) the control housing  34 . As such, the control housing  34  is not covered by any covering layer so that the patient  14  is directly exposed to the control housing  34 . 
     The control assembly  28  can further include a connector assembly  68  ( FIGS. 16 and 17 ). The connector assembly  68  can include a cap  69 , a feed through pin  74 , and a case connector  76 . The cap  69  can be round, flat, and disc-shaped with a ring-shaped flange  97  ( FIGS. 16 and 17 ). The flange  97  can include a plurality of openings  98  that are spaced about the axis X. The cap  69  can be fixed to the control housing  34  in any suitable fashion. For instance, the cap  69  can be partially received in the control housing  34 , adhesively fixed to the tape  66   b , and fixed to the control housing  34  (e.g., via laser welding). Moreover, the feed through pin  74  can extend from within the control housing  34 , through the cap  69 , to an area outside the control housing  34  as shown in  FIG. 17 . The feed through pin  74  can be electrically insulated from the cap  69  (e.g., via a layer of glass or other insulator between the pin  74  and cap  69 ). Also, the case connector  76  can be a bent, stiff wire that is electrically and mechanically connected to the cap  69  (e.g., via welding). 
     When assembled, the pin  74  can extend through the tape  66   b , through the central opening  57   b  of the spacer  43   b  to electrically connect to the control components  32 . More specifically, as shown in  FIGS. 16-17  and  19 , the control assembly  28  can also include a bent wire  89  that extends generally perpendicular to the axis X. The bent wire  89  can extend between and be electrically connected to one of the control components  32  and the pin  74 . As such, the pin  74  need not be bent in order to electrically connect to the control components  32 . Accordingly, proper electrical connection can be ensured, and manufacturing can be facilitated. 
     Moreover, when the generator  18  is assembled, the case connector  76  can extend through one of the lead openings  61   b  in the spacer  43   b  to electrically connect to one of the control components  32 . As will be discussed, the case connector  76  can have an opposite electrical charge than the pin  74 . For instance, the case connector  76  can have a negative electrical charge, and the pin  74  can have a positive electrical charge. 
     Furthermore, when the generator  18  is assembled, the recess  93   b  can receive a portion of the case connector  76 . More specifically, a weldment (not specifically shown) connecting the case connector  76  to the cap  69  can be received within the recess  93 . As such, the generator  18  can be more compact. 
     As stated above, the generator  18  can additionally include a lead connector  35  ( FIGS. 1 ,  16 , and  17 ) for operably coupling the lead  20  to the generator  18 . The lead connector  35  can be cylindrical and can be made out of any suitable material, such as an electrically insulative polymeric material. The lead connector  35  can include an opening  37  ( FIG. 17 ) and an electrically conductive wire  78  embedded therein. The lead connector  35  can further include a fastener  86 , such as a set screw. 
     The lead connector  35  can be received within the flange  97  and can be fixed to the cap  69  (e.g., via adhesives, via sonic welding, and the like). When connected, the wire  78  within the lead connector  35  can be electrically connected to the pin  74  of the control assembly  28 . Furthermore, the opening  37  of the lead connector  35  can receive the proximal end  22  of the lead  20 , and the fastener  86  can fixedly secure the lead  20  to the lead connector  35 . When fixed to the lead connector  35 , the lead  20  can be electrically connected to the wire  78 . Moreover, adhesive (not shown) can be used to fill any empty space within the lead connector  35  for more robust connection. 
     In addition, the housing assembly  41  of the battery assembly  30  can be fixedly coupled and substantially hermetically sealed to the control housing  34  in any suitable fashion. In some exemplary embodiments, the cover  59  of the battery assembly  30  can be affixed to the adhesive tape  66   a  of the control assembly  28 , and the control housing  34  can be welded to the cover  59  and the battery case  42  (e.g., via laser welding) to produce a continuous, ring-shaped weldment  45  ( FIGS. 1 and 17 ). Also, the pin  60  of the battery assembly  30  can extend into the control housing  34 , through the tape  66   a , and through the central opening  55   a  of the spacer  43   a  to electrically connect to the control components  32 . More specifically, as shown in  FIGS. 16-18 , the control assembly  28  can include a bent wire  88  that extends generally perpendicular to the axis X. The bent wire  88  can extend between and be electrically connected to one of the control components  32  and the pin  60 . As such, the pin  60  need not be bent in order to electrically connect the battery assembly  30  to the control components  32 . Accordingly, proper electrical connection can be ensured, and manufacturing can be facilitated. 
     Thus, during operation, the pin  60  of the battery assembly  30  can supply power to the control components  32  of the control assembly  28 , and the control components  32  can be grounded to the control housing  34  and the battery case  42  via the case connector  76 . Also, the control components  32  can supply a signal (e.g., a cardiac pacing signal) to the cardiac tissue  26  via the pin  74 , the wire  78 , and the lead  20 , and the outer control housing  34  and the battery case  42  can be grounded to complete the circuit. This configuration can be employed if the pacemaker device  12  is a unipolar type because the control housing  34  and battery case  42  can be one pole, and the distal end  24  of the lead  20  can be the antipole. Thus, it will be appreciated that the control housing  34 , the cover  59 , and the cap  69  (collectively, an outer housing assembly  54  of the generator  18 ) can be electrically charged and act as an electrode for transmitting electrical signals between the generator  18  and the cardiac tissue  26 . As such, a housing and/or insulation on the exterior of the generator  18  may not be necessary, and the generator  18  can be very compact and yet still have a high energy density. Also, manufacturing costs and manufacturing time can be reduced because fewer parts are included in the generator  18 . 
     However, it will be appreciated that the control housing  34  and the battery case  42  can be covered externally by an insulator or another component without departing from the scope of the present disclosure. For instance, the pacemaker device  12  can be employed in a bi-polar type of pacemaker device  12 , wherein the lead  20  includes coaxial conductors (not specifically shown), and the pacing signal flows between the two conductors via the cardiac tissue  26 . In this exemplary embodiment, the control housing  34  and battery case  42  can be covered externally by an electrical insulator (not specifically shown). For instance, the control housing  34  and the battery case  42  can be coated with a thin layer of parylene (e.g., approximately 0.005-0.010 inches thick). As such, the control housing  34  and the battery case  42  can be visually exposed to the biological tissue of the patent (i.e., form the external surface of the generator  18 ), and the insulated coating can ensure proper function of the generator  18 . Also, in this exemplary embodiment, the generator  18  can be very compact, and yet still have a high energy density. 
     Referring now to  FIGS. 1 ,  3 ,  4 , and  5 , the cathode  38  and the anode  36  of the battery assembly  30  will be discussed in greater detail. As shown, the anode  36  can be hollow and cylindrical, and the cathode  38  can be cylindrical with a substantially solid cross-section. The respective cross section of the anode  36  and cathode  38  can be circular, elliptical, ovate, etc. The shapes of the anode  36  and cathode  38  can be adapted according to the shape of the battery case  42 . Furthermore, the cathode  38  can be enclosed by and received within the anode  36 . The separator  40  can also be hollow and cylindrical, and the separator  40  can be disposed between the anode  36  and cathode  38 . Accordingly, the anode  36 , the cathode  38 , and the separator  40  can be substantially coaxial and centered along the axis X. 
     The anode  36 , cathode  38 , and separator  40  can each be made out of any suitable material. For instance, the anode  36  can include lithium, and the cathode  38  can include a hybrid mixture of carbon monofluoride (CF x ) and silver vanadium oxide (CSVO). Moreover, the separator  40  can include porous polypropylene film, such as commercially available Celgard 2500, Celgard 4560, and the like from Celgard, LLC of Charlotte, N.C. 
     As shown in  FIGS. 3 and 4 , the anode  36  can abut an inner surface  62  of the battery case  42 . More specifically, the outer radial surface of the anode  36  extending substantially parallel to the axis X can abut the inner surface  62  of the battery case  42 . As such, the battery case  42  can be in electrical communication with the anode  36 . 
     It will be appreciated that the pin  60  can have a positive electrical charge, and the battery case  42  can have a negative electrical charge. Also, the battery case  42  can be exposed to and in direct electrical connection with tissue or other biological material of the patient  14 . For instance, the outer surface  46  of the battery case  42  can abut tissue or other biological material of the patient  14 . As such, the battery assembly  30  and the generator  18  can be substantially compact, making the pacemaker device  12  more comfortable to wear and more inconspicuous, and yet the battery assembly  30  can still provide adequate power over a long period of time. 
     For instance, if the battery assembly  30  provides about 2.5 volts, 0.15 ms pacing, 100% pacing, 60 bpm, and 825 ohm lead impedance, the expected operating life of the battery assembly  30  can be about 5.8 years. Furthermore, if the battery assembly  30  provides about 2.5 volts, 0.24 ms pacing, 100% pacing, 70 bpm, and 578 ohm lead impedance, the expected operating life of the battery assembly  30  can be about 4.8 years. Moreover, if the battery assembly  30  provides about 2.5 volts, 0.60 ms pacing, 100% pacing, 80 bpm, and 440 ohm lead impedance, the expected operating life of the battery assembly  30  can be about 2.7 years. 
     The battery assembly  30  can have a relatively high energy density (i.e., energy capacity/volume). For instance, in some embodiments, the battery assembly  30  can have an energy density of at least about 0.09 Ampere-hours/cubic centimeters (Ah/cc). Furthermore, the battery assembly  30  can have an energy density of between about 0.10 Ah/cc and 0.40 Ah/cc. Furthermore, the battery assembly  30  can have a capacity of about 190 mAh and a volume of about 0.63 cc for an energy density of about 0.30 Ah/cc. 
     Moreover, in some embodiments, the battery assembly  30  can have diameter from about 2 mm to 7.5 mm and a length from about 8 mm to 90 mm. The electrode area of the battery assembly  30  can be from about 0.137 cm 2  to 12.0 cm 2 . Furthermore, the battery assembly  30  can have an energy capacity from about 0.003 Ah to 1.589 Ah. Accordingly, the battery assembly  30  provides a relatively high energy capacity. 
     Additionally, as shown in  FIGS. 1 and 3 , the housing assembly  54  can include an aperture  56 , such as a through-hole that extends along an axis X 1  ( FIG. 3 ). Moreover, the axis X 1  of the aperture  56  can be substantially centered on the axis X so as to intersect the axis X. Also, the axis X 1  of the aperture  56  can be substantially perpendicular to the axis X of the housing assembly  54 . Moreover, the aperture  56  can be included adjacent the closed end  48  of the battery case  42  such that the battery assembly  30  is disposed between the aperture  56  and the control assembly  28 . It will be appreciated that the aperture  56  could be defined in any region of the housing assembly  54  and that the aperture  56  could be of any suitable type other than a through-hole. 
     The aperture  56  can enable the housing assembly  54  to be coupled to the patient  14 . For instance, as shown in  FIG. 1 , a suture  58  can extend through the aperture  56 , and the suture  58  can be mechanically coupled to anatomical tissue of the patient  14 . The suture  58  can be of any suitable type. As discussed above, the generator  18  of the pacemaker device  12  can be implanted within a blood vessel  16  of the patient  14 . The suture  58  can couple the generator  18  to the wall of the blood vessel  16 . In other embodiments, the suture  58  can extend out of the blood vessel  16  and attach to connective tissue (not shown) outside the blood vessel  16 . As such, the generator  18  is unlikely to move downstream with the flow of blood through the blood vessel  16  or into an organ located downstream (e.g., the lungs). Accordingly, the aperture  56  allows the generator  18  to be secured to the patient  14  in a convenient, secure, safe, and compact fashion. 
     In addition, the suture  58  can facilitate handling of the generator  18 . For instance, when the generator  18  needs to be removed from the patient  14  (e.g., when the battery assembly  30  needs to be replaced), the suture  58  can be grabbed onto (e.g., with a gripping tool) to pull the generator  18  from the blood vessel  16 . 
     Referring now to  FIGS. 6 and 7 , an alternative exemplary embodiment of the battery assembly  130  is illustrated. Components that are similar to the embodiments of  FIGS. 1-5  are indicated with corresponding reference numerals increased by 100. 
     As shown in  FIGS. 6 and 7 , the cathode  138  can be hollow and substantially cylindrical. In addition, the anode  136  can be substantially cylindrical and received within the cathode  138 . Also, the separator  140  can be included between the anode  136  and the cathode  138 . The cathode  138  can abut the inner surface  162  of the battery case so as to electrically couple the cathode  138  and the battery case  142 . Also, the battery assembly  130  can include a connector  170  that electrically connects the anode  136  to the pin  160  of the header assembly  144 . The connector  170  can be substantially flat and elongate and can be made out of a flexible material. 
     It will be appreciated that the pin  160  can have a negative electrical charge because it is electrically connected of the anode  136 , and the battery case  142  can have a positive electrical charge because it is electrically connected to the cathode  138 . The battery case  142  can be electrically coupled to tissue of the patient  14 , or the battery case  142  can be electrically coupled to the control components  32  of the control assembly  28  in any suitable manner. Also, the pin  160  can be grounded to any suitable ground. 
     Furthermore, it will be appreciated that, over the operating lifetime of the battery assembly  130 , the cathode  138  can increase in size. Because the cathode  138  is in abutment with the inner surface  162  of the battery case  142 , such increase in size of the cathode  138  can cause increased abutment between the cathode  138  and the inner surface  162  of the battery case  142 . Accordingly, electrical connection between the cathode  138  and the battery case  142  is ensured over the operating life of the battery assembly  130 . 
     Moreover, it will be appreciated that, as the battery assembly  130  discharges energy, the anode  136  can decrease in size. However, the connector  170  can be thin and flexible so as to maintain connection between the anode and the header assembly  144 , even if the anode  136  decreases in size. 
     Referring now to  FIG. 8 , another exemplary embodiment of the battery assembly  230  is illustrated. Components similar to the embodiments of  FIGS. 1-5  are indicated with corresponding reference numerals increased by 200. 
     As shown, the anode  236  can be substantially cylindrical with a solid cross-section. Likewise, the cathode  238  can be substantially cylindrical with a substantially solid cross-section. Both the anode  236  and the cathode  238  can be coaxial and centered along the axis X. Furthermore, the cathode and the anode  238 ,  236  can be disposed in spaced relationship in a direction substantially parallel to the axis X. The separator  240  can be substantially flat and circular and disposed between the anode  236  and the cathode  238 . The battery assembly  230  can also include an additional separator (not shown), for instance, between anode  236  and the battery case. 
     The anode  236  can be connected electrically to the pin  260 , and the cathode  238  can abut the inner surface of the battery case, as discussed above. Accordingly, the battery assembly  230  can be relatively compact and yet provide sufficiently high energy density, as discussed above. Furthermore, in some embodiments, the cathode  238  can be electrically connected to the pin  260 , and the anode  236  can be electrically connected to the battery case without departing from the scope of the present disclosure. 
     In some embodiments, the battery assembly  230  can have diameter from about 2 mm to 7.5 mm and a length from about 8 mm to 90 mm. The electrode area of the battery assembly  230  can be from about 0.011 cm 2  to 0.356 cm 2 . Furthermore, the battery assembly  230  can have an energy capacity from about 0.005 Ah to 1.6 Ah. Accordingly, the battery assembly  230  provides a relatively high energy capacity. 
     Referring now to  FIG. 9 , another exemplary embodiment of the battery assembly  330  is illustrated. Components that are similar to the embodiments of  FIGS. 1-5  are indicated with corresponding reference numerals increased by 300. 
     As shown, the cathode  338  can include a first portion  372   a  and a second portion  372   b . Each of the portions  372   a ,  372   b  can be elongate and can have a substantially D-shaped cross-section. Furthermore, the first and second portions  372   a ,  372   b  can be disposed on opposite sides of the axis X and spaced away from each other in a direction perpendicular to the axis X. The anode  336  can be elongate and can have a rectangular cross-section. Also, the anode  336  can be substantially centered on the axis X. The anode  336  can be disposed between the first and second portions  372   a ,  372   b  of the cathode  338 . More specifically, the anode  336  is disposed adjacent the respective flat portions of the first and second portions  372   a ,  372   b . The separator  340  can be disposed between the anode  336  and the first and second portions  372   a ,  372   b  of the cathode  338 . 
     The anode  336  can be electrically coupled to the pin  360  as discussed above. Furthermore, as shown in  FIG. 9 , respective connectors  370  can electrically couple one of the first and second portions  372   a ,  372   b  to the cover  359  of the header assembly  344 . In addition, the pin  360  can be electrically insulated from the cover  359 . It will be appreciated that the connectors  370  can be substantially flexible such that, as the first and second portions  372   a ,  372   b  of the cathode change in size during operation, the connectors  370  can flex to maintain a proper electrical connection between the respective portion  372   a ,  372   b  and the cover  359 . 
     In the embodiment of  FIGS. 10 and 11 , the configuration of the anode  336 ′ and the cathode  338 ′ is substantially similar to the configuration of  FIG. 9 . However, the connectors  370 ′ are configured differently. For instance, connectors  370 ′ can extend from each of the first and second portions  372   a ′,  372   b ′ and electrically connect to the pin  360 ′ such that the pin  360 ′ has a positive electrical charge. In addition, a connector  370 ′ can extend from an opposite end of the anode  336 ′ and electrically connect to the battery case  342 ′ such that the battery case  342 ′ has a negative electrical charge. It will be appreciated that the connectors  370 ′ can be flexible so as to maintain electrical connection despite changes in size of the anode  336 ′ and/or cathode  338 ′. 
     In some embodiments, the battery assembly  330 ,  330 ′ can have diameter from about 2 mm to 7.5 mm and a length from about 8 mm to 90 mm. The electrode area of the battery assembly  330 ,  330 ′ can be from about 0.091 cm 2  to 8.0 cm 2 . Furthermore, the battery assembly  330 ,  330 ′ can have an energy capacity from about 0.103 Ah to 0.4 Ah. Accordingly, the battery assembly  330 ,  330 ′ provides a relatively high energy capacity. 
     Referring now to  FIGS. 12 and 13 , another exemplary embodiment of the battery assembly  430  is illustrated. Components that are similar to the embodiments of  FIGS. 1-5  are indicated with corresponding reference numerals increased by 400. 
     As shown, the anode  436  can include a first portion  480   a  and a second portion  480   b . The first and second portions  480   a ,  480   b  can be substantially elongate and can have a D-shaped cross-section ( FIG. 13 ). Also, the first and second portions  480   a ,  480   b  can be disposed on opposite sides of the axis X. In addition, the cathode  438  can have a substantially rectangular cross-section and can be disposed between the first and second portions  480   a ,  480   b  of the anode  436 . 
     In addition, connectors can electrically couple the first and second portions  480   a ,  480   b  and the cover  459  of the header assembly  444 . Also, a connector can electrically couple the cathode  438  and the pin  460  of the header assembly  444 . Furthermore, the pin  460  can be electrically insulated from the cover  459  of the header assembly  444 . As discussed above, the connectors  470  can be flexible to accommodate any change in size of the anode  436  and/or cathode  438 . 
     Referring now to  FIGS. 14 and 15 , another exemplary embodiment of the battery assembly  530  is illustrated. Components that are similar to the embodiments of  FIGS. 1-5  are indicated with corresponding reference numerals increased by 500. 
     As shown, the anode  536  and the cathode  538  can be both substantially D-shaped in cross-section ( FIG. 15 ), and the anode and cathode  536 ,  538  can be both elongate. More specifically, the anode  536  can define a flat portion  582 , and the cathode  538  can includes a flat portion  581 . The flat portions  582 ,  581  substantially face each other. Also, both the anode  536  and the cathode  538  can include a rounded portion  584 ,  583 , respectively. The rounded portions  584 ,  583  can face the inner surface  562  of the battery case  542 . Also, the separator  540  can be thin and elongate and can be disposed between the anode  536  and the cathode  538 . 
     Furthermore, as shown in  FIG. 14 , the battery assembly  530  can include a plurality of connectors  570 . For instance, a connector  570  can extend between the anode  536  and the cover  559  of the header assembly  544 . Likewise, a connector  570  can extend between the cathode  538  and the pin  560 . It will be appreciated that the connectors  570  can be flexible to accommodate any change in size of the anode  536  and/or the cathode  538 . Furthermore, it will be appreciated that a connector  570  could electrically connect the cathode  538  and the cover  559  while a different connector  570  could electrically connect the anode  536  and the pin  560  without departing from the scope of the present disclosure. 
     Referring now to  FIGS. 20 and 21 , another exemplary embodiment is illustrated. Components that are similar to the embodiments of  FIGS. 1-5  and  16 - 19  are indicated by similar reference numerals increased by 600. 
     As shown, the lead connector  635  can be substantially similar to the lead connector  35  of the embodiments shown in  FIGS. 16 and 17 . However, the lead connector  635  can include one or more conductive members  671  ( FIG. 20 ). In some embodiments, there are a plurality of conductive members  671  spaced apart about the axis X. The conductive member(s)  671  can be made out of any suitable electrically conductive material, such as titanium. The conductive member(s)  671  can be embedded within surrounding polymeric material of the lead connector  635 . 
     Moreover, the cap  669  of the control assembly  628  can include a projection  673  extending toward the lead connector  635 . The projection  673  can be made out of electrically conductive material and can be integrally connected to other portions of the cap  669  so as to be monolithic. The projection  673  can be received within a slot  675  of the lead connector  635 , and the projection  673  can electrically connect with the conductive member(s)  671  inside the lead connector  635 . 
     In some exemplary embodiments, the lead connector  635  can be coupled to the control assembly  628  via welding. For instance, the lead connector  635  can be joined via a laser spot welding process, wherein the conductive member(s)  671  serve as an electrical contact for the welding process, and the control housing  634  or the battery case  642  serves as another electrical contact for the welding process. Accordingly, it will be appreciated that the lead connector  635  can be fixedly coupled to the control housing  634  in a very robust manner. 
     Thus, in summary, each of the exemplary embodiments of the implantable medical device  10  can be substantially compact, while still having a sufficient operating life. As such, the generator  18  can be implanted inconspicuously and comfortably within the patient  14 , and yet the generator  18  can operate for an extended period of time before repair and/or replacement of the generator  18  becomes necessary. 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the invention, and all such modifications are intended to be included within the scope of the invention. 
     Exemplary embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that exemplary embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some exemplary embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. 
     The terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to be limiting. As used herein, the singular forms “a”, “an” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
     When an element or layer is referred to as being “on”, “engaged to”, “connected to” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to”, “directly connected to” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the exemplary embodiments. 
     Spatially relative terms, such as “inner,” “outer,” “beneath”, “below”, “lower”, “above”, “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.