Volumetrically efficient battery for implantable medical devices

A high rate battery having a coiled electrode assembly housed in a case that efficiently utilizes the space available in many implantable medical devices is disclosed. The battery case provides a planar surface opposite an arcuate surface to allow for the close abutting of other components located within the implantable device while also providing for efficient location of the battery within an arcuate edge of the device. The battery cases include at least three planar sides extending between a top and a base of the battery case, wherein the arcuate side is located directly opposite one of the planar sides. The battery case may form a prismatic solid shape with one arcuate surface and five planar surfaces. The batteries may include a coiled electrode assembly including an anode and a cathode; electrolyte; and a case liner containing the electrode assembly. The coiled electrode assembly can have an elliptical cross-section including two arcuate ends, wherein one of the arcuate ends is nested within an arcuate side of the case. The batteries are capable of delivering about 20 joules or more in about 20 seconds or less; and may also be capable of delivering about 20 joules or more at least twice in a period of about 30 seconds. Also included are implantable defibrillator devices incorporating the batteries and methods of manufacturing the batteries including drawing the battery case from metal.

FIELD OF THE INVENTION 
The present invention relates to the field of batteries for implantable 
medical devices. More particularly, the present invention relates to 
volumetrically efficient batteries for implantable medical devices. 
BACKGROUND 
Implantable medical devices are used to treat patients suffering from a 
variety of conditions. One example of an implantable medical device is a 
cardiac defibrillator used to treat patients suffering from ventricular 
fibrillation, also referred to as tachyarrhythmia. In operation, the 
defibrillator device constantly monitors the electrical activity of the 
heart of the patient, detects ventricular fibrillation, and in response to 
that detection, delivers appropriate shocks to restore normal heart 
rhythm. Shocks as large as 30-35 joules or more may be needed. The shocks 
are typically delivered from capacitors capable of providing that energy 
in a fraction of a second. To provide timely therapy when ventricular 
fibrillation is detected, the capacitors should be charged with sufficient 
energy in only a few seconds. As a result, the power source should have a 
high current rate capability to provide the necessary amount of energy to 
the capacitors in the limited amount of time, it should also have a low 
self-discharge rate to extend its useful life, and it should be highly 
reliable to provide the desired therapy when required. Typically, the 
power sources used in such devices are lithium electrochemical cells 
because they provide the desired characteristics identified above. 
Implantable defibrillator devices are preferably designed with shapes that 
are easily accepted by the patient's body and which also minimize patient 
discomfort. As a result, the corners and edges of the devices are 
typically designed with generous radii to present a package having 
smoothly contoured surfaces. It is also desirable to minimize the volume 
occupied by the devices as well as their mass to further limit patient 
discomfort. As a result, the devices continue to become thinner, smaller, 
and lighter. 
Known high current rate power sources used in implantable defibrillator 
devices employ prismatic, six-sided rectangular solid shapes in packaging 
of the electrode assemblies. Examples of such package shapes can be found 
in, e.g., U.S. Pat. No. 5,486,215 (Kelm et al.). Typical device layout 
includes two such power sources centrally located within the device. 
Although the use of curved battery cases in implantable devices is known, 
they are typically found in devices requiring only low current rate 
discharge such as pacemakers. Batteries with curved cases have been used 
in connection with the high current rate batteries required for, e.g., 
implantable defibrillator devices. However, these high current rate 
batteries used thin, flat layered electrodes that do not package 
efficiently within curved cases. 
Although not admitted as prior art, examples of battery designs can be 
found in the issued U.S. Patents listed in Table 1 below. 
______________________________________ 
U.S. Pat. No. 
Inventor(s) Issue Date 
______________________________________ 
2,928,888 Vogt March 15, 1960 
3,373,060 Gray March 12, 1968 
3,395,043 Schoeld July 30, 1968 
3,558,358 Ropp, Jr. January 26, 1971 
4,051,304 Snook September 27, 1977 
4,105,832 Sugalski August 8, 1978 
4,332,867 Tsuda et al. June 1, 1982 
4,335,191 Peled June 15, 1982 
4,539,271 Crabtree September 3, 1985 
4,539,274 Goebel September 3, 1985 
4,550,064 Yen et al. October 29, 1985 
4,565,752 Goebel et al. January 21, 1986 
4,565,753 Goebel et al. January 21, 1986 
4,663,247 Smilanich et al. May 5, 1987 
4,664,989 Johnson May 12, 1987 
4,668,320 Crabtree May 26, 1987 
4,767,682 Dorogi et al. August 30, 1988 
4,794,056 Pedicini December 27, 1988 
4,830,940 Keister et al. May 16, 1989 
4,863,815 Chang et al. September 5, 1989 
4,963,445 Marple et al. October 16, 1990 
5,439,760 Howard et al. August 8, 1995 
5,443,925 Machida et al. August 22, 1995 
5,458,993 Terao et al. October 17, 1995 
5,458,997 Crespi et al. October 17, 1995 
5,486,215 Kelm et al. January 23, 1996 
5,549,717 Takeuchi et al. August 27, 1996 
5,569,558 Takeuchi et al. October 29, 1996 
5,603,737 Marincic et al. February 18, 1997 
5,616,429 Klementowski April 1, 1997 
______________________________________ 
All patents listed in Table 1 above are hereby incorporated by reference in 
their respective entireties. As those of ordinary skill in the art will 
appreciate readily upon reading the Summary of the Invention, Detailed 
Description of the Preferred Embodiments and Claims set forth below, many 
of the devices and methods disclosed in the patents of Table 1 may be 
modified advantageously by using the teachings of the present invention. 
SUMMARY OF THE INVENTION 
The present invention has certain objects, i.e., various embodiments of the 
present invention provide solutions to one or more problems existing in 
the prior art respecting efficient high rate battery case design for 
implantable medical devices. Among the problems in the prior art is the 
lack of a high current rate battery case design for use with coiled 
electrode assemblies that can be: a) efficiently packaged within an 
arcuate edge of the device housings; and b) provide a planar surface 
opposite the arcuate surface nested within the arcuate edge of the device 
housing. 
Accordingly, it is an object of the invention to provide a high rate 
battery having a coiled electrode assembly housed in a case that 
efficiently utilizes the space available in many implantable medical 
devices. 
It is another object of the invention to provide a high rate battery housed 
in a case that provides a planar surface opposite an arcuate surface to 
allow for the close abutting of other components located within the 
implantable device while also providing for efficient location of the 
battery within an arcuate edge of the device. 
In comparison to known high current rate batteries and battery cases, 
various embodiments of the present invention may provide one or more of 
the following advantages: (a) efficient utilization of the volume located 
within an arcuate edge of an implantable medical device; (b) efficient 
location of other components in a closely abutting relationship with the 
planar end of the battery case opposite the arcuate end of the case; (c) 
ease of manufacturing the case by drawing and other methods; and (d) 
compatibility with coiled electrode assemblies. 
Battery cases in embodiments of the invention may include one or more of 
the following features: (a) a top; (b) a base located opposite the top; 
(c) an arcuate side extending between the top and the base; (d) at least 
three generally planar sides extending between the top and the base of the 
battery case, wherein the arcuate side is located directly opposite one of 
the generally planar sides; (e) a battery case wherein the top, base, 
generally planar sides and arcuate side form a prismatic solid shape with 
one arcuate surface and five generally planar surfaces; (f) an arcuate 
side including a generally planar section and at least one arcuate 
section; (g) an arcuate side including a generally planar section located 
between two arcuate sections; (h) a case having a generally planar top and 
generally planar bottom; (i) an open top and a cover for hermetically 
sealing the top; (j) a cover is welded to the battery case; and (k) a 
battery case is fabricated from a material selected from the group of 
stainless steel, aluminum, and titanium. 
Batteries in one or more embodiments of the present invention may include 
one or more of the following features: (a) a coiled electrode assembly 
including an anode and a cathode; (b) electrolyte; (c) a case liner 
containing the electrode assembly; (d) a case enclosing the electrode 
assembly, electrolyte and case liner, the case including a cover, a base 
located opposite the cover, an arcuate side extending between the cover 
and the base, and at least three generally planar sides extending between 
the top and the base of the battery case, wherein the arcuate side is 
located directly opposite one of the generally planar sides; (e) a battery 
case forming a prismatic solid shape with one arcuate surface and five 
generally planar surfaces; (f) a battery case in which the arcuate side 
includes a generally planar section and at least one arcuate section; (g) 
a battery case in which the arcuate side includes a generally planar 
section located between two arcuate sections; (h) a battery in which the 
cover and the base of the case are generally planar; (i) a hermetically 
sealed battery case; (j) a battery case having a cover welded to the case; 
(k) a battery case fabricated from a material selected from the group of 
stainless steel, aluminum, and titanium; (l) a coiled electrode assembly 
having an elliptical cross-section including two generally arcuate ends, 
wherein one of the generally arcuate ends is nested within an arcuate side 
of the case; (m) a battery capable of delivering about 20 joules or more 
in about 20 seconds or less; and (n) a battery capable of delivering about 
20 joules or more at least twice in a period of about 30 seconds. 
Implantable defibrillator devices in one or more embodiments of the present 
invention may include one or more of the following features: (a) a device 
housing including at least one arcuate edge; (b) a capacitor located 
within the device housing; (c) a battery located within the device housing 
and operatively connected to a capacitor, the battery including a coiled 
electrode assembly, electrolyte, a case liner; and a hermetically sealed 
battery case enclosing the electrode assembly, electrolyte and case liner, 
the case including a cover, a base located opposite the cover, an arcuate 
side extending between the cover and the base, and at least three 
generally planar sides extending between the top and the base of the 
battery case, wherein the arcuate side is located directly opposite one of 
the generally planar sides, and further wherein the arcuate side of the 
battery case is nested within one of the arcuate edges of the device 
housing; (d) a battery case in which the generally planar side of the 
battery case opposite the arcuate side faces an interior of the device 
housing; (e) a battery case forming a prismatic solid shape with one 
arcuate surface and five generally planar surfaces; (f) a coiled electrode 
assembly having an elliptical cross-section including two generally 
arcuate ends, wherein one of the generally arcuate ends is nested within 
an arcuate side of the case; (g) a battery capable of delivering about 20 
joules or more in about 20 seconds or less; and (h) a battery capable of 
delivering about 20 joules or more at least twice in a period of about 30 
seconds. 
Methods of manufacturing batteries for implantable medical devices 
according to the present invention may include one or more of the 
following steps: (a) drawing metal to form a battery case having an open 
top, a base located opposite the top, an arcuate side extending between 
the top and the base, and at least three generally planar sides extending 
between the top and the base of the battery case, wherein the arcuate side 
is located directly opposite one of the generally planar sides; (b) 
inserting a case liner into the battery case; (c) inserting a coiled 
electrode assembly into the case liner; (d) inserting electrolyte into the 
battery case, (e) attaching a cover to the arcuate side and generally 
planar sides of a battery case to hermetically seal the open top of the 
case; (f) drawing a battery case forming a prismatic solid shape with one 
arcuate surface and five generally planar surfaces; (g) welding a cover to 
the case; (h) drawing the case from a material selected from the group of 
stainless steel, aluminum, and titanium; (i) inserting a coiled electrode 
assembly into a battery case, the coiled electrode assembly having an 
elliptical cross-section including two generally arcuate ends, wherein one 
of the generally arcuate ends is nested within an arcuate side of the 
case; (j) manufacturing a battery capable of delivering about 20 joules or 
more in about 20 seconds or less; and (k) manufacturing a battery capable 
of delivering about 20 joules or more at least twice in a period of about 
30 seconds.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As used herein, the terms battery or batteries include a single 
electrochemical cell or cells. Batteries are volumetrically constrained 
systems in which the components in the case of the battery cannot exceed 
the available volume of the battery case. Furthermore, the relative 
amounts of some of the components can be important to provide the desired 
amount of energy at the desired discharge rates. A discussion of the 
various considerations in designing the electrodes and the desired volume 
of electrolyte needed to accompany them in, for example, a lithium/silver 
vanadium oxide (Li/SVO) battery is discussed in U.S. Pat. No. 5,458,997 
(Crespi et al.). Generally, however, the battery must include the 
electrodes and additional volume for the electrolyte required to provide a 
functioning battery. 
The present invention is particularly directed to high current rate 
batteries that are capable of charging capacitors with the desired amount 
of energy, preferably about 20 joules or more, typically about 20 joules 
to about 70 joules, in the desired amount of time, preferably about 20 
seconds or less, more preferably about 10 seconds or less. These values 
can typically be attained during the useful life of the battery as well as 
when the battery is new. As a result, the batteries must typically deliver 
up to about 1 to about 4 amps at about 1.5 to about 2.5 volts, in contrast 
to low rate batteries that are typically discharged at much lower rates. 
Furthermore, the preferred batteries must be able to provide these amounts 
of energy repeatedly separated by about 30 seconds or less, more 
preferably by about 10 seconds or less. 
One preferred battery according to the present invention is depicted in 
FIGS. 1 and 2 and includes a case 20 and electrode assembly 30. The case 
20 is designed to enclose the electrode assembly 30 and be sealed by a 
case cover 60. The side 14 of the case 20 is preferably generally arcuate 
in shape while the opposing side 16 of the case 20 is preferably generally 
planar. This construction provides a number of advantages including the 
ability to accommodate one of the curved or arcuate ends of a preferred 
coiled electrode assembly 30. As will be more fully discussed below, the 
arcuate side 14 can also nest within an arcuate edge of an implantable 
medical device such as an implantable cardiac defibrillator. When the 
arcuate side 14 is located within the edge of a device, the planar surface 
on the opposing side 16 faces inward to assist in the efficient use of 
space within a device case. 
The details regarding construction of the electrode assembly, such as 
connector tabs, electrode pouches, etc., are secondary to the present 
invention and will be described generally below with a more complete 
discussion being found in, e.g., U.S. Pat. No. 5,458,997 (Crespi et al.). 
The electrode assembly 30 depicted in FIGS. 1 and 2 is preferably a wound 
or coiled structure similar to those disclosed in, e.g., U.S. Pat. No. 
5,486,215 (Kelm et al.) and U.S. Pat. No. 5,549,717 (Takeuchi et al.). As 
a result, the electrode assemblies typically exhibit two generally planar 
sides, bounded by two opposing generally arcuate edges and two opposing 
generally planar ends. The composition of the electrode assemblies can 
vary, although one preferred electrode assembly includes a wound core of 
lithium/silver vanadium oxide (Li/SVO) battery as discussed in, e.g., U.S. 
Pat. No. 5,458,997 (Crespi et al.). Other battery chemistries are also 
anticipated, such as those described in U.S. Pat. No. 5,616,429 to 
Klementowski, with the preferred cores comprising wound electrodes having 
at least one generally semicircular or arcuate end that is adapted to nest 
within the arcuate side 14 of the case 20. Such a design provides a 
volumetrically efficient high current rate battery useful in many 
different implantable devices. 
The electrode assembly 30 preferably includes an anode, a cathode and a 
porous, electrically non-conductive separator material encapsulating 
either or both of the anode and cathode. These three components are 
preferably laminated together and wound to form the electrode assembly 30. 
The anode portion of the electrode assembly can comprise a number of 
different materials including an anode active material located on an anode 
conductor element. Examples of suitable anode active materials include, 
but are not limited to: alkali metals, materials selected from Group IA of 
the Periodic Table of Elements, including lithium, sodium, potassium, 
etc., and their alloys and intermetallic compounds including, e.g., 
Li--Si, Li--B, and Li--Si--B alloys and intermetallic compounds, insertion 
or intercalation materials such as carbon, or tin-oxide. Examples of 
suitable materials for the anode conductor element include, but are not 
limited to: stainless steel, nickel, titanium, or aluminum. 
The cathode portion of the electrode assembly preferably includes a cathode 
active material located on a cathode current collector that also conducts 
the flow of electrons between the cathode active material and the cathode 
terminals of the electrode assembly 30. Examples of materials suitable for 
use as the cathode active material include, but are not limited to: a 
metal oxide, a mixed metal oxide, a metal sulfide or carbonaceous 
compounds, and combinations thereof. Suitable cathode active materials 
include silver vanadium oxide (SVO), copper vanadium oxide, copper silver 
vanadium oxide (CSVO), manganese dioxide, titanium disulfide, copper 
oxide, copper sulfide, iron sulfide, iron disulfide, carbon and 
fluorinated carbon, and mixtures thereof, including lithiated oxides of 
metals such as manganese, cobalt, and nickel. 
Preferably, the cathode active material comprises a mixed metal oxide 
formed by chemical addition, reaction or otherwise intimate contact or by 
thermal spray coating process of various metal sulfides, metal oxides or 
metal oxide/elemental metal combinations. The materials thereby produced 
contain metals and oxides of Groups IB, IIB, IIIB, IVB, VB, VIB, VIIB, and 
VIII of the Periodic Table of Elements, which includes noble metals and/or 
their oxide compounds. 
The cathode active materials can be provided in a binder material such as a 
fluoro-resin powder, preferably polytetrafluoroethylene (PTFE) powder that 
also includes another electrically conductive material such as graphite 
powder, acetylene black powder and carbon black powder. In some cases, 
however, no binder or other conductive material is required for the 
cathode. 
The separator material should electrically insulate the anode from the 
cathode. The material is preferably wettable by the cell electrolyte, 
sufficiently porous to allow the electrolyte to flow through the separator 
material, and maintain physical and chemical integrity within the cell 
during operation. Examples of suitable separator materials include, but 
are not limited to: polyethylenetetrafluoroethylene, ceramics, non-woven 
glass, glass fiber material, polypropylene, and polyethylene. 
Insertion of the electrode assembly 30 into case 20 is also depicted in 
FIG. 2. As best seen in FIG. 1, however, a coil insulator 40 is placed on 
the electrode assembly 30. The coil insulator 40 includes a notch 42 to 
accommodate one of the connectors tabs 32 on the electrode assembly 30 and 
slits 44, 46 and 48 to accommodate other connector tabs 32. 
The electrode assembly 30 is also preferably inserted into an electrically 
non-conductive case liner 50. The case liner 50 preferably extends at its 
top edge above the edge of the electrode assembly 30 to overlap with other 
electrically non-conductive elements. If the case liner 50 does extend 
above the electrode assembly 30, it preferably includes a notch 52 on one 
side to allow for the connection between one set of the connector tabs 32 
to the case 20. The electrode assembly 30, coil insulator 40 and case 
liner 50 are then preferably inserted into the case 20. 
FIG. 2 also depicts the case cover 60 and a headspace insulator 70 along 
with the case 20 and the electrode assembly 30. One preferred case cover 
60 includes a feedthrough 62 through which feedthrough pin 64 is inserted. 
The feedthrough pin 64 is preferably conductively insulated from the cover 
60 by any suitable material where it passes through the cover 60. The 
feedthrough pin 64 preferably is bent to align itself with the desired 
connector tabs 32 extending from the electrode assembly 30. The preferred 
case cover 60 also includes a fill port 66 that is used to introduce an 
appropriate electrolyte solution after which the fill port 66 is 
hermetically sealed by any suitable method. 
The headspace insulator 70 is preferably located below the case cover 60 
and above the coil insulator 40, i.e., in the headspace above the coiled 
electrode assembly 30 and below the cover 60 The preferred headspace 
insulator 70 includes a raised surface 72 supported above the electrode 
assembly 30 by a sidewall or skirt 74 that preferably extends about the 
periphery of the headspace insulator 70. A well 76 is preferably formed in 
the raised surface 72 where the feedthrough pin 64 is inserted through the 
headspace insulator 72. The well 76 in the headspace insulator 72 is 
preferably adapted to receive the structure surrounding the feedthrough 62 
formed in the cover 60 (which typically extends below the lower surface of 
the cover 60 by some distance). The headspace insulator 70 is provided to 
electrically insulate the feedthrough pin 64 from the case 20 and the case 
cover 60. The headspace insulator 70 forms a chamber in connection with 
the upper surface of the coil insulator 40 that isolates the feedthrough 
pin 64 and the connector tabs 32 to which is attached. Additional 
insulation in the form of tubing or a coating (not shown) around or on the 
feedthrough pin 64 may also be included to further insure electrical 
isolation of the feedthrough pin 64. 
Although one specific coil insulator, headspace insulator, cover, and 
electrode assembly with connector tabs is depicted in FIGS. 1 and 2, it 
should be understood that that any suitable apparatus could be substituted 
for those depicted as long as the function of insulating the tabs and the 
feedthrough pin is accomplished. 
The case 20 and case cover 60 are preferably constructed of an electrically 
conductive material including, but not limited to: stainless steel, 
aluminum, titanium, etc. It is preferred that the case 20 be manufactured 
by drawing the metal into the desired shape, although other methods of 
construction are also envisioned. It is also preferable that the case 20 
and case cover 60 be made of materials that can be easily joined and 
hermetically sealed by, e.g., welding. The feedthrough pin 64 should also 
be electrically conductive. Examples of suitable materials for the 
feedthrough pin 64 include, but are not limited to: niobium and 
molybdenum. The coil insulator 40, case liner 50 and headspace insulator 
70 are preferably made of an electrically non-conductive material 
including, but not limited to: a polyolefin polymer and a fluoropolymer 
(e.g., PETFE and PECTFE). 
After the electrode assembly 30 is located within case 20 and the cover 60 
has been sealed in place, the battery can be filled with the electrolyte 
required to activate the battery. Examples of suitable electrolytes 
include any suitable nonaqueous, tonically conductive electrolyte to serve 
as a medium for migration of ions between the anode and cathode during the 
electrochemical reactions of the cell. Typically the electrolyte includes 
an inorganic, ionically conductive salt dissolved in a nonaqueous solvent, 
more preferably the electrolyte includes an ionizable alkali metal salt 
dissolved in a mixture of aprotic organic solvents including a low 
viscosity solvent and a high permittivity solvent. 
It should be noted that the present invention is not directed to the 
composition of the electrode assembly. Rather, the present invention 
provides a battery case and methods of manufacturing and using the same 
that efficiently packages a coiled electrode assembly in a case having an 
arcuate side. 
The battery case 20 depicted in FIGS. 1 and 2 includes a top 10 and base 12 
connected by four sides 14, 15, 16 and 17. Sides 15 and 17 are generally 
opposed to each other and sides 14 and 16 are also generally opposed to 
each other. The top 10 is typically open as shown to allow for the 
insertion of an electrode assembly 30 and any other desired components. 
Although top 10 is open in the depicted case 20, it will be understood 
that any portion of the battery case 20 could be open in place of top 10. 
A cross-sectional view of the case 20 is depicted in FIG. 3 (with the 
electrode assembly 30 removed). The side 14 of the case 20 is preferably 
generally arcuate in shape while the opposing side 16 of the case 20 is 
preferably generally planar. This construction provides a number of 
advantages including the ability to accommodate one of the curved or 
arcuate ends of a preferred coiled electrode assembly 30. As will be more 
fully discussed below, the arcuate side 14 can also nest within an arcuate 
edge of an implantable medical device such as an implantable cardiac 
defibrillator. When the arcuate side 14 is located within the edge of a 
device, the planar surface on the opposing side 16 faces inward to assist 
in the efficient use of space within a device case. 
FIG. 3 also illustrates that the opposing sides 15 and 17 of the case 20 
are preferably generally parallel to each other and are also preferably 
generally planar. Likewise, the base 12 of the case 20 is also preferably 
generally planar. The base 12 is preferably attached to the sides 14, 15, 
16, and 17 at ninety degree angles. In other words, the case 20 can be 
described as including five generally planar surfaces (top 10, base 12, 
and sides 15, 16, 17) arranged in the shape of prismatic rectangular solid 
in which one side 14 of the solid is an arcuate surface as opposed to a 
generally planar surface. 
One important advantage of this design is that, as compared to a completely 
prismatic six-sided case (as disclosed in, e.g., U.S. Pat. No. 5,603,737 
to Marincic et al.) the present invention provides a battery having 
increased volumetric efficiency. That increase in volumetric efficiency is 
provided as a result of a better, more conformal fit between one arcuate 
or rounded end of the coiled electrode assembly 30 and the arcuate side 14 
of the battery case 20. The space at the opposite end of the battery case 
20 that is not occupied by the electrode assembly 30 can be advantageously 
used as a portion of the reservoir needed to contain the electrolyte 
solution. 
One measure of volumetric efficiency of a battery can be stated in terms of 
ampere hours per cubic centimeter. In one example of a battery according 
to the present invention in which surface area of the electrodes is 90 
square centimeters, the volume of a battery 10 including one arcuate side 
designed to enclose the electrode assembly and associated electrolyte etc. 
is 8.6 cubic centimeters and yields a battery 10 having a volumetric 
efficiency of 182 milliampere-hours per cubic centimeter. To enclose an 
electrode assembly having the same dimensions in a battery case in which 
all of the six sides were generally planar would result in battery having 
a volume of about 9.0 cubic centimeters, resulting in a volumetric 
efficiency of about 174 milliampere-hours per cubic centimeter. 
The shape of the arcuate side 14 of the case 20 is depicted as generally 
semicircular, but it will be understood that a side having any suitable 
arcuate shape that connects the base 12 and two opposing sides 15 and 17 
could be substituted. Examples of some suitable alternate arcuate shapes 
for the arcuate side 14 of the case 20 include elliptical, parabolic, and 
other arcuate shapes. 
In addition to a pure arcuate side, i.e., a side in which all of the 
surfaces are arcuate in shape, the arcuate side of the case could be 
provided as the composite of two arcuate sections between which one or 
more planar surfaces are located. One example of an alternate case 120 
having an arcuate side 114 with a composite shape is depicted in FIG. 4. 
The two opposing sides 115 and 117 of the case 120 are each connected to 
an arcuate section 114a/114b between which generally planar section 114c 
is interposed. In a further alternative, the central section 114c could be 
another arcuate section having a different radius of curvature or profile 
than the two sections 114a/114b on either side. 
The shape of the arcuate side 114 of the battery case 120 can be 
distinguished from a battery case having a prismatic six-sided rectangular 
solid shape in which generally planar sides are joined along their edges 
by a radiused joint (drawn or otherwise formed). One distinguishing 
feature is that the arcuate surface or surfaces that form the arcuate side 
of the battery case preferably generally conform to the arcuate shape of a 
coiled electrode assembly to be placed in the battery case. Radiused edges 
used in connecting the planar sides of a battery case would typically have 
a radius of curvature that is too small to generally conform to the shape 
of a wound electrode assembly. It may be preferred that the ratio of the 
radius of curvature of the arcuate side of the battery case to the radius 
of curvature of the arcuate end of a wound electrode assembly be about 
0.5:1 to about 2:1, more preferably about 0.75:1 to about 1.5:1, and even 
more preferably about 1:1. In one embodiment similar to that depicted in 
FIG. 4, the radius of curvature of the arcuate sections 114a/114b is about 
0.12 inches (3 millimeters) or more. 
The batteries and battery cases according to the present invention can be 
used in a variety of implantable medical devices. FIG. 5 illustrates one 
defibrillator 80 and lead set 90 in which the defibrillator includes a 
battery with an arcuate side according to the present invention. The 
ventricular lead includes an elongated lead body 92 carrying three 
concentric coiled conductors separated from each other by tubular 
insulative sheaths. A ring electrode 94, extendible helix electrode 95 
retractably mounted within an insulative electrode head 96, and an 
elongated defibrillation coil electrode 97 are located adjacent the distal 
end of the lead body 92. Each of the electrodes 94 and 95 is coupled to 
one of the coiled conductors within the lead body 92. Electrodes 94 and 95 
can be used for cardiac pacing and for sensing ventricular depolarization. 
At the proximal end of the lead body 92 is a bifurcated connector 93 that 
carries three electrical connectors, each coupled to one of the coiled 
conductors in the lead body 92. The defibrillation coil electrode 97 may 
be fabricated from platinum, platinum alloy or other materials known to be 
usable in implantable defibrillation electrodes and may be, e.g., about 5 
centimeters in length. 
The atrial/SVC lead includes an elongated insulative lead body 98 carrying 
three concentric coiled conductors separated from each other by tubular 
insulative sheaths corresponding to the structure of the ventricular lead 
body 92. Located adjacent the J-shaped distal end of the lead body 98 are 
a ring electrode 99 and an extendible helix electrode 100, mounted 
retractably within an insulative electrode head 101. Each of the 
electrodes 99 and 100 is coupled to one of the coiled conductors within 
the lead body 98. Electrodes 99 and 100 are used for atrial pacing and for 
sensing atrial depolarizations. An elongated coil electrode 102 is 
provided proximal to the ring electrode 99 and coupled to the third 
conductor within the lead body 98. The atrial/SVC electrode is preferably 
about 10 centimeters or more in length and is configured to extend from 
the SVC toward the tricuspid valve. In one preferred embodiment, 
approximately 5 centimeters of the right atrium/SVC electrode was located 
in the right atrium, with the remaining 5 centimeters located in the SVC. 
At the proximal end of the lead body 98 is a bifurcated connector 103 that 
carries three electrical connectors, each coupled to one of the coiled 
conductors in the lead body 98. 
The coronary sinus lead includes an elongated insulative lead body 104 
carrying one coiled conductor coupled to a defibrillation electrode 105. 
The defibrillation electrode 105, illustrated in broken outline in FIG. 5, 
is located within the coronary sinus and great vein of the heart. At the 
proximal end of the lead body 104 is a connector plug 106 that carries an 
electrical connector coupled to the coiled conductor in the lead body 104. 
The coronary sinus/great vein electrode 105 may be about 5 centimeters in 
length. 
The implantable pacemaker/cardioverter/defibrillator 80 is shown with the 
lead connector assemblies 93, 103, and 106 inserted into the connector 
block 84 mounted on housing 82. Optionally, insulation of the outward 
facing portion of the housing 82 of the 
pacemaker/cardioverter/defibrillator 80 may be provided using a plastic 
coating, e.g., parylene or silicone rubber as is currently employed in 
some unipolar cardiac pacemakers. However, the outward facing portion may 
instead be left uninsulated, or some other division between the insulated 
and uninsulated portions may be employed. The uninsulated portion of the 
housing 82 optionally serves as a subcutaneous defibrillation electrode, 
used to defibrillate either the atria or ventricles. Other lead 
configurations and electrode locations may of course be substituted for 
the lead set illustrated. For example, atrial defibrillation and sensing 
electrodes might be added to either the coronary sinus lead or the right 
ventricular lead instead of being located on a separate atrial lead, 
thereby allowing for a two-lead system. 
The batteries used in pacemaker/cardioverter/defibrillator 80 must be 
reliable because of the critical functions they perform, which is 
especially true for defibrillators used to prevent death from lethal 
arrhythmia. Defibrillators often operate in combination with a pacemaker. 
During operation, defibrillators continuously monitor a patient's heart 
rate. Thus, it is important that such implantable device batteries be able 
to deliver the desired pulsing current with a minimal voltage drop during 
the pulse. As a result, it is important that the batteries do not exhibit 
a high increase in internal resistance over discharge time of the battery. 
As illustrated in FIG. 5, the housing 82 includes two spaced-apart opposing 
sides 83 that are connected about their periphery by edges 85. At least 
some of the edges 85 are preferably arcuate in shape to limit the presence 
of sharp corners or edges that may cause or increase patient discomfort. 
The exact dimensions of the device housing 82 are variable as is the exact 
shape of the edges 85. 
Similar to the battery design described above, the device 80 is also a 
volumetrically constrained system in which the components in the device 
housing 82 cannot exceed the available volume. The components of such a 
device 80 are schematically depicted in FIG. 6 and include, within the 
housing 82, a power source 86 (typically one or more batteries) and other 
components 81a and 81b required to both monitor heart rhythm and provide 
the desired therapy when required. 
FIG. 7 is an enlarged partial cross-sectional view of the device 80 in 
which a battery 86 including a case having an arcuate side 87 nested 
within one of the arcuate edges 85 of the device housing 82. By providing 
a battery 86 that efficiently fits within the arcuate edge 85 of the 
housing 82, the overall volume within the housing 82 of the device 80 may 
be more efficiently utilized. 
In addition to nesting the arcuate side 87 of the battery 86 in the arcuate 
edge 85 of the housing 82, the side 88 of the battery 86 opposite the 
arcuate side 87 is preferably generally planar as shown in FIG. 7. This 
generally planar surface is advantageous in that other components within 
the device 80 will typically include at least one planar surface that can 
be placed in an abutting relationship with the planar side 88 of the 
battery 86. As a result, the other components within the device 80 may be 
more efficiently packaged within the device housing 82. 
The preceding specific embodiments are illustrative of the practice of the 
invention. It is to be understood, therefore, that other expedients known 
to those skilled in the art or disclosed herein, may be employed without 
departing from the invention or the scope of the appended claims. For 
example, the present invention is not limited to battery cases including 
ends formed with arcuate edges having constant radii of curvature, but 
could include battery cases with edges having varying radii of curvature 
or sections having different radii of curvature. The present invention is 
also not limited to battery cases for implantable defibrillator devices 
per se, but may also find further application in the design of battery 
cases for other implantable medical devices such as pacemakers, infusion 
pumps, etc. The present invention further includes within its scope 
methods of making and using the battery cases described above.