Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
2000-03-20
2004-01-13
Bockelman, Mark (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
C361S503000
Reexamination Certificate
active
06678559
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to implantable medical devices such as defibrillators and automatic implantable defibrillators (AIDs), and their various components. More particularly, it relates to an implantable medical device including a flat capacitor with case liner configured to optimize an overall size and shape of the device.
BACKGROUND OF THE INVENTION
Implantable medical devices (IMDs) for therapeutic stimulation of the heart are well known in the art. Examples of various forms of IMDs and their respective functions include: a programmable demand pacemaker disclosed in U.S. Pat. No. 4,253,466 issued to Hartlaub et al. to deliver electrical energy, typically ranging in magnitude between about 5 and about 25 micro Joules, to the heart to initiate the depolarization of cardiac tissue to treat the heart by providing pacemaker spike in the absence of naturally occurring spontaneous cardiac depolarizations; an automatic implantable defibrillator (AID), such as those described in U.S. Pat. No. Re. 27,757 to Mirowski et al. and U.S. Pat. No. 4,030,509 to Heilman et al., deliver a nonsynchronous high-voltage energy pulse (about 40 Joules) to the heart to interrupt ventricular fibrillation through widely spaced electrodes located outside of the heart, thus mimicking transthoracic defibrillation; a pacemaker/cardioverter/defibrillator (PCD) disclosed in U.S. Pat. No. 4,375,817 to Engle et al., to detect the onset and progression of tachyarrhythmia so that progressively greater energy levels may be applied to the heart to interrupt a ventricular tachycardia or fibrillation; an external synchronized cardioverter, such as that described in “Clinical Application of Cardioversion” in Cardiovascular Clinics, 1970, Vol. 2, pp. 239-260 by Douglas P. Zipes, provides cardioversion shocks synchronized with ventricular depolarization to ensure that the cardioverting energy is not delivered during the vulnerable T-wave portion of the cardiac cycle; an implantable cardioverter, such as those disclosed in U.S. Pat. No. 4,384,585 to Douglas P. Zipes and in U.S. Pat. No. 3,738,370 to Charms, detect the intrinsic depolarizations of cardiac tissue and pulse generator circuitry delivers moderate energy level stimuli (in the range of about 0.1 to about 10 Joules) to the heart synchronously with the detected cardiac activity.
An IMD consists generally of a sealed housing maintaining a capacitor(s), an electronics module(s) and an energy source. The electronics module normally includes a circuit board maintaining a variety of electrical components designed, for example, to perform sensing and monitoring functions or routines, as well as to accumulate data related to IMD operation. The electronics module is electrically connected to the capacitor and the power source such that amongst other functions, the electronics module causes the power source to charge and recharge the capacitor. To satisfy power and safety requirements, the power source typically consists of two series-connected batteries. So as to optimize volumetric efficiency, the batteries are typically formed to assume a cube-like shape. For example, a well accepted IMD configuration includes two, three-volt cube-like batteries connected in series.
Typically, the electrical energy required to power an implantable cardiac pacemaker is supplied by a low voltage, low current drain, long-lived power source such as a lithium iodine pacemaker battery of the type manufactured by Wilson Greatbatch, Ltd. or Medtronic, Inc. While the energy density of such power sources is typically relatively high, they are generally not capable of being rapidly and repeatedly discharged at high current drains in the manner required to directly cardiovert the heart with cardioversion energies in the range of 0.1 to 10 Joules. Moreover, the nominal voltage at which such batteries operate is generally too low for cardioversion applications. Higher energy density battery systems are known which can be more rapidly or more often discharged, such as lithium thionyl chloride power sources. Neither of the foregoing battery types, however, may have the capacity or the voltage required to provide an impulse of the required magnitude on a repeatable basis to the heart following the onset of tachyarrhythmia.
Generally speaking, it is necessary to employ a DC-DC converter to convert electrical energy from a low voltage, low current power supply to a high voltage energy level stored in a high-energy storage capacitor. Charging of the high-energy capacitor is accomplished by inducing a voltage in the primary winding of a transformer creating a magnetic field in the secondary winding. When the current in the primary winding is interrupted, the collapsing field develops a current in the secondary winding which is applied to the high-energy capacitor to charge it. The repeated interruption of the supply current charges the high-energy capacitor to a desired level over time.
Energy, volume, thickness and mass are critical features in the design of IMDs. IMDs typically have a volume of about 40 to about 60 cc, a thickness of about 13 mm to about 16 mm and a mass of approximately 100 grams. One of the components important to optimization of those features is the high voltage capacitor used to store the energy required for defibrillation. Such capacitor a typically deliver energy in the range of about 25 to 40 Joules.
It is desirable to reduce the volume, thickness and mass of such capacitors and devices without reducing deliverable energy. Doing so is beneficial to patient comfort and minimizes complications due to erosion of tissue around the device. Reductions in size of the capacitors may also allow for the balanced addition of volume to the battery, thereby increasing longevity of the device, or balanced addition of new components, thereby adding functionality to the device. It is also desirable to provide such devices at low cost while retaining the highest level of performance.
Most conventional IMDs employ commercial photoflash capacitors similar to those described by Troup in “Implantable Cardioverters and Defibrillators,” Current Problems in Cardiology, Volume XIV, Number 12, December 1989, Year Book Medical Publishers, Chicago, and U.S. Pat. No. 4,254,775 for “Implantable Defibrillator and Package Therefor.” The electrodes in such capacitors are typically spirally wound to form a coiled electrode assembly. Most commercial photoflash capacitors contain a core of separator paper intended to prevent brittle anode foils from fracturing during coiling. The anode, cathode and separator are typically wound around such a paper core. The core limits both the thinness and volume of the IMDs in which they are placed. The cylindrical shape of commercial photoflash capacitors also limits the volumetric packaging efficiency and thickness of an IMD made using same.
Recently developed flat aluminum electrolytic capacitors have overcome some disadvantages inherent in commercial cylindrical capacitors. For example, U.S. Pat. No. 5,131,388 to Pless et al. discloses a relatively volumetrically efficient flat capacitor having a plurality of planar layers arranged in a stack. Each layer contains an anode layer, a cathode layer and means for separating the anode layers and cathode layers (such as paper). The anode layers and the cathode layers are electrically connected in parallel.
A segment of today's IMD market employs flat capacitors to overcome some of the packaging and volume disadvantages associated with cylindrical photoflash capacitors. Examples of such flat capacitors are described in the '388 patent to Pless et al. for “Implantable Cardiac Defibrillator with Improved Capacitors,” and in U.S. Pat. No. 5,522,851 to Fayram for “Capacitor for an Implantable Cardiac Defibrillators.” Additionally, flat capacitors are described in a paper entitled “High Energy Density Capacitors for Implantable Defibrillators” by P. Lunsmann and D. MacFarlane presented at the 16th Capacitor and Resistor Technology Symposium.
Numerous efforts have been made to improve upon the size, shape
Breyen Mark D.
Haeg Dan C.
Jacobs Andrew M.
Bockelman Mark
Chapik Daniel G.
Medtronic Inc.
Wolde-Michael Girma
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