The present invention generally relates to implantable medical devices, and more particularly to a method and apparatus for reducing the volume of an implantable medical device.
Implantable medical devices (IMDs) such as cardiac stimulators, neuro-stimulators, muscular stimulators, etc. are well known. While the present invention will be described in connection with implantable medical devices such as pacemakers or defibrillators, it should be understood that the principles herein may have applicability to other implantable medical devices as well.
An implantable medical device (IMD) such as an implantable pulse generator (IPG), commonly referred to as a pacemaker, may be used to stimulate the heart into a contraction when the associated rhythm of the heart is an abnormal rhythm. Modern cardiac devices also perform many other functions beyond that of pacing. For example, some cardiac devices such as implantable cardioverter defibrillators (IMD) may also perform therapies such as defibrillation and cardioversion as well as providing several different pacing therapies, depending upon the needs of the user or patient and the physiologic condition of the patient's heart. For convenience, all types of implantable medical devices will be referred to herein as IMDs, it being understood that the term, unless otherwise indicated, is inclusive of an implantable device capable of administering any one of a number of therapies to the heart of a patient.
Typically, an IMD is implanted in a convenient location usually under the skin of a patient in the vicinity of the one or more major arteries or veins. One (or more) electrical leads connected to the IMD is inserted into or deployed on the heart of the user, usually through a convenient vein or artery. The ends of the leads are placed in contact with the walls or surface of one or more chambers of the heart, depending upon the particular therapy deemed appropriate for the patient.
One or more of the leads is adapted to carry a current from the IMD to the heart tissue to stimulate the heart in one of several ways, again depending upon the particular therapy being delivered. The leads are simultaneously used for sensing the physiologic signals provided by the heart to determine when to deliver a therapeutic pulse to the heart, and the nature of the pulse; e.g., a pacing pulse or a defibrillation shock. Such IMDs are typically housed in a container or can that is made Of metal or some other conductive material. The can is made of conductive material because in some circumstances the can itself is used as one of the electrodes for sensing the physiologic indicia of the patient.
In IMDs that deliver defibrillation or cardioversion therapies, it is necessary to develop high voltages, perhaps 750 volts or more, within the IMD in order to administer a sufficient shock to a patient to correct an arrhythmia or a fibrillation, particularly a ventricular fibrillation. To generate such high voltages, a large battery and a large capacitor (usually, two capacitors) may be used. Typically the battery is encased in a first metal container within the IMD, and the capacitors are encased within a separate metal container. Thus, there are at least two layers of metal between the battery and the capacitor(s), adding to the volume of the IMD. Additionally, to facilitate fabrication and assembly, the separately metal-encased battery and capacitor(s) may be inserted into a cradle (e.g. plastic) having separate battery and capacitor positioning compartments. Thus, in addition to the two layers of metal, there may also be a plastic region separating the battery and capacitor(s), further increasing the volume of the IMD. Volume is a major consideration in the design of implantable medical devices since the device must be placed within a patient's body, and a large device may be more difficult to implant and/or more uncomfortable to the user. However, because the form factor of the batteries and capacitors currently in use are dissimilar and non-compatible when packaged together, the problem of volume retention is somewhat difficult to address.
Accordingly, it is desirable to provide a method and apparatus for reducing the volume of an implantable medical device. In addition, it is desirable to modify the form function of a battery and capacitor for use in an implantable medical device. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.
According to an aspect of the invention, there is provided a battery/capacitor assembly for use in an implantable medical device. The assembly comprises a battery, at least one capacitor, and a unitary metal encasement for retaining the battery and the at least one capacitor in proximity.
According to a further aspect of the invention, there is provided a method for reducing the volume of an implantable medical device of the type that utilizes a battery and at least one capacitor. The battery and the at least one capacitor are encased in a unitary metal housing.
According to a still further aspect of the invention, there is provided a battery/capacitor assembly for use in an implantable medical device. The assembly comprises a battery, a capacitor, a unitary metal encasement for retaining the battery and the capacitor in proximity, and an electrically insulating layer disposed around one of the battery and the capacitor.
The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and
The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description.
An implantable cardiac device (IMD) according to an embodiment of the present invention includes a pulse generator for producing pulses that are used to pace the heart; i.e., cause a depolarization of the heart tissue or issue a defibrillation pulse to shock the heart from arrhythmia to a normal heart beat. A processor within the IMD analyzes the sensed pulses to determine whether a therapy should be administered. As noted above, although the present invention may have applicability to a number of types of implantable medical devices and particularly to IMDs, the following description will utilize as exemplary an implantable cardiac device.
Referring to
As can be seen, the negative terminal of battery 64 and the negative side of capacitor 72 are at the same electrical potential. Depending on the design of battery 62 and capacitor 72, it is possible to eliminate the thin layer of electrically isolating material referred to above between battery 62 and capacitor 72 thus saving volume. Alternatively, the isolating layer may be replaced by a thin conductive layer. There are several options to the solution of providing electrical and chemical isolation and the amount of chemical isolation required between the battery and the capacitors. As noted above, if a circuit is designed such that the battery and capacitor have a terminal at the same electrical potential, then isolation is required only to keep the battery and capacitors chemically separate. If necessary, both electrical and chemical isolation may be provided as described more fully below.
The layer of insulating material 78 electrically isolates capacitor 76 from battery 80. Additional isolation (e.g. chemical isolation) may be provided by placing a metallic wall 86 (
Thus, there has been provided, a battery/capacitor assembly for use in an implantable medical device wherein the volume of the battery/capacitor assembly has been significantly reduced. That is, it has been shown how separate metallic canister walls between the battery and the capacitor can be eliminated by employing a single unitary metallic canister which houses both the battery and capacitor. Furthermore, the intermediate cradle wall utilized in the prior art has been eliminated producing additional volume savings. The embodiments in the present invention described above illustrate how both electrical and/or chemical isolation may be provided. While certain of the embodiments include the addition of a metallic separator between the battery and capacitor, the width of this wall is less than the combined width of the dual metallic canister walls employed in the prior art.