Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
2001-10-11
2004-07-20
Evanisko, George R. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
C607S004000
Reexamination Certificate
active
06766193
ABSTRACT:
FIELD OF THE INVENTION
The subject matter disclosed and claimed herein relates to an improved method of operation of pacemakers and implantable cardioverter-defibrillators (ICDs) having pacing capabilities, which improved method serves to prolong battery longevity by deactivating certain power-consuming features while not needed and reactivating as necessary. Also provided herein are improved devices employing these methods.
BACKGROUND OF THE INVENTION
The heart functions to pump life-sustaining blood throughout one's body. The human heart comprises a left side and a right side with each side having a first chamber known as the atrium and a second chamber known as the ventricle. The right atrium receives blood from the body after the body has extracted the oxygen therefrom and the left atrium receives oxygenated blood from the lungs. At an appropriate time, an electrical stimulus is provided to the atria that causes the muscle tissue to depolarize. Immediately following depolarization, the atrial muscle tissue physically contracts, forcing the blood held in the right and left atria through one-way valves into the right and left ventricles, respectively.
The electrical stimulus provided to the atria also stimulates the ventricles after a delay which is sometimes referred to as the “natural conduction time” of the heart. Upon stimulation, the ventricular muscle tissue depolarizes and then contracts. This forces the blood held within the right ventricle to pass through the pulmonary artery to the lungs and the blood held within the left ventricle to pass through the aorta to the rest of the body. In this manner, then, the heart “beats” or pumps blood by having the atria contract and, after the natural conduction time, by having the ventricles contract. After a longer delay, during which delay the right atrium is refilled with blood returning from throughout the body, the process repeats.
Implantable pacemakers and cardioverter-defibrillators (ICDs) are electronic medical devices that monitor the electrical activity of the heart and provide electrical stimulation to one or more heart chambers, when necessary. For example, a pacemaker senses an arrhythmia, i.e., a disturbance in heart rhythm, and provides appropriate electrical stimulation pulses, at a controlled rate, to selected chambers of the heart in order to correct the arrhythmia and restore the proper heart rhythm. The type of arrhythmias that may be detected and corrected by pacemakers include bradycardias, which are unusually slow heart rates, and certain tachycardias, which are unusually fast heart rates.
Implantable cardioverter-defibrillators (ICDs) also detect arrhythmias and provide appropriate electrical stimulation pulses to selected chambers of the heart to correct the abnormal heart rate. In contrast to pacemakers, however, the pulses from an ICD are much stronger and less frequent. This is because ICDs are generally designed to correct fibrillations, which are rapid, unsynchronized quiverings of one or more heart chambers, and severe tachycardias, where the heart beats are very fast but coordinated. To correct such arrhythmias, an ICD delivers a low, moderate or high energy shock to the heart. In addition to functioning as a cardioverter-defibrillator, some ICDs are designed to provide pacing support to the heart. Such ICDs sense the occurrence of a cardiac arrhythmia and automatically apply an appropriate therapy to the heart aimed at terminating the specific arrhythmia detected. This type of therapy is referred to as “tiered therapy”.
In a tiered therapy ICD, each “tier” or level of therapy generally corresponds to a different type of arrhythmia and typically to a specified number of shocks of varying energies and pulse durations intended to most efficiently terminate the specific type of arrhythmia detected. Thus, such tiered therapy may include antitachycardia pacing for painless termination of monomorphic ventricular tachycardia (i.e., tachycardia that originates from one ventricular focus); programmable low-energy cardioversion also for treatment of ventricular tachycardia (e.g., when antitachycardia pacing fails to terminate the tachycardia); high-energy defibrillation for termination of ventricular fibrillation; and back-up bradycardia pacing, for ensuring the heart beats, particularly following cardioversion or defibrillation. For examples of tiered therapy ICDs, see U.S. Pat. Nos. 4,427,011; 4,541,430; 4,398,536; and 5,103,822; each of which is incorporated herein, in its entirety, by reference.
Because the invention described and claimed herein is useful in pacemakers, ICDs and tiered therapy ICDs, these devices will be collectively referred to as “ICD/pacemakers”. It will be appreciated by those of skill in the art that discussions herein of the pacing functions of an implantable device generally refer only to pacemakers and/or ICDs having pacing capabilities, whereas discussions of cardioverting-defibrillating functions generally only refer to ICDs with or without pacing capabilities.
The pacing functions of ICD/pacemakers are described as either single-chamber or dual-chamber systems. A single-chamber ICD stimulates and senses the ventricular chamber of the heart. A dual-chamber system stimulates and/or senses in two chambers of the heart (an atrium and a ventricle). Dual-chamber systems may typically be programmed to operate in either a dual-chamber mode or a single-chamber mode.
A three-letter code (sometimes expanded to a five letter code) is used to describe the basic mode in which the ICD/pacemaker is operating. The three-letter code concerns how the device operates to sense the need for and provide electrical stimulation to the heart. A fourth position (when used) identifies the degree of programmability and rate modulation of the device, and a fifth position (when used) refers to electrical stimulation therapy for the primary treatment of tachycardias and fibrillations.
The first position of the three letter pacemaker code identifies the chamber to which the electrical stimulus is delivered. If the device is not capable of bradycardia support pacing, an “O” occupies this first position. If the unit paces in the ventricle, this is identified by a “V”; if it paces in the atrium, the first position is identified as an “A”. If stimuli can be delivered to either the atrium or ventricle, the letter “D” is used to reflect dual-chamber stimulation.
The second position of the pacemaker code identifies the chamber or chambers in which sensing occurs. Sensing is the ability of the pacemaker to recognize the intrinsic electrical activity of the heart. The letters used in this position are identical to those used in the first position, i.e., “V” for ventricular sensing; “A” for atrial sensing; “D” for dual-chamber sensing; and “O” if no sensing capability is present.
The third position of the pacemaker code identifies the way the pacemaker responds to a sensed signal. An “I” means that the pacemaker will be inhibited. The inhibited mode of response indicates that when the pacemaker senses or sees an intrinsic electrical signal, it inhibits its own output pulse and resets one or more internal timers within the pacemaker's circuitry. The other basic response is represented by a “T”, which means triggered. The triggered mode of response indicates that when the pacemaker senses an intrinsic electrical signal, it not only resets various internal timers within the pacemaker, it also initiates or releases a stimulus in response to that sensed event.
The most sophisticated response mode is represented by a “D” in the third position and refers to both modes of sensing response. Most commonly, a sensed signal arising from the atrium and sensed on the atrial channel of a dual-chamber pacemaker will inhibit the atrial output but trigger a ventricular output after a brief delay (the AV delay). If a native ventricular depolarization does not occur before the AV delay timer completes, a ventricular stimulus will be released at the end of this AV delay. If a native ventricular signal is sensed within the AV d
Causey, III James D.
Mouchawar Gabriel A.
Evanisko George R.
Pacesetter Inc.
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