Implantable cardiac pacer with programmable antitachycardia mechanisms

#Incorporated herein by reference is a microfiche appendix consisting of two microfiches containing 83 pages of annotated microprocessor instruction listings.

#The invention relates generally to implantable biological tissue stimulators, and the specific embodiment relates particularly to advanced implantable cardiac pacers employing microcomputer technology, telemetry and antitachycardia systems.

#The major pumping chambers in the human heart are the left and right ventricles. Simultaneously contracting these chambers expel blood into the aorta and the pulmonary artery. Blood enters the ventricles from smaller antechambers called the left and right atria which contract about 100 milliseconds (ms) before the ventricles. This interval is known as the atrioventricular (AV) delay. The contractions are induced by a wave of spontaneous electrical excitation which begins in the right atrium, spreads to the left atrium and then enters the AV node which delays its passage to the ventricles via the so-called bundle of His. The frequency of the waves of excitation is normally regulated metabolically by the sinus node. The atrial rate is thus referred to as the sinus rate or sinus rhythm of the heart.

#FIG. 1 is a functional block diagram of a cardiac pacer according to the invention.

#FIG. 2 is a timing diagram of the microprocessor timing cycle.

#FIG. 3 is an electrical schematic diagram of the I/O hybrid of FIG. 1.

#FIG. 1 illustrates in functional form the overall electronic circuit configuration for an implantable ROM-less, single channel, multi-programmable, microprocessor-based cardiac pacer according to the invention. The electronic components of the pacer are sealed together with the lithium compound battery cells (FIG. 5) in a biologically compatible hermetic enclosure, as in the "Orthocor Theta".TM. manufactured by Cordis Corporation, the assignee of the present application. The pacer enclosure itself is implanted at a suitable location in the patient's body and is electrically interconnected with a single standard unipolar or bipolar pervenous pacer lead which terminates in single or dual electrodes, respectively. The lead extends into contact with either the right atrium or the bottom of the right ventricle. The electrically conductive case of the pacer (e.g., titanium) forms the return path or ground electrode in a conventional unipolar electrode arrangement. Since the present pacer is designed for patients with a history of tachycardia, the single channel design was chosen because it allows the bipolar lead necessary for good tachycardia detection, to be used without the dual channel cross talk present in AV sequential pacers.

#Linear bipolar leads are required when programming from unipolar to bipolar and are particularly recommended for use because polarity should be programmed to bipolar when the pacer is programmed to an automatic antitachycardia mechanism. Because they have superior sensing and stimulation threshhold characteristics, leads with porous-surface electrodes are recommended for use.

#TABLE I ______________________________________ VVI (Lead in Ventricle) R-wave inhibited ventricular pacing AAI (Lead in Atrium) P-wave inhibited atrial pacing VVT (Lead in Ventricle) R-wave triggered ventricular pacing AAT (Lead in Atrium) P-wave triggered atrial pacing VOO (Lead in Ventricle) Asynchronous ventricular pacing AOO (Lead in Atrium) Asynchronous atrial pacing ______________________________________