Low-power consumption cardiac pacer based on automatic verification of

Abstract

A low-power consumption implantable pacer includes a system for detecting evoked cardiac contractions in which pacing pulses are initially applied to a patient's heart in pairs such that at most only one pulse of a pair can induce capture. The lead recovery waveforms produced in response to each of the pulses of a pair are detected and compared. By selectively varying the pulse energy level, the patient's capture threshold is determined. Pulse energy is then increased such that the first pulse of each pair induces capture and the lead recovery waveform resulting from the second, non-capturing pulse is stored. To conserve battery current, single pacing pulses are then supplied to the heart, and the lead recovery waveforms developed by the single pulses are compared against the stored waveform to yield a reference difference signal which verifies capture. When a significant change in difference signals is detected, the pacer automatically repeats the foregoing paired-pulse autocapture threshold determination and output level adjustment algorithm.