System and method of performing automatic capture in an implantable cardiac stimulation device

Abstract

An implantable cardiac stimulation device possessing pacing, cardioversion and defibrillation functions and automatic capture capabilities, for automatically verifying capture during stimulation operations and, as necessary, automatically delivering back-up stimulation pulses when capture is lost, and subsequently adjusting the stimulation energy to a level safely above that needed to achieve capture. The stimulation device utilizes a method for maintaining capture by means of a capture search algorithm, so that whenever loss of capture is detected, it re-determines the minimum stimulation energy required to achieve capture. Another aspect of the stimulation device is the automatic threshold testing which is invoked to determine the minimum stimulation pulse energy needed to ensure capture. When the automatic capture function is enabled, the stimulation device initiates a stimulation refractory period, upon the expiration of which, the stimulation device sets a sensing threshold to a predetermined level and then either maintaining this level fixed or causing it to decay, during an alert interval. Concurrently, the stimulation device verifies capture during the alert interval.