Methods for sensing arrhythmias in a pacemaker/defibrillator and a pacemaker/defibrillator programmed to implement the same

Abstract

A method for detecting an arrhythmia hidden by rapid pacing in a rate adaptive pacemaker/defibrillator. Unmasking a potential arrhythmia is accomplished by lengthening the pace cycle length by a small amount for a number of cycles followed by a shortening of the pace cycle length for the same number of cycles giving an average pacing rate equivalent to the desired rate. This can occur at all times or only when conditions make arrhythmia masking possible. Changing the pace cycle by a small amount over a number of cycles will move the arrhythmia and paced rhythm out of synchronization. Forcing the pacer to continue sensing the arrhythmia is accomplished by insuring that the pacer's sense refractory is less than one half of the pacing cycle length. This is done by constraining the programming of that value to one half the minimum pacing cycle length or using an adaptive sense refractory period. In another embodiment, a hidden arrhythmia is detected by periodically checking a relative refractory portion of the pace refractory period to see if a signal indicative of arrhythmia can be detected. This relative refractory period is produced by shortening the established refractory period by a calculated adaptive relative refractory period.