Patent ID: 7245965

Claim:
An implantable cardiac stimulation device comprising: an atrial sensing circuit that senses atrial activity of a heart and provides an atrial activity signal, the sensing circuit having an adjustable sensitivity threshold; an arrhythmia detector, responsive to the atrial activity signal, that detects an atrial tachyarrhythmia; a pacing circuit that paces the heart in an atrial non-tracking mode responsive to the arrhythmia detector detecting an atrial tachyarrhythmia and an atrial tracking mode absent detection of an atrial tachyarrhythmia; a noise level measuring circuit that measures a noise level in the atrial sensing circuit; and a threshold control that immediately reduces the sensitivity threshold from a first threshold to a second threshold between the first threshold and the noise level when the pacing circuit transitions from the atrial tracking mode to the atrial non-tracking mode; wherein the threshold control immediately reduces the sensitivity threshold from the first threshold to the second threshold irrespective of whether the atrial sensing circuit senses P-waves immediately after the pacing circuit transitions from the atrial tracking mode to the atrial non-tracking mode; wherein the threshold control sets the sensitivity threshold to the second threshold while operating in the atrial-non-tracking pacing mode to preclude mode switch oscillation; wherein the first threshold is Th i , wherein the second threshold is Th t , and wherein Th t =A(Th i −noise)+noise; and wherein A is a predetermined constant.