Paradoxical undersensing at a high sensitivity in dual chamber pacemakers

In view of the evolving indications for device therapy in atrial arrhythmia the accurate detection of high rate atrial events is a necessity. In a she ep model of atrial fibrillation (AF) we observed a contradictory behavior o f the Thera DR pacemaker. The pacemakers were programmed to deliver burst p acing on detection of sinus rhythm (SR). Paradoxically, progressively more inappropriate bursts were delivered during AF, at a higher sensitivity. Thi s implied that the pacemaker interpreted AF as SR. We assessed the atrial d etection of the Thera DR, Diamond, Saphir, and Marathon pacemakers during A F, in a sheep model and in vitro using a waveform generator, gr counting th e annotated atrial-sensed events reported by the pacemaker we charted the b ehavior of the pacemakers at different sensitivities. At a higher sensitivi ty both the Them DR and the Diamond paradoxically reported fewer atrial eve nts during AF. This behavior led to inappropriate mode switching and incorr ect diagnostic data collection. It could be reproduced in vitro. The Marath on did not show this paradoxical undersensing in vivo or in vitro. This par adoxical undersensing at a high sensitivity is dependent on the amplitude o f the input signal and could not be explained by an overlap of programmable timing parameters. It is caused by ringing of the atrial sensing amplifier . At high atrial rates and a high sensitivity the ringing of the repetitive atrial signal input results in blanking of the atrial amplifier. This obse rvation may be relevant in the device management of patients with paroxysma l AF.