Incessant atrioventricular dissociation due to far-field QRS oversensing and recurrent mode switch in a dual chamber pacemaker
We report the case of a repetitive and incessant activation of mode switch in a dual chamber pacemaker because of the inappropriate sensing by the atrial lead of far-fields signals from the ventricular evoked response. The incidence, consequences and prevention of the oversensing of far-field QRS complexes are discussed. A 65-year-old man was implanted with a dual chamber pacemaker (Inos 2 CLS/DR, Biotronik GmbH, Berlin, Germany) for permanent high grade atrio-ventricular block, using a bipolar
... ck, using a bipolar screw-in lead (Medtronic 4068, Medtronic Inc., Minneapolis, MN, U.S.A.) in the right atrial appendage and a unipolar tined lead (Biotronik Px-60-UP) in the right ventricle apex. The atrial parameters were found acceptable post-implant (threshold 1 V/0·4 ms, P wave 3·5 mV, impedance 474 Ohms). Four months later, the patient underwent a coronary artery by-pass. In the early postoperative stage, atrial sensitivity was increased to 0·5 mV because of intermittent loss of detection leading to haemodynamic problems. At discharge, the atrial pacing and sensing parameters were satisfactory (threshold 1·2 V/0·4 ms, P wave 2·5 mV, impedance 341 Ohms) and DDD mode, with automatic mode switching (threshold rate: 170 bpm=350 ms), using an atrial output of 3 V/0·5 ms and bipolar atrial sensing at 0·5 mV was programmed. Atrial oversensing was not observed during myopotential provocative tests.