Shock-Induced Ventricular Tachycardia: What Is the Mechanism?

A 67-year-old man with a history of coronary artery disease, atrial fibrillation, left ventricular dysfunction, congestive heart failure, and a dualchamber implantable cardioverter defibrillator (ICD; Medtronic Maximo DRTM , Medtronic Inc., Minneapolis, MN, USA) presents to clinic after he receives two ICD shocks. His ICD was interrogated. He is programmed in a DDD pacing mode, with a long atrioventricular delay. His lower rate limit is 70 beats/min. He is programmed as a single zone for detection and therapy with detection set at 350 ms (171 beats/min) and therapy of 20 J for the initial shock, followed by 35 J for the remaining shock. No antitachycardia pacing is programmed. The atrial and ventricular leads thresholds, impedances, and intrinsic amplitudes were normal. Examination of stored episodes revealed two shocks (Fig. 1). What caused the detection? Should this device be reprogrammed? © 2013, The Authors. Journal compilation © 2013 Wiley Periodicals, Inc.