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Mechanisms of Inappropriate Defibrillator Therapy in a Modern Cohort of Remotely Monitored Patients


  • Conflict of interest: None.

  • Sources of funding: Biotronik Inc.

Address for reprints: Samir Saba, M.D., Director, Cardiac Electrophysiology, University of Pittsburgh, 200 Lothrop Street, PUH B535, Pittsburgh, PA 15213. Fax: 412-647-7979; e-mail:



Defibrillator (ICD) technology and monitoring are evolving rapidly. We investigated the mechanisms of inappropriate ICD therapies in a modern cohort of patients followed at our institution via remote monitoring.


From September 2009 to March 2011, a total of 2,050 ICD patients (19,600 patient-months) were remotely followed. All events (shocks and antitachycardia pacing) were adjudicated by arrhythmia specialists.


A total of 249 patients received ICD therapy (34% inappropriate therapy). Inappropriate ICD shocks affected 33 (1.6%) patients. There were a total of 249 inappropriate episodes in 85 patients. Supraventricular tachycardia (SVT) with 1:1 atrioventricular association was the predominant mechanism accounting for 133 episodes in 50 patients, followed by atrial fibrillation (97 episodes in 27 patients). T-wave oversensing (16 episodes in five patients), electromagnetic interference (two episodes in two patients), and ectopic beats (one episode in one patient) accounted for a small proportion of events. There were 35 arrhythmic episodes in five patients that could not be classified, all in patients with single-chamber devices. There were no differences in these results by device manufacturer.


Despite many technological advances, inappropriate ICD shocks still occur but at very low rates and SVT with 1:1 atrioventricular association represents their most common mechanism.