First beat antitachycardia pacing termination of monomorphic ventricular tachycardia by an extravascular defibrillator.

Antitachycardia pacing (ATP) delivered by implantable cardioverter-defibrillators (ICD) is a well-established therapy for monomorphic ventricular tachycardia (VT). Recently, extravascular ICD has emerged as a novel technique that provides ATP with an entirely extravenous system, at the epicardial level. ECG documentation of a succesful ATP delivery by this innovative ICD is a rare but stimulating report. We present a case of sustained monomorphic VT successfully terminated by the first ATP stimulus delivered by an extravascular ICD, with surface ECG documentation of the termination beat. Beyond documenting successful ATP therapy, the recording also provides insight into the electrophysiological interaction between the paced impulse and the VT circuit, suggesting potential mechanistic information about the underlying reentrant substrate.