Indian Pacing Electrophysiol. J.

ISSN 0972-6292

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Indian Pacing Electrophysiol. J. 2004;4(4):221-222           Arrhythmia Quiz 4

Arrhythmia Diagnosis Following An ICD Shock - Answer

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Roy M. John, MD, PhD

Address for correspondence: Roy M. John, MD, PhD, Section of Cardiology, Lahey Clinic  Medical Center, 41 Mall Road, Burlington, MA 01805. Email:


1. A ventricular arrhythmia is appropriately converted by the ICD shock

            The initial part of the tracing shows atrial tachycardia or flutter with atrial rates in excess of ventricular rates with irregular ventricular responses. Ventricular tachycardia begins from the  9th electrogram on the ventricular channel (see arrow). The electrograms during ventricular tachycardia are distinctly different from the preceding electrograms with an initial negative deflection as opposed to an initial positive deflection during conducted atrial arrhythmia (initial part of the trace) or during sinus rhythm (end of the trace). During the latter part of the trace, ventricular tachycardia cycle lengths (210 msec) are shorter than that of atrial tachycardia  (230 msec) confirming ventricular tachycardia as the mechanism. Most SVT algorithms have an upper limit for SVT rates. The rate of this arrhythmia would have exceeded the SVT upper limit and classified this arrhythmia as ventricular tachycardia. There is no evidence for 1:1 relationship between the atrium and the ventricles.

            This is an example of tachycardia induced tachycardia wherein an atrial arrhythmia with rapid ventricular rates induces ventricular tachycardia, Atrial fibrillation is well recognized as a trigger for both ventricular fibrillation and tachycardia even in the absence of a bypass tract.

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