Inadequacy of qualitative implantable cardioverter defibrillator electrogram analysis to distinguish supraventricular from ventricular tachycardia due to electrogram changes during normally conducted complexes.

Stored electrograms (EGMs) recorded from ICD leads are used to evaluate the appropriateness of ICD therapies. Stored EGMs different from sinus have been interpreted as ventricular in origin. We present a patient with an ICD for VT who received multiple shocks for a tachycardia with a stored EGM different than sinus, suggesting VT. An electrophysiological study demonstrated EGMs different than sinus during atrial pacing and induced supraventricular arrhythmias. This case points out the limitations of stored EGMs and suggests complete electrophysiological study with analysis of EGMs during induced arrhythmias should be performed prior to discharge.