Clinical usefulness of stored electrograms in the diagnosis of tachyarrhythmias in patients with implantable cardioverter defibrillators

The advent of new telemetric capabilities and in particular of stored electrograms (EGMs) has greatly improved the diagnostic specificity of implantable cardioverter defibrillators (ICDs). We report our experience with recent devices having EGMs storage capability implanted in 24 patients in association with a single endocardial lead system. We analysed the EGMs recorded at implant and retrieved from the ICD memory during a mean follow-up of 13.4 months (range 1-33), in order to identify the characteristics helpful in differentiating ventricular from supraventricular tachyarrhythmias (SVT). Atrio-ventricular dissociation (56.5% of cases at implant and 52% at follow-up) and changes in ventricular EGM duration (100%) and morphology (78% of cases at implant and 75% at follow-up) compared with baseline sinus rhythm, were diagnostic clues for ventricular tachycardia. Wide and irregular ventricular EGMs with no recognisable atrial activity were observed during ventricular fibrillation. No changes in ventricular EGM duration and morphology occurred during SVT. We conclude that EGMs recorded from shocking electrodes allow a correct diagnosis of the events precipitating ICD intervention in the vast majority of cases.