Sensing aberration by the automatic implantable cardioverter defibrillator during intraoperative testing

A 50-year-old man underwent replacement of his automatic implantable cardioverter defibrillator (AICD) because a magnet test revealed severe battery depletion. He had had his unit implanted 18 months previously after an episode of sudden cardiac death. He had documented torsades de pointes and inducible ventricular tachycardia, confirmed by electrophysiologic study. Before a new unit was implanted thresholds were measured by an external cardioverter defibrillator. Ventricular fibrillation (VF) was induced by alternating current through a standard, line-operated battery charger with stimulation delivered to the epicardium via rate-sensing electrodes. VF was allowed to continue for 10 seconds before shock was delivered. Termination of VF required 15 joules, which was higher than that required at initial implantation 18 months earlier. The new pulse generator was activated for testing and VF was again induced. The AICD discharged after 12.3 seconds. Prior to wound closing, the AICD was deactivated by magnet. Instead of R-wave synchronous beeping tones during deactivation, double beeping tones were heard. Electrogram recordings revealed abnormalities of the T-wave and ST segment of the rate-sensing electrodes, which were the cause of the tone irregularities. Stabilization of the T-wave and ST segment occurred within 8 minutes and the tones became normal. The procedure was then completed.