The automatic implantable cardioverter-defibrillator: evaluating suspected inappropriate shocks.

Two patients who received inappropriate shocks from an implanted defibrillator are presented. In one case, fracture of a sensing lead was responsible and in the other case, sensing of both pacemaker stimuli and the evoked ventricular electrogram resulted in inappropriate shocks. In both cases, phonograms recorded over the generator area with a magnet in place revealed audible tones synchronous with each sensed event which allowed noninvasive documentation of a sensing problem. This procedure appears to be a valuable step both in the confirmation of sensing problems, including pacemaker-defibrillator interactions, and in evaluating suspected inappropriate shocks.