Inappropriate shock therapy in a heart failure defibrillator

A 63-year-old male with dilated cardiomyopathy underwent implantation of a "heart failure" defibrillator capable of biventricular pacing. He received an inappropriate shock 5 hours after the procedure. Stored electrograms rev ealed that during each sinus beat the ventricular channel recorded up to th ree separate events. These resulted from far-field a trial sensing by the c oronary venous lead, appropriate right ventricular sensing, then delayed le ft ventricular sensing (the result of left bundle branch block). As a conse quence of far-field left atrial sensing the two subsequent ventricular elec trograms fell within the VF zone. Following an atrial premature beat, VF de tection criteria were satisfied and shock therapy delivered. Although coron ary venous lead repositioning eliminated far-field atrial sensing, double c ounting of the widely split right and left ventricular electrograms still o ccurred during sinus rhythm. Shortening the programmed AV delay resulted in constant biventricular pacing with a single electrogram.