Efficacy of low-energy t wave shocks for induction of ventricular fibrillation in patients with implantable cardioverter defibrillators

Abstract The efficacy of low-energy T wave shocks for induction of ventricular fibrillation (VF) was evaluated in 33 patients undergoing implantable cardioverter defibrillator (ICD) implantation (33 sessions) or predischarge ICD testing (20 sessions). To induce VF, the ventricle was paced for eight cycles at a 400-ms cycle length (S 1 -S 1 ), and the T wave was scanned with a monophasic shock (S 2 ) delivered via the defibrillating lead system. Of 294 attempts, the T wave shocks induced VF in 65%, nonsustained ventricular tachycardia in 10%, and less than five ventricular beats in 25%. As compared with the failed T shocks, the mean energy of successful T wave shocks was higher and the S 1 -S 2 coupling interval was shorter. When the S 2 timing was examined in relation to the T wave peak, the VF induction efficacy was 37% for shocks delivered more than 70 ms before the T wave peak, 82% for shocks delivered 30–70 ms before the T wave peak, and 50% for shocks delivered less than 30 ms before or just after the T wave peak ( P