LONG-TERM REPRODUCIBILITY OF VENTRICULAR-TACHYCARDIA INDUCTION IN PATIENTS WITH IMPLANTABLE CARDIOVERTER-DEFIBRILLATORS - SERIAL NONINVASIVE STUDIES

Background Noninvasive electrophysiological studies (EPSs) can be perf ormed in current implantable antitachycardia pacemaker/cardioverter/de fibrillators (ICDs). Thus, these devices may be used as tools to study changes in the electrophysiological substrate and ventricular tachyca rdia characteristics over time. Methods and Results Fifty-five patient s receiving an ICD for treatment of sustained ventricular tachyarrhyth mias underwent serial EPSs after implantation of the ICD. Studies were performed before hospital discharge and 1, 3, 5, 9, 12, 18, 24, and 3 6 months after ICD implantation. Sustained monomorphic ventricular tac hycardia (VT) was induced in 37 patients (group 1) at the predischarge EPS, whereas no sustained arrhythmia could be induced in 18 patients (group 2) at baseline. Group 1 patients underwent 165 noninvasive EPSs after discharge. Sustained monomorphic VT was induced during 72% of t he follow-up EPSs, ventricular fibrillation (VF) was induced during 11 % of follow-up EPSs, and no sustained VT or VF was induced during 17% of follow-up visits. Sustained VT was induced at every follow-up EPS i n 23 patients (62%), whereas no sustained VT/VF could be induced at le ast once during follow-up in 14 patients (38%). Clinical or electrophy siological variables did not predict noninducibility during followup. However, the probability that a patient would experience spontaneous V T decreased significantly over time in patients in whom VT was not ind ucible during at least 1 follow-up EPS (P=.05). Group 2 patients under went 86 noninvasive EPSs after discharge. Sustained monomorphic VT was induced during 22% of follow-up EPSs, VF was induced during 19% of fo llow-up EPSs, and no sustained VT/VF could be induced during 68% of fo llow-up EPSs. No sustained VT/VF could be induced during every follow- up EPS in 9 patients (50%), whereas sustained monomorphic VT was induc ed at least once during follow-up in 7 patients (34%). Persistent noni nducibility of VT during follow-up was associated with low probability of occurrence of spontaneous VT (11%), whereas inducibility of VT at least once during follow-up was associated with the occurrence of spon taneous VT (89%, P=.003). Conclusions Considerable variability of VT i nduction is observed over a lengthy period in patients presenting with sustained VT/VF. Persistent noninducibility of VT is associated with a reduced probability of spontaneous VT. These observations suggest th at the substrates for inducible and spontaneous VT change in parallel over time.