EXPERIENCE WITH A 3RD-GENERATION IMPLANTABLE CARDIOVERTER-DEFIBRILLATOR

A Medtronic 7216A pacemaker cardioverter-defibrillator was implanted in 16 patients (mean age 56 years) with sustained ventricular tachycardia (VT) or ventricular fibrillation (VF) and organic heart disease with a mean left ventricular ejection fraction of 33%. Endocardial and epicardial defibrillation shock efficacy was evaluated before or at implant using 1 to 3 shock patterns, i.e., monophasic single, sequential or simultaneous shocks with dual and triple electrode configurations. Endocardial leads used a common right ventricular cathode and dual anodes, whereas epicardial leads used 2 or 3 helical coil patches. VT termination was evaluated using pacing or shock therapy, or both, whereas only shocks were used in VF. Programmable bradycardia pacing, individual zones for VT and VF detection and individualized pacing and shock therapy for VT and VF were used. Monophasic shocks had epicardial defibrillation thresholds ranging from 3 to 18 (mean 10) J and were comparable for sequential and simultaneous shocks (p > 0.2). VT detection rates ranged from 340 to 470 ms and VF detection rates from 270 to 330 ms. VT or VF induction, or both, was performed noninvasively in 13 patients after implant and was reproducibly terminated by rapid pacing alone (5 patients), low-energy shocks (2 patients), high-energy shocks (3 patients) and combined therapy (3 patients). Intermediate or high-energy shocks terminated all induced VF episodes. During follow-up (2 to 12 months), there have been 2 noncardiac deaths. Electrical therapy was delivered in 7 patients, for VT (3 patients), VT and VF (3 patients) and indeterminate tachyarrhythmia (1 patient). All VT/VF episodes were successfully terminated, with 78 of 96 (81%) spontaneous VT episodes terminated by pacing. Follow-up reprogramming was required in 5 patients. It is concluded that successful application of individualized electrical therapy prescriptions in patients with VT/VF is feasible. Pacing therapies, which are effective for induced VT, can be reliably used for effective long-term spontaneous VT termination in conjunction with shock therapy and can permit reduced patient exposure to shock therapy. Thus, a programmable hybrid pacemaker cardioverter-defibrillator system provides nonthoracotomy implantation, effective VT/VF termination, demand ventricular pacing and noninvasive modes for arrhythmia induction, event monitoring and clinical trouble-shooting.