EXPERIENCE WITH AN IMPLANTABLE TIERED THERAPY DEVICE INCORPORATING ANTITACHYCARDIA PACING AND CARDIOVERTER DEFIBRILLATOR THERAPY

The implantable cardioverter-defibrillator provides an alternative therapy for medically refractory ventricular tachyarrhythmias in patients who are not candidates for ventricular operations or in whom these operations have failed. Currently, however, available devices have limitations. In this report we describe our experience with a programmable, tiered therapy device with anti-ventricular tachyarrhythmia pacing and VVI pacing capabilities (Cadence V-100, Ventritex Inc, Sunnyvale, Calif.). This device offers certain advantages compared with conventional implantable cardioverter-defibrillators: (1) tiered, anti-ventricular tachyarrhythmia therapy incorporating programmable, rate-adaptive burst pacing in addition to energy-programmable cardioversion/defibrillation, (2) biphasic cardioversion/defibrillation waveforms, resulting in lower defibrillation thresholds, (3) the ability to abort therapy for nonsustained ventricular tachyarrhythmias, (4) electrogram storage of detected events for later retrieval and analysis, (5) noninvasive, device-generated programmed stimulation for system testing, and (6) backup VVI pacing capability. Forty patients (aged 14 to 79 years) with ventricular tachyarrhythmias refractory to medical therapy received this device. The mean left ventricular ejection fraction was 33 % +/- 16 %. Preoperative electrophysiologic testing revealed inducible monomorphic ventricular tachyarrhythmia responsive to rapid ventricular pacing in 36 patients (90 %). An extrapericardial two-patch configuration was used with either epicardial screw-in or bipolar endocardial sensing/pacing wires. No operative mortality and no device-related infection occurred. During a follow-up period of 16 +/- 7 months (range 3 to 30 months), 38 patients remained active with the implanted device; one patient died of congestive heart failure 4 months after implantation, and the system was explanted in one patient who underwent cardiac transplantation. In 33 patients a total of 1815 ventricular tachyarrhythmias were detected that resulted in therapy. Rate-adaptive burst pacing was used as the initial therapy in 1470 episodes and was successful in 1352 instances (92 %). Pacing-induced ventricular tachyarrhythmia acceleration occurred in 4 % of episodes. The remaining ventricular tachyarrhythmia episodes were treated with cardioversion. In 18 patients (45 %) cardioversion therapy was aborted after spontaneous termination of ventricular tachyarrhythmia. This device may be advantageous for patients with ventricular tachyarrhythmias treated by implantable cardioverter-defibrillator in whom (1) the ventricular tachyarrhythmia can be terminated with burst pacing, thus avoiding shocks, (2) frequent runs of nonsustained ventricular tachyarrhythmia occur, and reconfirmation of the presence of ventricular tachyarrhythmia is desirable to avoid unnecessary therapy, (3) electrogram retrieval can guide future therapy, and (4) VVI pacing may be needed for bradycardia, particularly after cardioversion.