COMPARISON OF INITIAL DETECTION AND REDETECTION OF VENTRICULAR-FIBRILLATION IN A TRANSVENOUS DEFIBRILLATOR SYSTEM WITH AUTOMATIC GAIN-CONTROL

Objectives. The purpose of this study was to prospectively evaluate po stshock redetection of ventricular fibrillation by a system that coupl ed an implantable cardioverter-defibrillator with an automatic gain co ntrol sense amplifier and a transvenous lead system. Background. Redet ection of ventricular fibrillation after an unsuccessful first shock h as not been systematically evaluated. Previous studies base suggested that sensing performance of some lead systems may be adversely affecte d by the delivery of subthreshold shocks. Methods. The time required f or both initial detection and redetection of ventricular fibrillation was compared in 22 patients. These times were estimated by subtracting the capacitor charge time from the total event time. Results. A total of 113 successful and 57 unsuccessful initial shocks were delivered d uring induced ventricular fibrillation. The mean +/- SD initial time t o detection of ventricular fibrillation was 5.5 +/- 1.7 s (range 2.4 t o 10.8); the time to redetection ranged from 1.5 to 18.5 s (mean 4.5 /- 2.8, p = NS vs. detection time). Abnormal redetection episodes, def ined as a redetection time >10.2 s (i.e., >2 SD above the mean redetec tion time), were observed in 4 (18%) of 22 patients. Conclusions. Rede tection of ventricular fibrillation after a subthreshold first shock m ag be delayed. Device testing with intentional delivery of subthreshol d shocks to verify successful postshock redetection of ventricular fib rillation should be performed routinely in all patients.