Objectives: The purpose of this study was to prospectively evaluate postshock redetection of ventricular fibrillation by a system that coupled an implantable cardioverter-defibrillator with an automatic gain control sense amplifier and a transvenous lead system.
Background: Redetection of ventricular fibrillation after an unsuccessful first shock has not been systematically evaluated. Previous studies have suggested that sensing performance of some lead systems may be adversely affected by the delivery of subthreshold shocks.
Methods: The time required for 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 during induced ventricular fibrillation. The mean +/- SD initial time to detection of ventricular fibrillation was 5.5 +/- 1.7 s (range 2.4 to 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, defined as a redetection time > 10.2 s (i.e., > 2 SD above the mean redetection time), were observed in 4 (18%) of 22 patients.
Conclusions: Redetection of ventricular fibrillation after a subthreshold first shock may be delayed. Device testing with intentional delivery of subthreshold shocks to verify successful postshock redetection of ventricular fibrillation should be performed routinely in all patients.