Appropriate sensing of ventricular fibrillation after failed shocks in a transvenous cardioverter-defibrillator system

Abstract

Background: Reduction in R-wave amplitude immediately after defibrillation shocks in an integrated shock/sense transvenous cardioverter-defibrillator (TCD) lead system has prompted concerns regarding adequate sensing after failed shocks. We therefore studied redetection characteristics for ventricular fibrillation after unsuccessful defibrillation shocks in a TCD system to determine if these observations have clinical relevance. Methods and Results: Fifty patients with this shock/sense TCD lead system underwent conversion testing of their TCD at several time intervals. There were a total of 142 failed shocks events recorded, including 10, 15, 70, and 47 events at implantation, predischarge, and 2- and 6-month testing, respectively. Initial detection time (IDT) and redetection time (RDT) for ventricular fibrillation were measured from event markers for all unsuccessful defibrillation shocks. To assess the effect of failed shocks on electrogram quality, 54 failed shock episodes were evaluated in 37 of the 50 patients by measuring electrograms during VF before and after shock. Mean RDT for the entire group was 5.3±3.5 seconds compared with an IDT of 4.5±3.3 seconds (P=NS). There were no significant differences between IDT and RDT at implantation or any follow-up testing period, despite a significant decline in R-wave amplitude from 8.1±3.5 to 6.8±2.8 mV (P