HIGH-VOLTAGE ICD LEAD IMPEDANCES ARE NOT INCREASED BY ROUTINE DEFIBRILLATION TESTING: Results FROM THE SIMPLE STUDY

Abstract

The SIMPLE trial demonstrated that routine defibrillation testing (DT) at the time of ICD implantation does not improve clinical shock efficacy. In fact, patients randomized to DT had a non-significantly lower rate of successful clinical shocks (88.5% vs. 92%, p=0.08). As there were only 27 failed clinical shocks in SIMPLE, it is possible that this apparent difference in efficacy is due to chance alone; however, an alternative hypothesis is that the delivery of high voltage (HV) energy at the time of ICD implant led to tissue injury and fibrosis; which would result in a higher impedance and lower current delivery at the time of clinical ICD shocks. Among 380 patients with an appropriate clinical shock, HV-lead impedance at the time of ICD implantation and the time of clinical shock was compared between patients randomized to DT or no DT using an independent t-test. Complete HV impedance data were available for 275 patients who experienced clinical appropriate shocks (Table 1). The average number of shocks given at the time of ICD implantation in the DT group was 1.7±1.6 and the mean time to first clinical shock was 428.2 days in the DT group and 445.9 days in the no DT group (p= 0.644). There were no significant differences between the DT and No DT group in terms of HV-lead impedance at baseline, at the time of first clinical shock, nor in the change over time. Implant DT does not appear to increase HV impedance. The non-significant difference in clinical shock efficacy between treatment groups in SIMPLE is most likely due to chance.