1026-86 The Influence of Sodium Channel Blockade on the Defibrillation Threshold of Biphasic versus Monophasic Defibrillation Waveforms

Abstract

Several Class I antiarrhythmic drugs are known to increase the defibrillation threshold (DFT) of monophasic shock waveforms delivered by implantable defibrillators (ICD). The influence of sodium channel blockade on biphasic shocks is unknown. The purpose of this study was to determine the effects of lidocaine (LIDO) on the DFT with biphasic versus monophasic shock waveforms in an anesthetized canine model of transvenous defibrillation (n = 101. The DFT was determined by the iterative increment-decrement protocol. Monophasic and biphasic shock OFT's were tested in random order at baseline and during LIDO infusion (8 mg/kg load; 400 microgm/kg/min) and presented below. Monophasic DFT (Joules) Biphasic DFT (Joules) P Value * Baseline 160 ± 56 11.1 ±2.7 0.006 LIDO 264 ± 109 16.9 ± 9.0 0.018 P Value ** 0.009 0.054 * p value of monophasic vs biphasic ** p value of baseline vs LIDO In 2 dogs, the DFT during LIDO was > 50 joules with monophasic shock and 27.9 ± 5.6 joules with biphasic shocks. LIDO caused a 13.1 ± 9.8% increase in ventricular refractoriness (p < 0.037) and a 29.8 ± 22.7% increase in GAS duration (p < 0.01). neither of which were predictive of DFT response. Sodium channel blockade does increase the DFT of biphasic shocks but to a lesser extent than observed with monophasic shock DFT's. These results may have favorable implications for the use of Class I antiarrhythmics in patients with newer generation lCD's.