Antifibrillatory Effect of Esmolol Alone and in Combination with Lidocaine

The primary objective of this study was to determine the effect of esmolol, administered alone and in combination with lidocaine, on ventricular fibrillation threshold (VFT) in pigs. A secondary objective was to determine the relationship between blood esmolol concentrations and VFT. We determined VFT using a train of electrical stimuli delivered to the right ventricle after eight paced beats at a basic cycle length of 285 ms. Current was increased in 2-mA increments until VF occurred. VFT determinations were performed during administration of esmolol 1,000 mu g/kg/min, during a continuous infusion of lidocaine, and during infusion of esmolol and lidocaine in combination. Mean increases in VFT from baseline during infusion of esmolol and lidocaine alone were 32.3 +/- 12.9 and 8.5 +/- 7.2 mA, respectively (p < 0.05, each drug compared with baseline; p < 0.05, esmolol vs. lidocaine). Mean increase in VFT from baseline during infusion of the combination was 52.0 +/- 22.0 mA (p < 0.05 as compared with baseline and with esmolol or lidocaine alone). The relationship between blood esmolol concentrations and VFT was described by a counterclockwise hysteresis curve, suggesting delay in equilibration of esmolol between blood and site of effect. The antifibrillatory efficacy of esmolol is significantly greater than that of lidocaine in this model. Administration of the two agents in combination resulted in significantly greater antifibrillatory efficacy than that associated with either drug administered alone.