Effects of Combination of Sotalol and Verapamil on Initiation, Maintenance and Termination of Ventricular Fibrillation in Swine Hearts.

Introduction: Sotalol and verapamil alone reduce reentry incidence during ventricular fibrillation (VF). We tested whether the combination of these two drugs had a synergistic effect on initiation, maintenance, and termination of VF. Methods: Six open-chest pigs received intravenous sotalol (1.5mg/kg) followed by verapamil (0.136mg/kg). VF threshold (VFT) was determined by a burst pacing protocol. Two 20seconds episodes of VF were recorded from a 21 x 24 unipolar electrode plaque on the lateral posterior left ventricular epicardium before and after each drug. VF activation patterns were quantified. The duration of long duration VF (LDVF) maintenance was compared to our previously published data. Results: Sotalol alone and combined with verapamil significantly increased the VFT from 12.3 +/- 4.1 to 20.3 +/- 7.1 and 26.7 +/- 8.6mA compared with baseline (P < .05). Sotalol decreased the number of wavefronts by 20%, VF activation rate by 17% and conduction velocity 11%, while the addition of verapamil neutralized these effects. Addition of verapamil to sotalol further decreased the fractionation incidence from 14% to 29% and multiplicity from 24% to 31% compared with baseline. The combination of the two drugs increased the VF cycle length, decreased synchronicity, increased regularity index and shortened the duration of LDVF maintenance compared with our previous data of verapamil alone or no drug. Synchronicity index was lower and regularity index was higher in animals in which VF spontaneously terminated earlier than 10minutes than in animals in which VF terminated longer than 10minutes. Conclusion: The combination of sotalol and verapamil increased VFT but accelerated LDVF termination.