[Antiarrhythmic Efficacy of a New Class III Antiarrhythmic Drug RG-2.]

We studied effects of a new class III antiarrhythmic drug RG-2 in a canine model of vagally-mediated atrial fibrillation (AF). RG-2 was intravenously infused to anesthetized open-chest dogs in progressive doses (5, 10, 20 and 40 mg/kg, n=6) during vagally-induced AF. RG-2 significantly dose-dependently increased atrial effective refractory period (AERP) with and without vagal stimulation, but did not change conduction velocity. Five mg/kg terminated vagally-induced AF in 4 of 6 dogs but did not prevent AF reinduction. However, additional doses of drug 20 and 40 mg/kg successfully terminated AF in 100% as well as prevented AF reinduction in 50% and 72% of cases, respectively. Activation mapping (224 epicardial electrodes) showed that under drug influence there was gradual reduction of wavelet number until termination of the reentrant excitation. AF cycle length increased before AF termination from 91+/-4 to 140+/-8 ms (p<0.01). These changes correlated with drug-induced increasing of AERP. In conclusion, the ability of RG-2 to terminate and prevent reinduction of experimental AF appears to be associated with a significant prolongation of the AERP.