Influence of tedisamil on the initiation and maintenance of ventricular fibrillation: chemical defibrillation by Ito blockade?

We examined the effects of tedisamil on ventricular fibrillation (VF) elicited by regional ischemia and by reperfusion in isolated rat hearts (n = 12/group). During 30 min of ischemia, 0.1, 0.55, and 3 microM tedisamil had no influence on the incidence of VF (an index of VF initiation). However, sustained VF (SVF, defined as that lasting greater than 120 s, an index of VF maintenance) was reduced in a concentration-dependent manner from 73 to 54, 17 (p less than 0.05), and 0% (p less than 0.05), respectively. Tedisamil caused sinus bradycardia but this was not the basis for tedisamil's antiarrhythmic activity since SVF was also inhibited in separate groups of hearts that were paced throughout the study. Tedisamil had no effect on reperfusion-induced VF initiation. However, VF maintenance was, again, inhibited, with SVF incidence reduced from 75% to 40, 20, and 0% (p less than 0.05), respectively, by increasing concentrations of tedisamil. A similar effect was, again, observed in paced hearts. The average cycle length of the electrogram during VF correlated with preceding width of the ventricular complex; both of these variables were concentration-dependently increased by tedisamil and mean values of each correlated inversely with the incidence of SVF. The ratio of SVF cycle length to ventricular tachycardia cycle length was 1:3, and this ratio was conserved in the presence and absence of drug. The data are consistent with a drug-induced increase in the probability of spontaneous termination of multiple wave-front re-entry.