Antifibrillatory efficacy of encainide, loracainide and ORG 6001 compared with lignocaine in isolated hearts of rabbits and guinea-pigs.

1 In Langendorff-perfused rabbit hearts, electrical stimulation threshold and ventricular fibrillation threshold (VFT) were measured by applying rectangular impulses of 3 ms duration and increasing current at frequencies of 4 and 20 Hz respectively. 2 Perfusion with lignocaine or one of three new antiarrhythmic drugs, encainide, lorcainide and ORG 6001, produced significant, dose-dependent increases in both thresholds. 3 On a dosage basis, encainide was seven times, lorcainide fourteen times and ORG 6001 twice as potent as lignocaine in raising VFT. 4 In Langendorff-perfused guinea-pig hearts, only lorcainide provided complete protection against ouabain-induced ventricular fibrillation, while 6 of 6, 3 of 6 and 2 of 6 hearts fibrillated in the presence of encainide, lignocaine and ORG 6001 respectively, but with infusion durations significantly higher than control. 5 These results indicate the potential antifibrillatory activity of these new antiarrhythmic agents.