WAY-123,398 increased the ventricular fibrillation threshold and induced defibrillation in 2 of 6 anesthetized dogs, comparable to UK-68798 (2 of 6) and E-4031 (1 of 6).
Previous studies in isolated ventricular myocytes showed that WAY-123,398 is a selective blocker of the delayed rectifier K+ current (IK). In this report, we studied the electrophysiological and hemodynamic effects of WAY-123,398 in open-chest anesthetized dogs. WAY-123,398 prolonged atrial and ventricular refractoriness without affecting conduction; WAY-123,398 was as effective as UK-68798, E-4031, and dl-sotalol, but less potent than UK-68798 and E-4031. The increase in atrial refractoriness was approximately twice as large as the ventricular increase with all compounds. The hemodynamic effects of WAY-123,398 were similar to those of UK-68798; at the ED20 for increasing ventricular refractoriness, WAY-123,398 did not affect the mean arterial pressure and decreased the heart rate by 20%. In a different series of experiments, all four compounds produced large and comparable increases in the ventricular fibrillation threshold in anesthetized dogs; WAY-123,398 and UK-68798 induced defibrillation and restoration of sinus rhythm in two of six dogs each and E-4031 in one of six dogs. No episodes of drug-induced restoration to sinus rhythm were observed in dogs treated with sotalol or vehicle. In conclusion, WAY-123,398 is an effective Class III agent without Class I actions and with a favorable hemodynamic profile.
Spinelli et al. (Tue,) conducted a other in Anesthetized dogs. WAY-123,398 vs. UK-68798, E-4031, dl-sotalol, and vehicle was evaluated on Cardiac refractoriness and ventricular fibrillation threshold. WAY-123,398 increased the ventricular fibrillation threshold and induced defibrillation in 2 of 6 anesthetized dogs, comparable to UK-68798 (2 of 6) and E-4031 (1 of 6).