Electrophysiological Effects of MS‐551 in Humans: A Class III Antiarrhythmic Agent

To investigate the clinical effects of MS‐551, a Class III antiarrhythmic agent, 11 patients underwent electrophysiological study. MS‐551 was given intravenously as an initial dose of 0.2 or 0.3 mg/kg for 5 minutes followed by the continuous infusion at 0.2 or 0.3 mg/kg for 30 minutes, respectively, in all patients. The rate corrected QT interval increased significantly from 3 minutes after the beginning of MS‐551 infusion. The sinus heart rate decreased significantly by 8% at 10 minutes after the drug administration (P ± 0.025). Mean PR and QRS intervals, and blood pressure were not significantly affected by the drug. Mean PA, AH, and HV intervals during sinus rhythm were also not affected. The effective refractory periods (ERPs) of the atrium and ventricle were significantly prolonged by 13% from 202 ± 24 ms to 231 ± 26 ms (P ± 0.0005), and by 7% from 238 ± 11 ms to 257 ± 13 ms (P ± 0.002), respectively, by MS‐551. The ERP of the atrioventricular node and sinoatrial nodal recovery time were not changed significantly by the drug. This is a report of the effects of MS‐551 in humans. This agent could be useful for treatment of tachyarrhythmias by prolongation of ERPs of the atrium and ventricle without significant variations of blood pressure and intracardiac conduction times. It is noteworthy that MS‐551 slightly but significantly decreased heart rate.