ELECTROPHYSIOLOGICAL EFFECTS OF MS-551 IN HUMANS - A CLASS-III ANTIARRHYTHMIC AGENT

To investigate the clinical effects of MS-551, a Class III antiarrhyth mic agent, 11 patients underwent electrophysiological study. MS-551 wa s given intravenously as an initial dose of 0.2 or 0.3 mg/kg for 5 min utes followed by the continuous infusion at 0.2 or 0.3 mg/kg for 30 mi nutes, respectively, in all patients. The rate corrected QT interval i ncreased significantly from 3 minutes after the beginning of MS-551 in fusion. The sinus heart rate decreased significantly by 8% at 10 minut es after the drug administration (P < 0.025). Mean PR and QRS interval s, and blood pressure were not significantly affected by the drug. Mea n PA, AH, and HV intervals during sinus rhythm were also not affected. The effective refractory periods (ERPs) of the atrium and ventricle w ere 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 < 0.00 2), respectively, by MS-551. The ERP of the atrioventricular node and sinoatrial nodal recovery lime were not changed significantly by the d rug. This is a report of the effects of MS-551 in humans. This agent c ould be useful for treatment of tachyarrhythmias by prolongation of ER Ps 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.