Electrophysiologic Effects of Intravenous MS-551, a Novel Class III Antiarrhythmic Agent, on Human Atrium and Ventricle

The effects of intravenous MS-551, a new class III antiarrhythmic drug, on atrium and ventricle were evaluated in 6 patients with ventricular tachyarrhythmias (4 males and 2 females; mean age 45±21 years) in an electrophysiologic study. Two patients had sustained ventricular tachycardia (VT) and 4 patients had ventricular fibrillation (VF). Electrophysiologic study was performed before and after the administration of MS-551 (loading infusion 0.3mg/kg for 5min+0.01mg/kg/min). The QT and QTc intervals were significantly prolonged by MS-551 from 359±52 to 411±63 msec (p=0.01) and from 410±36 to 452±47 (p=0.0172), respectively. No effect was observed on the sinus cycle length, QRS duration, or AH and HV intervals in sinus rhythm. The effective refractory periods of the right atrium (AERP) were significantly prolonged at paced cycle lengths of 600 (from 222±19 to 250±23 msec, p=0.0009), 400 (from 207±15 to 228±15, p