Effects of Class I and III Antiarrhythmic Drugs on Ventricular Tachycardia-Interrupting Critical Paced Cycle Length With Rapid Pacing

The most common mechanism of sustained ventricular tachycardia (VT) is re-entry with an excitable gap, but the electrophysiologic properties and response to antiarrhythmic drugs in the area of slow conduction are not yet fully known. The purpose of this study was to assess the effects of a class I antiarrhythmic drug (procainamide) and class III agents (amiodarone, E-4031, and MS-551) on re-entrant VT using the width of the zone of entrainment. The cycle length (CL) of VT (VTCL) , the block CL that was the longest paced CL that interrupted the VT, and the width of the zone of entrainment, defined as the difference between VTCL and block CL, were compared before and after treatment with antiarrhythmic drugs. The VTCL was prolonged significantly from 308±63 to 410±77 msec after procainamide (p