Electrophysiologic effects of changrolin on cardiac conduction system in anesthetized rabbits

The electrophysiologic effects of changrolin (CRL) and procainamide (PA) were evaluated in anesthetized rabbits by His-bundle electrogram and computer controlled stimulation. CRL significantly decreased the mean spontaneous cycle length (SCL) (from 251±32 to 240±26). Corrected sinus nodal recovery time (SNRTc) had no significant changes during atrial pacing. PA, however, increased SCL and SNRTc. Both drugs definitely prolonged atrial effective refractory period (AERP), atrioventricular nodal functional refractory period (AVNF-RP), ventricular relative, effective and absolute refractory period (VRRP, VERP, VARP). CRL, unlike PA, prolonged atrioventricular nodal conduction time (A-H) (from 54±7 to 65±9)， His-Purkinje system (H-V) (from 22±2 to 29±3) and ventricular conduction time (V) (from 45±5 to 53±5). It also increased ventricular threshold current in late diastole and shifted the ventricular strength-interval (S-I) curve to the right. This finding indicates that CRL decreases ventricular excitability throughout the cardiac cycle. PA only shifted the steep portion of the curve to the right and decreased excitability in the early diastole.