Electrophysiologic Effects of Nicorandil on the Human Cardiac Conduction System and its Antiarrhythmic Action

Recently, nicorandil, an anti anginal drug, has been shown to increase membranepotassium conductance in cardiac fibers. Therefore, electrophysiologic effects ofnicoandil 4mg iv were studied in 20 patients (pat.) with sick sinus syndrome (8 pat.), AV block (5 pat.), and paroxysmal supraventricular tachycardia (7 pat.). The plasmalevel of nicorandil was also estimated.Nicorandil did not change sino-atrial conduction time, AH interval, HV interval, AVnodal effective refractory period (ERP), ventricular ERP, or ERP of the accessorypathway. The sinus cycle length and sinus recovery time were shortened from 914.8±51.7 to 819.8±44.0 msec (mean±SE, P<0.01) and from 1, 375.1±111 to 1, 284.3±101 msec (P<0.05), respectively. The minimum atrial pacing rate resulting in Wenckebach AV block was increased from 152.5±12.0 to 158.3±10.9/min (P<0.05)The atrial ERP was shortened from 267.2±10.7 to 250.6±9.6 msec (P<0.01).Intraatrial reentrant tachycardia could not be initiated by electrical stimuli afternicorandil in one case. However, these changes might have been attributable toanatonomic nervous reflexes caused by vasodilating action, rather than any direct effectof nicorandil. In conclusion, nicorandil can be used safely even for cases of coronaryartery disease associated with sick sinus syndrome or AV block, because nicorandil hasno negative chronotropic effect on human hearts. Additionaly, nicorandil may beeffective for intraatrial reentrant tachycardia.