Electrophysiological effects of haloperidol on isolated rabbit Purkinje fibers and guinea pigs papillary muscles under normal and simulated ischemia

AbstractAim:Overdoses of haloperidol are associated with major ventricular arrhythmias, cardiac conduction block, and sudden death. The aim of this experiment was to study the effect of haloperidol on the action potentials in cardiac Purkinje fibers and papillary muscles under normal and simulated ischemia conditions in rabbits and guinea pigs.Methods:Using the standard intracellular microelectrode technique, we examined the effects of haloperidol on the action potential parameters [action potential amplitude (APA), phase 0 maximum upstroke velocity (Vmax), action potential amplitude at 90% of repolarization (APD90), and effective refractory period (ERP)] in rabbit cardiac Purkinje fibers and guinea pig cardiac papillary cells, in which both tissues were under simulated ischemic conditions.Results:Under ischemic conditions, different concentrations of haloperidol depressed APA and prolonged APD90 in a concentration-dependent manner in rabbit Purkinje fibers. Haloperidol (3 μmol/L) significantly depressed APA and prolonged APD90, and from 1 μmol/L, haloperidol showed significant depression on Vmax; ERP was not significantly affected. In guinea pig cardiac papillary muscles, the thresholds of significant reduction in APA, Vmax, EPR, and APD90 were 10, 0.3, 1, and 1 μmol/L, respectively, for haloperidol.Conclusion:Compared with cardiac conductive tissues, papillary muscles were more sensitive to ischemic conditions. Under ischemia, haloperidol prolonged ERP and APD90 in a concentration-dependent manner and precipitated the decrease in Vmax induced by ischemia. The shortening of ERP and APD90 in papillary muscle action potentials may be inhibited by haloperidol.