EFFECTS OF KETAMINE ON VENTRICULAR CONDUCTION, REFRACTORINESS, AND WAVELENGTH - POTENTIAL ANTIARRHYTHMIC EFFECTS - A HIGH-RESOLUTION EPICARDIAL MAPPING IN RABBIT HEARTS

Background: The aims of the study were to verify the effects of ketami ne on ventricular conduction velocity and on the ventricular effective refractory period, to determine its effects on anisotropy and on homo geneity of refractoriness, and to use wavelength to determine whether ketamine has antiarrhythmic or arrhythmogenic properties, Methods: A h igh-resolution epicardial mapping system was used to study the effects of 50, 100, 150, and 200 mu M racemic ketamine in 15 isolated, Langen dorff-perfused rabbit hearts, Five hearts were kept intact to study th e effects of ketamine on spontaneous sinus cycle length (RR) interval and its putative arrhythmogenic effects, In 10 other hearts, a thin ep icardial layer was obtained by an endocardial cryoprocedure (frozen he arts) to study ventricular conduction velocity, ventricular effective refractory periods (five sites), and ventricular wavelength, Results: Ketamine induced a concentration-dependent lengthening of the RR inter val, Ketamine slowed longitudinal and transverse ventricular-conductio n velocity with no anisotropic change, and it prolonged the ventricula r effective refractory period with no significant increase in dispersi on, Ventricular longitudinal and transverse wavelengths tend to increa se, but this was not statistically significant, Finally, no arrhythmia could be induced regardless of the ketamine concentration, Conclusion : Ketamine slowed ventricular conduction and prolonged refractoriness without changing anisotropy or increasing dispersion of refractoriness . Although these effects should result in significant antiarrhythmic e ffects of ketamine, this should not be construed to suggest a protecti ve effect in ischemic or other abnormal myocardium.