Effects of Halothane and Enflurane on Ventricular Conduction, Refractoriness, and Wavelength

Abstract

Background Effects of halothane and enflurane on ventricular conduction, anisotropy, duration and dispersion of refractory periods, and wavelengths were studied, and putative antiarrhythmic or arrhythmogenic properties on ventricles were discussed. Methods High-resolution epicardial mapping system was used to study the effects of 1, 3, and 5 vol% halothane and enflurane in 30 isolated rabbit hearts. Ten hearts were kept intact to study the effects on spontaneous sinus cycle length (RR interval), perfusion pressure, and the occurrence of spontaneous dysrhythmias. In 20 other hearts, a thin epicardial layer was obtained (frozen hearts) to study ventricular conduction velocity, ventricular effective refractory period (VERP in four sites) and wavelengths. Results Halothane induced a concentration-dependent lengthening of RR interval, whereas enflurane did not. Both agents slowed longitudinal and transverse ventricular conduction velocity with no anisotropic change. Ventricular effective refractory period was prolonged at 1 vol% and was shortened at higher concentrations, with no significant increase in dispersion. Ventricular longitudinal and transverse wavelengths decreased in a concentration-dependent manner. Although changes in wavelengths could express proarrhythmic effects of volatile anesthetics, no arrhythmia occurred in spontaneously beating hearts or in frozen hearts. Conclusions The ventricular electrophysiologic effects of halothane and enflurane were slight, suggesting that both agents are unable per se to induce functional conduction block and therefore reentrant ventricular arrhythmias.