Effects of halothane and enflurane on ventricular conduction, refractoriness, and wavelength - A concentration-response study in isolated hearts

Background: Effects of halothane and enflurane on ventricular conduction, a nisotropy, duration and dispersion of refractory periods, and wavelengths w ere studied and putative antiarrhythmic or arrhythmogenic properties on ven tricles were discussed. Methods: High-resolution epicardial mapping system was used to study the ef fects of 1, 3, and 5 vol% halothane and enflurane in 30 isolated rabbit hea rts. Ten hearts were kept intact to study the effects on spontaneous sinus cycle length (RR interval), perfusion pressure, and the occurrence of spont aneous dysrhythmias. In 20 other hearts, a thin epicardial layer was obtain ed (frozen hearts) to study ventricular conduction velocity, ventricular ef fective refractory period (VERP in four sites) and wavelengths. Results: Halothane induced a concentration-dependent lengthening of RR inte rval, whereas enflurane did not. Both agents slowed longitudinal and transv erse ventricular conduction velocity with no anisotropic change. Ventricula r effective refractory period was prolonged at 1 vol% and was shortened at higher concentrations, with no significant increase in dispersion. Ventricu lar longitudinal and transverse wavelengths decreased in a concentration-de pendent manner. Although changes in wavelengths could express proarrhythmic effects of volatile anesthetics, no arrhythmia occurred in spontaneously b eating hearts or in frozen hearts. Conclusions: The ventricular electrophysiologic effects of halothane and en flurane were slight, suggesting that both agents are unable per se to induc e functional conduction block and therefore reentrant ventricular arrhythmi as.