Effects of halothane and enflurane on conduction velocity and maximum rate of rise of action potential upstroke in guinea pig papillary muscles.

Using standard microelectrode techniques, the effects of halothane and enflurane on the maximum rate of rise of action potential upstroke (Vmax) and conduction velocity of excitation were compared with those of fast sodium channel blockers in isolated guinea pig papillary muscles. Lidocaine and tetrodotoxin decreased the square of the conduction velocity in proportion to the decrease in Vmax. In contrast, halothane and enflurane only slightly affected Vmax, but decreased the conduction velocity in a concentration-dependent manner. These results suggest that these volatile anesthetics affect conduction velocity by a mechanism different from that of fast sodium channel blockers. Caution should be used when these anesthetics are administered to patients receiving class 1 antiarrhythmic agents or who have pre-existing intraventricular conduction disease.