Effects of halothane on single atrial, ventricular, and Purkinje fibers.

The action of halothane on sinoatrial, ventricular, and Purkinje fibers was studied by means of intracellular microelectrodes. Rabbit atrial fibers were not very sensitive to even high (2%) concentrations of halothane. Sheep Purkinje fibers showed a significant hyperpolarization from 82 mv to 87 mv, a marked shortening of the duration of the action potential from 370 msec to 233 msec, and a diminution of the overshoot from 30 mv to 21 mv under the influence of 1% halothane. The rate of rise was not significantly changed with this concentration. In the presence of 2% halothane the resting potential did not differ significantly from the value obtained with 1% halothane. The duration of the action potential and of the refractory period were further diminished to 165 msec and to 109 msec, respectively. The rate of rise was now significantly reduced to 245 v/sec and the overshoot further decreased to 17 mv. Conduction time was increased by about 20% with 1% halothane and more than twofold with 2% halothane. Ventricular fibers of sheep did not show significant changes of the resting potential under the influence of 2% halothane. However, the duration of the action potential was markedly shortened from 338 msec to 231 msec, the effective refractory period was significantly reduced from 295 msec to 208 msec, and the overshoot decreased from 21 mv to 11 mv. Possible mechanisms underlying these changes and which may cause arrhythmias are discussed. ADDITIONAL