The electrophysiologic effects of amiodarone and halothane on canine Purkinje fibers.

Amiodarone may cause serious complications in patients receiving general anesthetics. Potentially adverse electrophysiologic interactions between amiodarone and halothane were studied with the use of standard microelectrode techniques to record intracellular action potentials (APs) from excised canine Purkinje fibers. A second dog (support dog) was anesthetized and a femoral arteriovenous bypass circuit created in which arterial blood from the support dog superfused the Purkinje fiber in a tissue bath. The applicability of this model was established by first comparing the AP effects of halothane during blood perfusion with those in Tyrode's solution. Halothane reduced AP duration (APD; P less than 0.05) during Tyrode's solution superfusion and blood cross-perfusion. After the blood perfusion-Purkinje fiber model was validated, the interaction between halothane and amiodarone was studied using Purkinje fibers from dogs chronically treated with oral amiodarone, superfused with blood from chronically amiodarone-treated support dogs. Amiodarone reduced resting membrane potential and prolonged APD. Depression of AP amplitude and reduction of the maximum rate of increase of phase 0 of the AP (Vmax) by halothane (both P less than 0.05) suggested risk of conduction defects if halothane is administered to patients receiving chronic amiodarone therapy.