Actions of Halothane, Isoflurane, and Enflurane on the Regional Action Potential Characteristics of Canine Purkinje Fibers

The effects of halothane, isoflurane, and enflurane on proximal (false tendon) and distal (apical) canine Purkinje fibers were measured in vitro to assess their comparative effects on fibers exhibiting characteristically long (proximal) and short (distal) action potential duration. High- and low-dose anesthetic effects were evaluated in three groups of six left ventricular preparations and were compared with the changes occurring at identical times in six control preparations using analysis of variance with repeated measures. Under control conditions in all groups, the action potential duration, measured at 90% repolarization (APD90, mean ± sem), of proximal fibers was longer than that of distal fibers (320 ± 16 vs 252 ± 11 ms, P ≤ 0.01). Halothane (0.3 and 0.7 mM), isoflurane (0.4 and 0.8 mM), and enflurane (0.6 and 1.0 mM) produced a dose-dependent decrease (P ≤ 0.01) of proximal fiber APD90, with less (P ≤ 0.01) change of distal fiber APD, and reduced (P ≤ 0.05) regional differences of APD90, at the higher dose. The decreases of proximal fiber APD90, were greater (P ≤ 0.01) for 1.0 mM (1.7 MAC) enflurane (−66 ± 7 ms) and 0.8 mM (3.0 MAC) isoflurane (−69 ± 9 ms) than for 0.7 mM (2.9 MAC) halothane (−33 ± 8 ms). We conclude that the regional actions of anesthetics on Purkinje fiber repolarization may influence conduction during the relative refractory period und the occurrence of arrhythmias associated with isparity of regional refractory characteristics in the ventricular conduction system.