Actions of volatile anesthetics on ischemic and nonischemic Purkinje fibers in the canine heart: regional action potential characteristics.

Abstract

The effects of halothane, isoflurane, and enflurane on proximal (false tendon) and distal (apical) Purkinje fibers were measured in vitro in infarcted canine hearts to assess their effects on action potentials of fibers located within the nonischemic and ischemic regions, respectively. High- and low-dose anesthetic effects were evaluated in three groups of eight preparations and compared to changes occurring at identical times in eight infarcted control preparations. Under control conditions in all groups, the action potential duration at 90% repolarization (APD90, mean +/- SEM) of ischemic distal fibers (396 +/- 9 ms) was longer (P < or = 0.01) than that of nonischemic proximal fibers (344 +/- 5 ms) and the ischemic fibers exhibited (P < or = 0.05) reduced maximum diastolic potential, amplitude, and Vmax relative to nonischemic fibers. Halothane (0.25 and 0.6 mM), isoflurane (0.4 and 0.8 mM), and enflurane (0.8 and 1.6 mM) produced dose-dependent decreases of nonischemic fiber APD90 with less decrease (P < or = 0.01) of ischemic fiber APD90 and thereby accentuated (P < or = 0.05) regional differences of APD90 at high dose. The decreases of nonischemic fiber APD90 were greater (P < or = 0.01) for 0.8 mM (2.9 minimum alveolar anesthetic concentration [MAC]) isoflurane (-95 +/- 5 ms) and 1.6 mM (2.5 MAC) enflurane (-79 +/- 12 ms) than for 0.6 mM (2.2 MAC) halothane (-41 +/- 3 ms). Isoflurane increased the pathologic difference (ischemic > nonischemic) between the repolarization times (APD90) of Purkinje fibers in the infarcted heart more (P < or = 0.05) than halothane.(ABSTRACT TRUNCATED AT 250 WORDS)