Effects of halothane on impulse propagation in Purkinje fibers and at Purkinje-muscle junctions: relationship of Vmax to conduction velocity.

Abstract

Alterations in Purkinje-to-muscle conduction may play a role in the development of cardiac arrhythmias. We compared the effects of halothane on impulse propagation in Purkinje fibers with its effects on impulse propagation across the Purkinje-muscle (P-M) junction. In canine Purkinje fibers, halothane (3%) significantly depressed conduction (P less than 0.05). Exposure to halothane altered conduction velocity (theta) in a manner predicted by cable theory; a significant correlation was noted between depression of Vmax and depression of the square of conduction velocity (theta 2) in Purkinje fibers exposed to 3% halothane (n = 11, r = 0.78, P less than 0.01). Halothane (3%) significantly slowed impulse propagation across the P-M junction (P less than 0.05). Vmax and the square of apparent P-M conduction velocity were not significantly correlated (n = 7, r = 0.34, P = 0.45). The data demonstrate that alteration of active membrane properties can account for halothane's slowing of conduction in Purkinje fibers but not for its slowing of conduction across the P-M junction. The data also suggest that a reduction in cell-to-cell coupling may contribute to depression of Purkinje-to-muscle conduction by halothane.