Alpha-adrenoceptor stimulation in the presence of halothane: effects on impulse propagation in cardiac Purkinje fibers;

Halothane effects on action potential characteristics and conduction were determined in canine Purkinje fibers, before and during alpha-adrenergic stimulation. Halothane significantly decreased effective refractory period and action potential duration in Purkinje fibers. alpha-Adrenergic stimulation restored effective refractory period and action potential duration in Purkinje fibers exposed to halothane via an alpha 1-adrenoceptor mediated effect antagonized by prazosin. Halothane significantly slowed propagation of impulses initiated at a basic cycle length of 500 ms, and conduction of premature impulses, in Purkinje fibers. In the presence of halothane, alpha-adrenergic stimulation had no additional effects on normal impulse propagation; however, alpha-adrenergic stimulation significantly slowed the conduction of premature impulses in Purkinje fibers exposed to halothane. These data refute a previous report that alpha-adrenergic stimulation enhances halothane's negative dromotropic effect in Purkinje fibers paced at a basic drive cycle length. alpha-Adrenergic prolongation of the conduction times of premature stimuli in Purkinje fibers exposed to halothane is a new finding.