ABSTRACT
Alpha adrenergic stimulation was shown to prolong repolarization of ventricular myocardial and specialized conducting fibers in 1970s. As for alpha adrenergic actions on cardiac electrophysiologic properties, reports of prolongation of the Purkinje fiber action potential had appeared, as had descriptions of suppression of automaticity, but there was little understanding of mechanism. In the dog with complete heart block, infusions of epinephrine in the presence of beta adrenergic blockage decreased the rate of impulse initiation by idioventricular pacemakers (which have high levels of membrane potential), but had no effect on impulse initiation by the sinus node (which has a low membrane potential). A question of increasing concern to us recently has been how alpha adrenergic stimulation, a mechanism that inhibits impulse initiation in the normal ventricle, becomes arrhythmogenic with ischemia and reperfusion. To study this question, the authors used isolated adult canine Purkinje fiber bundles.
