Autonomic modulation of refractoriness in canine specialized His-Purkinje system

Abstract

The effects of autonomic efferent stimulation on refractoriness of the specialized His-Purkinje system were examined in open-chest dogs anesthetized with 1.0% halothane. In eight animals submaximal bilateral stimulation of the ventral ansae subclavia decreased (P less than or equal to 0.01) the average functional refractory period for the propagation of His bundle extrastimuli to five ventricular recording sites (HP-FRP) by 10.9 +/- 0.6 ms. Submaximal stimulation of the decentralized vagal nerves that produced first degree atrioventricular block did not affect ventricular refractoriness. Combined vagosympathetic stimulation produced a smaller (P less than or equal to 0.01) decrease of the average HP-FRP (7.2 +/- 1.1 ms) than that produced by sympathetic stimulation alone. Administration of atropine abolished (P less than or equal to 0.05) vagal antagonism of the shortening effect of isoproterenol on the average HP-FRP. Treatment with propranolol reversed (P less than or equal to 0.01) the sympathetic effect on the average HP-FRP and nonuniformly increased refractoriness in the His-Purkinje system. The latter changes were abolished (P less than or equal to 0.05) by infusion of phentolamine. The autonomic nervous system modulates His-Purkinje refractoriness by actions mediated by cholinergic and both alpha- and beta-adrenergic receptors.