Reentry within the isolated canine bundle of his: Possible mechanism for reciprocal rhythm

Abstract

Microelectrode techniques were utilized to investigate reentrant activity in the isolated canine bundle of His. The bundle was exposed by dissection in a muscle chamber superfused with oxygenated Tyrode solution. Isolation of the bundle was completed by resection of the atrioventricular (A-V) junction and the proximal bundle branches. Extracellular stimuli were delivered to the proximal bundle. Depression of conduction induced by Tyrode solution containing 13.5 mM potassium ion was monitored by two recording intracellular microelectrodes impaled into cells of the proximal and distal bundle of His. As interelectrode activation times prolonged, second depolarizations of the proximal cell occurred. These second depolarizations often appeared as full amplitude action potentials. When block of conduction occurred immediately distal to the proximal cell, that cell was not reactivated. When conduction failed nearer the distal cell, reactivation of the proximal cell occurred followed by activation of the distal cell after various periods of delay. Occasionally, repetitive reactivation of both cells occurred. We conclude that prolongation of action potential duration proximal to sites of conduction depression may be due to reentry. Furthermore, these data suggest that functional longitudinal dissociation of conduction and reentry can occur within the bundle of His without participation of either the atria or the A-V junction. Thus, reentry within the bundle of His may be a mechanism for reciprocating rhythms.