Functional properties of the left septal Purkinje network in premature activation of the ventricular conduction system

Abstract

To elucidate the mechanism underlying ventricular aberrant conduction, in each of 18 experiments we measured action potential durations (APD) and functional refractory periods (FRP) of the Purkinje fiber along the following four conduction pathways in a pair of the right and left specimens isolated from the same canine heart: (1) the right bundle branch (RBB) and its subsequent false tendon, (2) the anterior fascicle (AF), (3) the posterior fascicle (PF), and (4) the septal Purkinje fiber of the left bundle branch (LBB) system. Both the APD and the FRP of the septal Purkinje fiber on the left septal surface were significantly shorter than those of the RBB, the AF, and PF of the LBB system, though we found no meaningful differences in the APD and the FRP among the false tendons of the RBB, the AF, and Pf. It was thus suggested that the electrophysiological properties of the septal Purkinje fiber might have functional significance in premature activation of the LBB system. In order to verify this hypothesis, furthermore, we studied the sequential activation of the left conducting tissue and muscle cells of the left septal surface, applying a premature stimulus to the main LBB at a critical coupling interval which was nearly equal to the refractory periods of the AF and PF. The test impulse was propagated to the entire septal surface through the septal Purkinje fiber, resulting in the initial muscle activation at almost the same area of the middle or lower third of the midseptum as in normal activation of the LBB system. The result indicates that the septal Purkinje network functions as the quickest pathway for conduction of premature impulses to the septal myocardium, and suggests that the functional properties of this fiber group contribute to the higher incidence of RBB block in ventricular aberrant conduction of supraventricular premature beats.