Experimental Study on the Cause of Ventricular Aberrant Conduction

Abstract

Aberrant ventricular conduction of premature supraventricular beats results in a right bundle branch block pattern in the majority of clinical or experimental electrocardiograms. As a possible cause of this phenomenon, it has been suggested that there is a longer refractory period on the right side of the conduction system. However, detailed electrophysiological mechanisms underlying aberrant conduction remain unsolved and have been still a matter of discussion. The present study was carried out to make a comparison of refractory periods between the canine right (RBB) and left bundle branch (LBB) specimens superfused with oxygenated Tyrode solution. Electrophysiological properties of the septal Purkinje fibers in the LBB system were found to play an important role in the genesis of the RBB block pattern. Methods: Specimens of both the LBB and RBB systems obtained from the canine heart were immersed in a single tissue bath and were superfused with oxygenated Tyrode solution composed of (mM), NaCl 147, KCI 4.0, CaCl2 1.8, MgCl2 0.5, dextrose 5.5, NaH2P04 1.5, Na2HP04 4.5. The specimen of the LBB system consists of the left septal endocardium, the main left bundle, the anterior fascicle (AF), the posterior fascicle (PF), and a profuse subendocardial network of the septal Purkinje fibers (SEP). The specimen of the RBB system consists of the main RBB in the right upper septum and its subsequent two or three false tendons which terminate in the free wall . Action potential durations (APD, 80% of repolarization time) of the Purkinje fibers were measured along the following four conduction pathways in the left and right specimens which were simultaneously driven by basic stimuli (cycle length = 750 msec): (1) the main RBB and its subsequent false tendons, (2) the AF, (3) the PF, and (4) the SEP of the LBB system. The functional refractory period (FRP) was defined as the minimum interval between the basic and premature responses. ResuIts: 1. Comparison of APD between the left and right conduction pathways. In eighteen experiments, APD was measured at I 5-20 points along each course of the above-mentioned four conduction pathways. The maximum APD of the SEP in the LBB system was shortest among the four pathways (p < 0.005). There was no significant difference in the