Does Atrial Electrical Stimulation Influence the Sequence of Ventricular Depolarization in the Heart of a Rainbow Trout Oncorhynchus mykiss?

Abstract

Depolarization of the heart ventricles at an increasing heart rate was investigated in a rainbow trout Oncorhynchus mykiss (n = 14). It was shown that at an imposed supraventricular rhythm ranging from 30 to 60 bpm the depolarization wave initially propagates from the loci of earliest atrial excitation located near the atrioventricular orifice to the subendocardial trabecular layer of the noncompact myocardium and then travels towards the epicardium as well as along the wall. This indicates some preferential pathways of cardiac excitation conduction from the pacemaker zone to subendocardial myocytes. Regardless of the heart rate, the basic pattern of ventricular excitation in the rainbow trout heart consists in the propagation of the depolarization wave, which captures the entire thickness of the myocardial wall and activates the subendocardium faster than the subepicardium, from the dorsal regions of the cardiac base in basoapical and ventral directions. At a rhythm of 50–60 bpm, propagation of the depolarization wave in the basal ventricular areas is inverted from the dorsoventral to ventrodorsal direction.