Spread of activation in the left ventricular wall of the dog. IV: Two and three dimensional analysis

Abstract

Needle electrodes were used for the spatial analysis of the activation of the left ventricular wall of the dog. Two and three electrodes of this type were introduced perpendicular to the epicardial surface into the lateral part of the left ventricular wall. With two-needle electrodes the angle of the activation front with the epicardial surface in the outer layers of the lateral, left ventricular wall, propagating in an apico-basal direction was estimated and found to be small, approximately 5 to 10°. This and the fact that the activation front has small bulges explains the complicated activation pattern at the epicardial surface. The activation pattern of the inner layers of the lateral part was investigated with three needles. The inner layers are activated in a very short time interval, considered in an endo-epicardial direction. In an apico-basal direction the experimental findings show well-developed complexes, pointing to an excess of apico-basal propagation in small areas activated by single Purkinje fibers. This explanation must be considered as a working hypothesis. The lead points of one needle electrode introduced perpendicularly to the epicardial surface were also used as stimulating electrodes. In this way it was proved that stimulation in the endocardial layers gives rise to an activation wave in endo-epicardial direction of all layers of that part of the wall investigated. The bipolar complexes of a needle electrode had approximately the same form and duration in all layers, indicating a nonfunctioning Purkinje system in the inner layers of the investigated part. Epicardial stimulation showed reversed complexes in all intramural bipolar leads of the investigated area. In experiments with two-needle electrodes placed in an apico-basal direction it was shown that the two-needle complexes in the inner layers did not reverse their polarity if two of the lead points of the apical needle electrode were used as a stimulating electrode, but reversed their polarity if the basal needle electrode was used. It was made plausible that the Purkinje system in the neighborhood of the stimulating electrode was not activated but that this occurred at a distance from the needle.