VENTRICULAR MECHANICS AND INTRACARDIAC ELECTROGRAM IN EXPERIMENTAL BUNDLE-BRANCH BLOCK

Abstract

In order to examine the influence of bundle-branch block on mechanical systole and the intracavitary electrogram, we recorded the ventricular pressure curves and the intracavitary electrogram of both ventricles before and after section of the right and left branches of the bundle of His in the dog. In the blocked ventricle the delay between electrical and mechanical events increases, and the mechanical systole is delayed: this delay corresponds to the delay in the intrinsic deflection of the same ventricle. The delay between electrical and mechanical events in the opposite ventricle is unchanged. In normal conditions we have always recorded a QS complex or else an rS complex in the left ventricle according to the position of the electrode in the ventricular cavity. The T wave in both ventricles is generally positive, though occasionally negative: this variation too is probably related to the position of the intracavitary electrode. After section of the right bundle of His a large R wave is recorded in the blocked ventricle; its relation to the S wave does not vary with the degree of the block but with the position of the intracavitary electrode. After section of the left branch a small q wave is often recorded in the left ventricular cavity. This records the activation of part of the septum from left to right, probably by some offshoot of the left branch which has remained intact above the point of section. The R wave recorded in the cavity of the blocked ventricle is not delayed, but begins simultaneously with the beginning of ventricular depolarization. In the blocked ventricle the end of the intrinsic deflection is delayed, while the section between the lowest point of the S wave and the end of the complex remains normal. This shows that the spread of the stimulus is impaired until it reaches the blocked ventricle, whereas the subsequent process of ventricular depolarization remains unchanged. In accordance with the changes in the repolarization of the blocked ventricle the T wave in the corresponding intracavity tracing becomes negative. In the opposite ventricle the T wave becomes positive or more positive.