ARE VENTRICULAR CONDUCTION CHANGES OF IMPORTANCE IN THE DYNAMICS OF VENTRICULAR CONTRACTION?

Abstract

Theoretical considerations had led to the supposition that variations in the rapidity of conduction of the excitatory process to the fractions of ventricular muscle and consequent variations in their summation might affect the gradient, height, and duration of the resulting pressure curve. The author submitted this supposition to the test of experiment, and determined whether changes in ventricular conduction occur under various experimental conditions, and whether phasic changes in the fractionate contractions rather than changes in their form determine the characteristics of the pressure curve. Changes in the conditions under which the heart worked were effected by increasing the aortic resistance, by augmenting the venous return and cardiac filling, and by altering the heart rate. Even when considerable differences in A-V conduction occurred there was no change in conduction from point to point of the ventricular surface. Changes in ventricular excitation leading to changes in the phasic summation of fractionate contractions can not, therefore, be responsible for the effects seen in the intraventricular pressure curves under the conditions just mentioned. Variations in the characteristics of the pressure curves must therefore be produced by similar variations in the character of the fractionate contractions as long as the ventricles receive their stimulus over normal pathways.