Relative Contributions of the Atrial Systole-Ventricular Systole Interval and of Patterns of Ventricular Activation to Ventricular Function during Electrical Pacing of the Dog Heart

In areflexic canine right heart bypass preparations, little difference in ventricular function was observed as a result of atrial pacing, sequential atrioventricular pacing, or atrial-His bundle pacing at an appropriate atrial systole-ventricular systole (As-Vs) interval. Ventricular function was depressed during ventricular pacing and during atrioventricular pacing with an inappropriate As-Vs interval. In areflexic isovolumic left ventricle preparations, ventricular function was depressed during ventricular pacing compared to atrial pacing, and changes in the As-Vs interval during atrioventricular pacing were accompanied by changes in ventricular function only in association with changing patterns of ventricular activation. In animals with heart block under conditions of right heart bypass, wherein changes in the pattern of ventricular activation were precluded during atrioventricular pacing, ventricular function deteriorated pari passu with shortening of the As-Vs interval. These data indicate that both the temporal relation between atrial and ventricular contraction and the pattern of ventricular activation importantly influence ventricular function during cardiac pacing. The marked changes in ventricular function observed as a function of the As-Vs interval, for any given pattern of electrical activation, suggest that the As-Vs interval is the more important determinant of ventricular function during cardiac pacing.