Alterations in Cardiac Synchrony Induced by the Cardiac Sympathetic Nerves

Abstract

While pressures were recorded separately from the four chambers of the heart in openchest dog preparations, together with a standard limb lead of the ECG, the right and left stellate ganglia were stimulated. Measurements from the beginning of the P wave to the initial rise in chamber pressures revealed that pressure in the left ventricle began to rise approximately 20 msec prior to that in the right ventricle. This interval was significantly shortened during electrical stimulation of the stellate ganglion. Although the interval between P wave and the initial pressure elevations in the right atrium (RA) and the left atrium (LA) both shortened during stellate stimulation, P-RA decreased considerably more than P-LA. The P wave, PR interval, and the QRS complex all shortened markedly, indicating increased conduction velocity over the atria, the nodal conducting tissue, and the ventricles during stellate stimulation. These events occurred with or without alterations in heart rate and were correlated with large increases in the rate of change of ventricular pressures. Simple algebraic summation of individual muscle segment contractions may achieve significantly greater intraventricular pressure as the contractions become more synchronous. The total pressure developed is further augmented when each individual unit contracts with greater force and greater velocity. The recruitment of additional functional units would result in further summation and thus in still greater augmentation in total force and pressure. Alterations in pacemaker site are common during stellate stimulation.