Hemodynamic effects of altering the timing of atrial systole

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Abstract
The use of heart block dog preparations allowed an investigation at constant ventricular rates of the hemodynamic effects which resulted when the timing of atrial systole was altered relative to ventricular systole. Ganglionic blockade and vagotomy precluded sympathetic reflex compensation in these animals. Lengthening or shortening the interval between left atrial and left ventricular systole (As-Vs interval) produced a decrease in left ventricular end-diastolic pressure (LVEDP), mean aortic pressure, and aortic flow. Mean left atrial pressure (MLAP) increased as did the relation of MLAP to LVEDP. The absence of atrial systole produced similar changes. Lengthening or shortening the As-Vs interval while holding aortic pressure and stroke volume constant resulted in an increase in MLAP and the relation of MLAP to LVEDP. The changes observed in the left atrial pressure tracings suggested and a platinum electrode technique demonstrated that mitral regurgitation can occur with improper timing of atrial systole. The data indicate that properly timed, effective atrial activity can enhance ventricular filling and can preclose the atrioventricular valve.