Effect of Atrial Systole on Ventricular Pressure and Closure of the A-V Valves

Abstract

Right atrial and ventricular pressures were simultaneously recorded with optical manometers from dogs having an open chest. The effect of atrial systole on ventricular pressure was studied under varying degrees of venous return. In the presence of a low but not necessarily abnormal venous return, the increase in ventricular pressure resulting from atrial systole is sufficient to reverse the atrial-ventricular pressure gradient before the onset of ventricular contraction. This reversal is sufficient to completely close the A-V valves before the onset of ventricular contraction. When venous return is moderately increased, the fall in atrial pressure during atrial relaxation is reduced. This results in a reduction in the atrial-ventricular gradient or equilibration of pressures before ventricular systole. The back flow of blood from the ventricle, however, tends to swing the valve toward a position of closure and the sudden onset of ventricular systole completes their apposition. As a result of this sudden great increase in ventricular pressure closing the valve there is some regurgitation into the auricle. When the ventricle contracts without a preceding atrial systole, the valves swing closed with a hinge-like movement from the open position and a large regurgitation into the auricle results. It is questionable whether the use of atrial pressure measured at the end of atrial systole (Z point) is a valid measure of ventricular diastolic pressure under all dynamic conditions. There is a slight delay in transmission to the ventricle of the increase in atrial pressure resulting from atrial systole. The cause of this time lag remains speculative.