What is not true of “a” wave of venous pulsations in neck?

There is no valve at junction of superior vena cava (SVC) and right atrium (RA) therefore right atrial pressure changes are transmitted to the jugular vein in the neck. “a” wave is due to atrial systole. Some blood regurgitates into the great veins when atria contracts, even though the orifices of IVC and SVC are constricted. In addition veins inflow stops, causing rise in venous pressure, contributing to the” a” wave.