Mechanism of x Descent in Atrial Pressure Pulse

Normally, there are three positive (a, c, v) and two negative (x, y) waves in the atrial pressure pulse. Although there is unanimity regarding the genesis of the a, c, v, and y waves, the mechanism of the x descent is still open to question. Many believe that the negative systolic descent results from the drawing down of the atrioventricular plane during ventricular contraction and the increase in negative intrathoracic pressures due to the ejection of ventricular blood.¹ Thus, a diminution or lack of the x descent in the atrial pressure pulse has been taken to indicate various degrees of atrioventricular valvular regurgitation where the absence of the negative x descent or its replacement by a positive systolic wave (the so-called s wave) results from the transmission of regurgitant blood flow during ventricular systole through the incompetent atrioventricular valve. On the other hand, others ascribe the x descent to