Effect of Atrial Systole on Ventricular Pressure at Variable P-Q Intervals

Eight dogs with complete atrioventricular heart block showed a definitive relation between the P-Q interval and the systolic left ventricular pressure if the P-Q interval increased or decreased slowly at a regular rate. The ventricular pressure reached a ‘plateau-like’ maximum at a P-Q interval between 0.1 and 0.2 second, and decreased only slightly with somewhat longer P-Q intervals. The lack of abrupt decrease in pressure suggests that the mitral valve closes passively during early atrial diastole and that this prevents rapid regurgitation of blood into the left atrium.