DYNAMICS OF EXPERIMENTAL ATRIAL SEPTAL DEFECTS

Abstract

Atrial septal defects were surgically produced in open chest dogs and right and left atrial pressure pulses were simultaneously recorded by calibrated optical manometers. Atrial pressure was measured just before the 2d heart sound, the V point. The use of other points on the atrial pressure pulse as a measure of a trial pressure is discussed. In 11 out of 12 expts. left atrial pressure was higher than right at the V point and the left to right pressure gradient persisted during the entire cardiac cycle, or for all but a short period before or during atrial systole. Increasing venous return by rapid saline infusion elevates both right and left atrial pressure in the presence of atrial septal defects, but left atrial pressure rises more than right. However, in the presence of a large defect the pressures tend to equalize after considerable fluid has been given. The suggestion that in the presence of atrial septal defects the atria would act as a common cavity was tested. When ventricular action was stopped by vagal stimulation, right and left atrial pressure equalized within 2 sec. and then rose together for the duration of ventricular systole. Following the first ventricular beat, the left to right pressure differential was again present. Thus the inter-atrlal pressure gradient is shown to be produced by dynamic events. Evidence derived from in vivo observations, atrial volume elasticity measurements, and expts. with a physical model prove that the left to right pressure gradient between the atria in hearts with atrial septal defects depends on the lesser distensibility of the left atrium and the increase in right ventricular output.