Atrial Pressure-Flow Dynamics in Atrial Septal Defects (Secundum Type)

This study was conducted to determine the instantaneous pressure-flow relationships across secundum atrial septal defects. Simultaneous right and left atrial pressures and the pressure difference (determined with an analog computer) were recorded with matched catheter systems. Biplane cineangiocardiography was used to evaluate the timing of the shunts in various phases of the cardiac cycle.These studies indicated that the major left-to-right shunt and pressure gradient occurred over an interval encompassing late ventricular systole and early diastole. Also, there was augmentation of the left-to-right shunt during atrial contraction. Minute right-to-left shunting and pressure gradients occurred at two times in the cardiac cycle: (1) with the onset of ventricular contraction; and (2) during early ventricular diastole (heart rate, 80 to 100 beats/min). Detection of systemic right-to-left shunts by dye curves was enhanced by relatively slow heart rates (prolonged diastasis) which allowed the shunted blood to flow into the left venrticle. The effects of respiration during phasic changes in intrathoracic pressure resulted in an increasing left-to-right gradient during periods of increasing intrathoracic pressure and a fall in the left-to-right gradient across the defect during periods of decreasing intrathoracic pressure.