Dynamics of interatrial shunting in children with obstruction of the tricuspid and pulmonic valves.

The interatrial pressure-flow dynamics in patients with right-to-left shunting at the atrial level in the presence of right heart obstruction were studied. In tricuspid atresia most of the right-to-left gradient occurred during right atrial systole. This gradient, as well as the cineangiocardiograms, indicated that almost all systemic venous return was transferred from the right to the left atrium through the interatrial communication during right atrial contraction. Cine studies also suggesed that right atrial systole (1) contributed significantly to left ventricular filling and (2) produced regurgitant venous flow, especially into the hepatic veins. In two patients with secundum atrial defect and associated marked pulmonic valve stenosis, bidirectional shunting at the atrial level was defined by pressure gradient and cine and dye-dilution curve technics. The right-to-left gradient and shunt occurred during ventricular diastole with accentuation of this gradient by atrial contraction; the leftto-right interatrial flow and gradient occurred during ventricular systole when both A-V valves were closed. These studies indicate that, in the presence of an interatrial communication, increasing degrees of right heart obstruction not only produce right-to-left shunting but (1) do so primarily by right-to-left flow across the interatrial communication during ventricular diastole and (2) with complete right atrial obstruction, right atrial contraction plays a dominant role in the transfer of systemic venous return to the left atrium.