Ventricular Pressure-Flow Dynamics in Tetralogy of Fallot

The present study was conducted to determine the instantaneous pressure-flow relationships across the ventricular septal defect in tetralogy of Fallot. Simultaneous right and left ventricular pressures and the pressure gradient were recorded with matched catheter systems. Biplane cineangiocardiography was used to evaluate the timing of the bi-directional shunts during various phases of the cardiac cycle. The instantaneous pressure differences between the two ventricles and the direction of the pressure gradient correlated well with the timing of the shunt across the defect.In 27 patients with moderate tetralogy of Fallot, a consistent pattern of bidirectional shunting was shown. The right-to-left shunt occurred at two places and two sites during the cardiac cycle; namely, during early ventricular ejection into the aorta, and during isovolumic ventricular relaxation directly across the ventricular defect into the left ventricle. Left-to-right gradients and shunting across the defect were found to occur during isovolumic ventricular contraction and during diastole. The results of this study suggest that further investigation of various cardiac defects may yield important information concerning shunting mechanisms.