PREPONDERANT LEFT-TO-RIGHT FLOW THROUGH A VENTRICULAR SEPTAL DEFECT IN THE PRESENCE OF PULMONARY STENOSIS

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Abstract
Three examples of physiologic variant of Fallot''s tetralogy are reported in which the preponderant shunt at rest was from left to right. The most important factor in determining the pressure gradient, and hence the direction of flow across the defect, seems to be the severity of the pulmonary stenosis. The shunt may reverse with exercise, since an increased cardiac output in the presence of a fixed right ventricular outflow tract resistance may elevate the right ventricular pressure to a level in excess of that in the left ventricle. Cyclic variations in the pressure gradient across the septal defect may account for slight arterial un-saturation at rest, although the major flow is from left to right. This combination of anomalies is theoretically completely correctable by surgical techniques now available.