The Presence of Venoarterial Shunts in Patients with Interatrial Communications

Evidence is presented which indicates that shunting of small amounts of blood from right to left occurs frequently through interatrial communications. Such right-to-left shunts are of small magni-tude in the usual case of atrial septal defect, but it appears that of the fractions of blood shunted, a greater proportion has originated from the inferior vena cava than from the superior vena cava. IN the majority of cases of uncomplicated atrial septal defect the major hemo-dynamic change is an arteriovenous (left-to-right) shunt of considerable magnitude. Because cyanosis or significant desaturation of the systemic arterial blood is uncommon, a shunt in the opposite direction (venoarterial, or right-to-left) is now considered unusual in this condition.', 2 In certain reports, which included a number of atypical cases3 or cases in which the complete diagnosis was not clearly established,4 significant arterial de-saturation has been noted. The oxygen saturation of the systemic arterial blood determined by manometric methods in normal persons has been found to average 97.6 per cent with a range of analytic values of from 94 to 101 per cent.5 This varia-bility in normal subjects may preclude the detection of venoarterial shunts of less than 15 per cent of systemic flow on the basis of desaturation of the systemic arterial blood. When significant arterial desaturation due to a venoarterial shunt is found, an additional structural anomaly or pulmonary hypertension or cardiac failure, singly or in combination, is likely to be present. Right-to-left shunts may frequently be associated with pulmonary stenosis with intact ventricular septum and occur through a "valve-competent, " patent, foramen ovale6 or through a coexistent atrial septal defect. The term "interatrial communi