Hypoxia and Cyanosis due to Unusual Right-to-Left Shunt in a Patient with an Atrial Septal Defect

Hypoxia due to an Atrial Septal Defect (ASD), without Eisenmenger physiology, is reported rarely and may be underestimated due to difficulty in its diagnosis. We report the case of a 67-year-old woman with chronic cyanosis and hypoxia, in whom a large ASD was diagnosed by cardiac catheterization after an extensive workup to clarify the aetiology of the hypoxia. The right-to-left shunt at the ASD occurred probably due to a well-developed Eustachian valve, partly directing the right atrial flow into the left atrium, in the absence of pulmonary arterial hypertension.