A 29 year old woman with hypoxia of unknown aetiology, which was found one day after she underwent a knee joint operation, was admitted to our hospital. She had undergone an atrial septal defect (ASD) closure 20 years previously. Arterial Po₂ (Pao₂) was 74 mm Hg despite administration of 10 ml/min of oxygen (Pao₂ was 58 mm Hg in room air). She had no symptoms and was not cyanotic. Chest x ray was normal and there were no ECG abnormalities. There were no findings of pressure overload in the right atrium (RA) and right ventricle (RV) by transthoracic echocardiography (TTE). TTE revealed continuous abnormal flow signal, flowing into the left atrium (LA) on colour and pulsed Doppler, located just in the anterior side of the right pulmonary artery. Intravenous contrast (Levovist, Schering) injected from both upper limbs reached the LA and then the left ventricle (LV), with little contrast filling in the RA and RV. Intravenous contrast injected from the lower limb reached the RA normally (upper panel). Transoesophageal echocardiography showed distal superior vena cava (SVC) stenosis with SVC dilatation, and incomplete closure of sinus venous ASD. An SVC to LA (right to left) shunt flow signal was revealed by colour Doppler (lower panel). Mean pressures measured by using cardiac catheterisation were as follows: SVC 9 mm Hg, LA 5 mm Hg, RA 2 mm Hg.

As a result of distal SVC stenosis and residual ASD after inappropriate sinus venous ASD closure, SVC pressure exceeded LA pressure, and hence, SVC to LA shunt occurred through the residual ASD. This right to left shunt resulted in the patient’s chronic hypoxia. Intravenous contrast echocardiography was useful for detecting that this patient had right to left shunting from the SVC to the LA, and transoesophageal echocardiography clearly revealed the complicated anatomical and physiological abnormality.

Fortunately, the patient had no history of systemic embolism for the preceding 20 years, or symptoms of hypoxia. After the successful corrective surgery, her hypoxia improved dramatically and she is doing well.