Platypnea-orthodeoxia syndrome caused by a latent atrial septal defect.

A 79-year-old woman presented with unexplained hypoxia that became exacerbated by an upright posture (platypnea-orthodeoxia syndrome). A (99m)Tc-macroaggregated albumin pulmonary perfusion scan revealed a right to left shunt of 25.5% in the supine position and 32.3% in the sitting position. A dynamic CT scan and a transoesophageal echocardiogram confirmed the presence of a shunt across an atrial septal defect (ASD). A percutaneous transcatheter closure of the defect significantly improved the patient's blood oxygenation levels when she was in the upright position. An ASD should therefore be included in the differential diagnosis of platypnea-orthodeoxia syndrome, regardless of the patient's age.