Congenitally divided left atrium: diagnostic pitfalls in cross-sectional echocardiography.

A 20-month-old patient with a previously diagnosed atrial septal defect presented with acute heart failure. The clinical and echocardiographic features at admission to hospital were of a congenitally partitioned left atrium. At surgery a medially displaced and infolded left atrial appendage together with infolded left atrial wall was found, which gave a false appearance of a left atrial 'membrane'. This unusual arrangement was subsequently correctly identified by transoesophageal echocardiography. It is speculated that the abnormal orientation of the appendage may have produced a physiologic and haemodynamic situation akin to anomalous drainage of the pulmonary veins, which would account for the clinical features in this patient.