[Atrial septal defect associated with an abnormal chamber of the right ventricle: report of a case].

A case of atrial septal defect associated with an abnormal chamber behind the right ventricle, which was heretofore undescribed, was reported. A 41-year-old woman was admitted to our hospital for the evaluation of a heart murmur. A Levine 3/6 ejection systolic murmur and a fixed splitting of the second heart sound were audible. Two-dimensional echocardiography disclosed an atrial septal defect and an abnormal chamber behind the right ventricle. This accessory chamber communicating with the right atrium was separated from the right ventricle by a membranous structure. The motion of this membrane showed a wide excursion just like that of the atrio-ventricular valve. On the M-mode echocardiogram, the anterior tricuspid leaflet and this membrane were recorded simultaneously without intervening septal echoes and this finding was very similar to that obtained in the single ventricle. Cardiac catheterization revealed that the pressure pattern in the abnormal chamber was that of the right atrium but its intracardiac electrocardiogram showed a right ventricular pattern. The complex morphological aspect of this case was confirmed by angiography and surgery. The developmental process of this very unusual anomaly is not clear, but it may be a kind of congenital anomaly related to Ebstein's anomaly.