[Juxtaposition of the atria].

Left juxtaposition of atrial appendages is an anomaly of their origin and position which is associated with a high incidence of complex congenital heart defects. We studied six cases of juxtaposed right atrial appendages. They emerged from the anterior wall adjacent to the atrial septum and were situated to the left of the origin of the great arteries. Associated congenital heart defects were: single outlet, right ventricular hypoplasia, absent right atrioventricular connection, ventricular and atrial septal defects and pulmonary outflow obstruction. Other abnormal morphological features present were anatomically corrected malposition of the great arteries, bilateral infundibulum and right aortic arch. Although the association of these malformations with juxtaposed atrial appendages does not per se constitute a syndrome, its presence is an ominous sign of severe cyanotic congenital heart disease which should alert both clinicians and surgeons. There are various possible embryological explanations for the genesis of this malformation. We believe that juxtaposition is the consequence of the ectopic origin of the atrial appendage rudiment, which in the presence of truncal alterations grows behind and to the left of the great arteries.