A rare cause of abnormal pulmonary venous drainage: septum primum malposition

Divided left atrium with totally anomalous drainage of normally connected pulmonary veins

In the December 2021 issue of Cardiology in the Young, Hubrechts and colleagues, from Brussels and Leuven in Belgium, describe their experience in which the pulmonary veins were normally connected to the morphologically left atrium. By virtue of the presence of a shelf dividing the morphologically left atrium, however, the venous return was to the morphologically right atrium, with no evidence of formation of the superior interatrial fold, meaning that there was no obstruction of flow into the systemic venous circulation. The question posed by the Belgian authors is whether the shelf dividing the morphologically left atrium is a deviated primary atrial septum, as the arrangement has previously been interpreted. As they discuss, it is currently impossible to arbitrate this conundrum. In our commentary, we discuss the background to the dilemma. We point out that, as yet, it is not possible to code accurately this congenital cardiac malformation within The International Paediatric and Congenital Cardiac Code (IPCCC), nor within the newly produced 11th Revision of the International Classification of Diseases (ICD-11).

Leftward deviation of the primary septum or dividing left atrial shelf?

Isolated leftward prolapse or deviation of the primary atrial septum is a rare CHD that can mimic abnormal pulmonary venous return at first sight. We present a case of a newborn infant, referred for surgical correction of totally anomalous pulmonary venous return into the right atrium, with the peri-operative finding of a leftward deviation of the superior margin of the primary atrial septum. The distinction with a dividing atrial shelf could not be confirmed with certainty. Fifty-three similar cases from the literature are incorporated. A detailed review of the current account on atrial septation is studied. The embryological and clinical features of a dividing partition of the left atrium are discussed.