Partial or total direct pulmonary venous drainage to right atrium due to malposition of septum primum. Anatomic and echocardiographic findings and surgical treatment: a study based on 36 cases.

The clinical and anatomic findings in 36 patients (21 postmortem cases and 15 living patients) with partially anomalous (16 [44%]) or totally anomalous (20 [56%]) pulmonary venous drainage directly to the right atrium constitute the material basis of this report. Displacement of septum primum--leftward in atrial situs solitus or rightward in atrial situs inversus--was present in all and appeared responsible for the anomalous pulmonary venous drainage. The pulmonary veins were connected with what normally constitutes the posterior wall of the left atrium, which became incorporated into the right atrium because of atrial septal displacement. This abnormality occurred predominantly in patients with visceral heterotaxy, usually with polysplenia, or rarely with asplenia or a normally formed spleen. Poor development or absence of septum secundum appeared responsible for the malposition of septum primum. Echocardiographic recognition of the displacement of septum primum facilitated surgical management.