Cor Triatriatum (Divided Atrium)

Divided left atrium or cor triatriatum sinister is a rare congenital anomaly characterized by a fibromuscular partition between a proximal left atrial compartment containing the pulmonary veins and a distal left atrial compartment in continuity with the left atrial appendage and the mitral valve. The clinical presentation is variable and based on the degree of restriction of the distal chamber and left ventricular inflow and the associated cardiac lesions (found in up to 80% of patients with this congenital malformation). Clinical features are similar to mitral stenosis and severe cases may require urgent neonatal repair for pulmonary congestion and low cardiac output. Echocardiography is the diagnostic test of choice. Surgical excision of the membrane is the definitive management and has excellent outcomes. A divided right atrium (cor triatriatum dexter) has been described as well and refers to a functional division by large remnants of embryonic valvar structures between the sinus venosus and the distal right atrium.