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Key Concepts

  • Epidemiology

    • Cor triatriatum is an uncommon congenital cardiac anomaly in which either the left (cor triatriatum sinister) or right (cor triatriatum dexter) atrium is divided into two chambers by a membrane. Subdivided left atrium represents the most frequent anatomic variant of this lesion, and accounts from 0.1 to 0.4 percent of all congenital heart defects.

  • Morphology

    • The pulmonary veins enter a proximal chamber (common pulmonary venous chamber) separated by a fibromuscular membrane from a distal chamber where the left atrial appendage and the mitral valve are found. The proximal and distal chambers may communicate through one or more openings within the dividing membrane, and an atrial septal defect (ASD) is usually present.

  • Pathophysiology

    • In the absence of associated cardiac lesions, the pathophysiology of subdivided left atrium depends on the resulting obstruction to pulmonary blood flow. Pulmonary overcirculation is present when left-to-right shunting occurs through an ASD between common pulmonary venous chamber and right atrium.

  • Clinical features

    • The clinical presentation in infancy is similar to that of total anomalous pulmonary venous connection, with low cardiac output, pallor, tachypnea, poor peripheral pulses, and failure to thrive. Death may occur within the first year of life in 75 percent of untreated patients with significant obstruction. Children and young adults present with signs of pulmonary venous hypertension of various importance.

  • Diagnosis

    • Diagnosis is usually established by transthoracic and transesophageal echocardiography, although magnetic resonance imaging (MRI) can be used in selected cases. Cardiac catheterization may be indicated in the presence of associated cardiac lesions.

  • Treatment

    • Resection of the membrane through a right atrial approach is recommended in infants, whereas a left atrial approach through the common pulmonary venous chamber may be used in older children and adults and in the presence of associated anomalies. Percutaneous catheter disruption of the membrane may represent an alternative to surgery in selected cases of subdivided right atrium. Outcomes are dependent on the preoperative clinical condition.


The classic definition of cor triatriatum is based on the recognition that either the left atrium (cor triatriatum sinister) or the right atrium (cor triatriatum dexter) is divided into two chambers by an abnormal fibromuscular membrane. The terms subdivided left or right atrium14 will be used throughout this chapter, highlighting in a more comprehensible fashion the basic anomaly of this uncommon cardiac malformation.

In the commonest left-sided variant of this lesion, the pulmonary veins enter a proximal common pulmonary venous chamber, which is separated by a fibromuscular membrane from a distal chamber containing the mitral valve and left atrial appendage.

Subdivided right atrium is a much rarer anomaly in which a membrane, originating from the crista terminalis, divides the trabecular portion of the right atrium from the venae cavae. This entity should be distinguished5 from the more common occurrence of prominent eustachian or thebesian valves.

Historical Background


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