Cor Triatriatum Sinister with Restrictive Membrane - A Late Presentation

Introduction

Cor triatriatum sinister is a rare congenital anomaly (0.1%–0.4% of congenital heart disease) in which a fibromuscular membrane divides the left atrium into two chambers: a proximal chamber receiving pulmonary venous return and a distal chamber containing the mitral valve and left atrial appendage. One or more small fenestrations within the membrane restrict pulmonary venous drainage. Embryologically, the proximal chamber corresponds to a dilated common pulmonary vein, while the distal chamber represents the true left atrium. The resulting hemodynamic profile mirrors that of mitral stenosis, leading to pulmonary venous congestion and pulmonary arterial hypertension. The degree of obstruction is determined by the size of the fenestration, and restrictive variants clinically resemble severe pulmonary venous obstruction. Delayed presentation, particularly beyond infancy, is associated with progressive pulmonary venous hypertension, pulmonary edema, and right-sided heart failure. Prognosis largely depends on the membrane orifice size. Once pulmonary edema or right-sided failure occurs, survival is usually limited to only a few months without intervention. With timely surgical repair, long-term outcomes are generally excellent, and associated pulmonary hypertension is often reversible.

Discussion 

Cor triatriatum sinister is an uncommon but critical cause of post-capillary pulmonary hypertension in infants and young children. Three key concepts should be emphasized: 

• The restrictive membrane produces a hemodynamic profile that closely resembles obstructed total anomalous pulmonary venous return, necessitating careful echocardiographic evaluation of pulmonary venous inflow using multiplanar imaging. 

• Despite extremely elevated pulmonary pressures, the obstruction is generally reversible rather than reflective of fixed pulmonary vascular disease, making timely surgical intervention both urgent and highly effective. 

• Delayed diagnosis can result in pulmonary edema, progressive right-ventricular dysfunction, and rapid clinical deterioration. Although historical series such as Niwayama’s described survival of only a few months with fenestrations <3 mm, this 2½-year-old patient with a 2-mm orifice illustrates that severe obstruction may be tolerated longer than expected. This variability reinforces the need for early recognition and prompt surgical correction, which typically leads to excellent outcomes. Conclusion Severely obstructive cor triatriatum sinister can present with life-threatening pulmonary venous hypertension and clinical features mimicking obstructed TAPVR. However, pulmonary hypertension is often reversible once the obstruction is relieved. Accurate echocardiographic assessment and urgent surgical repair remain essential to ensuring optimal survival and recovery.

Echocardiography

• Parasternal long-axis imaging revealed a mid–left atrial membrane, with color Doppler demonstrating turbulent flow across a restrictive opening. 

• The parasternal short-axis view showed marked bowing of the interventricular septum into the left ventricle, consistent with suprasystemic right-ventricular pressures. The right ventricle was severely dilated and mildly hypertrophied, with significantly impaired systolic function.

• Apical four-chamber imaging demonstrated a thick mid-left atrial membrane dividing the left atrium into two chambers, with severe obstruction (mean gradient 31 mmHg). The right ventricle was markedly dilated with systolic dysfunction. Severe tricuspid regurgitation (peak velocity 6.25 m/s; TR gradient 156 mmHg) confirmed suprasystemic right-ventricular pressures. A pulmonary insufficiency end-diastolic velocity of 2.88 m/s corresponded to an estimated diastolic pulmonary artery pressure of approximately 53 mmHg. With a central venous pressure of 20 mmHg, estimated systolic, diastolic, and mean pulmonary artery pressures were 176, 53, and 94 mmHg, respectively, consistent with severe post-capillary pulmonary hypertension secondary to pulmonary venous obstruction from cor triatriatum sinister. The membrane fenestration measured 2 mm in diameter.

• Apical two-chamber imaging delineated a mid–left atrial membrane with a mean Doppler gradient of 25 mmHg, consistent with severe obstruction.