Cor Triatriatum

Cor triatriatum sinister is a rare congenital anomaly (about 0.1 to 0.4% of congenital heart disease) in which a fibromuscular membrane divides the left atrium into a proximal accessory chamber that receives the pulmonary veins and a distal true chamber that contains the left atrial appendage and the mitral valve.

Cor triatriatum dexter is far rarer and results from a persistent right sinus venosus valve dividing the right atrium.

Associated lesions are atrial septal defect or PFO, partial anomalous pulmonary venous connection, persistent left superior vena cava, ventricular septal defect, atrioventricular septal defect, tetralogy of Fallot and coarctation.

Pathophysiology. The membrane arises from abnormal incorporation of the common pulmonary vein into the left atrium. The size of its opening decides physiology. A restrictive opening of about 3 mm or less usually produces symptoms in infancy.

Larger openings may remain silent until adulthood. Pulmonary venous obstruction raises pulmonary venous and arterial pressures and causes pulmonary oedema and pulmonary hypertension. The haemodynamics resemble mitral stenosis with a normal sized left atrium.

An associated atrial septal defect may communicate with either chamber and modifies the physiology.

• Infants: tachypnoea, respiratory distress, poor feeding, failure to thrive, recurrent chest infections, pulmonary oedema, and cyanosis if there is right-to-left shunting.
• Older children and adults: exertional dyspnoea, orthopnoea, paroxysmal nocturnal dyspnoea, palpitations from atrial fibrillation, haemoptysis, and systemic embolism.
• Examination: loud pulmonary component of the second sound, right ventricular heave, signs of pulmonary hypertension and right heart failure. A soft low pitched diastolic or continuous murmur may be present, or none.

Red flags.

• Infant with unexplained respiratory distress and pulmonary venous congestion
• Haemoptysis
• Refractory or rapidly progressive pulmonary hypertension
• Systemic embolism or stroke
• Cyanosis

• Chest X-ray: pulmonary venous congestion with a normal sized left atrium.
• Transthoracic echocardiography: a linear membrane within the left atrium in parasternal long axis and apical four chamber views, separate from the mitral annulus. The left atrial appendage and mitral valve lie distal to the membrane and the pulmonary veins drain proximal to it. Colour Doppler shows turbulent flow across the membrane, and continuous wave Doppler gives the mean gradient. The mitral valve is structurally normal.
• Transoesophageal echocardiography: defines fenestrations and any septal defect.
• CT or MRI: pulmonary vein anatomy and associated anomalies.
• Cardiac catheterisation: reserved for assessing pulmonary vascular resistance when pulmonary hypertension is severe.

Differential diagnosis.

• Supramitral ring (lies between the left atrial appendage and mitral valve, so the appendage is proximal to the ring)
• Congenital or rheumatic mitral stenosis
• Pulmonary vein stenosis
• Obstructed total anomalous pulmonary venous connection
• Left atrial myxoma or thrombus
• Pulmonary veno occlusive disease

Definitive treatment is surgical excision of the membrane on cardiopulmonary bypass, with closure of any associated atrial septal defect. Indications are symptoms, a significant gradient, or pulmonary hypertension. Early results are excellent and residual obstruction is uncommon. A wide opening with no gradient and no symptoms can be observed with echocardiography. Catheter balloon dilatation or fenestration is reserved for selected patients.

Bridging medical therapy.

• Furosemide in infants and children: 0.5 to 1 mg/kg intravenously every 6 to 12 hours, or 1 to 2 mg/kg orally every 6 to 12 hours, maximum 6 mg/kg daily. Monitor sodium, potassium, creatinine and weight. Diuretics relieve congestion only and do not treat the obstruction.
• Atrial fibrillation in adults: anticoagulation with apixaban 5 mg orally twice daily, reduced to 2.5 mg twice daily when at least two of age 80 years or over, weight 60 kg or under and serum creatinine 133 micromol/L or over are present. Also 2.5 mg twice daily at creatinine clearance 15 to 29 mL/min, and avoided under 15 mL/min. Maximum 10 mg daily.

Special groups. Pregnancy with unrepaired obstruction or pulmonary hypertension is high risk. Repair before conception.

Monitoring. Echocardiography at 6 to 12 months after repair, then every 1 to 2 years, looking for residual gradient, pulmonary vein stenosis, atrial arrhythmia and pulmonary hypertension.

Referral and escalation. Refer every symptomatic infant to a paediatric cardiac surgical centre on the day of diagnosis. In adults, refer to a congenital heart disease centre when there is a gradient, atrial fibrillation or pulmonary hypertension.