Cor Triatriatum

Etiology

Cor triatriatum sinistrum results from the incomplete absorption of the common pulmonary vein, which is typically reabsorbed during fetal development and fuses with the left atrium. This phenomenon could explain why there often are concurrent anomalies of the atrial septum (atrioseptal defects) and the pulmonary venous connection. The incomplete absorption results in the formation of a diagonal membrane that subdivides the left atrium into 2 chambers—pulmonary venous and vestibular chambers. No known genetic mutations or risk factors are found to be associated with the development of this condition. Cor triatriatum dextrum develops from the persistence of a right sinus venosus valve.[4]

Epidemiology

Cor triatriatum sinister has an estimated incidence of 0.4%, resulting from abnormal left atrial septation.[5] Cor triatriatum sinisterum is associated with other congenital cardiac defects, such as tetralogy of Fallot, atrial septal defect, ventricular septal defect, and partial anomalous pulmonary venous connection, and represents only 0.1% to 0.4% of all congenital abnormalities.[6][7] The membrane may be complete or contain 1 or more fenestrations of differing sizes.

Cor triatriatum dextrum has an incidence of 0.025% among all congenital heart diseases. This anomaly often coexists with right-sided cardiac defects. The most common related heart defects include pulmonary valve stenosis or atresia, abnormalities of the tricuspid valve, and an atrial septal defect.[8]

Pathophysiology

A malincorporation theory presented by Parsons explains how cor triatriatum sinister occurs.[9] During normal fetal development, the pulmonary vein incorporates into the left atrium. When this process fails, the common pulmonary venous ostium remains narrow, resulting in a septum-like structure called the atrial appendage. The appendage then further divides the left atrium into 2 compartments. Although widely accepted, this theory fails to explain the presence of fossa ovalis and atrial muscle fibers in the proximal atrial chamber.[10]

Two other theories, malseptation and entrapment, also explain the pathophysiology of cor triatriatum. The malseptation theory suggests that the fibromuscular membrane is an abnormal growth of the septum primum. In contrast, the entrapment theory emphasizes the entrapment of the common pulmonary vein in the embryonic sinus venosus, thereby preventing its incorporation into the left atrium. The malincorporation theory remains the most widely accepted etiologic theory.

History and Physical

Classically, cor triatriatum presents in infancy with signs and symptoms of pulmonary hypertension and pulmonary venous obstruction. Due to low cardiac output, children can show poor growth and weight gain, feeding difficulties, respiratory distress, and tet spells. In childhood and adulthood, the signs and symptoms of pulmonary venous hypertension and right heart failure dominate as the membrane calcifies and the opening becomes smaller and smaller, decreasing cardiac output even further. Mitral valve regurgitation and atrial fibrillation impose serious dangers. Most patients present with the following features:

• Exertional dyspnea, dyspnea at rest, and orthopnea
• Easy fatigability
• Hemoptysis
• Palpitations [11]

Atrial fibrillation can cause systemic thromboembolism and present as pulmonary embolism or stroke. The left atrial enlarges due to the backing up of blood and can present as life-threatening arrhythmias.

Cor triatriatum sinister initially presenting in adulthood is rare but possible. The presentation is similar to mitral stenosis, but the absence of loud S1 and an opening snap helps to distinguish between the 2 conditions. Chest radiography revealing pulmonary congestion with an absence of left atrial enlargement is characteristic of cor triatriatum. A continuous gradient on Doppler echocardiography confirms the diagnosis.[10][12]

Physical Examination

The following physical examination findings are due to right heart failure and pulmonary congestion:

• Accentuated pulmonary component of S2
• A soft midsystolic murmur at the upper left sternal border
• Right ventricular heave
• Basilar rales
• Diminished peripheral pulses
• Hepatomegaly and right upper quadrant tenderness
• Ascites
• Peripheral edema
• Distended peripheral veins
• Jugular venous distension and elevated jugular venous pressure
• Pallor
• Poor weight gain

Evaluation

The mainstay of diagnosing and evaluating cor triatriatum includes imaging studies such as chest radiography, electrocardiography, echocardiography, angiography, and left and right heart catheterization.[13][14]

Chest Radiography

A chest radiograph is the initial diagnostic tool of choice. Typical findings include:

• Pulmonary congestion with haziness
• Ground glass appearance of acute pulmonary edema
• Prominent pulmonary vessels
• Pleural effusion
• Left atrial enlargement
• Cardiomegaly

Electrocardiography

Electrocardiography findings are nonspecific in cor triatriatum. Studies may reveal atrial fibrillation and no specific P-wave changes to right axis deviation due to pulmonary congestion and right ventricular hypertrophy.

Echocardiography

Echocardiography is the diagnostic modality of choice when cor triatriatum is suspected. This modality allows for definitive diagnosis; the 3-dimensional reconstruction of echocardiographic images pinpoints the exact location of the defect and appendage and helps direct the surgical approach to the disease. In the case of cor triatriatum sinisterum, the left atrial appendage and its fenestrations can be easily visualized with an atrial septal defect, pulmonary stenosis, mitral valve stenosis, or regurgitation. Pulmonary arterial and venous drainage patterns can also be observed on echocardiography. Echocardiography differentiates between cor triatriatum and supravalvular mitral stenosis by clearly visualizing the left atrial appendage in the left atrium.

Sometimes, ambiguous anatomy not properly elucidated on a transthoracic window warrants further investigation with transesophageal echocardiography with or without bubble study.[15][16]

Cardiac Catheterization and Angiography

Angiography helps determine the severity of obstruction and the timing of surgical intervention. In addition, catheterization helps quantify pulmonary hypertension, the degree of shunting between the left and right hearts, and oxygen saturation changes in the cardiac chambers.

Computed Tomography and Magnetic Resonance Imaging

Such advanced imaging techniques are typically reserved for complex anatomy, such as multiple combined cardiac anomalies, or to help formulate an intraoperative strategy for a stratified case.

Treatment / Management

Medical Management

Asymptomatic patients: Asymptomatic patients require no specific treatment. Observe them for the development of signs and symptoms and schedule regular medical follow-ups.

Symptomatic patients: Treatment options for symptomatic patients include conservative medical management and surgical repair. Medical treatment is reserved mainly for preoperative management of unstable or symptomatic patients and includes:

• Hemodynamic stabilization of fluid overload and pulmonary edema.[17]
• Rate and rhythm control, along with anticoagulation for patients with atrial fibrillation.[18]
• Thromboembolic prophylaxis with anticoagulation against deep vein thrombosis, pulmonary embolism, and stroke.[19]
(B3)

American Heart Association Guidelines for Adults with Cor Triatriatum (2018)

• Adult patients (symptomatic or asymptomatic) with evidence of cor triatriatum should be screened for other congenital anomalies, particularly septal defects, such as atrial septal and ventricular septal defects. Pulmonary vein defects are also associated with cor triatriatum and should be suspected.

• Investigating pulmonary vein stenosis is prudent in symptomatic patients who have undergone successful repair of cor triatriatum in the past.

• Symptoms attributed to pulmonary venous inflow obstruction or a high-pressure gradient across a restrictive fibromuscular membrane are reasonable indications for surgical repair.[20]
(A1)

Surgical Management

Surgery is the definitive treatment for cor triatriatum.[6][21] Complete surgical resection of the atrial accessory membrane with optional left atrial appendage exclusion is performed through a midline sternotomy under aorto-bicaval cardiopulmonary bypass. If an atrial septal defect is present, it is closed with a pericardial patch, providing the optimum cure. Typically, these patients have prolonged mitral stenosis and an enlarged left atrium, making access through the heart through the interatrial groove a better choice. Achieving the right visibility of the surgical area involves making a large cut in the left atrium and using special sutures to pull the edge of the heart closer into the surgical field to remove the membrane. A Beaver blade is used to carefully separate the fibrous ring from the atrial wall in a manner similar to endarterectomy. Meticulous dissection is essential to remove the fibrous ring safely without damaging the mitral valve apparatus or the conduction system.

Once the membrane is completely removed, mitral regurgitation is expected. The function of the mitral valve is then checked by injecting it with saline using a syringe. The left atrium is then stitched up carefully, de-airing is done, and the aortic clamp is removed. After the patient is warmed up and taken off the bypass machine, transesophageal echocardiography is used to examine the repaired area to ensure the surgery is successful. The 10-year survival rate following surgery is 83%, whereas patients with coexisting congenital heart diseases have a greater risk of adverse outcomes and a lower survival rate.[22][23](B2)

Differential Diagnosis

Many congenital heart diseases can present similarly to cor triatriatum and should be taken into consideration when making a diagnosis of this disorder. These include:

• Supravalvular mitral stenosis: This condition is the closest entity to cor atriatum sinistrum, both clinically and anatomically. Healthcare providers should be able to distinguish between the 2 conditions to arrive at a conclusive diagnosis more quickly and reduce unnecessary healthcare expenses. Typically, the fibromuscular membrane in cor triatriatum sinistrum is diagonal and separates the atrial appendage from the pulmonary veins with no continuity with the mitral valve annulus. In contrast, supravalvar mitral stenosis is continuous with the mitral valve annulus and does not separate the left atrial appendage from the pulmonary veins. Noteworthily, although cor triatriatum is still not associated with any genetic mutation or disease, the supravalvular mitral stenosis is a recognized component of the Shone complex.
• Mitral stenosis
• Idiopathic pediatric pulmonary arterial hypertension
• Pulmonary venous hypertension
• Total anomalous pulmonary venous return
• Partial anomalous pulmonary venous return
• Atrial septal defect/ventricular septal defect
• Ventricular septal defect
• Idiopathic pulmonary hypertension
• Tricuspid stenosis
• Atrial myxoma

An experienced surgical team should evaluate imaging results, as high suspicion can accelerate diagnosis and delay or prevent unfavorable outcomes.

Complications

Complications of cor triatriatum include:

• Right-sided heart failure
• Reduced cardiac output
• Stunted growth
• Pulmonary edema/hypertension
• Atrial arrhythmias
• Thromboembolism
• Death