Supravalvular Mitral Ring

Definition

The supravalvular mitral ring is a rare congenital anomaly characterized by the presence of a membrane or fibrous tissue that develops above the mitral valve, leading to a narrowing of the inflow tract to the left ventricle. This alteration causes mitral inflow obstruction and may be associated with other congenital heart defects, such as subvalvular aortic stenosis, coarctation of the aorta, or hypoplastic left ventricle.

Embryology and Pathogenesis

The development of the mitral valve occurs during the early weeks of fetal life through the fusion of endocardial cushions and the formation of valvular and subvalvular structures. An anomaly in this process may lead to the persistence of supravalvular abnormal tissue, reducing the available valvular surface and generating functional stenosis. The proposed pathogenetic mechanisms include:

• Defects in the development of endocardial cushions: may lead to anomalies of the mitral ring.
• Genetic alterations: conditions such as Shone’s syndrome include this anomaly along with other left heart tract obstructions.
• Reduced cellular apoptosis: may lead to the formation of persistent supravalvular fibrous tissue.

Classification

The supravalvular mitral ring can be classified based on its morphology:

• Thin fibrous ring: causes mild obstruction with minimal hemodynamic impact.
• Thickened and rigid ring: leads to significant stenosis with altered mitral inflow.
• Ring associated with other cardiac anomalies: may be part of complex defects such as Shone’s syndrome.

Pathophysiology

The supravalvular mitral ring acts as a barrier to left ventricular filling, generating a pressure gradient between the left atrium and the left ventricle. The main pathophysiological consequences include:

• Increased left atrial pressure: leads to atrial dilation and a possible risk of atrial fibrillation.
• Pulmonary congestion: blood stasis in the lungs may cause exertional dyspnea and pulmonary edema.
• Heart failure: in severe cases, there is pressure and volume overload of the left ventricle.

Clinical Manifestations

The severity of symptoms depends on the degree of mitral stenosis caused by the supravalvular ring:

• Mild forms: may be asymptomatic and detected incidentally.
• Moderate forms: characterized by fatigue, exertional dyspnea, and palpitations.
• Severe forms: associated with heart failure, pulmonary hypertension, and reduced exercise tolerance.

Diagnosis

The diagnosis is based on advanced cardiac imaging techniques:

• Transthoracic echocardiography with Doppler: first-line examination to assess mitral pressure gradient and supravalvular ring anatomy.
• Transesophageal echocardiography: useful for a detailed evaluation in complex cases.
• Cardiac magnetic resonance imaging (CMR): allows three-dimensional visualization of cardiac anatomy.
• Cardiac catheterization: used in cases requiring precise hemodynamic assessment before surgery.

Treatment

The management of the supravalvular mitral ring depends on the severity of stenosis and the presence of symptoms:

• Clinical monitoring: indicated in asymptomatic patients with preserved mitral inflow.
• Surgical intervention: in symptomatic patients with significant stenosis, the preferred approach is excision of the supravalvular mitral ring with possible valve repair.
• Mitral valve replacement: indicated in cases of severe stenosis that cannot be corrected with valve repair.

Prognosis

If treated early, the prognosis is favorable with significant improvement in cardiac function. However, long-term follow-up is essential to monitor for potential restenosis or secondary valvular alterations.

Conclusion

The supravalvular mitral ring is a rare congenital anomaly that can cause significant mitral stenosis and heart failure if left untreated. Early diagnosis and timely surgical intervention are crucial to ensuring a favorable clinical outcome and improved quality of life.