Anomalous Mitral Arch

Definition

Anomalous mitral arch is a rare congenital abnormality of the mitral apparatus characterized by a fibrous or muscular bridge extending between the papillary muscles or mitral valve leaflets. This condition can alter mitral valve dynamics, leading to obstruction of blood flow from the left ventricle or causing varying degrees of mitral regurgitation. Anomalous mitral arch has been described in association with other congenital malformations, such as hypoplastic left ventricle, congenital mitral stenosis, and Shone’s syndrome, a condition characterized by multiple obstructive anomalies in the left ventricular outflow tract.

Embryology and Pathogenesis

During fetal development, the mitral apparatus forms through a complex process involving neural crest cell migration, fusion of endocardial cushions, and remodeling of valvular structures. A defect in the regression of myocardial trabeculae may lead to the persistence of abnormal fibromuscular structures connecting the mitral leaflets or papillary muscles, forming an anomalous mitral arch. The main proposed pathogenic mechanisms include:

• Defects in embryological development: Failure in the regression of primitive myocardial bridges can result in arch formation.
• Genetic alterations: Mutations in genes involved in left ventricular outflow tract development (e.g., NOTCH1, ELN) may be associated with this anomaly.
• Persistence of embryonic structures: Fibromuscular remnants from the remodeling of chordae tendineae may contribute to the development of an anomalous arch.

Pathophysiology

The hemodynamic impact of an anomalous mitral arch varies depending on its morphology and position. 1. **Mitral inflow obstruction**: If the arch is prominent and located near the mitral orifice, it can cause mitral stenosis, leading to increased left atrial pressure and pulmonary congestion. 2. **Impairment of mitral leaflet motion**: The arch can interfere with the normal systolic-diastolic movement of the mitral valve, resulting in mitral regurgitation. 3. **Left ventricular dysfunction**: In severe cases, the obstruction caused by the arch may contribute to increased left ventricular pressure and volume overload, leading to ventricular hypertrophy.

Clinical Manifestations

The clinical presentation of an anomalous mitral arch varies depending on the severity of the obstruction and the presence of associated cardiac anomalies. In mild cases, the condition may be asymptomatic, whereas severe cases can present with heart failure symptoms and mitral stenosis. The most common signs and symptoms include:

• Exertional dyspnea: Due to increased left atrial pressure and pulmonary congestion.
• Fatigue: Secondary to reduced cardiac output in cases with significant mitral obstruction.
• Palpitations: Often associated with atrial fibrillation caused by left atrial overload.
• Heart murmur: Heard as a diastolic murmur in cases of mitral stenosis or a systolic murmur in the presence of mitral regurgitation.

In neonates and young children with severe forms, an anomalous mitral arch can cause tachypnea, feeding difficulties, and growth retardation, typical signs of early heart failure.

Diagnosis

The diagnosis of an anomalous mitral arch relies on advanced cardiac imaging techniques:

• Transthoracic echocardiography with Doppler: First-line examination to identify the abnormal structure and assess mitral pressure gradients.
• Transesophageal echocardiography: Particularly useful for detailed visualization in complex cases.
• Cardiac magnetic resonance imaging (CMR): Allows three-dimensional characterization of mitral anatomy and adjacent structures.
• Cardiac catheterization: Reserved for cases with suspected pulmonary hypertension or for precise hemodynamic assessment.

Treatment

The treatment of an anomalous mitral arch depends on the severity of stenosis and the patient’s symptoms. In mild cases, where mitral inflow is preserved and no symptoms are present, regular clinical monitoring may be sufficient. For moderate to severe cases, therapeutic interventions include:

• Surgical resection of the arch: The preferred approach for symptomatic cases, aimed at eliminating mitral obstruction and restoring normal hemodynamics.
• Mitral valve repair: Indicated when the arch alters mitral leaflet function.
• Mitral valve replacement: Considered in patients with severe structural mitral valve damage that cannot be corrected with repair.

Prognosis

The prognosis for patients with an anomalous mitral arch depends on early diagnosis and effective treatment. When treated promptly, surgical resection significantly improves quality of life and restores normal mitral function. However, in cases of late diagnosis or advanced mitral stenosis, long-term complications such as pulmonary hypertension or heart failure may develop.

Conclusion

Anomalous mitral arch is a rare congenital abnormality that can lead to mitral stenosis or regurgitation. Early diagnosis through echocardiography is essential in determining the need for surgical intervention. In cases requiring treatment, resection of the arch provides excellent long-term outcomes, significantly improving patient prognosis.