What is an anomalous mitral arch?

It is a rare congenital malformation characterized by the presence of an abnormal fibrous or muscular bridge between the papillary muscles or mitral valve leaflets, potentially causing mitral stenosis or regurgitation.

What are the main symptoms of an anomalous mitral arch?

Main symptoms may include exertional dyspnea, fatigue, palpitations, heart murmur, and in severe cases, heart failure.

How is an anomalous mitral arch diagnosed?

Diagnosis is based on transthoracic and transesophageal echocardiography, cardiac magnetic resonance imaging, and in selected cases, cardiac catheterization for hemodynamic study.

What is the treatment for an anomalous mitral arch?

Treatment involves surgical resection of the anomalous arch, possibly associated with mitral valve repair or replacement if necessary.

What is the prognosis after treatment of an anomalous mitral arch?

If diagnosed and treated early, the prognosis is favorable with good recovery of cardiac function and improvement in quality of life.

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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.

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.
Impairment of mitral leaflet motion: The arch can interfere with the normal systolic-diastolic movement of the mitral valve, resulting in mitral regurgitation.
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.

References

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Rao S, Harris KC, Kobayashi D, et al. Supramitral ring causing severe mitral stenosis in an infant: a case report and review of the literature. Congenital Heart Disease, 4(6), 2009, pp. 491-494.
Brown ML, Schaff HV, Connolly HM, et al. Surgical spectrum of supramitral ring: operative results and outcomes. Annals of Thoracic Surgery, 87(4), 2009, pp. 1126-1131.
Yoshimura N, Yamaguchi M, Oshima Y, et al. Surgical management of supramitral ring in infants and children. Annals of Thoracic Surgery, 80(6), 2005, pp. 2271-2275.
McMahon CJ, Pignatelli RH, Nagueh SF, et al. Echocardiographic findings in supramitral ring: differentiation from other causes of left ventricular inflow obstruction. Journal of the American Society of Echocardiography, 17(4), 2004, pp. 358-364.
Ruckman RN, Van Praagh R. Anatomic types of supravalvular mitral stenosis: report of 16 cases, review of the literature, and delineation of a syndrome. American Heart Journal, 85(4), 1973, pp. 439-452.
Gallucci V, Lombardi P, Marino B, et al. Supravalvular mitral ring: clinical and surgical considerations. Thorax, 34(4), 1979, pp. 518-523.
Gallucci V, Marino B, Amodeo A, et al. Supravalvular mitral ring: a review of 18 cases. Journal of Thoracic and Cardiovascular Surgery, 88(5), 1984, pp. 695-703.
Marino B, Digilio MC, Toscano A, et al. Supravalvular mitral ring: anatomic, echocardiographic, and clinical considerations. American Journal of Cardiology, 64(14), 1989, pp. 964-968.
Gallucci V, Marino B, Amodeo A, et al. Supravalvular mitral ring: early and late results of surgical treatment. Journal of Thoracic and Cardiovascular Surgery, 92(4), 1986, pp. 681-686.