Accessory mitral valve tissue

Accessory mitral valve tissue (AMVT) is a rare congenital cardiac anomaly in which additional tissue, distinct from the normal mitral valve leaflets, is present in the left ventricular outflow tract (LVOT) or attached to the mitral valve apparatus. This accessory tissue may be a membrane, a fibrous strand, or a mobile mass that can cause obstruction of the LVOT, leading to subaortic stenosis. It is classified under congenital malformations of the mitral valve (ICD-10: Q23.8). AMVT may occur as an isolated finding or in association with other congenital heart defects such as ventricular septal defect, subaortic membrane, or other left-sided obstructive lesions. Clinically, many patients with accessory mitral valve tissue are asymptomatic and the condition is discovered incidentally during echocardiography performed for other reasons. When symptomatic, patients may present with exertional dyspnea, syncope, chest pain, or heart murmur due to LVOT obstruction. In some cases, the accessory tissue can also cause mitral regurgitation. The severity of symptoms depends on the degree of outflow tract obstruction and the mobility and size of the accessory tissue. Diagnosis is typically made by transthoracic or transesophageal echocardiography, which can delineate the morphology and hemodynamic significance of the accessory tissue. Treatment depends on the clinical significance of the anomaly. Asymptomatic patients with no significant LVOT obstruction may be managed conservatively with regular echocardiographic surveillance. Surgical excision of the accessory tissue is recommended for patients with significant LVOT obstruction (typically a mean gradient greater than 30-50 mmHg), progressive symptoms, or associated complications such as endocarditis or embolism. Surgical outcomes are generally favorable, with low recurrence rates, though long-term follow-up is recommended to monitor for recurrence of obstruction or development of mitral valve dysfunction.

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