Mitral Valve Stenosis: Understanding Its Causes and Development

Mitral valve stenosis is a cardiovascular condition characterized by the narrowing of the mitral valve opening, which restricts blood flow from the left atrium to the left ventricle. Understanding the causes behind this condition is essential for effective prevention and treatment strategies.

Primary Cause: Acute Rheumatic Fever

Acute rheumatic fever is the leading cause of mitral valve stenosis, accounting for approximately 80% to 90% of all cases. This inflammatory disease, often triggered by untreated or inadequately treated streptococcal infections, affects the heart valves, particularly the mitral valve.

During an episode of rheumatic fever, the body's immune response leads to swelling and fluid buildup along the edges of the valve leaflets. This inflammation promotes the deposition of fibrinogen and the formation of fibrous tissue, ultimately causing the leaflets to thicken and fuse at their edges. Over time, this fibrotic process reduces the effective size of the mitral valve orifice, resulting in restricted blood flow.

In addition to affecting the leaflets themselves, fibrous changes can also extend into the subvalvular structures such as the chordae tendineae and papillary muscles. This further compromises valve function and contributes to the progression of stenosis.

Other Contributing Factors and Conditions

Calcification of the Valve and Annulus

As people age, calcium deposits can accumulate on the mitral valve leaflets and annulus. This calcification stiffens the valve, limiting its ability to open fully and potentially leading to stenosis. This process is more common in elderly patients and may coexist with other degenerative heart valve diseases.

Infective Endocarditis and Valve Vegetations

Infective endocarditis, a bacterial infection of the heart lining or valves, can result in the formation of large vegetations on the mitral valve. These growths can physically obstruct blood flow through the valve, mimicking the effects of stenosis. In some cases, the infection may also cause scarring and structural changes that contribute to valve narrowing.

Cardiac Tumors and Endomyocardial Fibrosis

Rarely, tumors within the heart—especially left atrial myxomas—can obstruct the mitral valve orifice, causing symptoms similar to stenosis. Similarly, endomyocardial fibrosis, a condition characterized by thickening and scarring of the heart's inner lining, can involve the mitral valve apparatus and impair its function.

These secondary causes, while less common than rheumatic fever, are important to consider in the differential diagnosis of mitral valve stenosis, especially in non-rheumatic cases or in patients without a history of rheumatic disease.