Mitral Stenosis - Acquired Valvular Disorders

MITRAL STENOSIS

Mitral stenosis is an obstruction of blood flowing from the left atrium into the left ventricle. It is most often caused by rheumatic endocarditis, which progressively thickens the mitral valve leaflets and chordae tendineae. The leaflets often fuse together. Eventually, the mitral valve orifice narrows and progressively obstructs blood flow into the ventricle.

Pathophysiology

Normally, the mitral valve opening is as wide as the diameter of three fingers. In cases of marked stenosis, the opening narrows to the width of a pencil. The left atrium has great difficulty moving blood into the ventricle because of the increased resistance of the narrowed orifice; it dilates (stretches) and hypertrophies (thickens) because of the increased blood volume it holds. Because there is no valve to protect the pulmonary veins from the backward flow of blood from the atrium, the pulmonary circulation becomes congested. As a result, the right ventricle must contract against an abnormally high pulmonary arterial pressure and is subjected to excessive strain. Eventually, the right ventricle fails.

Clinical Manifestations

The first symptom of mitral stenosis is often breathing difficulty (ie, dyspnea) on exertion as a result of pulmonary venous hyper-tension. Patients with mitral stenosis are likely to show progressive fatigue as a result of low cardiac output. They may expectorate blood (ie, hemoptysis), cough, and experience repeated respira-tory infections.

Assessment and Diagnostic Findings

The pulse is weak and often irregular because of atrial fibrillation (caused by the strain on the atrium). A low-pitched, rumbling, diastolic murmur is heard at the apex. As a result of the increased blood volume and pressure, the atrium dilates, hypertrophies, and becomes electrically unstable, and the patient experiences atrial dys-rhythmias. Echocardiography is used to diagnose mitral stenosis. Electrocardiography (ECG) and cardiac catheterization with an-giography are used to determine the severity of the mitral stenosis.

Medical Management

Antibiotic prophylaxis therapy is instituted to prevent recurrence of infections. Patients with mitral stenosis may benefit from anti-coagulants to decrease the risk for developing atrial thrombus. They may also require treatment for anemia.

Surgical intervention consists of valvuloplasty, usually a com-missurotomy to open or rupture the fused commissures of the mitral valve. Percutaneous transluminal valvuloplasty or mitral valve replacement may be performed.