Mitral Regurgitation (Mitral Insufficiency)

Essentials of Diagnosis

• Variable causes determine clinical presentation.
  
• May be asymptomatic for many years (or for life) or may cause left-sided heart failure.
  
• Pansystolic murmur at the apex, radiating into the axilla; associated with S₃.
  
• ECG shows left atrial abnormality or atrial fibrillation and left ventricular hypertrophy; x-ray shows left atrial and ventricular enlargement. Echo-Doppler confirms diagnosis and estimates severity.

General Considerations

Mitral regurgitation may result from many processes. Rheumatic disease is associated with a thickened valve with reduced mobility and often a mixed picture of stenosis and regurgitation. In developed countries, more common causes of mitral regurgitation include myxomatous degeneration (eg, mitral valve prolapse with or without connective tissue diseases such as Marfan's syndrome), infective endocarditis, and subvalvular dysfunction (due to papillary muscle dysfunction or ruptured chordae tendineae).

Cardiac tumors, chiefly left atrial myxoma, are a rare cause of mitral regurgitation.

Clinical Findings

A. Symptoms and Signs
During left ventricular systole, the mitral leaflets do not close normally, and blood is ejected into the left atrium as well as through the aortic valve. The net effect is an increased volume load on the left ventricle, and the presentation depends on the rapidity with which the lesion develops. In acute regurgitation, left atrial pressure rises abruptly, leading to pulmonary edema if severe. When it is chronic, the left atrium enlarges progressively, but the pressure in pulmonary veins and capillaries rises only transiently during exertion. Exertional dyspnea and fatigue progress gradually over many years.

Marfan's syndrome is a genetic (inherited) disorder that affects the body's connective tissue. Connective tissue is the tough, fibrous, elastic tissue that connects one part of the body with another, and forms much of the structural support for other body tissues. It is a major component of tendons, ligaments, bones, cartilage and the walls of large blood vessels. In Marfan's syndrome, a mutation (alteration) in a gene causes a defect in the body's production of fibrillin, an important building block of connective tissue. A gene is a segment of DNA that directs production of a particular body protein. In many families with inherited Marfan's syndrome, the mutation affects the FBN1 gene on chromosome 15, although a second gene on chromosome 5 may be involved in some cases.
Mitral regurgitation leads to left atrial enlargement and may cause subsequent atrial fibrillation. Systemic embolization is relatively unusual compared with other conditions causing atrial fibrillation. Mitral regurgitation may predispose to infective endocarditis.