Chronic Mitral Regurgitation

Long-standing retrograde blood flow from the left ventricle into the left atrium through an incompetent mitral valve during ventricular systole, with eccentric left ventricular hypertrophy.

Chronic rather than acute mitral regurgitation is the most common type of mitral valve disease in the elderly. About half of patients with rheumatic mitral regurgitation have associated aortic valve disease, usually aortic regurgitation.

In the elderly, isolated chronic mitral regurgitation often results from papillary muscle dysfunction after myocardial infarction. Chronic mitral regurgitation may also be due to mitral annular calcification, myxomatous valve degeneration (with mitral valve prolapse), chordal rupture, or rheumatic heart disease. Mitral annular calcification occurs in about 6% of persons > 60, predominantly women. The incidence of myxomatous valvular degeneration increases with age.

Pathophysiology

In chronic mitral regurgitation, the regurgitant volume gradually increases, increasing the volume of the left atrium during systole and that of the left ventricle during diastole. Enlargement of the left ventricle results in eccentric hypertrophy. Eventually, stretching of the left atrium results in atrial fibrillation, and the left ventricle can no longer maintain a normal effective forward stroke volume because of decreased myocardial contractility. Left ventricular failure develops, leading to increased pulmonary artery and right ventricular systolic pressure. Thus, right ventricular failure develops very late in the course of the disorder.

Mitral regurgitation due to mitral annular calcification prevents annular systolic contraction and may limit valve leaflet closure. It is rarely hemodynamically significant; however, calcification may involve the conduction system, causing various degrees of atrioventricular block, and may double the risk of stroke.

Symptoms, Signs, and Diagnosis

Patients may be asymptomatic or present with only a pansystolic apical murmur or a decrease in exercise tolerance with easy fatigability. Atrial fibrillation may occur later than it does in patients with mitral stenosis. Atrial fibrillation may precipitate hemodynamic deterioration, with an apical holosystolic murmur engulfing the first heart sound, and symptoms and signs of left-sided heart failure. Systemic embolism occurs predominantly when atrial fibrillation or heart failure is present but is less common among patients with chronic mitral regurgitation than among those with mitral stenosis.

If the cause is mitral valve prolapse, presenting symptoms and signs may include atypical chest pain, palpitations or syncope due to arrhythmia, and heart failure (more common among men). A midsystolic click or clicks and a late systolic or holosystolic murmur may be heard. The mitral regurgitant murmur predominates in elderly patients, whereas clicks and late crescendo systolic murmurs predominate in younger patients. An ECG often shows ST-T wave changes, but when mitral regurgitation is severe, it may show left ventricular hypertrophy. Ventricular arrhythmias are common, even in patients with normal ventricular function. With severe mitral regurgitation, the onset of atrial fibrillation may accentuate mitral and tricuspid valve prolapse and often precipitates hemodynamic deterioration. Systemic embolism and sudden death may occur.

Doppler echocardiography can be used to determine the magnitude of the mitral regurgitation and to assess overall ventricular size and function. It can sometimes determine the etiology of the mitral insufficiency. For example, vegetations suggest infective endocarditis; prolapse and thickening of the leaflets suggest myxomatous degeneration; flail mitral valve suggests chordal rupture; and thickened retracted leaflets and chordal fusion suggest rheumatic heart disease. Doppler echocardiography can differentiate mitral valve prolapse from other causes of mitral regurgitation. A ringlike calcification in the area of the mitral valve on a chest x-ray and dense horseshoe-shaped calcifications on an echocardiogram indicate mitral annular calcification.

Coronary arteriography may be needed to differentiate the chest pain due to mitral valve prolapse from that due to coronary atherosclerosis.

Treatment

Atrial fibrillation and heart failure are managed with standard therapy. Anticoagulants are given to prevent systemic embolism. Most symptomatic elderly patients with chronic mitral regurgitation respond readily to medical therapy.

Surgery is indicated when medical therapy does not control symptoms and/or when ventricular function deteriorates, as indicated by a progressive increase in left ventricular end-diastolic and end-systolic volumes and a decrease in ejection fraction. The ejection fraction should not be allowed to decrease below 55%. Elderly men with mitral valve prolapse are more likely to require surgery than are elderly women. If high-degree atrioventricular block occurs, a pacemaker should be placed.

For patients with papillary muscle dysfunction due to CAD, an annuloplasty ring placed during coronary artery bypass grafting can reduce the degree of regurgitation.