Pathophysiology

Mitral insufficiency is the result of structural changes that usually include some loss of valvular substance and shortening and thickening of the chordae tendineae. During acute rheumatic fever with severe cardiac involvement, heart failure is caused by a combination of mitral insufficiency coupled with inflammatory disease of the pericardium, myocardium, endocardium, and epicardium. Because of the high volume load and inflammatory process, the left ventricle becomes enlarged. The left atrium dilates as blood regurgitates into this chamber. Increased left atrial pressure results in pulmonary congestion and symptoms of left-sided heart failure. Spontaneous improvement usually occurs with time, even in patients in whom mitral insufficiency is severe at the onset. The resultant chronic lesion is most often mild or moderate in severity, and the patient is asymptomatic. More than half of patients with acute mitral insufficiency no longer have the mitral murmur 1 yr later. In patients with severe chronic mitral insufficiency, pulmonary arterial pressure becomes elevated, the right ventricle and atrium become enlarged, and right-sided heart failure subsequently develops.

Clinical Manifestations

The physical signs of mitral insufficiency depend on its severity. With mild disease, signs of heart failure are not present, the precordium is quiet, and auscultation reveals a high-pitched holosystolic murmur at the apex that radiates to the axilla. With severe mitral insufficiency, signs of chronic heart failure may be noted. The heart is enlarged, with a heaving apical left ventricular impulse and often an apical systolic thrill. The 2nd heart sound may be accentuated if pulmonary hypertension is present. A 3rd heart sound is generally prominent. A holosystolic murmur is heard at the apex with radiation to the axilla. A short mid-diastolic rumbling murmur is caused by increased blood flow across the mitral valve as a result of the insufficiency. Auscultation of a diastolic murmur does not necessarily mean that mitral stenosis is present. The latter lesion takes many years to develop and is characterized by a diastolic murmur of greater length, usually with presystolic accentuation.

The electrocardiogram and roentgenograms are normal if the lesion is mild. With more severe insufficiency, the electrocardiogram shows prominent bifid P waves, signs of left ventricular hypertrophy, and associated right ventricular hypertrophy if pulmonary hypertension is present. Roentgenographically, prominence of the left atrium and ventricle can be seen. Congestion of perihilar vessels, a sign of pulmonary venous hypertension, may also be evident. Calcification of the mitral valve is rare in children. Echocardiography shows enlargement of the left atrium and ventricle, an abnormally thickened mitral valve, and Doppler studies demonstrate the severity of the mitral regurgitation. Heart catheterization and left ventriculography are considered only if diagnostic questions are not totally resolved by noninvasive assessment.

Complications

Severe mitral insufficiency may result in cardiac failure that may be precipitated by progression of the rheumatic process, the onset of atrial fibrillation, or infective endocarditis. The effects of chronic mitral insufficiency may become manifest after many years and include right ventricular failure and atrial and ventricular arrhythmias.

Treatment

In patients with mild mitral insufficiency, prophylaxis against recurrences of rheumatic fever is all that is required. Treatment of complicating heart failure (Chapter 436), arrhythmias (Chapter 429), and infective endocarditis (Chapter 431) is described elsewhere. Afterload-reducing agents (ACE inhibitors or angiotensin receptor blockers) may reduce the regurgitant volume and preserve left ventricular function. Surgical treatment is indicated for patients who despite adequate medical therapy have persistent heart failure, dyspnea with moderate activity, and progressive cardiomegaly, often with pulmonary hypertension. Although annuloplasty provides good results in some children and adolescents, valve replacement may be required. In patients with a prosthetic mitral valve replacement, prophylaxis against bacterial endocarditis is warranted for dental procedures, as the routine antibiotics taken by these patients for rheumatic fever prophylaxis are insufficient to prevent endocarditis.

Pathophysiology

Mitral stenosis of rheumatic origin results from fibrosis of the mitral ring, commissural adhesions, and contracture of the valve leaflets, chordae, and papillary muscles over time. It usually takes 10 yr or more for the lesion to become fully established, although the process may occasionally be accelerated. Rheumatic mitral stenosis is seldom encountered before adolescence and is not usually recognized until adult life. Significant mitral stenosis results in increased pressure and enlargement and hypertrophy of the left atrium, pulmonary venous hypertension, increased pulmonary vascular resistance, and pulmonary hypertension. Right ventricular hypertrophy and right atrial dilatation ensue and are followed by right ventricular dilation, tricuspid regurgitation, and clinical signs of right-sided heart failure.

Clinical Manifestations

Generally, the correlation between symptoms and the severity of obstruction is good. Patients with mild lesions are asymptomatic. More severe degrees of obstruction are associated with exercise intolerance and dyspnea. Critical lesions can result in orthopnea, paroxysmal nocturnal dyspnea, and overt pulmonary edema, as well as atrial arrhythmias. When pulmonary hypertension has developed, right ventricular dilatation may result in functional tricuspid insufficiency, hepatomegaly, ascites, and edema. Hemoptysis caused by rupture of bronchial or pleurohilar veins and, occasionally, by pulmonary infarction may occur.

Jugular venous pressure is increased in severe disease with heart failure, tricuspid valve disease, or severe pulmonary hypertension. In mild disease, heart size is normal; however, moderate cardiomegaly is usual with severe mitral stenosis. Cardiac enlargement can be massive when atrial fibrillation and heart failure supervene. A parasternal right ventricular lift is palpable when pulmonary pressure is high. The principal auscultatory findings are a loud 1st heart sound, an opening snap of the mitral valve, and a long, low-pitched, rumbling mitral diastolic murmur with presystolic accentuation at the apex. The mitral diastolic murmur may be virtually absent in patients who are in significant heart failure. A holosystolic murmur secondary to tricuspid insufficiency may be audible. In the presence of pulmonary hypertension, the pulmonic component of the 2nd heart sound is accentuated. An early diastolic murmur may be caused by associated rheumatic aortic insufficiency or pulmonary valvular insufficiency secondary to pulmonary hypertension.

Electrocardiograms and roentgenograms are normal if the lesion is mild; as the severity increases, prominent and notched P waves and varying degrees of right ventricular hypertrophy become evident. Atrial fibrillation is a common late manifestation. Moderate or severe lesions are associated with roentgenographic signs of left atrial enlargement and prominence of the pulmonary artery and right-sided heart chambers; calcifications may be noted in the region of the mitral valve. Severe obstruction is associated with a redistribution of pulmonary blood flow so that the apices of the lung have greater perfusion (the reverse of normal). Echocardiography shows thickening of the mitral valve, distinct narrowing of the mitral orifice during diastole and left atrial enlargement. Doppler can estimate the transmitral pressure gradient. Cardiac catheterization quantitates the diastolic gradient across the mitral valve, allows for the calculation of valve area, and assesses the degree of elevation of pulmonary arterial pressure.

Treatment

Intervention is indicated in patients with clinical signs and hemodynamic evidence of severe obstruction but before the severe manifestations outlined earlier. Surgical valvotomy or balloon catheter mitral valvuloplasty generally yields good results; valve replacement is avoided unless absolutely necessary. Balloon valvuloplasty is indicated for symptomatic, stenotic, pliable, noncalcified valves of patients without atrial arrhythmias or thrombi.

Clinical Manifestations

Symptoms are unusual except in severe aortic insufficiency. The large stroke volume and forceful left ventricular contractions may result in palpitations. Sweating and heat intolerance are related to excessive vasodilation. Dyspnea on exertion can progress to orthopnea and pulmonary edema; angina may be precipitated by heavy exercise. Nocturnal attacks with sweating, tachycardia, chest pain, and hypertension may occur.

The pulse pressure is wide with bounding peripheral pulses. Systolic blood pressure is elevated, and diastolic pressure is lowered. In severe aortic insufficiency, the heart is enlarged, with a left ventricular apical heave. A diastolic thrill may be present. The typical murmur begins immediately with the 2nd heart sound and continues until late in diastole. The murmur is heard over the upper and midleft sternal border with radiation to the apex and upper right sternal border. Characteristically, it has a high-pitched blowing quality and is easily audible in full expiration with the diaphragm of the stethoscope placed firmly on the chest and the patient leaning forward. An aortic systolic ejection murmur is frequent because of the increased stroke volume. An apical presystolic murmur (Austin Flint murmur) resembling that of mitral stenosis is sometimes heard and is a result of the large regurgitant aortic flow in diastole preventing the mitral valve from opening fully.

Roentgenograms show enlargement of the left ventricle and aorta. The electrocardiogram may be normal, but in advanced cases it reveals signs of left ventricular hypertrophy and strain with prominent P waves. The echocardiogram shows a large left ventricle and diastolic mitral valve flutter or oscillation caused by regurgitant flow hitting the valve leaflets. Doppler studies demonstrate the degree of aortic runoff into the left ventricle. Magnetic resonance angiography (MRA) can be useful in quantitating regurgitant volume. Cardiac catheterization is necessary only when the echocardiographic data are equivocal.

Prognosis and Treatment

Mild and moderate lesions are well tolerated. Unlike mitral insufficiency, aortic insufficiency does not regress. Patients with combined lesions during the episode of acute rheumatic fever may have only aortic involvement 1-2 yr later. Treatment consists of afterload reducers (ACE inhibitors or angiotensin receptor blockers) and prophylaxis against recurrence of acute rheumatic fever. Surgical intervention (valve replacement) should be carried out well in advance of the onset of heart failure, pulmonary edema, or angina, when signs of decreasing myocardial performance become evident as manifested by increasing left ventricular dimensions on the echocardiogram. Surgery is considered when early symptoms are present, ST-T wave changes are seen on the electrocardiogram, or evidence of decreasing left ventricular ejection fraction is noted.