The mitral valve is made up of the annulus, anterior and posterior leaflets, and chordae, which attach the leaflets to their respective papillary muscles. A normally functioning valve allows blood to flow unimpeded from the left atrium to the left ventricle during diastole and prevents regurgitation during systole. Normal mitral valve function is dependent not only on the integrity of the underlying valvular structure, but on that of the adjacent myocardium as well.
Three types of mitral valve disease are mentioned below:
Mitral stenosis
Definition and Etiology
Mitral stenosis (MS) refers to narrowing of the mitral valve orifice, resulting in impedance of filling of the left ventricle in diastole. It is usually caused by rheumatic heart disease. Less common causes include severe calcification of the mitral annulus, infective endocarditis, systemic lupus erythematosus, rheumatoid arthritis, and carcinoid heart disease.
Signs and Symptoms
Patients with mitral stenosis may present with exertional dyspnea, fatigue, atrial arrhythmias, embolic events, angina-like chest pain, hemoptysis, or even right-sided heart failure. Previously asymptomatic or stable patients may decompensate acutely during exercise, emotional stress, pregnancy, infection, or with uncontrolled atrial fibrillation.
The characteristic findings of MS on auscultation are an accentuated first heart sound, an opening snap, and a mid-diastolic rumble. The first heart sound may be diminished in intensity if the valve is heavily calcified, with limited mobility. If the patient is in sinus rhythm, there is presystolic accentuation of the murmur during atrial contraction. With increasingly severe stenosis, the duration of the murmur increases and the opening snap occurs earlier during diastole as a result of higher left atrial pressure. There is accentuation of P2 when pulmonary hypertension is present. If flow across the mitral valve is reduced because of heart failure, pulmonary hypertension, or aortic stenosis the murmur of mitral stenosis may be reduced in intensity or may be inaudible.
Left atrial myxoma may be distinguished from MS by the presence of a “tumor plop” versus an opening snap in early diastole.
Summary
- Transthoracic echocardiography is necessary to diagnose and determine the severity of mitral stenosis.
- Transesophageal echocardiography is indicated in patients before percutaneous mitral balloon valvotomy or cardioversion.
- Stress echocardiography and cardiac catheterization may be helpful in those cases in which there is a discrepancy between the severity of symptoms and baseline echocardiographic findings.
Mitral Regurgitation
Definition and Causes
Mitral regurgitation (MR) is leakage of blood from the left ventricle into the left atrium during systole. It is caused by various mechanisms related to structural or functional abnormalities of the mitral apparatus, adjacent myocardium, or both. The most common causes of mitral regurgitation in the United States are myxomatous degeneration, chordal rupture, rheumatic heart disease, infective endocarditis, coronary artery disease, and cardiomyopathy.
revalence and Risk Factors
Significant mitral valve regurgitation occurs in about 2% of the population with a similar prevalence in males and females.11Myxomatous disease is the most common cause of nonischemic mitral regurgitation in the United States (Fig. 4).
Pathophysiology and Natural History
Significant MR leads to volume overload of the left ventricle, because it has to accommodate both the stroke volume and regurgitant volume with each heartbeat. To compensate, the left ventricle dilates and becomes hyperdynamic. In acute severe MR, the left atrial and pulmonary venous pressures increase quickly, leading to pulmonary congestion and pulmonary edema. In chronic MR, a gradual increase in left atrial size and compliance compensate so that left atrial and pulmonary venous pressures do not increase until late in the course of the disease. Progressive left ventricular dilation eventually leads to an increase in afterload, contractile dysfunction, and heart failure. Left atrial enlargement predisposes the patient to atrial fibrillation and arterial thromboembolism. In long-standing MR, patients may develop pulmonary hypertension and right-sided heart failure.
Signs and Symptoms
Patients with chronic, severe mitral regurgitation may remain asymptomatic for years because the regurgitant volume load is well tolerated as a result of compensatory ventricular and atrial dilation. When symptoms do develop, the most common are dyspnea, fatigue, orthopnea, paroxysmal nocturnal dyspnea, and palpitations caused by atrial fibrillation. Acute severe MR, as occurs with chordal rupture or papillary muscle rupture, is almost always symptomatic because the sudden regurgitant volume load in the nondilated left ventricle and atrium leads to pulmonary venous hypertension and congestion.
The characteristic finding in a patient with MR is a blowing holosystolic murmur heard best at the cardiac apex. When ventricular enlargement is present, the apical impulse may be diffuse and laterally displaced, and a third heart sound may be heard.
Diagnosis
The chest radiograph demonstrates left atrial enlargement and cardiomegaly. Two-dimensional and Doppler echocardiography is indicated for all patients with suspected mitral regurgitation to confirm its presence and determine its severity (Class I).1 Two-dimensional echocardiography usually reveals the cause (e.g., the presence of myxomatous mitral valve disease and leaflet prolapse or evidence of underlying dilated cardiomyopathy). Evaluation of the severity of mitral regurgitation on echocardiography requires an integrated assessment of several parameters, including regurgitant jet size by color Doppler, regurgitant jet density by continuous-wave (CW) Doppler, and pulmonary vein and mitral valve inflow by pulse-wave (PW) Doppler. Newer applications of Doppler echocardiography allow quantitative measurement of mitral regurgitation, including the regurgitant volume and the regurgitant orifice area (ROA)—that is, the area through which the valve leaks in systole. In asymptomatic patients with significant mitral regurgitation, serial echocardiography every 6 to 12 months to assess LV size and systolic function is important for optimal timing of surgery (Class I). Transesophageal echocardiography is indicated for patients who are not adequately imaged by transthoracic echocardiography and before surgery to assess feasibility for repair (Class I).Stress echocardiography may be useful to assess exercise tolerance and the response of mitral regurgitation severity, pulmonary pressure, and contractile reserve to exercise in asymptomatic patients with significant MR (Class IIa).
Cardiac catheterization is no longer routinely performed to evaluate mitral regurgitation severity, but it is indicated for those patients in whom noninvasive test results are inconclusive, and also to detect concomitant coronary artery disease in patients undergoing mitral valve surgery (Class I). A more detailed discussion of the diagnosis of mitral regurgitation may be found in the AHA/ACC guidelines.
Summary
- Determining the severity of mitral regurgitation requires an integrated assessment of several parameters on echocardiography.
- Serial echocardiography with measurement of LV size and function is important for timing surgical intervention in asymptomatic patients.
- Transesophageal echocardiography is necessary before surgery to assess feasibility for repair, as well as for patients who are not adequately imaged by transthoracic echocardiography.
Surgery
The two available surgical options are mitral valve repair (Fig. 5) and mitral valve replacement. Mitral valve repair is the procedure of choice in the surgical management of MR caused by degenerative valve disease and in some cases of MR caused by infective endocarditis and ischemic heart disease. Repair offers several advantages over replacement, including lower operative and long-term mortality, better preservation of LV function, a lower risk of subsequent infective endocarditis, and no need for long-term anticoagulation. Reoperation rates for mitral valve repair and replacement are similar, occurring at a rate of 1% to 2% per year. On the other hand, repair is technically more difficult than replacement, and many cases of mitral regurgitation are not amenable to valve repair. Percutaneous mitral valve repair is currently being investigated. The techniques involved include a clip that joins the mitral leaflets at their midpoint and an annuloplasty ring delivered via the coronary sinus.
A more detailed discussion of the management of mitral regurgitation may be found in the AHA/ACC guidelines.(1)
Summary
- Medical therapy has no role in the treatment of patients with primary mitral regurgitation but is the mainstay of treatment in patients with functional mitral regurgitation.
- In patients with primary mitral regurgitation, surgery is indicated in the presence of symptoms or, in asymptomatic patients, if there is evidence of secondary LV dysfunction.
- Mitral valve repair is the procedure of choice for the surgical management of mitral regurgitation and is associated with lower mortality and better preservation of LV function.
Mitral Valve Prolapse
Definition and Causes
Mitral valve prolapse (MVP) is the systolic billowing of one or both mitral leaflets into the left atrium during systole. It may occur in the setting of myxomatous valve disease or in persons with normal mitral valve leaflets.
Prevalence and Risk Factors
MVP is the most common valvular disorder in the United States, occurring in 2.4% of the general population. There is a similar prevalence in men and women, with a greater risk of complications in men.
Pathophysiology and Natural History
Many patients with MVP have normal mitral leaflets, with little or no mitral regurgitation, and a benign prognosis. Survival rates among affected patients are similar to those of age- and gender-matched individuals without MVP.24 In other patients, MVP is caused by myxomatous valve disease, with typical findings of elongated and thickened leaflets, interchordal hooding, and chordal elongation. Patients with myxomatous MVP are at increased risk for cardiovascular complications, particularly when prolapse is associated with at least moderate mitral regurgitation or LV dysfunction. Although most patients with MVP do not develop severe mitral regurgitation, MVP is a common underlying cause of progressive mitral regurgitation, often necessitating mitral valve repair or replacement.
The causes of myxomatous mitral valve disease are not certain, but appear to involve dysregulation of extracellular matrix proteins. Myxomatous mitral valve disease usually occurs sporadically, although there are well-described cases of familial clustering that involve an autosomal dominant mode of inheritance. Three genetic loci for autosomal dominant myxomatous mitral valve disease have been described, but the precise genes and mutations have not yet been identified. Myxomatous MVP also may occur in conjunction with certain connective tissue disorders, such as Marfan syndrome and Ehlers-Danlos syndrome.
Signs and Symptoms
Most patients with MVP are asymptomatic. In the past, multiple nonspecific symptoms (atypical chest pain, dyspnea, palpitations, anxiety, and syncope) and clinical findings (low body weight, low blood pressure, and pectus excavatum) were associated with MVP and termed mitral valve prolapse syndrome. Prospective testing has failed to confirm most of these associations. The classic findings of MVP on physical examination are a midsystolic click, with a late systolic murmur, heard best at the cardiac apex.
Diagnosis
Two-dimensional echocardiography is the most important test for diagnosing MVP (Class I). The diagnosis is made when there is displacement of one or both mitral leaflets by 2 mm or more into the left atrium during systole . Because the mitral annulus is known to have a saddle shape, a normal mitral valve can appear to prolapse in certain echocardiographic views, most notably in the apical two- and four-chamber views. Therefore, the diagnosis of MVP should be based on a long-axis parasternal or apical three-chamber view. In patients with MVP, echocardiography is also useful in determining the presence and severity of MR and assessing left atrial and ventricular chamber size, LV function, and leaflet thickening and redundancy. Unless severe mitral regurgitation is present, findings on the chest radiograph and ECG typically are unremarkable. A more detailed discussion of the diagnosis of mitral valve prolapse may be found in the AHA/ACC guidelines.(1)
Summary
- Mitral valve prolapse is present if there is more than 2 mm displacement of the mitral valve leaflets into the left atrium during systole in a parasternal long-axis or apical three-chamber view on echocardiography.
References:
- Bonow RO, Carabello BA, Chatterjee K, et al: 2006 Writing Committee Members; American College of Cardiology/American Heart Association Task Force. 2008 Focused update incorporated into the ACC/AHA 2006 guidelines for the management of patients with valvular heart disease: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Writing Committee to Revise the 1998 Guidelines for the Management of Patients With Valvular Heart Disease). Circulation. 2008, 118: e523-e661.
- Ronan J. Curtin MD (Cleveland Clinic)
- Brian P. Griffin MD, FACC (Cleveland Clinic)
- Cleveland Clinic