Mitral Valve Disease: Stenosis and Regurgitation

Mitral Valve Disease


Stenosis and Regurgitation



Ronan J. Curtin, Brian P. Griffin


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.


This chapter reviews three types of mitral valve disease: mitral stenosis, mitral regurgitation, and mitral valve prolapse. Practice guidelines published jointly by the American College of Cardiology (ACC) and the American Heart Association (AHA) for the management of patients with valvular heart disease are referenced in this chapter.1 Where relevant, we refer in the text to the ACC/AHA evidence grading for diagnostic and therapeutic procedures, as follows:


Class I: There is evidence and/or general agreement in favor of a given procedure or treatment.

Class II: There is conflicting evidence and/or a divergence of opinion about the efficacy of a given procedure or treatment.

Class IIa: The weight of evidence or opinion is in favor of efficacy.

Class IIb: Efficacy is less well established by evidence or opinion.

Class III: There is evidence and/or general agreement that the procedure or treatment is not useful and in some cases may be harmful.


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.



Prevalence and Risk Factors


Although the incidence of rheumatic heart disease has steeply declined during the past four decades in the United States, it is still a major cause of cardiovascular disease in developing countries. It is estimated that 15.6 million people suffer from rheumatic heart disease worldwide, with approximately 282,000 new cases and 233,000 related deaths each year.2



Pathophysiology and Natural History


Patients with MS typically present more than 20 years after an episode of rheumatic fever. Single or recurrent bouts of rheumatic carditis cause progressive thickening, scarring, and calcification of the mitral leaflets and chordae. Fusion of the commissures and chordae decreases the size of the mitral opening. This obstruction results in the development of a pressure gradient across the valve in diastole and causes an elevation in left atrial and pulmonary venous pressures. Elevated left atrial pressures lead to left atrial enlargement, predisposing the patient to atrial fibrillation and arterial thromboembolism. Elevated pulmonary venous pressure results in pulmonary congestion and pulmonary edema. In advanced mitral stenosis, patients develop pulmonary hypertension and right-sided heart failure.



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.



Diagnosis


On chest radiography, the characteristic findings of mitral stenosis are pulmonary congestion, enlargement of the main pulmonary arteries, and enlargement of the left atrium without cardiomegaly (Fig. 1). An electrocardiogram (ECG) may reveal evidence of left atrial enlargement, atrial fibrillation or, in advanced disease, right ventricular hypertrophy consistent with pulmonary hypertension (Fig. 2).


image

Figure 1 Chest radiograph of a patient with severe mitral stenosis showing pulmonary congestion and left atrial enlargement, with a normal left ventricular silhouette.


image

Figure 2 Electrocardiogram of a patient with severe mitral stenosis showing right ventricular hypertrophy and left atrial enlargement.


Two-dimensional (2D) and Doppler echocardiography is indicated for all patients with suspected MS to confirm the diagnosis and determine its severity (Class I indication).1 Characteristic findings of MS include valve thickening, restricted valve opening, anterior leaflet doming, and fusion of the leaflets at the commissures. The mean pressure gradient across the mitral valve on Doppler echocardiography (echo) in MS is at least 5 mm Hg; in severe stenosis, it is usually higher than 10 mm Hg. Because the gradient across the mitral valve is flow dependent, the severity of MS is more accurately defined by the mitral valve area (MVA). The normal valve area is 4 to 5 cm2. In mild mitral stenosis, the MVA is 1.5 to 2 cm2, in moderate stenosis it is 1 to 1.5 cm2, and in severe stenosis it is less than 1 cm2. The valve area may be measured by tracing the mitral valve opening in cross section by 2D echo. Alternatively, the MVA is calculated using the pressure half-time (P × 1/2t), which is the amount of time it takes for the transmitral pressure to fall to one half its initial value (MVA = 220/[P × 1/2t]).


Echocardiography also allows assessment of pulmonary artery pressures, detection of other valve disease, visualization of left atrial thrombus, and identification of important differential diagnoses, such as left atrial myxoma. Transesophageal echo is superior to transthoracic echo at identifying left atrial thrombus in patients who are being considered for percutaneous mitral balloon valvotomy or cardioversion (Class I).1 Stress echocardiography may be helpful if there is a discrepancy between a patient’s severity of symptoms and the baseline hemodynamic data. An exercise mean transmitral gradient of more than 15 mm Hg and peak right ventricular systolic pressure of more than 60 mm Hg indicate hemodynamically significant MS (Class I).1


Cardiac catheterization is not necessary in all cases but, like stress echocardiography, may be helpful in characterizing the severity of mitral stenosis when there is a discrepancy between symptoms and findings on echocardiography (Class I).1 A more detailed discussion of the diagnosis of mitral stenosis may be found in the AHA/ACC guidelines.1




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.


Treatment



Medical Treatment


Medical therapy has no role in altering the natural history or delaying the need for surgery in patients with MS. Medical treatment is directed toward alleviating pulmonary congestion with diuretics, treating atrial fibrillation, and anticoagulating patients who are at increased risk of arterial embolic events.


Development of atrial fibrillation frequently leads to an acute deterioration in patients with mitral stenosis. The rapid ventricular response results in a decrease in the diastolic filling time. Beta blockers, calcium channel blockers, or digoxin may be used to control ventricular rate. An attempt to restore sinus rhythm with direct current electrical cardioversion or antiarrhythmic drugs may be considered. Anticoagulation with warfarin is indicated to prevent thromboembolism when atrial fibrillation is present, if there is a prior history of thromboembolism, or a thrombus is detected in the left atrium (Class I).1 Although controversial, anticoagulation may also be considered if the left atrium is markedly dilated (5.0-5.5 mm) or if there is spontaneous contrast on echocardiography (Class IIb).1,3,4


Antibiotic therapy is important for the secondary prevention of rheumatic carditis. Patients with a history of rheumatic fever are at high risk of recurrence. Long-term secondary prophylaxis, preferentially with penicillin, is therefore recommended for all patients with a history of rheumatic fever or suspected rheumatic valve disease. The duration of prophylaxis depends on a number of factors, including the time lapsed since the last attack, the age of the patient, the presence or absence of cardiac involvement, and the patient’s risk of exposure to streptococcal infections.1,5 Routine antibiotic prophylaxis for endocarditis is no longer recommended for patients with mitral stenosis.6



Surgery


Three invasive options are available for patients with MS: percutaneous mitral balloon valvotomy (PMBV), surgical mitral commissurotomy, and mitral valve replacement (MVR). In experienced centers, PMBV is the initial procedure of choice and should be considered for (1) symptomatic patients (NYHA functional Classes II to IV) with moderate or severe MS (Class I) and (2) asymptomatic patients with moderate or severe MS and pulmonary hypertension (Class I).1 PMBV is a catheter-based technique in which a balloon is inflated across the stenotic valve to split the fused commissures and increase the valve area. The MVA typically doubles in size, and hemodynamic as well as clinical improvements are seen immediately (Fig. 3).7 The results are comparable with those achieved with open mitral commissurotomy, but it is less invasive and less costly.7,8 The mitral valve morphology is an important predictor of successful balloon valvotomy. Severe valve calcification or significant involvement of the subvalvular apparatus on echocardiography before PMBV is associated with a higher complication rate and a greater risk of recurrence. In addition, balloon valvotomy should not be performed in patients who have left atrial thrombus or more than 2+ (moderate) mitral regurgitation, because the degree of mitral regurgitation usually increases following the procedure. Complications of balloon mitral valvotomy include severe mitral regurgitation (3%), thromboembolism (3%), and residual atrial septal defect with significant shunting (<5%). Mortality with the procedure is lower than 1% in experienced hands. At 7 years after balloon valvotomy, 50% to 69% of patients remain free of cardiovascular events and up to 90% of patients remain free of reintervention.8,9 However, both balloon valvotomy and surgical commissurotomy are palliative procedures and, in most cases, further intervention is eventually required, usually in the form of a mitral valve replacement.


image

Figure 3 Echocardiogram (parasternal short-axis view) shows the mitral orifice before (A) and after (B) percutaneous mitral balloon valvotomy (PMBV).


Although closed mitral commissurotomy is still widely used in many developing countries, open mitral commissurotomy is more frequently performed in the United States. It involves the use of cardiopulmonary bypass and the surgical repair of a diseased mitral valve by direct visualization. Open mitral commissurotomy may be considered in the presence of a left atrial thrombus or significant mitral regurgitation if the valve anatomy is suitable. Commissurotomy may also be indicated for patients who have other concomitant valvular disease or coronary artery disease that requires surgery. In patients with calcified valves that cannot be treated by valvotomy or commissurotomy, or in those with significant mitral regurgitation that is not suitable for repair, mitral valve replacement may be necessary. The threshold for mitral valve surgery (commissurotomy or MVR) is higher than for PMBV in patients with mitral stenosis, and commissurotomy or repair is preferable to MVR, if feasible. Surgery for moderate to severe mitral stenosis is indicated for symptomatic patients (New York Heart Association [NYHA] functional Class III or IV) where PMBV is unavailable or contraindicated (Class I).1 MVR may also be considered for patients with severe MS and severe pulmonary hypertension with NYHA functional Classes I or II symptoms who are not candidates for PMBV or mitral valve repair (Class IIa). Both mechanical and biologic prostheses are used for mitral valve replacement; the choice of valve often depends on factors such as age, need for concomitant anticoagulation, and left ventricular (LV) size. Morbidity and mortality are higher with prosthetic valve replacement than with surgical or balloon valvotomy.


A more detailed discussion of the management of mitral stenosis may be found in the AHA/ACC guidelines.1




Summary



• Medical therapy in patients with mitral stenosis includes diuretic therapy, rate control of atrial fibrillation, anticoagulation to prevent thromboembolism, and antibiotic prophylaxis against recurrent rheumatic carditis.

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Jul 18, 2017 | Posted by in GENERAL SURGERY | Comments Off on Mitral Valve Disease: Stenosis and Regurgitation

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