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Mitral Stenosis

by Guy P. Armstrong, MD

Mitral stenosis (MS) is narrowing of the mitral orifice that impedes blood flow from the left atrium to the left ventricle. The (almost) invariable cause is rheumatic fever. Common complications are pulmonary hypertension, atrial fibrillation, and thromboembolism. Symptoms are those of heart failure; signs include an opening snap and a diastolic murmur. Diagnosis is by physical examination and echocardiography. Prognosis is good. Medical treatment includes diuretics, β-blockers or rate-limiting Ca channel blockers, and anticoagulants. Effective treatment for more severe disease consists of balloon commissurotomy, surgical commissurotomy, or valve replacement.

In MS, mitral valve leaflets become thickened and immobile and the mitral orifice becomes narrowed due to fusion of the commissures and the presence of shortened, thickened and matted chordae. The most common cause is rheumatic fever (see Rheumatic Fever), even though many patients do not recall the disorder. Very rare causes include mitral annular calcification with extension of calcification into the leaflets, causing them to stiffen and not open fully. Occasionally, MS is congenital. If the valve cannot close completely, mitral regurgitation (MR) may coexist with MS. Patients with MS due to rheumatic fever may also have lesions of the aortic or tricuspid valve or both.

Left atrial (LA) size and pressure increase progressively to compensate for MS; pulmonary venous and capillary pressures also increase and may cause secondary pulmonary hypertension, leading to right ventricular (RV) heart failure and tricuspid and pulmonic regurgitation. Rate of progression varies.

LA enlargement predisposes to atrial fibrillation (AF), a risk factor for thromboembolism. The faster heart rate and loss of atrial contraction with onset of AF often lead to sudden worsening of symptoms.

Symptoms and Signs

Symptoms correlate poorly with disease severity because the disease often progresses slowly, and patients unconsciously reduce their activity. Many patients are asymptomatic until they become pregnant or AF develops. Initial symptoms are usually those of heart failure (eg, exertional dyspnea, orthopnea, paroxysmal nocturnal dyspnea, fatigue). They typically do not appear until 15 to 40 yr after an episode of rheumatic fever, but in developing countries, young children may become symptomatic because streptococcal infections may not be treated with antibiotics and recurrent infections are common. Paroxysmal or chronic AF further reduces blood flow into the left ventricle (LV), precipitating pulmonary edema and acute dyspnea when ventricular rate is poorly controlled. AF may also cause palpitations; in up to 15% of patients not taking anticoagulants, it causes systemic embolism with symptoms of stroke or other organ ischemia.

Less common symptoms include hemoptysis due to rupture of small pulmonary vessels and pulmonary edema, particularly during pregnancy when blood volume increases; hoarseness due to compression of the left recurrent laryngeal nerve by a dilated LA or pulmonary artery (Ortner syndrome); and symptoms of pulmonary hypertension (see Pulmonary Hypertension : Symptoms and Signs) and RV failure (see Heart Failure:RV failure).

Inspection and palpation may detect palpable 1st and 2nd heart sounds (S 1 and S 2 ). S 1 is best palpated at the apex, and S 2 at the upper left sternal border. The pulmonic component of S 2 (P 2 ) is responsible for the impulse and results from pulmonary hypertension. An RV impulse (heave) palpable at the left sternal border may accompany jugular venous distention when pulmonary hypertension is present and RV diastolic dysfunction develops.

Auscultatory findings include a loud S 1 caused by the leaflets of a stenotic mitral valve closing abruptly (M 1 ); it is heard best at the apex. S 1 may be absent when the valve is heavily calcified and immobile. A normally split S 2 with an exaggerated P 2 due to pulmonary hypertension is also heard. Most prominent is an early diastolic opening snap as the leaflets billow into the LV, which is loudest close to left lower sternal border; it is followed by a low-pitched decrescendo-crescendo rumbling diastolic murmur, heard best with the bell of the stethoscope at the apex (or over the palpable apex beat) at end-expiration when the patient is in the left lateral decubitus position. The opening snap may be soft or absent if the mitral valve is calcified; the snap moves closer to S 2 (increasing duration of the murmur) as MS becomes more severe and LA pressure increases. The diastolic murmur increases after a Valsalva maneuver (when blood pours into the LA), after exercise, and in response to maneuvers that increase afterload (eg, squatting, isometric handgrip). The murmur may be softer or absent when an enlarged RV displaces the LV posteriorly and when other disorders (pulmonary hypertension, right-sided valve abnormalities, AF with fast ventricular rate) decrease blood flow across the mitral valve. The presystolic crescendo is caused by increased flow with atrial contraction. However, the closing mitral valve leaflets during LV contraction may also contribute to this finding but only at the end of short diastoles when LA pressure is still high.

Prominent mitral stenosis murmur with presystolic accentuation, described as resembling a growl and bark. Mitral stenosis murmurs are typically rumbling and low-pitched and crescendo through diastole.

Mitral Stenosis Murmur

Intensity of the murmur of mitral stenosis varies with changes in length of the cardiac cycles. In this sample of atrial fibrillation, the murmur increases in intensity with longer cycles and decreases in intensity with shorter cycles, because the volume of blood flowing across the mitral valve changes. Overall intensity is decreased because atrial contraction is lost.

Mitral Stenosis in Atrial Fibrillation

Diastolic murmurs that may coexist with the MS murmur are

  • Early diastolic murmur of coexisting aortic regurgitation (AR), which may be conducted to the apex

  • Austin Flint murmur (a low-pitched mid-diastolic murmur heard at the apex due to AR)

  • Graham Steell murmur (a soft decrescendo diastolic murmur heard best along the left sternal border and caused by pulmonic regurgitation secondary to severe pulmonary hypertension)

  • Diastolic flow murmur in the presence of severe MR

  • Obstructing left atrial myxoma or ball thrombus (rare)

MS may cause signs of cor pulmonale (see Cor Pulmonale). The classic facial appearance in MS, a plum-colored malar flush, occurs only when cardiac output is low and pulmonary hypertension is severe; cause is cutaneous vasodilation and chronic hypoxemia.

Occasionally, the initial symptoms and signs of MS are those of an embolic event such as stroke. Endocarditis is rare in MS unless MR is also present.

Sample illustrates typical features of mitral stenosis: The murmur is rumbling or low-pitched and begins early in diastole with crescendo to S 2 .

Mitral Stenosis

Diagnosis

  • Echocardiography

Diagnosis is suspected clinically and confirmed by echocardiography. Typically, 2-dimensional echocardiography shows abnormal valve and subvalve structures. It also provides information about the degree of valvular calcification and stenosis and LA size. Doppler echocardiography provides information about the transvalvular gradient and pulmonary artery pressure. The normal area of the mitral valve orifice is 4 to 5 cm 2 .

Severity is characterized echocardiographically as

  • Moderate: Valve area 1.5 to 2.5 cm 2

  • Severe: Valve area < 1.5 cm 2 ; symptoms are often present

  • Very severe: Valve area < 1.0 cm 2

However, the relationship between the area of the valve orifice and symptoms is not always consistent. Color Doppler echocardiography detects associated MR. Transesophageal echocardiography can be used to detect or exclude small LA thrombi, especially those in the LA appendage, which usually cannot be seen transthoracically.

An ECG and chest x-ray are usually obtained. The ECG may show LA enlargement, manifest as a P wave lasting > 0.12 msec with prominent negative deflection of its terminal component (duration: > 0.04 msec; amplitude: > 0.10 mV) in V 1 ; broad, notched P waves in lead II; or both. Low voltage in V 1 , right axis QRS deviation, and tall R waves in V 1 suggest RV hypertrophy.

Chest x-ray usually shows straightening of the left cardiac border due to a dilated LA appendage, and widening of the carina. With barium in the esophagus, the lateral chest x-ray will show the dilated LA displacing the esophagus posteriorly. The main pulmonary artery (trunk) may be prominent; the descending right pulmonary artery diameter is ≥ 16 mm if pulmonary hypertension is significant. The upper lobe pulmonary veins may be dilated. A double shadow of an enlarged LA may be seen along the right cardiac border. Horizontal lines in the lower posterior lung fields (Kerley B lines) indicate interstitial edema associated with high LA pressure.

Cardiac catheterization, indicated only for perioperative assessment of coronary artery disease (CAD) before surgical repair, can confirm elevated LA and pulmonary artery pressures, mitral gradient and valve area.

Prognosis

The natural history of MS varies, but the interval between onset of symptoms and severe disability is about 7 to 9 yr. Outcome is affected by the patient’s preprocedural age and functional status, pulmonary hypertension, and degree of MR. Symptomatic results of balloon or surgical commissurotomy are equivalent in patients with valves that are not calcified. However, after a variable period of time, function deteriorates in most patients due to restenosis, and valve replacement may become necessary. Risk factors for death are AF and pulmonary hypertension. Cause of death is most commonly heart failure or pulmonary or cerebrovascular embolism.

Treatment

  • Diuretics and sometimes β-blockers or Ca channel blockers

  • Anticoagulation for AF

  • Commissurotomy or valve replacement

Asymptomatic patients require no treatment other than appropriate prophylaxis against rheumatic fever recurrence.

Mildly symptomatic patients usually respond to diuretics and, if sinus tachycardia or AF is present, to β-blockers or Ca channel blockers, which can control ventricular rate. Anticoagulants are indicated to prevent thromboembolism if patients have or have had AF, embolism, or a left atrial clot. Anticoagulation may also be considered in the presence of dense spontaneous contrast or an enlarged left atrium (M-mode diameter > 50 mm). All patients should be encouraged to continue at least low levels of physical exercise despite exertional dyspnea.

Antibiotic prophylaxis against endocarditis is no longer recommended except for patients who have had valve replacement (see Table: Recommended Endocarditis Prophylaxis During Oral-Dental or Respiratory Tract Procedures*).

Timing of intervention

For moderate MS, intervention may be indicated when there is ≥ 1 of the following:

  • Cardiac surgery is required for other indications

  • Patients are symptomatic and have exercise-induced mean transmitral gradient > 15 mm Hg or pulmonary capillary occlusion pressure > 25 mm Hg

For severe MS, intervention is indicated when there is ≥ 1 of the following:

  • Any symptoms if the valve is suitable for percutaneous balloon commissurotomy (may be considered in asymptomatic patients)

  • Cardiac surgery is required for other indications

For very severe MS, intervention is indicated for all patients (with or without symptoms) who are suitable candidates for percutaneous balloon commissurotomy.

Choice of intervention

Percutaneous balloon commissurotomy is the procedure of choice for younger patients and for patients without heavily calcified valve commissures, subvalvular distortion, LA thrombi, or significant MR. In this fluoroscopic- and echocardiographic-guided procedure, a transvenous catheter with an inflatable distal balloon is passed transseptally from the right atrium to the LA and inflated to separate fused mitral valve commissures. Outcomes are equivalent to those of more invasive procedures. Complications are uncommon but include MR, embolism, and tamponade.

Patients with severe subvalvular disease, valvular calcification, or LA thrombi may be candidates for surgical commissurotomy, in which fused mitral valve leaflets are separated using a dilator passed through the LV (closed commissurotomy) via a thoracotomy, or by direct vision (open commissurotomy) via a sternotomy. Choice of procedure is based on surgeon’s experience and the morphology of the valve, although closed valvotomy is now done less frequently in Western countries. Because of its greater risks, surgery is usually deferred until symptoms reach New York Heart Association class III (see Table: New York Heart Association (NYHA) Classification of Heart Failure). During surgery, some clinicians ligate the left atrial appendage to reduce thromboembolism.

Valve replacement is confined to patients with severe morphologic changes that make the valve unsuitable for balloon or surgical commissurotomy.

When the etiology is annular calcification, there is no benefit from percutaneous balloon commissurotomy because there is no commissural fusion. Furthermore, surgical valve replacement is technically demanding because of the annular calcification and often high risk because many patients are elderly and have comorbidities. Therefore, intervention is delayed until symptoms become severe despite use of diuretic and rate control drugs.

Key Points

  • Mitral stenosis is almost always caused by rheumatic fever.

  • Pulmonary hypertension and atrial fibrillation (with consequent thromboembolism) may develop.

  • Heart sounds include a loud S 1 and an early diastolic opening snap followed by a low-pitched decrescendo-crescendo rumbling diastolic murmur, heard best at the apex at end-expiration when the patient is in the left lateral decubitus position; the murmur increases after a Valsalva maneuver, exercise, squatting, and isometric handgrip.

  • Mildly symptomatic patients usually respond to diuretics and, if sinus tachycardia or AF is present, to β-blockers or Ca channel blockers for rate control.

  • Severely symptomatic patients and those with evidence of pulmonary hypertension require commissurotomy or valve replacement.

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