(See also Overview of Cardiac Valvular Disorders.)
In mitral stenosis, 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, 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, mitral stenosis is congenital. If the valve cannot close completely, mitral regurgitation (MR) may coexist with mitral stenosis. Patients with mitral stenosis 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 mitral stenosis; pulmonary venous and capillary pressures also increase and may cause secondary pulmonary hypertension, leading to right ventricular (RV) heart failure, tricuspid regurgitation, 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 of mitral stenosis 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).
Symptoms typically do not appear until 15 to 40 years after an episode of rheumatic fever. 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 atrial fibrillation 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 and RV failure may also occur.
Mitral stenosis may cause signs of cor pulmonale. The classic facial appearance in mitral stenosis, 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 mitral stenosis are those of an embolic event such as stroke. Endocarditis is rare in mitral stenosis unless mitral regurgitation is also present.
Palpation may detect palpable 1st and 2nd heart sounds (S1 and S2). S1 is best palpated at the apex, and S2 at the upper left sternal border. The pulmonic component of S2 (P2) 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 in mitral stenosis include a loud S1 caused by the leaflets of a stenotic mitral valve closing abruptly (M1); it is heard best at the apex. S1 may be absent when the valve is heavily calcified and immobile. A normally split S2 with an exaggerated P2 due to pulmonary hypertension is also heard (see table Distinguishing the Murmurs of Tricuspid Stenosis and Mitral Stenosis).
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 S2 (increasing duration of the murmur) as mitral stenosis 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.
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
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
Mid-diastolic murmur of obstructing left atrial myxoma or ball thrombus (rare)
Distinguishing the Murmurs of Tricuspid Stenosis and Mitral Stenosis
Diagnosis of mitral stenosis is suspected clinically and confirmed by echocardiography. Typically, 2-dimensional echocardiography shows abnormal valve and subvalvular 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 cm2.
Severity of mitral stenosis is characterized echocardiographically as
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 V1; broad, notched P waves in lead II; or both. Right axis QRS deviation and tall R waves in V1 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.
The natural history of mitral stenosis varies, but the interval between onset of symptoms and severe disability is about 7 to 9 years. Outcome is affected by the patient’s preprocedural age and functional status, pulmonary hypertension, and degree of mitral regurgitation. 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 atrial fibrillation and pulmonary hypertension. Cause of death is most commonly heart failure or pulmonary or cerebrovascular embolism.
Asymptomatic patients with mitral stenosis 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 beta-blockers or calcium channel blockers, which can control ventricular rate.
Anticoagulation with a vitamin K antagonist (not a direct-acting oral anticoagulant [DOAC]) is 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).
For moderate mitral stenosis, intervention may be indicated when there is ≥ 1 of the following:
For severe mitral stenosis, intervention is indicated when there is ≥ 1 of the following:
For very severe mitral stenosis, intervention is indicated for all patients (with or without symptoms) who are suitable candidates for percutaneous balloon commissurotomy.
Percutaneous balloon commissurotomy is the procedure of choice for younger patients and for patients without heavily calcified valve commissures, subvalvular distortion, LA thrombi, or severe 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.
Surgical commissurotomy may be used in patients with severe subvalvular disease, valvular calcification, or LA thrombi. In this procedure, fused mitral valve leaflets are separated using a dilator passed through the left ventricle (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 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. Lifelong anticoagulation with warfarin is required in patients with a mechanical valve to prevent thromboembolism. A mitral bioprosthetic valve requires anticoagulation with warfarin for 3 to 6 months postoperatively (see also Anticoagulation for patients with a prosthetic cardiac valve). Direct-acting oral anticoagulants (DOAC) are ineffective and should not be used.
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. Preliminary experience in inoperable patients suggests benefit from transcatheter implantation of a transcatheter aortic valve replacement (TAVR) bioprosthesis in the mitral position.
Mitral stenosis is almost always caused by rheumatic fever.
Pulmonary hypertension and atrial fibrillation (with consequent thromboembolism) may develop.
Heart sounds include a loud S1 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 atrial fibrillation is present, to beta-blockers or calcium channel blockers for rate control.
Severely symptomatic patients and those with evidence of pulmonary hypertension require commissurotomy or valve replacement.