Mitral Stenosis

Mitral stenosis is a valvular heart disease characterized by a narrowing of the mitral orifice, located between the left atrium and left ventricle, which impedes the normal blood flow during diastole. The resulting flow reduction leads to a progressive increase in left atrial pressure and a cascade of upstream hemodynamic changes involving the pulmonary circulation and the right heart. The disease typically presents with exertional dyspnea, peripheral edema, and signs of pulmonary or systemic congestion in advanced stages.

Etiology, Pathogenesis, and Pathophysiology

The most frequent cause of mitral stenosis is rheumatic fever, accounting for over 90% of cases worldwide. Rheumatic valvular disease results from an autoimmune response triggered by infection with Streptococcus pyogenes, leading to progressive damage of the valve leaflets, chordae tendineae, and commissures. Chronic inflammatory processes cause thickening, fibrosis, retraction, and fusion of valvular structures, with loss of normal leaflet mobility and reduction of the functional mitral orifice area.

Less common causes include:

• Congenital mitral stenosis, rare and often associated with other cardiac malformations;
• Degenerative calcifications of the mitral annulus, typical of advanced age, with progressive non-inflammatory narrowing and absence of commissural fusion;
• Intracavitary masses (e.g., atrial myxomas, thrombi, infective vegetations, neoplasms) causing functional mechanical obstruction;
• Prosthetic mitral valve dysfunction due to degeneration, thrombosis, or pannus formation.

Under physiological conditions, the mitral valve area ranges between 4 and 6 cm². A progressive reduction leads to an increased pressure gradient between the left atrium and ventricle. Hemodynamic changes occur below 2.5 cm²; the stenosis is considered hemodynamically significant below 1.5 cm², and severe below 1 cm².

The first compensatory mechanism is the increase in left atrial pressure to maintain ventricular filling. This elevated pressure is transmitted backward, causing pulmonary vein congestion, increased capillary pressure, and transudation of fluid into the interstitial and alveolar spaces, leading to pulmonary edema. Clinically, this results in progressive dyspnea, orthopnea, bendopnea, and in severe cases, acute pulmonary edema.

Pulmonary venous hypertension may activate collateral circulation via bronchial veins, which can rupture under pressure, causing hemoptysis. Chronic hypoxia and wall stress trigger a reactive vascular response with vasoconstriction and remodeling of pulmonary arteries (medial hypertrophy, intimal fibrosis), ultimately leading to fixed, irreversible pulmonary hypertension.

Progressive pulmonary hypertension imposes a chronic pressure overload on the right ventricle, which initially compensates via hypertrophy, but later dilates and progresses to right heart failure. Backward pressure extends to the vena cavae and right atrium, resulting in systemic congestion: jugular vein distension, peripheral edema, ascites, congestive hepatomegaly.

The left ventricular systolic function is generally preserved, but may decline due to chronic underfilling or associated conditions such as ischemic heart disease. Moreover, left atrial enlargement promotes intracavitary thrombus formation and constitutes a substrate for atrial fibrillation, which develops in 60–70% of patients. This arrhythmia leads to loss of atrial systole, increased heart rate, and a sudden hemodynamic deterioration.

Clinical Manifestations

Symptoms of mitral stenosis develop gradually, often years after the initial rheumatic infection. Early signs include exertional dyspnea, fatigue, palpitations, and easy fatigability. As stenosis worsens, patients experience rest dyspnea, orthopnea, bendopnea, and pulmonary edema. Hemoptysis may result from ruptured bronchial veins or pulmonary embolism, while hoarseness (Ortner’s syndrome) arises from compression of the recurrent laryngeal nerve by a dilated left atrium.

Other symptoms are due to complications: ischemic stroke and peripheral embolism from atrial thrombi, right heart failure symptoms (edema, ascites), syncope (due to hypotension in tachyarrhythmia). Palpitations are often related to supraventricular tachycardia, especially atrial fibrillation, which drastically impairs exercise tolerance.

On auscultation, an opening snap is heard just after the second heart sound, best at the apex in left lateral decubitus. This is followed by a low-pitched diastolic rumble that intensifies presystolically in sinus rhythm. The first heart sound is generally accentuated, but may be soft in advanced calcified cases. A diastolic thrill may be palpable at the apex.

The presence of a split second heart sound reflects pulmonary hypertension. In patients with right heart failure, clinical signs include sustained right parasternal impulse, jugular distension, hepatomegaly, ascites, and peripheral edema. The classic finding in advanced disease is the mitral facies: reddish-cyanotic cheeks with peripheral cyanosis and vasoconstriction.

Diagnosis

The electrocardiogram may show left atrial enlargement (bifid P waves in lead II), right ventricular hypertrophy (positive QRS in V1, right axis deviation), and frequently atrial fibrillation. Sinus rhythm suggests early-stage disease.

The chest X-ray reveals a triangular cardiac silhouette with double right atrial contour and straightening of the middle cardiac border (left atrial dilation). In lateral view, posterior displacement of the esophagus may be seen. Pulmonary signs include apical venous redistribution (>15 mmHg), Kerley B lines (interstitial edema, >20 mmHg), and butterfly-pattern alveolar edema (>30 mmHg).

Transthoracic echocardiography with Doppler is the diagnostic gold standard. It assesses valve anatomy (“hockey stick” anterior leaflet), leaflet mobility, calcifications, and estimates mitral valve area and mean transvalvular gradient.

For anatomic-functional evaluation, the Wilkins score is used, grading: leaflet thickening, mobility, calcification, and subvalvular involvement, each from 1 to 4. A total score ≤8 indicates suitability for percutaneous balloon mitral valvotomy (PBMV); >10 suggests a rigid, calcified valve, favoring surgical replacement.

Echocardiographic classification of severity:

• Mild: area >1.5 cm², mean gradient <5 mmHg
• Moderate: area 1–1.5 cm², gradient 5–10 mmHg
• Severe: area <1 cm², gradient >10 mmHg

Stress echocardiography (exercise or dobutamine) may be used in moderate cases with disproportionate symptoms to assess exercise-induced pulmonary hypertension and guide earlier intervention.

Cardiac catheterization is indicated when echocardiographic findings are inconclusive or for preoperative assessment. It allows direct measurement of transvalvular gradients and evaluation of pulmonary and coronary pressures.

Treatment

Mitral stenosis treatment includes both medical and interventional approaches aimed at symptom relief, prevention of complications, and correction of the mechanical obstruction. All patients should receive endocarditis prophylaxis and regular echocardiographic monitoring.

Medical therapy is palliative in early stages or for non-candidates for valve repair, and includes:

• Beta-blockers or non-dihydropyridine calcium channel blockers to lower heart rate and prolong diastole;
• Diuretics to manage pulmonary and systemic congestion;
• Digitalis and antiarrhythmics in the presence of atrial fibrillation;
• Oral anticoagulants (VKAs or DOACs, if appropriate) for embolic prevention in AF or visible atrial thrombi.

Percutaneous balloon mitral valvotomy (PBMV) is the treatment of choice for patients with severe, symptomatic mitral stenosis and favorable valve anatomy (Wilkins ≤8), in the absence of left atrial thrombi or moderate-to-severe mitral regurgitation. Contraindications include:

• Left atrial thrombi;
• Significant mitral regurgitation;
• Extensive calcification or severe subvalvular fusion;
• Active endocarditis.

Surgical commissurotomy is an option for patients not eligible for PBMV but with repairable valves. Mitral valve replacement (mechanical or bioprosthetic) is indicated in advanced cases with unfavorable valve morphology or failed conservative procedures.

Prognosis and Follow-up

The prognosis of mitral stenosis depends on stenosis severity, pulmonary hypertension, and presence of atrial fibrillation. Without treatment, 10-year survival after symptom onset is under 15%, especially with systemic embolism or heart failure.

Follow-up includes:

• Annual echocardiogram in severe cases or symptomatic patients; every 2–3 years in moderate cases;
• Rhythm monitoring (Holter or serial ECGs) for atrial fibrillation detection;
• INR control for patients on VKAs;
• Multidisciplinary evaluation at specialized centers for PBMV or surgical indication.

Complications

The main complications of mitral stenosis include:

• Atrial fibrillation, with loss of atrial systole, tachycardia, and reduced cardiac output;
• Atrial thrombi and systemic embolism (stroke, acute limb ischemia);
• Acute pulmonary edema in decompensated patients;
• Fixed pulmonary hypertension with irreversible right heart failure;
• Massive hemoptysis from rupture of congested bronchial veins;
• Valvular infections (endocarditis) in non-prophylaxed individuals.

Timely and appropriate treatment can prevent most of these complications and significantly improve both quality of life and life expectancy in affected patients.

References
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