Rheumatic mitral stenosis is one of the most common valvular heart diseases. It is caused by a hypersensitivity reaction (rheumatic fever) triggered by streptococcal infections affecting the oral cavity, skin, or urinary tract, which subsequently targets the heart valves. The mitral valve is the most frequently affected, followed by the aortic valve. Rheumatic involvement can affect a single valve or multiple valves simultaneously.
The incidence of rheumatic mitral stenosis is higher in women. Rheumatic fever occurring in childhood or adolescence typically manifests as clinical symptoms of mitral stenosis only after the age of 20–30 years.
Pathology
The two leaflets of the mitral valve adhere and fuse at their commissures, resulting in stenosis of the valve orifice. The leaflets become thickened, retracted, hardened, and calcified, restricting their movement and reducing the valve orifice area. If the subvalvular chordae tendineae and papillary muscles undergo fibrosis, fusion, and contraction, they may pull the leaflets downward, creating a funnel-like shape. Stiffened valve leaflets lose their ability to open and close properly.
Rheumatic mitral stenosis can be categorized into two types:
Membranous Stenosis
In this form, the anterior leaflet is less severely affected, with minimal movement restriction. The primary changes involve thickening and fusion at the commissures.
Funnel-Shaped Stenosis
Both the anterior and posterior leaflets are thickened, retracted, or calcified. The disease extends to the chordae tendineae and papillary muscles, pulling the leaflets downward. This results in a fish-mouth-shaped stenotic orifice, often accompanied by mitral regurgitation.
Pathophysiology
In healthy adults, the mitral valve orifice area is approximately 4–6 cm2, allowing 4–5 liters of blood to flow from the left atrium to the left ventricle during diastole each minute. When the orifice area is reduced to less than 1.5 cm2, blood flow becomes obstructed. A further reduction to less than 1 cm2 exacerbates the obstruction, leading to elevated left atrial pressure, left atrial enlargement, pulmonary vein congestion, and impaired gas exchange in the lungs. Exercise further elevates pulmonary capillary pressure, which is intensified when pressures exceed the normal plasma oncotic pressure of 30 mmHg, resulting in acute pulmonary edema.
In the early stages of the disease, acute pulmonary edema is more likely to occur. In later stages, prolonged pulmonary arteriolar spasm leads to thickening of the vascular walls, increased pulmonary arterial resistance, and significantly elevated pulmonary arterial pressure. Severe mitral stenosis increases right ventricular afterload, leading to right ventricular hypertrophy, dilation, and eventually right heart failure.
Clinical Manifestations
The clinical symptoms of mitral stenosis depend primarily on the severity of the narrowing. When the valve orifice area is approximately 2.5 cm2, auscultation reveals murmurs consistent with mitral stenosis, though patients may remain asymptomatic at rest. When the area decreases to less than 1.5 cm2, left atrial blood flow becomes impaired, chronic pulmonary congestion develops, and pulmonary compliance diminishes. This leads to symptoms such as dyspnea, cough, hemoptysis, and cyanosis.
Dyspnea is often exertional and varies in severity based on activity level. Situations such as intense exercise, emotional stress, respiratory infections, pregnancy, or atrial fibrillation may provoke orthopnea or acute pulmonary edema. Cough frequently occurs when pulmonary congestion worsens, such as following physical exertion or during sleep at night. Hemoptysis due to pulmonary congestion typically presents as blood-streaked sputum, while acute pulmonary edema may produce blood-tinged frothy sputum. In some cases, rupture of submucosal bronchial varices may cause massive hemoptysis. Palpitations, precordial discomfort, and fatigue are also frequently reported symptoms.
Physical Examination
Mitral facies, characterized by facial flushing and mild cyanosis of the lips, is often observed. Cardiac palpation may reveal a diastolic thrill at the apex and right ventricular heaving. Auscultation at the apex reveals a loud first heart sound, a diastolic rumbling murmur, and in cases where valve mobility is preserved, an opening snap (OS) can be heard at the left sternal border in the third or fourth intercostal space. Patients with pulmonary hypertension and right heart failure may exhibit accentuated or split second heart sound in the pulmonary valve area. Additional findings may include jugular vein distension, hepatomegaly, ascites, and edema of the lower extremities.
Auxiliary Examinations
Electrocardiography (ECG)
Findings often indicate right axis deviation, P-wave broadening, right ventricular hypertrophy with strain, and atrial fibrillation.
X-ray Examination
Mild cases frequently show no obvious abnormalities. Moderate or severe stenosis commonly demonstrates left atrial enlargement. Barium esophagography may reveal posterior compression of the esophagus by the left atrium. The right cardiac silhouette may show overlapping opacities of the left and right atria, forming a double atrial contour. Other findings include narrowing of the aortic knob, pulmonary artery segment prominence, left atrial bulging, and increased vascular markings in the pulmonary hilum. Interstitial pulmonary edema may present as horizontal linear opacities at the lower lung fields, known as Kerley B lines. Chronic pulmonary congestion can lead to dense, miliary, or reticular opacities due to hemosiderin deposition in lung tissue.
Echocardiography
Echocardiography provides the most effective method for evaluating the severity of the lesions. M-mode echocardiography reveals restricted valve leaflet motion, with the disappearance of the normal movement of the anterior leaflet, replaced by a rectangular "wall-like" motion pattern. The anterior and posterior leaflets display parallel motion. Left atrial anteroposterior diameter is increased. Two-dimensional or cross-sectional echocardiography can directly show thickened, deformed mitral valve leaflets; abnormal movement; a narrowed valve orifice; and left atrial enlargement. It may also assess the presence of left atrial thrombi, valve calcification, and pulmonary artery pressure.
Diagnosis
The diagnosis is established based on patient history, physical findings, and findings from X-ray, ECG, and echocardiographic examinations. Coronary angiography is recommended for suspected coexisting coronary artery disease.
Treatment
The goal of surgical treatment is to increase the mitral valve orifice area, resolve left atrial outflow obstruction, alleviate symptoms, and improve cardiac function.
Indications for Surgery
Surgery is generally not recommended for asymptomatic patients or those with New York Heart Association (NYHA) Class I cardiac function. Symptomatic patients with NYHA Class II or higher should undergo surgical intervention. Patients with membranous-type mitral stenosis, especially those with good leaflet mobility, no calcification, crisp first heart sound at the apex, and an audible opening snap, without atrial fibrillation or left atrial thrombi, are candidates for percutaneous balloon mitral valvuloplasty (PBMV) or closed mitral commissurotomy under general anesthesia. In cases with mitral stenosis and regurgitation, significant aortic valve disease, atrial fibrillation, funnel-shaped stenosis, severe leaflet disease, calcification, or left atrial thrombi, PBMV and closed mitral commissurotomy are not suitable, and open mitral valve replacement with cardiopulmonary bypass (CPB) is advised. Concomitant Maze surgery for atrial fibrillation may be performed during valve surgery.
Surgical Techniques
PBMV is described in the context of internal medicine. The techniques for closed and open mitral valve surgery are outlined below.
Closed Mitral Commissurotomy
This procedure involves a left posterolateral or left anterolateral thoracotomy. Through a left atrial appendage incision, the mitral valve leaflets and orifice are examined. A mitral valve dilator is inserted into the left ventricle through the apex and sequentially expanded across the valve orifice. The widespread use of PBMV has significantly reduced the frequency of closed commissurotomy.
Open Surgical Procedure
This approach requires cardiopulmonary bypass and typically involves a median sternotomy. The left atrium is accessed through an incision along the atrioventricular groove or by incising the interatrial septum through the right atrium. The mitral valve is exposed, and in cases of mild leaflet disease, fused commissures are incised, and the orifice is enlarged by separating fused chordae tendineae and papillary muscles to restore leaflet mobility. In cases of severe valve disease, characterized by extensive fibrosis, sclerosis, contraction, or calcification, partial or complete valve replacement with a prosthetic valve is necessary.