Mitral Stenosis

Mitral stenosis is usually due to rheumatic fever, or, more rarely, degenerative calcification in the elderly. Rheumatic fever is triggered by a throat infection with Group A β-haemolytic streptococci, which causes immune damage to the valve 20-40 years later. It remains common in Africa, Asia and the Middle East. Mitral stenosis increases left atrial and pulmonary arterial pressure (especially in tachycardia). Static blood flow in the left atrium (worsened in atrial fibrillation) can cause thromboemboli.¹

The main symptom is progressive breathlessness. Pulmonary oedema can be triggered by the onset of atrial fibrillation. More rarely patients present with systemic emboli.

Clinical diagnosis is difficult. Signs include a loud first heart sound, an opening snap in early diastole and a mid-late diastolic murmur in the left lateral position (best heard with the bell of the stethoscope). Atrial fibrillation is often present.

• Chest Xray may show left atrial enlargement and interstitial oedema (if severe). ECG may reveal atrial fibrillation and left atrial enlargement. Echocardiography is essential to confirm diagnosis (leaflet thickening and restricted movement) and to assess severity.

• Pulmonary hypertension
• Dilated left atrium
• Thrombus
• Right heart failure.

• Most asymptomatic patients with mild or moderate MS are monitored with annual echocardiograms, advised to report symptoms and require prophylactic antibodies prior to dental surgery.
• Anticoagulation is given for atrial fibrillation (target INR is 2-3) or if the left atrium is enlarged.
• Cardioversion for recent atrial fibrillation (after 1 month of anticoagulants).
• β-blockers to reduce heart rate (and trans-mitral gradient) are especially useful during pregnancy, when clinical tolerance of mitral stenosis is poor.
• Diuretics for breathlessness.
• Percutaneous mitral commissurotomy (PMC) with a balloon gives good results in experienced centres in patients with mild symptoms; it can be used as a prophylactic measure (eg women with severe mitral stenosis who wish to become pregnant). It is effective even in severe disease in patients under 50 in sinus rhythm, but is contra-indicated with massive calcification, left atrial thrombus or associated mitral regurgitation. It is a safe procedure with a short hospital stay. Re-stenosis occurs gradually, but valve dilation delays the need for valve replacement by around 10 years.
• Mitral valve replacement is considered mainly for disabling symptoms when valves are unsuitable for balloon dilatation. Mortality is 5% in younger patients but is 10% in elderly patients with co-morbidities. Cardiac catheterization may be needed to assess coronary arteries prior to surgery.