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1 Transthoracic echocardiogram; parasternal long axis view (left) and four chamber view (right).

View larger version (57K): [in this window] [in a new window] [PowerPoint Slide for Teaching]   Transthoracic echocardiogram, with colour Doppler (right). Ao=aorta, LA=left atrium, LV=left ventricle, MV=mitral valve, RA=right atrium, RV=right ventricle; arrow shows classic doming of mitral valve leaflet

2 Mitral stenosis.

3 Rheumatic fever with subsequent rheumatic heart disease.

Discussion
Rheumatic fever, and subsequent rheumatic heart disease, was once the most common cause of mitral valve disease in both the West and worldwide. Due to the increasing availability and use of antibiotics, together with improved housing and social conditions, the incidence of rheumatic heart disease has steadily declined in Western populations, with an estimated prevalence now of less than 1 per 100 000.^{1 2} But recent echocardiographic screening programmes estimate the prevalence at 21.5 per 1000 in Cambodia and 30.4 per 1000 in Mozambique,³ and worldwide an estimated 15.6 million people have rheumatic heart disease, with about 470 000 new cases and 233 000 deaths from rheumatic fever or rheumatic heart disease per year.⁴

Rheumatic mitral stenosis
The classic valvar involvement in rheumatic heart disease is mitral stenosis. Indeed, it is estimated that over 90% of patients with rheumatic heart disease have mitral stenosis. About 40% have isolated mitral stenosis, with the remainder having associated concomitant valvar involvement, including that of the aortic valve and the often overlooked tricuspid valve.⁵ Several autopsy studies have found aortic valve involvement in 45-65% of cases of rheumatic heart disease and tricuspid valve involvement in 22-44%.⁶ It is uncommon to find aortic disease in isolation from mitral disease and tricuspid involvement in isolation from both mitral and aortic disease.

The mitral valve normally has an area of 4-5 cm.⁷ It is an atrioventricular valve that communicates directly between the left atrium and the left ventricle. The rheumatic process leads to inflammation, resulting in valvar scarring, leaflet thickening, commissural fusion, and chordal shortening and fusion, and to a progressive reduction of the area of the valvar orifice.⁸ Although isolated rheumatic mitral stenosis is well tolerated, sequential narrowing of the valve orifice corresponds directly to a rise in left atrial pressure and dimensions. When the valve orifice is reduced to 2 cm², increased left atrial pressure becomes necessary for normal transmitral flow. Severe mitral stenosis is associated with a valvar area of less than 1 cm².

Presentation of rheumatic heart disease
As the severity of the valvar lesion increases, a rise in left atrial pressure becomes physiologically necessary to ensure normal cardiac output. This results in progressively raised pulmonary venous pressures. At a left atrial pressure greater than 18 mm Hg, pulmonary congestion occurs. Interstitial oedema results from a pressure greater than 25 mm Hg, and alveolar oedema from a pressure greater than 35 mm Hg.⁹ Oedema may be a relatively early presentation of mitral stenosis.

Atrial fibrillation may also develop—the risk is about 17 times that of the normal population,¹⁰ and it affects around 40% of people with rheumatic mitral valve disease.¹¹ Mitral stenosis must be considered in the differential diagnosis of aetiologies for atrial fibrillation. In Western populations, the important causes for atrial fibrillation are ischaemic heart disease, thyrotoxicosis, and excessive alcohol consumption.¹² In populations still exposed to rheumatic fever and consequent rheumatic heart disease, mitral stenosis is a common cause of atrial fibrillation. It is notoriously difficult to diagnose when allied with atrial fibrillation with a fast ventricular rate and, therefore, may be overlooked. When associated with a rapid ventricular response, atrial fibrillation may impair diastolic filling and, together with the loss of atrial contraction, lead to a decrease in cardiac output and a further increase in left atrial pressure. Atrial fibrillation carries an extremely high risk of thromboembolism, about 3-7 times that of solitary mitral stenosis,^{10 13} and needs rate reducing drugs such as digitalis and anticoagulation in the form of warfarin.

If left unchecked, the raised left atrial pressure results in pulmonary hypertension and the associated classic findings:

• Atrial fibrillation
  
• Raised jugular venous pressure (which may reflect right ventricle involvement, tricuspid stenosis, pulmonary hypertension)
  
• Tapping apex—palpable first heart sound (only with calcification of the anterior mitral valve leaflet)
  
• Opening snap—due to opening of the anterior mitral valve leaflet (the closer to the S2, the more severe the mitral stenosis)
  
• Mid-diastolic murmur.
  

Diagnosis and follow-up
The diagnosis of the condition relies on a detailed clinical examination being carried out and a thorough history having been taken, including symptoms of dyspnoea. History should be tailored to reflect symptoms, including dyspnoea and symptoms of right heart failure. The left ventricle is haemodynamically protected, and symptoms and signs of left ventricular failure should lead the clinician to suspect underlying disease.¹⁴

Once diagnosed, mitral stenosis requires follow-up with chest radiographs, electrocardiograms, and serial transthoracic echocardiography.¹⁵ Echocardiography is useful for gauging valvar dimensions, the pressure gradient across the mitral valve, and the concomitant rheumatic involvement of the aortic valve and of the tricuspid valve, which is often missed. In general, a valve area greater than 1.5 cm² represents mild mitral stenosis, an area between 1 cm² and 1.5 cm² moderate stenosis, and less than 1 cm² severe stenosis.^{15 16}

Surgical treatment
Once the symptoms and echo findings have progressed the patient may be referred for a closed balloon commisurotomy and eventually mitral valve replacement. According to American College of Cardiology/American Heart Association guidelines, percutaneous mitral balloon valvotomy is effective for patients with moderate or severe mitral stenosis and favourable morphology (mobile non-calcified leaflets, no commissural calcification, and little subvalvular fusion) in the presence either of symptoms (NYHA class II, III or IV) or of pulmonary hypertension, and in the absence of left atrial thrombus or moderate to severe mitral regurgitation.¹⁵ In contrast, mitral valve surgery (or repair if possible) is indicated in patients with moderate or severe mitral stenosis when

• Percutaneous mitral balloon valvotomy is not available
  
• Percutaneous mitral balloon valvotomy is contraindicated because of left atrial thrombus despite anticoagulation or because of concomitant moderate to severe mitral regurgitation
  
• The valve morphology is not favourable for percutaneous mitral balloon valvotomy in a patient with acceptable operative risk
  
• The patient is symptomatic and also has moderate to severe mitral regurgitation.¹⁵
  

Mitral stenosis in pregnancy
Mitral stenosis in pregnancy is associated with increased maternal morbidity and mortality.¹⁷ Once discovered, it calls for multidisciplinary team management involving specialists versed in both cardiac and obstetric care.

Cite this as: BMJ 2008;337:a3095