Mitral Valve Stenosis

What happens in mitral stenosis

The mitral valve has two leaflets that open to let oxygen-rich blood flow from the left atrium into the left ventricle, which pumps it to the body. In mitral stenosis the leaflets become thickened, stiff and partly fused, so the opening narrows.

To push blood through the narrowed valve, pressure in the left atrium rises. This pressure backs up into the lungs, causing fluid to leak into the air spaces and making breathing harder. Over time:

• the left atrium enlarges, which triggers atrial fibrillation
• blood pools in the enlarged atrium, so clots can form and travel to the brain
• pressure in the lung arteries rises (pulmonary hypertension), straining the right side of the heart

Anything that speeds the heart, such as exercise, fever, pregnancy or atrial fibrillation, shortens the time for blood to cross the valve and makes symptoms worse.

Causes

Rheumatic heart disease

Most mitral stenosis results from rheumatic fever, an immune reaction to an untreated strep throat infection, usually in childhood. The inflammation scars the valve, and stenosis develops slowly over 10 to 20 years or more. Rheumatic heart disease is now uncommon in the US and Western Europe but remains common in many low- and middle-income countries, and in people who grew up there. It affects women about twice as often as men.

Mitral annular calcification

In older adults, calcium can build up in the ring that supports the valve and extend into the leaflets. This degenerative form is increasingly common with age, kidney disease, diabetes and high blood pressure.

Rare causes

• Radiation to the chest
• Congenital mitral stenosis
• Lupus and rheumatoid arthritis
• Carcinoid heart disease
• A left atrial tumor (myxoma) blocking the valve, which mimics stenosis

Symptoms

Many people have no symptoms for years. When they appear, they often start during exertion, pregnancy or an illness, or with the onset of atrial fibrillation.

• Shortness of breath, first with exercise, later lying flat or waking at night breathless
• Fatigue and reduced exercise capacity
• Palpitations from atrial fibrillation
• Coughing up blood (hemoptysis), from burst small veins in the lungs
• Swollen ankles and an enlarged liver in advanced disease
• Hoarseness, rarely, from an enlarged atrium pressing on a nerve
• Flushed, purplish cheeks (mitral facies) in long-standing severe disease
• A stroke may be the first sign, from a clot formed in the atrium

How mitral stenosis is diagnosed

• Listening to the heart: a low-pitched rumbling murmur in mid-diastole, best heard at the apex, often with an "opening snap".
• Echocardiogram: the key test. It measures the valve area, the pressure gradient across the valve, and lung artery pressure, and assesses whether the valve is suitable for balloon treatment.
• Transesophageal echocardiogram: a probe in the esophagus gives a clearer view, and checks for clots in the left atrium before any procedure.
• ECG: may show atrial fibrillation or an enlarged left atrium.
• Chest X-ray: enlarged atrium and congestion in the lungs.
• Exercise testing when symptoms and echo findings do not match.

Stages of severity

Treatment

Medicines

Medicines do not widen the valve, but they relieve symptoms and prevent complications:

• Heart-rate slowing medicines such as beta-blockers or some calcium channel blockers, which give the atrium more time to empty
• Diuretics to reduce fluid in the lungs
• Anticoagulation for anyone with mitral stenosis and atrial fibrillation, a previous clot or stroke, or a clot in the atrium. Warfarin is recommended for rheumatic mitral stenosis; direct oral anticoagulants are not recommended for moderate or severe rheumatic mitral stenosis.
• Antibiotic prophylaxis against recurrent rheumatic fever (usually monthly penicillin injections for years) in people with rheumatic heart disease, according to age and time since the last episode

Balloon mitral valvotomy

For rheumatic mitral stenosis with suitable valve anatomy, a percutaneous balloon mitral commissurotomy is the preferred treatment. A catheter is passed from a vein in the groin, across the wall between the atria, and a balloon is inflated in the valve to split the fused leaflet edges. It typically doubles the valve area, with recovery in days. Results last many years, though the valve can narrow again.

It is not suitable if there is a clot in the left atrium, more than mild mitral regurgitation, or heavy calcification.

Surgery

• Mitral valve replacement with a mechanical or tissue valve when balloon treatment is not suitable or has failed. Mechanical valves need lifelong warfarin.
• Surgical commissurotomy (repairing the valve) in selected cases.
• Transcatheter options for calcific mitral stenosis are limited and being studied. Surgery for annular calcification is technically difficult, so treatment is often medical.

Mitral stenosis and pregnancy

Pregnancy increases blood volume and heart rate, so mitral stenosis that was silent can cause sudden breathlessness or pulmonary edema, often in the second or third trimester. Women with moderate or severe mitral stenosis should ideally have balloon valvotomy before pregnancy. During pregnancy, beta-blockers and diuretics are used carefully, and balloon valvotomy can be done if needed. Care should be with a cardio-obstetrics team.

Complications

• Atrial fibrillation
• Stroke and other clots
• Pulmonary hypertension and right heart failure
• Heart failure with pulmonary edema
• Infective endocarditis

Outlook

Mitral stenosis progresses slowly. People without symptoms may remain stable for years, but once symptoms appear, untreated severe disease worsens significantly over time. With timely balloon valvotomy or surgery, long-term survival improves substantially. Regular echocardiograms, typically every 1 to 5 years depending on severity, help time treatment.

Frequently asked questions

What is the most common cause of mitral stenosis?

Rheumatic heart disease, caused by rheumatic fever after untreated strep throat, is by far the most common cause worldwide. In older adults in high-income countries, calcium buildup in the valve ring is an increasingly common cause.

What are the symptoms of mitral stenosis?

The main symptoms are breathlessness on exertion or when lying flat, tiredness, palpitations from atrial fibrillation, and sometimes coughing up blood or ankle swelling. Many people have no symptoms until the narrowing is severe or something increases heart rate, such as pregnancy or an infection.

How is severe mitral stenosis treated?

If the valve anatomy is suitable, a balloon mitral valvotomy through a catheter is preferred. Otherwise, surgical valve replacement or repair is done. Medicines control heart rate and fluid, and anticoagulation prevents stroke in people with atrial fibrillation.

Can you live a long life with mitral stenosis?

Yes. Mild stenosis may not cause problems for decades. Severe stenosis with symptoms shortens life if untreated, but balloon valvotomy or valve replacement restores good function, and many people live for many years afterward with regular follow-up.

Why is mitral stenosis dangerous in pregnancy?

Pregnancy raises blood volume and heart rate, which increases pressure behind the narrowed valve. This can cause fluid in the lungs, atrial fibrillation and clots, especially in the second and third trimesters. Treating significant stenosis before pregnancy and specialist care during it reduce the risk.