Mitral Valve Stenosis: A Narrowed Valve That Often First Appears in Pregnancy

What happens

The mitral valve is the door between the left atrium and the left ventricle. It should open widely so the ventricle fills easily. In mitral stenosis the leaflets are thickened and fused at their edges, leaving a narrow, funnel-shaped opening.

The ventricle beyond the valve is usually normal. The problem lies upstream: blood cannot get out of the left atrium quickly enough, so pressure builds behind the valve — in the atrium, then in the pulmonary veins, then in the lungs themselves.

That chain explains every symptom and every complication that follows.

The cause is nearly always rheumatic

Unlike most valve disease in older populations, mitral stenosis is overwhelmingly a consequence of rheumatic fever following an untreated streptococcal throat infection, often decades earlier in childhood. Many patients have no memory of the illness at all.

This is why the condition remains common in our region while it has become rare in countries where strep throat is reliably treated. The prevention story is set out in our article on rheumatic heart disease.

Symptoms and the classic triggers

The narrowing progresses slowly and the body adapts, so patients often remain well for many years. Symptoms then appear:

• Breathlessness on exertion, later when lying flat or waking at night;
• Fatigue and reduced exercise tolerance;
• Palpitations;
• Coughing blood, a feature relatively specific to mitral stenosis;
• Hoarseness or difficulty swallowing in advanced cases, when the enlarged atrium presses on neighbouring structures.

What is distinctive is how symptoms are triggered. Anything that speeds the heart or increases circulating volume gives the atrium less time to empty, and a previously stable patient can deteriorate quickly. The classic precipitants are pregnancy, atrial fibrillation, fever, anaemia and exertion.

Pregnancy deserves its own warning

Blood volume rises substantially in pregnancy and the heart rate increases. In a woman with unrecognised moderate or severe mitral stenosis, this can unmask the disease dramatically in the second or third trimester — and the first presentation may be acute pulmonary oedema in a woman who considered herself healthy.

A woman known to have mitral stenosis should be assessed before conceiving, not after. Where the valve is significantly narrowed, treating it beforehand is far safer than managing decompensation during pregnancy.

Atrial fibrillation and stroke

The left atrium enlarges under sustained pressure, and an enlarged atrium is prone to atrial fibrillation. Two things follow. Losing organised atrial contraction reduces filling further, so symptoms worsen abruptly. And blood stagnates in the fibrillating atrium, which can form clot.

The stroke risk in rheumatic mitral stenosis with atrial fibrillation is high, and anticoagulation in this setting means warfarin — the newer direct oral anticoagulants are not appropriate for rheumatic mitral stenosis. This is a genuinely important distinction that patients sometimes encounter when a doctor unfamiliar with the history offers a newer drug.

Diagnosis

A characteristic murmur may be heard, though it is easily missed. Echocardiography is definitive: it measures valve area and the pressure gradient, assesses pulmonary artery pressure, and — crucially for treatment — scores the valve's suitability for balloon treatment by grading leaflet thickening, mobility, calcification and disease of the structures beneath the valve. Transoesophageal echocardiography is performed before balloon treatment to exclude clot in the atrium.

Treatment

Medication

Diuretics relieve congestion and rate-controlling drugs give the atrium more filling time. Anticoagulation is used where indicated. None of this widens the valve.

Balloon mitral valvuloplasty

The treatment of choice where anatomy is favourable. A balloon-tipped catheter is passed to the valve and inflated to split the fused leaflets. No chest incision, rapid recovery, and excellent results in suitable valves. It is unsuitable where there is clot in the atrium, significant mitral regurgitation, or a heavily calcified, immobile valve.

Surgery

Open commissurotomy or, more often, valve replacement is used where ballooning is unsuitable or has failed. Since these patients are frequently young, the prosthesis choice — and its implications for anticoagulation and future pregnancy — deserves careful discussion; see mechanical or tissue valve.

Ongoing care

Continue penicillin prophylaxis if prescribed after rheumatic fever, maintain meticulous dental hygiene because of endocarditis risk, treat anaemia and fever promptly, and report any new palpitations.

Further reading

MedlinePlus: heart valve diseases and NHS: mitral valve problems.

On this site: valve surgery.

General education, not advice about your own valve. If you have known valve disease and are planning pregnancy, seek cardiology assessment beforehand.