Mitral Stenosis
Mitral stenosis is a narrowing of the mitral valve, the valve between the left atrium and the left ventricle. The narrowed valve obstructs blood flow into the ventricle, raising the pressure in the left atrium, the lungs, and the right side of the heart. Untreated, severe mitral stenosis leads to atrial fibrillation, breathlessness, and right heart failure.
What causes mitral stenosis?
- Rheumatic heart disease — the most common cause worldwide, though now uncommon in the UK. Rheumatic mitral stenosis develops decades after a streptococcal infection in childhood or young adulthood.
- Calcific (degenerative) mitral stenosis — increasingly recognised in older patients, particularly those with chronic kidney disease, diabetes, or previous radiotherapy. Heavy calcification of the mitral annulus extends onto the leaflets and stiffens the valve.
- Congenital mitral stenosis — rare, usually presenting in childhood or early adulthood.
What are the symptoms?
Mild and moderate mitral stenosis rarely cause symptoms. As the narrowing becomes severe, patients may develop:
- Breathlessness on exertion (the most common first symptom)
- Fatigue and reduced exercise tolerance
- Palpitations, often from atrial fibrillation
- Coughing, sometimes with blood (haemoptysis), reflecting raised pulmonary pressures
- Right-sided heart failure with ankle swelling, abdominal swelling, and liver congestion
Atrial fibrillation is very common in mitral stenosis and substantially increases the risk of stroke; anticoagulation is recommended even when stenosis is moderate.
How is mitral stenosis assessed?
The diagnosis is made on echocardiography. The tests build a picture of how narrow the valve is, how the heart is coping, and whether intervention is appropriate.
- Electrocardiogram (ECG) — looks for atrial fibrillation and signs of right heart strain.
- Transthoracic echocardiogram (TTE) — the principal test. Measures the valve area and pressure gradient, and assesses the leaflets, the rest of the heart, and the pulmonary pressures. Mitral stenosis is graded mild, moderate or severe.
- Transoesophageal echocardiogram (TOE) — high-resolution images of the valve, used to score the leaflets for suitability for balloon valvuloplasty and to exclude clot in the left atrial appendage before any intervention.
- Cardiac MRI — selectively used, particularly when right heart function or pulmonary pressures need detailed quantification.
- Cardiac CT — used for procedural planning, particularly to assess heavy calcification.
- Stress echocardiography — useful in patients whose symptoms seem disproportionate to the resting findings.
- Blood tests — full blood count, kidney function, thyroid function (a contributor to AF).
What are the treatment options?
Mild and moderate mitral stenosis are managed with medication and observation, alongside management of atrial fibrillation and stroke prevention where relevant. Once stenosis becomes severe, with symptoms or rising pulmonary pressures, intervention is considered.
- Balloon mitral valvuloplasty — a transcatheter procedure in which a balloon is passed up to the mitral valve and inflated to split the fused leaflet edges. Most appropriate for rheumatic mitral stenosis with suitable leaflet anatomy on TOE scoring.
- Surgical mitral valve replacement — open-heart valve replacement with a tissue or mechanical valve. The mainstay of treatment for calcific mitral stenosis and for rheumatic disease where the leaflets are not suitable for valvuloplasty.
- Transcatheter mitral valve replacement (TMVR) — a transcatheter alternative for selected patients with calcific mitral stenosis at high surgical risk, anchoring a new valve within the heavily calcified annulus (valve-in-MAC).
- Medical therapy alone — for mild or moderate disease, or for patients in whom intervention is not appropriate.
The decision is always made in a structural valve multidisciplinary team meeting.