The mitral valve serves to ensure one-way blood flow from the left atrium to left ventricle of
the heart. It opens when left atrial pressure is higher than left ventricular pressure, allowing
blood to fill the left ventricle; and closes when the ventricles contract, to prevent blood from
flowing back to the atrium. The mitral valve has 2 flaps, or leaflets, supported by a fibrous ring.
Mitral stenosis occurs when these leaflets thicken and become stiff,
causing the valve opening to narrow, reducing blood flow. As a result, blood volume and
pressure in the left atrium increases, and, over time, this may have several consequences.
First, the left atrium enlarges and becomes a risk factor for developing atrial fibrillation,
a condition in which the atria beat rapidly and irregularly. The atrium quivers rather than
contracts, and does not empty completely into the ventricle. Ineffective pumping causes the
blood to stagnate, facilitating the formation of blood clots. These clots may then pass into the
bloodstream, get stuck in small arteries and block them, resulting in stroke and other problems.
Second, because the left atrium receives blood from the lungs,
pulmonary pressure may increase, causing secondary pulmonary hypertension, which in turn, may lead to
right ventricular heart failure, as well as tricuspid or pulmonary valve regurgitation.
Mitral stenosis is most commonly caused by rheumatic fever, a complication of untreated strep
throat or scarlet fever during childhood. For this reason, it is most prevalent in developing
countries where rheumatic fever is more common. Rarely, mitral stenosis may develop with age,
as a result of accumulated calcium deposits on the valve. Mitral stenosis can also be congenital.
Symptoms progress slowly, over years or even decades, so patients may not be aware until atrial
fibrillation or heart failure develops. Symptoms may appear or worsen with increased heart rates,
such as during exercise or stress. Women may suddenly discover they
have the condition as they become pregnant. Mitral stenosis produces a characteristic heart
murmur that can be heard with a stethoscope. Diagnosis is confirmed with echocardiography,
which uses ultrasound to visualize cardiac structures and blood flow.
Echocardiography also helps determine the severity of the disease by measuring the mitral valve area.
ECG recordings and chest X-ray may show signs of left atrial enlargement.
Because most cases of mitral stenosis are caused by rheumatic fever,
prompt treatment of strep throat with antibiotics effectively
prevents both rheumatic fever and mitral stenosis. Treatment is not needed for asymptomatic patients.
Patients with mild symptoms may be treated with diuretics to reduce blood pressure; beta-blockers
or calcium channel blockers to control heart rates; and anticoagulants to prevent blood clots.
Valve repair or replacement surgery may be indicated for moderate to severe cases.
In percutaneous valvuloplasty, a catheter with a balloon is threaded through a vein and into
the heart. The balloon is inflated to widen the opening of the valve, then deflated and removed.
Patients with heavy calcification may require open heart surgery to repair the valve.
Valve replacement is considered when repair is not possible.
Artificial valves can be mechanical or bio-prosthetic. Mechanical valves last longer
but usually require life-long anticoagulation to prevent formation of blood clots.
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