Mitral regurgitation (mitral valve regurgitation, mitral incompetence, mitral insufficiency) is leakage of blood backward through the mitral valve each time the left ventricle contracts.
As the left ventricle pumps blood into the aorta, some blood leaks backward into the left atrium, increasing blood volume and pressure there. The increased blood pressure in the left atrium increases blood pressure in the veins leading from the lungs to the heart (pulmonary veins) and causes the left atrium to enlarge to accommodate the extra blood leaking back from the ventricle. An extremely enlarged atrium often beats rapidly in an irregular pattern (a disorder called atrial fibrillation—see Abnormal Heart Rhythms: Atrial Fibrillation and Atrial Flutter), which reduces the heart's pumping efficiency because the fibrillating atrium is quivering rather than pumping. Consequently, blood does not flow through the atrium briskly, and blood clots may form inside the chamber. If a clot breaks loose (becoming an embolus), it is pumped out of the heart and may block an artery, possibly causing a stroke or other damage.
Severe regurgitation can result in heart failure, in which increased pressure in the atrium causes fluid accumulation (congestion) in the lungs, or in which reduced forward flow of blood from the ventricle to the body deprives organs of the proper amount of blood. The left ventricle may gradually enlarge and weaken, further worsening heart failure.
Rheumatic fever (see Bacterial Infections in Infants and Children: Rheumatic Fever)—a childhood illness that sometimes occurs after untreated strep throat or scarlet fever—used to be the most common cause of mitral regurgitation. But today, rheumatic fever is rare in North America, Australasia, Western Europe, and other regions where antibiotics are widely used to treat infections such as strep throat. In these regions, rheumatic fever is a common cause of mitral regurgitation only among older people who did not have the benefit of antibiotics during their youth and among people who have moved from regions where antibiotics are not widely used. In such regions, rheumatic fever is still common and still commonly causes mitral stenosis or regurgitation, sometimes 10 years or more after the initial infection. Repeated attacks of rheumatic fever hasten valve deterioration.
In North America, Western Europe, and Australasia, a more common cause of mitral regurgitation is a heart attack. A heart attack can damage the structures that support the mitral valve. Another common cause is a sometimes hereditary weakness in the tissue of the valve (myxomatous degeneration). As a result, the heart valve gradually becomes floppy (prolapse), does not close properly, and may bulge into the left atrium when the ventricle contracts (mitral prolapse—see Heart Valve Disorders: Mitral Valve Prolapse (MVP)). Infective endocarditis may cause mitral regurgitation.
Mitral regurgitation may also occur when a previously replaced mitral valve fails.
Mild mitral regurgitation may not cause any symptoms. When regurgitation is more severe or when there is atrial fibrillation, people may have palpitations (an awareness that their heart beat has changed rhythm) or unexplained shortness of breath. People with heart failure may have cough, shortness of breath during exertion or at rest, and swelling in the legs.
Mitral regurgitation is usually diagnosed based on the characteristics of the heart murmur heard through a stethoscope. The murmur is a distinctive sound produced by blood leaking backward into the left atrium when the left ventricle contracts. The disorder is sometimes diagnosed when a doctor hears this murmur during a routine physical examination.
Electrocardiography (ECG) and chest x-rays show that the left ventricle is enlarged. If mitral regurgitation is severe, the chest x-ray may also show fluid accumulation in the lungs.
Echocardiography (see Diagnosis of Heart and Blood Vessel Disorders: Echocardiography and Other Ultrasound Procedures), which uses ultrasound waves to produce an image of the heart structures and blood flow, provides the most information. This procedure can show the size of the atrium and ventricle and the amount of blood leaking, so that the severity of the regurgitation can be determined.
Cardiac catheterization is often done when surgery is planned to repair or replace a mitral valve so that doctors can identify coronary artery disease that could also be treated during the heart surgery.
If regurgitation is mild, no specific treatment may be required. However, the person may need to be evaluated periodically.
When more serious regurgitation causes heart failure, people are given certain drugs for heart failure, such as spironolactone and carvedilol. People with atrial fibrillation are given anticoagulants such as warfarin.
Sometimes surgery is necessary for people with severe regurgitation.
Surgery must be done before the left ventricle becomes irreversibly weakened. Therefore, echocardiography is usually done periodically to determine how rapidly the left ventricle is enlarging. Surgery may involve repairing the valve or replacing it with an artificial (prosthetic) valve. Repairing the valve eliminates regurgitation or reduces it enough to make the symptoms tolerable and prevent damage to the heart. Repairing the valve is preferable to replacing it, if possible, because a repaired valve usually functions better than a mechanical or bioprosthetic valve and the person does not require lifetime anticoagulation therapy. Replacing the valve eliminates regurgitation.
Prosthetic heart valves are susceptible to serious infection by bacteria (infective endocarditis). People with an artificial valve should take antibiotics before surgical, dental, or medical procedures (see Which Procedures Require Preventive Antibiotics?*) to reduce the risk of an infection on a valve, even though this risk is small. Atrial fibrillation, if present, may require treatment (see Abnormal Heart Rhythms: Atrial Fibrillation and Atrial Flutter), including use of anticoagulants to prevent clots.
Last full review/revision March 2013 by Guy P. Armstrong