Section 3. Heart and Blood Vessel Disorders

Chapter 28. Heart Valve Disorders

Topics: Introduction | Mitral Regurgitation | Mitral Valve Prolapse | Mitral Stenosis | Aortic Regurgitation | Aortic Stenosis | Tricuspid Regurgitation | Tricuspid Stenosis | Pulmonary Stenosis

Mitral Regurgitation

Mitral regurgitation (mitral valve regurgitation, mitral incompetence, mitral insufficiency) is leakage of blood backward through the mitral valve each time the left ventricle contracts.

See the animation Understanding Mitral Valve Regurgitation.

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). If regurgitation is severe, the increased pressure may result in fluid accumulation (congestion) in the lungs.

Rheumatic fever (see Section 23, Chapter 272)--a childhood illness that sometimes occurs after untreated strep throat--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 prevent 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. However, in regions in which antibiotics are not widely used, rheumatic fever is still common and still commonly causes mitral stenosis or regurgitation among all age groups.

In North America, Western Europe, and Australasia, a more common cause of mitral regurgitation is a heart attack, which can damage the supporting structures of the mitral valve. Another common cause is myxomatous degeneration, a hereditary connective tissue disorder that causes a jellylike deterioration of tissue. As a result, the heart valve gradually becomes floppy; rarely, the valve tears.

Symptoms

Mild mitral regurgitation may not produce any symptoms. When regurgitation is more severe, people, particularly when lying on their left side, may have palpitations; that is, they become aware of their heartbeats, which are more forceful. Heartbeats are more forceful because the left ventricle has to pump more blood, to compensate for the leakage back into the left atrium. The left ventricle gradually enlarges and thickens to increase the force of each heartbeat.

Similarly, the left atrium also tends to enlarge because it must accommodate the extra blood leaking back from the ventricle. A very enlarged atrium often beats rapidly in an irregular pattern (a disorder called atrial fibrillation), which reduces the heart's pumping efficiency. A fibrillating atrium is just quivering, not pumping. Consequently, blood does not flow through it normally, allowing blood clots to form. 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.

If regurgitation is severe, the forward flow of blood is reduced enough to cause heart failure, which may produce coughing, shortness of breath during exertion, and swelling in the legs.

Diagnosis

Mitral regurgitation is usually diagnosed based on the characteristic 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 doctors hear 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. The most informative procedure is echocardiography (see Section 3, Chapter 21), which uses ultrasound waves to produce an image of the faulty valve. 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.

Treatment

Atrial fibrillation, if present, may require treatment (see Section 3, Chapter 27), including use of anticoagulants to prevent clots.

If regurgitation is mild, mild heart failure can be treated with an angiotensin-converting inhibitor (ACE inhibitor), such as enalapril or lisinopril, with or without digoxin. However, in people with moderate regurgitation, surgery increases the chance of a good outcome and reduces the risk of worsening heart failure.

If regurgitation is severe, surgery is needed. Surgery must be performed before the left ventricle becomes so abnormal that the problem cannot be corrected. So, echocardiography is usually performed periodically to determine how rapidly the left ventricle is enlarging. Surgery may involve repairing the valve (valvuloplasty) 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. Replacing the valve eliminates regurgitation. The damaged valve can be replaced with a mechanical valve or a biologic one made partly from a pig's valve. Each type has advantages and disadvantages. Mechanical valves are usually effective and last a long time. However, they increase the risk of blood clots, so anticoagulants are usually taken indefinitely to reduce this risk. Biologic valves are effective and do not pose a risk of blood clots, but they do not last as long as mechanical valves. If an artificial valve malfunctions, it must be replaced immediately.

See the figure Replacing a Heart Valve.

Damaged heart valves are susceptible to a serious infection by bacteria (infective endocarditis). People with a damaged or an artificial valve should take antibiotics before surgical, dental, or medical procedures (see Section 3, Chapter 29) to reduce the risk of an infection on a valve, even though this risk is small.