Heart Valve Disorders
The heart has four chambers—two small upper chambers (atria) and two larger lower chambers (ventricles). Each chamber is closed by a one-way valve. For various reasons these valves can malfunction, causing leakage (regurgitation) or failure to open properly (stenosis). The mitral valve, which allows blood to ﬂow from the left atrium to the left ventricle (the main pumping chamber of the heart), and the aortic valve, which allows blood to ﬂow from the left ventricle to the aorta (the main artery of the body), are the most common sites for valve dis- ease. These valves are under great strain from the powerful contractions of the left ventricle, which pumps blood throughout most of the body.
Mitral Valve Prolapse
Mitral valve prolapse is the most common valve disorder. Usually it is an inher- ited structural defect. The two parts, or leaﬂets, of the mitral valve thicken, pre- venting them from coming together properly. The leaﬂets bulge back into the left atrium as the ventricle contracts, allowing small amounts of blood to leak back into the atrium. Prolapse is a term that means slippage out of position; in this case the valve leaﬂets have difﬁculty being in their correct position because they are too thick.
Most people with mitral valve prolapse experience no symptoms. Others may have a wide range of symptoms—such as chest pain, palpitations (an awareness of one’s heartbeat), migraine headaches, dizziness, and fatigue—that cannot be explained by the valve problem alone.
Physicians diagnose mitral valve prolapse by using a stethoscope to listen to the characteristic clicking sound produced by the valves as they hit against one another. The condition also produces a heart murmur, or slight rushing sound, that the physician hears through the stethoscope when the heart contracts. Echocardiography (an ultrasound examination of the heart) allows a doctor to view the prolapse and determine its severity.
Most people with mitral valve prolapse do not need treatment. When symp- toms such as extra heartbeats, a rapid heartbeat, or chest pain become bother- some, medications are prescribed to control them. In rare cases, when leakage becomes severe, surgical repair or valve replacement may be required. People with mitral valve prolapse are usually given antibiotics before dental or surgical procedures to decrease the risk that bloodborne bacteria will infect the heart valve.
Mitral Valve Regurgitation
Mitral valve regurgitation, also called mitral incompetence or mitral insufﬁ- ciency, is leakage of blood back through the mitral valve into the left atrium each time the left ventricle contracts. This increases the volume and pressure in the
left atrium, which, in turn, increases blood pressure in the vessels leading from the lungs to the heart. This results in lung congestion (ﬂuid buildup).
In the past, rheumatic fever was the most common cause of this condition. But with the advent of antibiotics, rheumatic fever is now rare in the United States, and the few cases that are seen are primarily in older people who had rheumatic fever in childhood. A more common cause of mitral valve regurgitation today is a heart attack, which can damage the supporting structures of the mitral valve.
Mild cases of mitral valve regurgitation may not cause any symptoms. The condition may be recognized during a routine chest examination with a stetho- scope, when a doctor hears a distinctive heart murmur caused by the blood leak- ing back into the left atrium when the left ventricle contracts. Diagnosis usually is conﬁrmed by electrocardiography (ECG; an examination of the electrical activity of the heart) and chest X rays that indicate the left ventricle is enlarged. Echocardiography (an ultrasound examination of the heart) can produce an image of the faulty valve and indicate the severity of the problem.
Since the left ventricle has to pump more blood to make up for the blood leak- ing back into the atrium, it gradually enlarges to increase the force of each heart- beat. The enlarged ventricle may cause palpitations (awareness of one’s heartbeat), which is particularly noticeable when the person lies on his left side.
The left atrium also tends to enlarge to accommodate the extra blood leaking back from the ventricle. A very enlarged atrium often beats rapidly in an irregu- lar fashion (atrial ﬁbrillation). This reduces the heart’s pumping efﬁciency, and the lack of proper blood ﬂow through the atrium allows blood clots to form. If a clot becomes detached, it may be pumped out of the heart and block a smaller artery elsewhere in the body, possibly causing a stroke or other damage. Finally, severe regurgitation reduces the forward ﬂow of blood, causing heart failure, which may lead to coughing, swollen legs, or shortness of breath on exertion.
Treatment for this condition can take several forms. Repairing the valve can either eliminate or reduce the regurgitation enough to make the symptoms toler- able and prevent heart damage. Atrial ﬁbrillation accompanying mitral valve regurgitation is usually treated with medications that slow the heart rate and help control the ﬁbrillation. In severe cases, the valve may be replaced surgically.
Mitral Valve Stenosis
Mitral valve stenosis is a narrowing of the mitral valve opening that increases resistance to blood ﬂow from the left atrium to the left ventricle. This resistance causes pressure to build up in the atrium; the pressure then backs up through the veins of the lungs, causing increased pressure and congestion in the lungs. The increased stress on the lungs can lead to shortness of breath and eventually to congestive heart failure. Typically, the valve leaﬂets fuse together. Surgery is needed to widen or replace the valve.
Mitral valve stenosis is almost always the result of rheumatic fever, which is
rare today in the United States, where most cases occur in older people who had rheumatic fever during childhood. However, rheumatic fever can sometimes occur after an untreated “strep” throat infection (infection with streptococcal bacteria). Mitral valve stenosis also can be congenital (present from birth). Infants born with this condition rarely live beyond age 2 unless they have sur- gery to correct the condition.
If stenosis is severe, blood pressure increases in the left atrium and in the veins in the lungs, resulting in heart failure and an accumulation of ﬂuid in the lungs (pulmonary edema). A person with heart failure easily becomes fatigued and short of breath. At ﬁrst, shortness of breath may occur only during physical activity. Later the symptoms may occur even during rest. Some people ﬁnd that they can breathe comfortably only when they are propped up with pillows or sit- ting upright.
Some people with mitral valve stenosis have a plum-colored ﬂush in their cheeks. High blood pressure in the veins of the lungs may cause a small vein or tiny capillaries to burst and bleed slightly or massively into the lungs. Enlarge- ment of the left atrium can result in atrial f ibrillation (an abnormally fast heartbeat).
To diagnose mitral valve stenosis, a physician uses a stethoscope to listen for a characteristic heart murmur as blood rushes through the narrowed valve from the left atrium. Unlike a normal valve, which opens silently, a valve affected by mitral valve stenosis often makes a snapping sound as it opens to allow blood into the left ventricle. The diagnosis of mitral valve stenosis is usu- ally conﬁrmed by electrocardiography (ECG; an examination of the electrical activity of the heart), a chest X ray showing an enlarged atrium, or echocardio- graphy (an ultrasound examination of the heart). Sometimes cardiac catheteri- zation (a diagnostic test in which a thin, ﬂexible tube is inserted into the heart through a blood vessel, to examine the heart) is performed to determine the extent and characteristics of the valve blockage.
Treatment for mitral valve stenosis may include a variety of drugs. Beta- blockers, digoxin, and verapamil are used to slow the heart rate and control atrial ﬁbrillation. Digoxin also strengthens the heartbeat if heart failure occurs. Diuret- ics are often prescribed to reduce the blood pressure in the lungs by reducing the volume of circulating blood.
If medication does not reduce the symptoms adequately, surgical valve repair or replacement may be needed. People with mitral valve stenosis are given antibiotics before dental and surgical procedures to reduce the risk of a heart valve infection.