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Overview of Heart Valve Disorders

by Guy P. Armstrong, MD

Heart valves regulate the flow of blood through the heart's four chambers—two small, round upper chambers (atria) and two larger, cone-shaped lower chambers (ventricles—see see ). Each ventricle has a one-way "in" (inlet) valve and a one-way "out" (outlet) valve. In the right ventricle, the inlet valve is the tricuspid valve, which opens from the right atrium, and the outlet valve is the pulmonary (pulmonic) valve, which opens into the pulmonary artery. In the left ventricle, the inlet valve is the mitral valve, which opens from the left atrium, and the outlet valve is the aortic valve, which opens into the aorta. Each valve consists of flaps (cusps or leaflets) that open and close like one-way swinging doors.

The heart valves can malfunction either by leaking (termed regurgitation) or by not opening adequately and thus partially blocking the flow of blood through the valve (termed stenosis). Either problem can greatly interfere with the heart's ability to pump blood. Sometimes a valve has both problems.

Faulty valves generally create murmurs and other abnormal heart sounds that a doctor can hear with a stethoscope. Faulty valves can be identified by using echocardiography. Often, minor degrees of regurgitation are not detected with a stethoscope but are detected during echocardiography. Doctors often regard this as a normal finding.

A faulty valve may be repaired or replaced. Repair may require surgery but may sometimes be accomplished during heart catheterization (see Cardiac Catheterization and Coronary Angiography), particularly when the problem is a valve with stenosis. A stenotic valve can sometimes be stretched open using a procedure called balloon valvuloplasty. In this procedure, a balloon-tipped catheter is threaded through a vein and eventually into the heart. Once inside the faulty valve, the balloon is inflated, separating the valve cusps. This procedure does not require a general anesthetic and allows a quick recovery.

Understanding Stenosis and Regurgitation

The heart valves can malfunction either by leaking (causing regurgitation) or by not opening adequately and thus partially blocking the flow of blood through the valve (causing stenosis). Stenosis and regurgitation can affect any of the heart valves. These two disorders are shown below affecting the mitral valve.

Normally, just after the left ventricle finishes contracting and starts to relax and fill with blood again (during diastole), the aortic valve closes, the mitral valve opens, and some blood flows from the left atrium into the left ventricle. Then the left atrium contracts, ejecting more blood into the left ventricle.

As the left ventricle begins to contract (during systole), the mitral valve closes, the aortic valve opens, and blood is ejected into the aorta.

In mitral stenosis, the mitral valve opening is narrowed, and blood flow from the left atrium into the left ventricle during diastole is reduced.

In mitral regurgitation, the mitral valve leaks when the left ventricle contracts (during systole), and some blood flows backward into the left atrium.

Two types of valves are available for replacement, a mechanical type and one made from the heart valve of a pig or cow (bioprosthetic). Mechanical valves last for many years, but people with mechanical valves must take anticoagulants for the rest of their lives to prevent blood clots from forming in the valve. Bioprosthetic valves generally deteriorate and require replacement after 10 to 12 years but do not require use of anticoagulants for more than a few months after surgery. Some newer bioprosthetic valves are more durable and may not require replacement.

Replacing a Heart Valve

A damaged heart valve may be replaced with a mechanical valve made of plastic and metal or with a bioprosthetic valve made of heart valve tissue, usually from pigs, placed in a synthetic ring. There are many types of mechanical valves. A St. Jude valve is commonly used.

Choice of a valve depends on many factors, including characteristics of the valve. A mechanical valve lasts longer than a bioprosthetic valve but requires that anticoagulants be taken indefinitely to prevent the formation of blood clots on the valve. A bioprosthetic valve rarely requires the use of anticoagulants. So whether a person can take anticoagulants is an important factor. For example, anticoagulants may not be appropriate for women of childbearing age because anticoagulants cross the placenta and may affect the fetus. Also considered are how old the person is, what the person's activity level is, how well the heart is working, and which heart valve is damaged.

For heart valve replacement, a general anesthetic is given. The heart must be still to be operated on, so a heart-lung machine is used to pump blood through the bloodstream. The damaged valve is removed, and the replacement valve is sewn in place. The incisions are closed, the heart-lung machine is disconnected, and the heart is restarted. The operation takes from 2 to 5 hours. For some people, a heart valve can be replaced using a less invasive procedure (without cutting through the sternum), available at some medical centers. The length of the hospital stay varies from person to person. Full recovery may take 6 to 8 weeks.

Abnormal valves and all replacement valves can become infected. People with replacement valves need to take prophylactic antibiotics, which are antibiotics taken at certain times (for example, before some dental or medical procedures) in order to prevent bacterial infection of the valves (infective endocarditis—see Infective Endocarditis).

Changes with aging

As people age, the mitral and aortic valves thicken. The aorta becomes stiffer, which increases blood pressure and stress on the mitral valve, and the heart requires additional oxygen to pump blood effectively. These age-related changes may lead to symptoms and complications in older people with heart disease.

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