Infective Endocarditis

Infective endocarditis is an infection of the lining of the heart (endocardium) and usually also of the heart valves.

Infective endocarditis affects twice as many men as women of all ages but 8 times as many older men as older women. It has become more common among older people: More than one fourth of all cases occur in people older than 60.

See the figure An Inside View of Infective Endocarditis.

Infective endocarditis refers specifically to infection of the lining of the heart, but the infection usually also affects the heart valves and often affects the muscle of the heart. There are two forms of infective endocarditis. One form, called acute infective endocarditis, develops suddenly and may become life threatening within days. The other form, called subacute infective endocarditis or subacute bacterial endocarditis, develops gradually and subtly over a period of weeks to several months.

Bacteria (or, less often, fungi) may be introduced into the bloodstream. These organisms can then lodge on heart valves and infect the endocardium. Abnormal or damaged valves are more susceptible to infection than normal valves. The bacteria that cause subacute bacterial endocarditis nearly always infect abnormal or damaged valves. However, normal valves can be infected by some aggressive bacteria, especially if many bacteria are present.

Risk factors for children and young adults include birth defects, particularly a defect that allows blood to leak from one part of the heart to another. One risk factor for older people is calcium deposits in the mitral valve (which opens from the left atrium into the left ventricle) or in the aortic valve (which opens from the left ventricle into the aorta). Damage to the heart by rheumatic fever as a child (rheumatic heart disease) (see Section 23, Chapter 272) is also a risk factor. Rheumatic fever has become a less common risk factor in countries where antibiotics have become widely available. In such countries, rheumatic fever is a risk factor for people who did not have the benefit of antibiotics during their childhood (such as immigrants).

People who inject illicit drugs are at high risk of endocarditis because they are likely to inject bacteria directly into their bloodstream through dirty needles, syringes, or drug solutions. People who have an artificial (prosthetic) heart valve are also at high risk. For them, the risk of infective endocarditis is greatest during the first year after heart valve surgery; after that, the risk decreases but remains slightly higher than normal. For unknown reasons, the risk is always greater with an artificial aortic valve than with an artificial mitral valve and with a mechanical valve rather than with a valve transplanted from a pig.

Causes

Although bacteria are not normally found in the blood, an injury to the skin, lining of the mouth, or gums (even an injury from a normal activity such as chewing or brushing the teeth) can allow a small number of bacteria to enter the bloodstream. Gingivitis (inflammation of the gums) with infection, minor skin infections, and infections elsewhere in the body may introduce bacteria into the bloodstream.

Certain surgical, dental, and medical procedures may also introduce bacteria into the bloodstream. Rarely, bacteria are introduced into the heart during open-heart surgery or heart valve replacement surgery. In people with normal heart valves, usually no harm is done, and the body's white blood cells rapidly destroy these bacteria. However, damaged heart valves may trap the bacteria, which can then lodge on the endocardium and start to multiply. Sepsis (see Section 17, Chapter 191), a severe blood infection, introduces a large number of bacteria into the bloodstream. When the number of bacteria in the bloodstream is large enough, endocarditis can develop, even in people who have normal heart valves.

If the cause of infective endocarditis is injection of illicit drugs or prolonged use of intravenous lines, the tricuspid valve (which opens from the right atrium into the right ventricle) is most often infected. In most other cases of endocarditis, the mitral valve or the aortic valve is infected.

Symptoms

Acute bacterial endocarditis usually begins suddenly with a high fever (102° to 104° F [38.9° to 40° C]), fast heart rate, fatigue, and rapid and extensive heart valve damage.

Subacute bacterial endocarditis may produce such symptoms as fatigue, mild fever (99° to 101° F [37.2° to 38.3° C]), a moderately fast heart rate, weight loss, sweating, and a low red blood cell count (anemia). These symptoms may occur for months before the endocarditis results in blockage of an artery or damages heart valves and thus makes the diagnosis clear to doctors.

Arteries may become blocked if accumulations of bacteria and blood clots on the valves (called vegetations) break loose (becoming emboli), travel through the bloodstream to other parts of the body, and lodge in an artery, blocking it. Sometimes blockage can have serious consequences. Blockage of an artery to the brain can cause a stroke, and blockage of an artery to the heart can cause a heart attack. Emboli can also cause an infection in the area in which they lodge. Collections of pus (abscesses) may develop at the base of infected heart valves or wherever infected emboli settle.

Heart valves may become perforated and may start to leak (causing regurgitation (see Section 3, Chapter 28)) significantly within a few days. Some people go into shock, and their kidneys and other organs stop functioning (a condition called septic shock (see Section 17, Chapter 191)). Infections in arteries can weaken artery walls, causing them to bulge or rupture. A rupture can be fatal, particularly if it occurs in the brain or near the heart.

Other symptoms of acute and subacute bacterial endocarditis may include chills, joint pain, paleness (pallor), painful nodules under the skin, and confusion. Tiny reddish spots that resemble freckles may appear on the skin and in the whites of the eyes. Small streaks of red (called splinter hemorrhages) may appear under the fingernails. These spots and streaks are caused by tiny emboli that have broken off the heart valves. Larger emboli may cause stomach pain, blood in the urine, or pain or numbness in an arm or a leg as well as a heart attack, or a stroke. Heart murmurs may develop, or preexisting ones may change. The spleen may enlarge.

Endocarditis of an artificial heart valve may be an acute or subacute infection. Compared with infection of a natural valve, infection of an artificial valve is more likely to spread to the heart muscle at the base of the valve and can loosen the valve. Alternatively, the heart's electrical conduction system may be interrupted, resulting in slowing of the heartbeat, which may lead to a sudden loss of consciousness or even death.

Diagnosis

Because many of the symptoms are vague and general, doctors may have difficulty making a diagnosis. Usually, people suspected of having acute or subacute infective endocarditis are hospitalized promptly for diagnosis as well as treatment.

Doctors may suspect endocarditis in people with a fever and no obvious source of infection, especially if they have characteristic symptoms; have a heart valve disorder; have recently had certain surgical, dental, or medical procedures; or inject illicit drugs. Development of a heart murmur or a change in a preexisting heart murmur further supports the diagnosis.

A blood sample is drawn to test for the presence of bacteria. Detecting bacteria in the blood helps doctors make the diagnosis.

To identify the disease-causing bacteria (so that a suitable antibiotic can be chosen), doctors send blood samples to be cultured. Because bacteria are continuously released from heart valve vegetations into the bloodstream, three or more blood samples are taken at different times to determine whether bacteria continue to be present in the bloodstream. Various antibiotics are tested against the bacteria to determine the best one to use. If endocarditis develops after a heart valve is replaced with an artificial one, the bacteria that caused the endocarditis may be resistant to antibiotics. Antibiotics are given before heart valve replacement surgery to prevent infection. If antibiotics do not prevent infection, the bacteria causing the resulting infection are probably resistant.

Sometimes bacteria cannot be cultured from blood samples. Special techniques may be needed to grow the particular bacteria, or the person may have taken antibiotics that did not cure the infection but did reduce the number of bacteria enough to be undetectable. Another possible explanation is that the person does not have endocarditis but has a disorder, such as a heart tumor (see Section 3, Chapter 31), that produces symptoms very similar to those of endocarditis.

Echocardiography, which uses ultrasound waves (see Section 3, Chapter 21), can produce images showing heart valve vegetations and damage to the heart. Transesophageal echocardiography (a procedure in which the ultrasound probe is passed down the throat into the esophagus just behind the heart) can detect endocarditis in more than 90% of affected people.

Prevention

As a preventive measure, people with heart valve abnormalities, artificial valves, or congenital heart defects are given antibiotics before certain surgical, dental, and medical procedures. Consequently, surgeons, dentists, and other health care practitioners need to know if a person has had a heart valve disorder. Although the risk of endocarditis is not very high for these procedures and preventive antibiotics are not always effective, the consequences of endocarditis are so severe that most doctors believe that giving antibiotics before these procedures is a reasonable precaution.

See the table Which Procedures Require Preventive Antibiotics?

Treatment and Prognosis

Treatment usually consists of at least 2 weeks and often up to 6 weeks of antibiotics given intravenously in high doses. Antibiotic therapy is almost always started in the hospital but may be finished at home with the help of a home nurse.

Antibiotics alone do not always cure an infection, particularly if the valve is artificial. Heart surgery may be needed to repair or replace damaged valves and remove vegetations. For example, if infection of an artificial heart valve loosens the valve, emergency surgery to replace the valve is needed, because heart failure from significant valvular leaks can be fatal.

If untreated, infective endocarditis is always fatal. When treatment is given, risk of death depends on factors such as the person's age, duration of the infection, the presence of an artificial heart valve, and the type of infecting organism. Nonetheless, with aggressive antibiotic treatment, most people survive.

See the sidebar Endocarditis Without Infection.