Infective Endocarditis (Acute and Subacute Bacterial Endocarditis)

Infective endocarditis is an infection of the endocardium or the inner lining of the heart, often involving the heart valves.

• Infective endocarditis is the bacterial infection of the heart valves resulting from bacteria that have entered the blood stream from some other sites of infection in the body.
• Acute bacterial endocarditis appears suddenly with symptoms such as high fever, severe fatigue, and rapid heart rate and it quickly damages the heart valves.
• Low grade fever, fast heart rate, marked loss of body weight, and lowered RBC count are symptoms of sub-acute endocarditis. Fatigue and sweating may also be present.
• Heart valve defects and injuries can be diagnosed by echocardiography.
• People who have pre-existing heart valve abnormalities or those who have artificial valves should take antibiotics as a precautionary measure prior to surgery or dental procedures to prevent possible infections that may result in endocarditis.
• Intravenous administration of antibiotics in large doses helps overcome the infection, but the existing damage of the heart valves may need to be surgically corrected.

Infective endocarditis is more prevalent in people above sixty, and in that age group, it affects men eight times more than women. In the general population too, the incidence of this disease in men is twice as that in women.

Endocardium is the inner lining of the heart and though infective endocarditis is a disease due to an infection of the endocardium, it is not always restricted to it. Endocarditis often involves the heart valves and the muscles and blood vessels of the heart too. Infective endocarditis occurs in an acute form as well as a subacute form. Acute infective endocarditis appears suddenly, starting with a high fever, and deteriorates quickly into a life threatening condition whereas the subacute infective endocarditis progresses slowly and steadily over weeks and months, often accompanied by a low grade persistent fever.

Blood is usually free of microorganisms such as bacteria, but due to some injury or infection elsewhere in the body, sometimes bacteria and even some fungi may enter the blood stream. These microorganisms have a tendency to settle on the heart valves and cause infection of the endocardium or the inner lining of the heart. Defective valves and those which are damaged due to some reason, as well as artificial valves are usually more prone to infection, especially subacute bacterial endocarditis. However, aggressive strains of bacteria, when present in large numbers do not spare even healthy valves.

Birth defects, especially abnormal connections that allow leakage of blood across the various chambers of the heart predispose children to infective endocarditis. In older people, damage to the valves resulting from aging or heart disease and calcium deposit formation in the aortic valve or in the mitral valve, are risk factors that increase susceptibility to endocarditis. Rheumatic fever in childhood, when not treated with antibiotics, often precipitates permanent valve damage which in turn becomes susceptible to infections later on.

Dirty needles, syringes, or drug solutions often used by drug abusers may introduce bacteria directly into the blood stream; hence, such people are at a very high risk of contracting endocarditis. Another high risk category is people with artificial valves, especially for a year following the valve replacement surgery. The risk factor varies according to the type of valve implanted; higher risk associated with a mechanical valve compared to a valve of animal origin and an implanted aortic valve compared to a mitral valve.

Causes

When bacteria are introduced into the blood through a cut in the skin or inside the mouth, or through minor infections such as gum disease or gingivitis, the body’s defense mechanism usually destroys them. But, if the bacteria get caught in the heart valves, especially when the valves are defective or damaged, or when artificial valves have replaced them, they colonize the valves, resulting in an infection of the valve which spreads to the lining of the heart (endocardium), resulting in infective endocarditis. Surgical procedures and some dental procedures may introduce bacteria into the blood stream. It may happen during open-heart surgery or when an artificial valve is fitted, but that is rare due to the precautions taken prior to and during such surgery.

When the immune response of the body is compromised, the risk increases, so does, when a large number of bacteria enter the blood stream. A severe infection of the blood called sepsis, which is life threatening in itself, can cause endocarditis even in people who have normal healthy heart valves because of the sheer number of bacteria circulating in the blood.

Infective endocarditis mostly affects the mitral valve and the aortic valve, except when infection results from unhygienic injection of illicit drugs and the use of intravenous lines for very long periods, in which cases the tricuspid valve between the right atrium and the right ventricle is usually affected.

Symptoms and complications

Acute bacterial endocarditis often makes a sudden appearance with a fever in the high range (38.9° to 40°C or 102° to 104°F). Other symptoms include fatigue and a fast heart rate, severe damage to the heart valves.

Subacute bacterial endocarditis which usually has milder symptoms such as a low-grade fever (99° to 101° F [37.2° to 38.3°C]), anemia, weight loss and fatigue, may often remain undiagnosed for several months till the steadily progressing disease causes a block in the arteries or damage to heart valves, which when detected and investigated brings the endocarditis into light.

When blood clots and bacteria accumulate on the valves, they are called vegetations. And when they get disengaged from the site of infection and travel in the blood stream (emboli), they may clog the arteries. A block in the artery supplying the heart muscle can precipitate a heart attack and if an artery supplying the brain is blocked, stroke can result. Emboli can settle in other places and cause infection wherever they settle, usually forming abscesses filled with pus, especially around the valves. Infected heart valves may develop perforations that result in leakage and regurgitation of blood in a short period, affecting the function of the heart. Infections that spread to arteries make the artery walls weak and cause them to rupture, which can be very dangerous, and even fatal, if it happens near the heart or in the brain. Septic shock also may develop, resulting in failure of vital organs like the kidney and liver.

Very small clots (emboli) may travel to various parts of the body and may appear as freckles or red spots in the white part of the eyes and on the skin or as red streaks under the fingernails. Emboli that are larger result in stomach pain, numbness and pain in the limbs or blood in urine. They can also cause stroke or heart attack, if a major artery supplying blood to the brain or heart gets blocked. Enlargement of spleen is a common occurrence. Painful nodules appearing under the skin, pain in the joints, pallor, chills and confusion are also symptoms associated with sub acute bacterial endocarditis.

Whether acute or sub acute, infective endocarditis of an artificial heart valve is more complicated, as the infection, often spreading into the tissue around the valve may loosen the valve. Also, disruption in the electrical conduction system of the heart may result in very slow heartbeat, which may cause fainting and even death.

Diagnosis

Since symptoms of infective endocarditis are not usually specific to that disease, diagnosis can be made only through detailed investigations. When doctors come across fever without any identifiable cause, in a patient having a defective or damaged heart valve or an artificial valve, endocarditis is suspected especially if the patient has also undergone any dental or surgical procedure recently. Since infective endocarditis is a dangerous disease with serious consequences, the patient is immediately hospitalized for further investigations and treatment.

A newly developed heart murmur or a change in the old murmur pattern may point to endocarditis, but echocardiography and blood cultures are the tests employed to make an accurate diagnosis. Echocardiography, which can project images of the heart, can detect accumulations (vegetations) at the heart valves as well as the damage caused to the heart.

If echocardiography done with the probe placed on the patient’s chest (transthoracic echocardiography) is not clear enough, a transesophageal echocardiography may be performed with the ultrasound probe introduced into the esophagus which is situated right behind the heart. This invasive procedure may be costly, but an accurate result may be obtained.

Several blood samples are taken and cultured to identify not only the particular type of bacteria causing the infection but also the most effective antibiotic to fight it. But sometimes, difficulties are encountered in culturing bacteria from the blood samples. If previous antibiotic therapy, which has not been successful in wiping out the infection, has reduced the bacterial count in the blood significantly, it may be very difficult to detect or culture bacteria from blood samples. There are a few disorders such as a tumor in the heart that may display symptoms of endocarditis, making diagnosis difficult.

Prognosis

Prolonged treatment with high doses of antibiotics may be necessary for surviving an episode of infective endocarditis. The outcome usually depends on the age of the patient, the type of infection and its duration and whether the person has an artificial valve implanted. Without treatment, prognosis is poor as infective endocarditis is fatal.

Prevention

When people with congenital heart defects or heart valve defects and those fitted with artificial heart valves undergo dental or surgical procedures, the medical practitioners concerned should be informed of these risk factors so that antibiotics may be given prior to the procedure as a precautionary measure against infective endocarditis. Even though antibiotics given as a precaution may not be very effective in preventing endocarditis and a minor surgical procedure may not pose a high risk of developing the disease, antibiotics are always justified considering the dangerous nature of endocarditis.

Treatment

Intravenous administration of high doses of antibiotics for prolonged periods (usually 2 to 8 weeks) is the first line of treatment, which is started in the hospital immediately on diagnosis, but later on, can be shifted to the patient’s home under the supervision of qualified medical personnel.

Following an episode of infective endocarditis, often corrective measures involving heart surgery may be necessary due to the following reasons:

• Accumulation of bacteria and blood clots (vegetations) should be removed.
• When antibiotics are not successful in getting rid of abscesses, they have to be drained surgically.
• Leaking or damaged heart valves should be repaired.
• In case of irreparable damage to the valves, they have to be replaced with artificial valves.
• Congenital septal defects (abnormal connections between the chambers of the heart) should be corrected.

When the infection involves artificial valves, antibiotics are not sufficient to clear it due to certain reasons. Since antibiotics had definitely been an integral part of treatment during valve replacement surgery, any bacteria that survived it could be a resistant type. Also, artificial materials do not respond to antibiotic treatment as human tissue does, necessitating surgical intervention.

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