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Definition

Endocarditis is an infection of the endocardium, the inner lining of the heart muscle and its four valves (tricuspid, pulmonary, mitral, and aortic). Abnormal or damaged endocardium is more likely to become infected when bacteria enter the bloodstream. When this happens, during surgical or dental procedures, for example, a condition called bacteremia results. The circulating bacteria can then enter the heart, where damaged tissue or other abnormalities allow them to multiply and cause an infection. Endocarditis is a life-threatening disease that interferes with the heart's ability to pump blood. Untreated, it is always fatal.

Description

Endocarditis most commonly occurs in people whose hearts have damaged valves. This may be the result of acquired valvular disease from rheumatic fever or other diseases. Patients with mitral valve prolapse, in which a poorly functioning mitral valve regurgitates blood back into the heart, allowing bacteria to multiply, are also at risk for endocarditis. Prosthetic (artificial) heart valves are more likely to become infected as well.

Bacteremia that causes endocarditis can occur in several ways:

• from a localized infection such as a urinary tract infection, pneumonia, skin infection, or dental infection
• as a result of certain medical conditions, such as severe periodontal disease, colon cancer, or inflammatory bowel disease
• during dental or surgical procedures, such as dental cleaning, tooth extractions, tonsil removal, or endoscopic examinations
• through in-dwelling catheters used for intravenous medications, intravenous feeding, or dialysis
• intravenous drug use using unsterilized, contaminated needles and syringes

The bacteria that cause most endocarditis are gram-positive cocci, such as Staphylococcus or Streptococcus. Staphylococcal endocarditis occurs most often among intravenous drug users and patients with in-dwelling venous catheters. Gram-negative bacterial endocarditis or fungal endocarditis is much less common; patients are usually intravenous drug users or those with prosthetic heart valves.

Endocarditis patients who appear critically ill are usually suffering from acute bacterial endocarditis, while those with subacute bacterial endocarditis have less severe but persistent symptoms such as weight loss, fatigue, and low-grade fever.

If not discovered and treated, endocarditis can permanently damage the heart valves. If a valve is damaged, it may allow blood to flow backward—a condition known as regurgitation. As a result of a poorly functioning

valve, the heart muscle has to work harder to pump blood and may become weakened, leading to congestive heart failure.

Another danger associated with endocarditis is that the overgrowth of bacteria colonizing heart valves may break off and form emboli that can become lodged in arteries. An embolism to an artery supplying the brain can cause a stroke; an embolus lodged in the blood vessels of the lungs may cause pneumonia.

Causes and symptoms

Most cases of infective endocarditis occur in patients between the ages of 15 and 60, with a median age at onset of about 50 years. Men are affected about twice as often as women. Other risk factors for endocarditis are congenital heart problems, heart surgery, past history of endocarditis, and intravenous drug use.

Patients with acute bacterial endocarditis are generally critically ill. Patients with subacute bacterial endocarditis tend to have a low-grade fever, which rarely rises above 102°F (38.9°C), chills, weakness, cough, difficulty breathing, headaches, arthralgias (aching joints), and loss of appetite, although these symptoms vary with individual patients.

Emboli may also cause a variety of symptoms, depending on their location. Emboli throughout the body may cause Osler's nodes, which are small, reddish, painful bumps most commonly found on the inside of fingers and toes. Emboli may also cause petechiae, which are tiny purple or red spots on the skin resulting from hemorrhages under the skin's surface. Tiny hemorrhages resembling splinters may also appear under the fingernails or toenails. If emboli become lodged in the blood vessels of the lungs, they may cause coughing or shortness of breath. Emboli lodged in the brain may cause a stroke, with such symptoms as numbness, weakness, or paralysis on one side of the body or sudden blindness or double vision. Emboli may also damage the kidneys, causing nephritis. Sometimes the capillaries on the surface of the spleen rupture, causing it to become enlarged and tender. Patients with any of these symptoms require immediate medical attention.

Diagnosis

Clinicians diagnose endocarditis by taking a history and performing a physical examination, during which they may observe such signs as fever, an enlarged spleen, signs of kidney disease, or hemorrhaging. The clinician may also detect a heart murmur. A heart murmur may indicate abnormal flow of blood through one of the heart chambers or valves. Laboratory analysis of the patient's blood identifies the bacteria or other microorganisms that may be causing the infection.

The diagnostic workup also involves echocardiography to check for abnormalities in the structure of the heart wall or valves. Conventional echocardiography uses ultrasound to view the structures of the heart. This diagnostic procedure is transthoracic; the ultrasound transducer is placed on the chest wall.

One of the hallmarks of endocarditis that may be observed during echocardiography is vegetation, which is the abnormal growth of tissue, composed of blood platelets, bacteria, and a clotting protein called fibrin, that grows around a valve. Another indicator is regurgitation, or the backward flow of blood, through one of the heart valves. A normal echocardiogram does not exclude the possibility of endocarditis, but an abnormal echocardiogram can confirm its presence. If an echocardiogram cannot be performed or its results are inconclusive, a modified technique called transesophageal echocardiography is sometimes performed. This technique involves passing an ultrasound device into the esophagus to get a clearer image of the heart.

Treatment

When infective endocarditis is suspected, the patient is admitted to the hospital and antibiotic treatment is started before the results of the blood culture are available. The choice of antibiotics depends on which infecting microorganism is suspected. Once the results of the blood culture become available, the physician will prescribe specific antibiotics known to be effective against the specific microorganism involved.

Today the treatment of endocarditis is more complicated as a result of antibiotic resistance. Over the past few years, especially as antibiotics have been overprescribed, more and more strains of bacteria have become increasingly resistant to a wider range of antibiotics. For this reason, a few different types of antibiotics—or even a combination of antibiotics—may be necessary to treat the infection successfully. Antibiotics are usually prescribed for about six weeks but may be given for an even longer period of time if the infection is resistant to treatment.

Once the fever and acute symptoms have resolved, most patients are able to continue antibiotic therapy at home. During this time, patients make regular visits to the health care team to ensure that the antibiotic therapy is working, that it is not causing adverse side effects, and that there are no complications such as emboli or congestive heart failure.

Patients must be advised to alert the health care team to any symptoms that could indicate serious complications. For instance, difficulty breathing or edema (swelling) in the legs could indicate congestive heart failure. Headache, joint pain, blood in the urine, or stroke symptoms could indicate an embolus; and fever and chills could indicate that the treatment is not working and the infection is worsening. Finally, diarrhea, rash, itching, or joint pain may suggest an adverse reaction to the antibiotics. Patients experiencing any of these symptoms should be advised to seek immediate medical attention.

In some cases surgical intervention may be needed to treat congestive heart failure, recurring emboli, infection that does not respond to treatment, poorly functioning heart valves, and endocarditis involving prosthetic (artificial) valves. The most common surgical treatment involves debriding (cutting away) damaged tissue and replacing the damaged valve.

Prognosis

Untreated infective endocarditis progresses and is always fatal. However, when diagnosed and properly treated within the first six weeks of infection, the infection can be completely cured in about 90% of the cases. The prognosis depends on a number of factors, such as the patient's age and overall physical condition; the severity of the diseases involved; the exact site of the infection; how vulnerable the microorganisms are to antibiotics; and the nature of the complications.

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KEY TERMS

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Aortic valve—The valve between the left ventricle of the heart and the aorta.

Congestive heart failure—A condition in which the heart muscle cannot pump blood as efficiently as it should.

Echocardiography—A diagnostic test using reflected sound waves to study the structure and motion of the heart muscle.

Embolus—A bit of foreign material, such as gas, a piece of tissue, or tiny clot, that circulates in the bloodstream until it becomes lodged in a blood vessel.

Endocardium—The inner wall of the heart muscle, which also covers the heart valves.

Mitral valve—The valve between the left atrium and the left ventricle of the heart.

Osler's nodes—Small, raised, reddish, tender areas associated with endocarditis, commonly found inside the fingers or toes.

Petechiae—Tiny purple or red spots on the skin associated with endocarditis, resulting from hemorrhages under the skin's surface.

Pulmonary valve—The valve between the right ventricle of the heart and the pulmonary artery.

Transducer—A device that converts electrical signals into ultrasound waves and ultrasound waves back into electrical impulses.

Transesophageal echocardiography—A diagnostic test using an ultrasound device passed into the esophagus of the patient to create a clear image of the heart muscle.

Tricuspid valve—The valve between the right atrium and the right ventricle of the heart.

Vegetation—An abnormal growth of tissue around a valve that can develop following a bacteremia. Vegetation is composed of blood platelets, the infecting bacteria, a few white blood cells, and fibrin, a protein involved in clotting.

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Health care team roles

Endocarditis is generally diagnosed by a primary care physician, emergency medicine physician, or cardiologist. Nurses, ECG technicians, laboratory technologists and other allied health professionals have important roles in the diagnosis of endocarditis as well as institution of timely treatment. Nurses and other practitioners involved in triage or screening in the emergency department, clinic, office, or other treatment setting must accurately assess patients with indications of endocarditis.

ECG technicians and laboratory technologists are responsible for performing the diagnostic tests, ECG, and blood cultures to confirm the diagnosis and causative microorganism. In the hospital, nurses and allied health professionals are responsible for closely monitoring patients for complications.

Prevention

Some individuals are especially prone to endocarditis. These include patients with past history of endocarditis, those with congenital heart problems or heart damage from rheumatic fever, and patients with prosthetic heart valves. Intravenous drug users are also at increased risk. Patients at high risk for endocarditis need to take a dose of prophylactic antibiotics before undergoing procedures likely to cause bacteria to enter the bloodstream, such as most dental procedures. The American Heart Association recommends two grams of amoxicillin (children: 50 mg/kg) taken by mouth one hour before dental appointments. Patients who are allergic to penicillin can take clindamycin, cephalexin, or azithromycin instead.

Barbara Wexler