What is bacterial endocarditis?

Bacterial endocarditis is a relatively uncommon, but potentially dangerous inflammation, usually caused by infection in vulnerable areas of the endocardium – the innermost layer of the heart's chambers and valves. It can be caused by bacteria, fungi or other infectious agents. The most common form of endocarditis is caused by bacteria that are somehow introduced into the bloodstream, often from the mouth.

When intact, the endocardium is resistant to infection from these bacteria. However, injury or deformity of the endocardium can cause clots to form on the injured surface. These act as traps for microorganisms, which multiply rapidly at the site of the damage and go on to cause endocarditis. Bacterial endocarditis is rare in people with healthy hearts, and most commonly affects individuals who have valvular heart disease, congenital heart disease or a history of rheumatic fever.

There are several types of endocarditis, classified according to the severity of the condition and the underlying cause:

Acute bacterial endocarditis involves a rapid development of symptoms. If the infection is severe, there may be serious damage to the valves and a significant decline in health in only a few weeks.

Subacute bacterial endocarditi entails a more gradual onset of symptoms that could take several months to a year to develop. During that time, it can cause serious damage to heart valves. It typically is not accompanied by the dramatic symptoms seen in the acute form of the disease.

Fungal endocarditis can occur in people with previously damaged heart tissue and in people who have a very low resistance to infection, especially those who are taking drugs that suppress the immune system (e.g., people who have just received an artifical transplant, pacemaker or implantable cardioverter defibrillator). Both fungal and bacterial endocarditis are commonly seen in people with a history of illegal intravenous (I.V.) drug use, because non-sterile needles can introduce a host of microorganisms directly into the bloodstream.

Nonbacterial endocarditis can be caused by some cancers (rarely) and by some autoimmune disorders such as systemic lupus erythematosus.

If the endocarditis is bacterial, it is critical to identify the exact bacteria before treatment. It is commonly caused by streptococcus, staphylococcus, pneumococcus or enterococci bacteria. The bacteria most often responsible for endocarditis are staphylococcus aureus. The presence of these virulent bacteria in the blood indicates an automatic screening for endocarditis.

Bacteria can enter the bloodstream through certain dental or medical procedures. An infection from something as simple as a skin cut can provide the opportunity for bacteria to enter the body. In addition, medical conditions such as a gum disease or an intestinal disorder can allow bacteria to enter the bloodstream as well.

Men are somewhat more likely to develop endocarditis than women. The condition is also more prevalent in older individuals. Compared with an overall rate of two per 100,000 people who acquire the condition, the rate for people over 60 can approach 30 per 100,000. This increase may be due to the fact that older Americans are more likely to have preexisting heart conditions such as rheumatic heart disease, mitral valve prolapse, degenerative heart disease or artificial heart valves – conditions that increase the risk of endocarditis. People who inject illegal drugs are at high risk for it, as are patients infected with HIV, have AIDS or other diseases that affect the immune system. Children are rarely affected by bacterial endocarditis.

How is it diagnosed?

Diagnosing endocarditis is complicated by the condition's large number of possible signs and symptoms. A physician may suspect bacterial endocarditis based on a patient's medical history and physical symptoms upon examination. However, endocarditis may present the same symptoms as pneumonia, heart attack or many other conditions. Furthermore, because it can be caused by a variety of bacteria, which are difficult to isolate, many physicians begin their diagnosis by ruling out other causes. In general, if a constellation of symptoms is present and there is no other known infection or condition, a physician may narrow down the diagnosis to endocarditis.

The two most common tests to confirm this diagnosis are blood tests and echocardiogram. Blood tests or cultures are used to detect the presence of bacteria, identify the bacteria and determine which antibiotics they are sensitive to. A sample of blood will be placed in a culture bottle containing a nutrient broth that supports the growth of the type of bacteria that commonly causes endocarditis. If the endocarditis is acute, these samples will be taken over a period of an hour. If the endocarditis is subacute, the samples may be taken over a period of days and treatment may be delayed. The object is to culture and isolate the organisms so physicians can identify which organism is responsible for the infection.

It is not easy to capture the bacteria in a blood culture, and physicians have a better chance of doing so when people have a fever, which may happen when large numbers of bacteria enter the bloodstream. Other blood samples may be taken to detect the presence of anemia. In about 2 percent to 5 percent of cases of bacterial endocarditis, the blood cultures are negative. This is especially true among patients who have already been treated with antibiotics. Therefore, negative blood cultures do not necessarily rule out endocarditis, and depending on the other signs and symptoms present, the physician may go ahead and recommend medical therapy.

The blood culture is frequently followed by an echocardiogram, especially among patients at moderate to high risk of endocarditis. This painless, noninvasive test uses sound waves to visualize the structures and functions of the heart. A moving image of the patient's beating heart is displayed on a video screen, where a physician can study and measure various factors. These include the heart's thickness, size, function and any buildup of vegetations (clumps of trapped bacteria or fungi layered with platelets, fibrin and immune cells) that may be present. The image also shows the motion pattern and structure of the four heart valves, revealing any potential leakage (regurgitation), narrowing (stenosis) or damage caused by infection.

In some cases, the physician may need to do a minimally invasive transesophageal echocardiogram. During this test, a flexible transducer is placed down the throat and into the esophagus to create very clear images of the heart and valves without interference from the chest wall or lungs. The goal is to determine if the heart valves have been compromised by the infection.

Other tests that may be ordered during the initial screening might include an electrocardiogram, which measures the heart's electrical rhythms, or a chest x-ray, which can reveal blood or fluid that has backed up into the lungs.

How is Bacterial endocarditis treated?

The treatment for patients diagnosed with endocarditis is intravenous (I.V.) antibiotic therapy. This use of antibiotics requires a significant dose for a long period of time – as long as six weeks, depending on the type of infectious agent causing the disease. It is important that the antibiotics used are the correct ones for the organism that is causing the infection.

Recently, some studies have shown that oral antibiotic therapy may work with certain patients. Oral therapy works if the exact bacterial cause of the endocarditis is known, if the bacteria are susceptible to antimicrobial therapy, and if there is some other reason to avoid I.V. therapy.

More and more frequently, surgery is also used to treat the damage to the heart valves caused by endocarditis. This is especially true:

• For patients with heart failure that is related to the heart valves
• In cases where repeated antibiotic therapy hasn't worked
• In cases where recurrent emboli (at least two) are present

The most common surgery associated with endocarditis is heart valve surgery repair or replacement.

Endocarditis Medication

Antibiotics for many weeks to fight infection. Antibiotic treatment is often intravenous.

Ilosone (Erythromycin), Biaxin (Clarithromycin), Keflex (Cephalexin)

Activity

• Rest in bed until fully recovered. While in bed, flex your legs often to prevent clots from forming in deep veins.
• Resume your normal activities, including sexual relations, when strength allows.

What might complicate it?

Complications include systemic emboli (blood vessels obstructed by fragments of tissue carried through the bloodstream), tissue death in the spleen (splenic infarction), stroke, brain hemorrhage, congestive heart failure, and kidney failure. The emboli may also be infected, which can lead to sepsis. Additional complications of therapy include infection and thrombophlebitis.

Predicted outcome

While 75 to 90 percent of patients properly diagnosed with endocarditis are successfully treated, endocarditis is likely to lead to death if left untreated. According to the American Heart Association, bacterial endocarditis was responsible for more than 2,300 deaths in 1999.

Alternatives

Conditions with similar symptoms include acute rheumatic fever with carditis, periarteritis nodosa, poststreptococcal glomerulonephritis, and reaction to drugs.

Appropriate specialists

Cardiologist, infectious disease specialist, and internist.

Last updated 30 June 2015