(USMLE topics) Endocarditis: causes, risk factors, pathophysiology, signs and symptoms, diagnosis and treatment.

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Infective endocarditis is infection of the endocardium - the inner lining of heart chambers and the covering of heart valves. Infection is caused by microorganisms, mainly bacteria, that have managed to enter the bloodstream.
Except for rare cases caused by massive blood infections or highly virulent organisms, a healthy heart is usually resistant to infection. This is because bacteria do not easily adhere to the surface of an intact endocardium; constant flow of blood also helps prevent bacterial attachment; and the bacteria are usually destroyed by the immune system before they can cause infection. An abnormality of the endocardium is typically required for endocarditis to occur. Major risk factors include having prosthetic valves or other intra-cardiac devices, congenital heart defects, heart valve disorders, hypertrophic cardiomyopathy, and previous endocarditis.
Endothelial injury allows for either direct colonization by virulent organisms, or the formation of blood clots, which then become the attachment site for bacteria. Infection of the endocardium occurs most often on the left side of the heart.
Organisms that cause endocarditis may come from distant infected sites, such as skin abscesses or urinary tract infections; or they may enter the body through a contaminated central line or injection. Bacteria of the normal flora of the mouth can also infect the endocardium if they get into the bloodstream, such as during invasive dental procedures. Causative organisms vary depending on the source of infection, but streptococci and staphylococci are responsible for the majority of cases.
Vegetations formed by bacterial growth may cause heart valve dysfunction, which can be heard as murmurs, and may lead to congestive heart failure.
Myocardial abscesses and tissue destruction may lead to cardiac conduction problems.
Pieces of bacterial vegetation may break free, forming so-called emboli. Emboli travel in the bloodstream and may block arteries. Right-sided infections produce emboli that travel to the lungs, causing pulmonary infarction and respiratory symptoms. Left-sided infections can send emboli to any other organs, including the brain, kidney, spleen, and the heart itself. Tiny emboli may also travel to the skin and eyes, producing small red streaks under fingernails, on fingers, toes, and the whites of eyes.
Other symptoms include fever, chills, fatigue and fast heart rates. Symptoms can develop abruptly or gradually depending on the type of endocarditis.
Endocarditis must be suspected when fever is combined with a heart valve disorder, especially when characteristic symptoms, such as reddish spots on fingers or the whites of the eyes, are present. But diagnosis usually requires evidence of blood infection, and imaging studies such as echocardiography, to show vegetations on heart valves or damage to the heart tissues.
Treatment consists of several weeks of intravenous antimicrobial therapy. Identification of the causative organism by blood culture is vital to determine appropriate antibiotic regimens. Empiric antibiotic therapy before organism identification may be necessary in seriously ill patients. Some cases may require surgeries to repair or replace heart valves. Potential source of infection must be removed.