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Endocarditis

Endocarditis is an inflammation of the inner layer of the heart, the endocardium[?]. The most common structures involved are the heart valves.

Endocarditis can be classified as either infective or non-infective, depending on whether a foreign organism is causing the problem.

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Infective Endocarditis As the valves of the heart do not actually receive any blood supply of their own, which may be surprising given their location, defense mechanisms (such as white blood cells) cannot enter. So if an organism (such as bacteria) establish hold on the valves, the body cannot get rid of them.

Normally, blood flows pretty smoothly through these valves. If they have been damaged (for instance in rheumatic fever[?]) bacteria have a chance to take hold.

Classification

Traditionally, infective endocarditis has been divided into acute and sub-acute endocarditis. This terminology is now discouraged, as the word sub-acute is considered an oxymoron.

Nowadays, the terms short incubation (meaning about less than six weeks), and long incubation (greater than six weeks), are preferred.

Aetiology and Pathogenesis

As previously mentioned, altered blood flow around the valves is a risk factor in obtaining endocarditis. The valves may being damaged congenitally, from surgery, by auto-immune[?] mechanisms, or simply as a consequence of old age.

In a healthy individual, a bacteraemia[?], (where bacteria get into the blood stream through a minor cut or wound,) would normally be cleared quickly with no adverse consequences. If a heart valve is damaged, this provides a place for the bacteria to multiply, and an infection is established.

The bacteraemia is often caused by minor dental procedures, such as a tooth removal. It is important that a dentist[?] is told of any heart problems before commencing.

Another group of causes result from a high number of bacteria getting into the bloodstream. Bowel cancer[?], bad urinary tract infections and IV drug[?] use, can all introduce large numbers of bacteria. With a large number of bacteria, even a normal heart valve may be infected. A more virulent organism (such as Staphylococcus aureus) is usually responsible for infecting a normal valve.

Intravenous drug users tend to get their right heart valves infected, the veins enter into the right side of the heart. The injured valve is most commonly affected when there is a pre-existing disease. (In rheumatic heart disease this is the aortic and the mitral valves, on the left side of the heart.)

Clinical and pathological features

  • Fever
  • Vegetations on valves etc.

Micro-organisms responsible

Many types of organism can cause infective endocarditis. These are generally isolated by blood culture[?], where the patient's blood is removed, and any growth is noted and identified.

Alpha-haemolytic streptococci, that are present in the mouth will often be the organism isolated if a dental procedure caused the bacteraemia.

If the bacteraemia was introduced through the skin, such as contamination in surgery, an catheterisation, or in an IV drug user, Staphylococcus epidermidis and S. aureus are common.

Some organism when isolated give valuable clues to the cause, as they tend to be specific.

Treatment

High dose antibiotics need to be used. This is also because of the limited blood supply to the valves.

This is continued for a long time. If not effective, surgical removal of the valve is possible.



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