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. 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:

If the endocarditis is bacterial, it is critical to identify the exact bacteria before treatment. Endocarditis 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 endocarditis, as are patients infected with HIV, have AIDS or other diseases that affect the immune system. Children are rarely affected by endocarditis.

One of the more serious complications of endocarditis is the development of vegetations within the heart or on the heart valves. Vegetations are clumps of trapped bacteria or fungi, platelets, fibrin strands and immune cells. If pieces of the vegetation break off and enter the bloodstream, they may lodge in a blood vessel (embolism). This blockage can prevent oxygen-rich blood from reaching the tissues on the other side of the blockage, which could be fatal. 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.