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Infective endocarditis is a form of endocarditis caused by infectious agents. The agents are usually bacterial, but other organisms can also be responsible.
The valves of the heart do not receive any dedicated blood supply, defensive immune mechanisms (such as white blood cells) cannot directly reach the valves via the bloodstream. If an organism (such as bacteria) attaches to a valve surface and forms a vegetation, the host immune response is blunted. The lack of blood supply to the valves also has implications on treatment, since drugs also have difficulty reaching the infected valve.
Normally, blood flows smoothly through these valves. If they have been damaged – from rheumatic fever, for example – the risk of bacteria attachment is increased.[1]
Historically, infective endocarditis has been clinically divided into acute and subacute[1] presentations (because untreated patients tended to live longer with the subacute as opposed to the acute form). This classifies both the rate of progression and severity of disease.
This terminology is now discouraged, because the ascribed associations (in terms of organism and prognosis) were not strong enough to be relied upon clinically. The terms short incubation (meaning less than about six weeks), and long incubation (greater than about six weeks) are preferred.[2]
Infective endocarditis may also be classified as culture-positive or culture-negative. Culture-negative endocarditis can be due to micro-organisms that require a longer period of time to be identified in the laboratory, such organisms are said to be fastidious because they have demanding growth requirements, or due to absence of an organism as in marantic endocarditis. Some pathogens responsible for culture-negative endocarditis include Aspergillus species, Brucella species, Coxiella burnetii, Chlamydia species, and HACEK bacteria. Another possible reason for culture negativity, even with the more typical pathogens, is prior antibiotic treatment.
Endocarditis can also be classified by the side of the heart affected:
Another form of endocarditis is nosocomial endocarditis which is when the patient is diagnosed with endocarditis and has had hospital care one month prior to the incident and is usually secondary to IV catheters, Total parenteral nutrition lines, pacemakers, etc.[3]
Finally, the distinction between native-valve endocarditis and prosthetic-valve endocarditis is clinically important. Prosthetic valve endocarditis can be early (< 2 months of valvular surgery) or late (> 2 months of valvular surgery).
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