How to classify IE?

IE is inflammation of the inner tissue of the heart, such as its valves, caused by infectious agents. The agents are usually bacterial, but other organisms can also be responsible.

Types of IE

1.By Duration

Historically, infective endocarditis has been clinically divided into acute and subacute 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.

• Subacute bacterial endocarditis(SBE) is often due to streptococci of low virulence and mild to moderate illness which progresses slowly over weeks and months and has low propensity to hematogenously seed extracardiac sites.
• Acute bacterial endocarditis (ABE) is a fulminant illness over days to weeks, and is more likely due to Staphylococcus aureus which has much greater virulence, or disease-producing capacity and frequently causes metastatic infection.

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. By culture results

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, Chlamydia species, and HACEK bacteria. Another possible reason for culture negativity, even with the more typical pathogens, is prior antibiotic treatment.

3.By heart side

Endocarditis can also be classified by the side of the heart affected:

• Patients who inject narcotics or other drugs intravenously may introduce infection which will travel to the right side of the heart classically affecting the tricuspid valves and most often caused by S. aureus.
• In other patients without a history of intravenous exposure, endocarditis is more frequently left-sided.

4. By infection type

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 parental nutrition lines, pace maker, etc.

5. By valve type

Finally, the distinction between native-valve endocarditis and prosthetic-valve endocarditis is clinically important. Prosthetic valve endocarditis can be early (< 60 days of valvular surgery) or late (> 60 days of valvular surgery).

• Early prosthetic valve endocarditis is usually due to intraoperative contamination or a postoperative bacterial contamination which is usually nosocomial  in nature.
• Late prosthetic valve endocarditis is usually due to community acquired microorganisms