Infective endocarditis is a rare, life-threatening infection of the endocardium by bacteria or fungi. Cardiac conditions such as abnormal or prosthetic heart valves and congenital abnormalities predispose patients to infective endocarditis. Preexisting endothelial damage leads to platelet and fibrin deposits upon which nonbacterial thrombotic endocardial lesions form. Subsequent bacteremia provides a source of bacteria that adhere to the complex and proliferate within an infective vegetation. Endocardial vegetations can cause valvular insufficiency, myocardial abscesses, or even septic emboli. Because of the high mortality rate, infective endocarditis requires immediate treatment.
Subacute bacterial endocarditis (SBE) is a slowly progressing form (weeks to months) of infective endocarditis. Certain invasive procedures, particularly dental, respiratory, gastrointestinal, and genitourinary, carry a higher risk of producing asymptomatic bacteremia with organisms known to cause SBE. Colonization is usually caused by a member of the viridans streptococci group, such as Streptococcus mutans or sanguinis. These bacterial group has a preference for native abnormal heart valves or congenital cardiac defects. Prosthetic heart valves are usually subject to colonization by Staphyloccus epidermidis or aureus. Other sources of bacteria leading to SBE include flora of the respiratory tract (S aureus) or urinary tract (Enterococcus).
Animal models of experimental infective endocarditis have shown that antibiotic prophylaxis effectively prevents this problem. Based on these findings, it has long been thought that the pre-procedure antibiotics also reduce the incidence of SBE in patients undergoing dental, gastrointestinal, and genitourinary procedures. Since 1955, the American Heart Association (AHA) has provided recommendations on this subject. In the past, patients with all types of valvular and congenital heart defects have been given antibiotics 1 hour before dental, oral, gastrointestinal, genital or urinary tract procedures. The prevention of bacterial endocarditis is always preferable to treating an established infection.
The value of this practice has recently been brought into question. In 2007 (and in a 2008 focused update), the AHA decided to revise the guidelines for several reasons based on recent evidence. Contrary to traditional thinking, the literature review showed that bacteremia associated with daily activities of living (e.g., brushing teeth, flossing) carried a higher risk of causing bacterial endocarditis than dental, gastrointestinal, or genitourinary operations. The benefits of antimicrobial prophylaxis were found to be small: prophylactic antibiotics only prevented a very low number of SBE cases for patients undergoing these procedures. Unless given to a high-risk patient, this small benefit is usually exceeded by the risks of antibiotic-associated adverse events (potential allergic or anaphylactic reaction, development of bacterial resistance, and Clostridium difficile colitis). For many patients, SBE risk reduction should rely more on maintaining best oral health and hygiene rather than receiving prophylactic antibiotics.
INDICATIONS FOR SBE PROPHYLAXIS
In the current guidelines published by the AHA, the highest recommendation classification for the use of prophylactic antibiotics to prevent SBE is Class IIa. This category describes a condition for which ...