Special Supplement: Prophylaxis of Endocarditis
Endocarditis is an infection of the internal structures of the heart. To develop this infection, there must be a defect in the myocardial endothelium that allows the pathogen to adhere. Major causes of endothelial disruption include surgical instrumentation and areas of high turbulence. Most congenital heart defects have both of these and, therefore, predispose the patient to the development of endocarditis. To prevent the development of infection, the current widely accepted practice is to use prophylactic measures during potentially significant episodes of bacteremia. Causes of bacteremia are numerous and often spontaneous. Any infection can lead to bacteremic episodes, but those involving mucosal surfaces are much more likely to do so. Some of the more obvious causes include focal infections, pneumonia, cellulitis, and urinary tract infections. In addition, procedures such as surgical, dental, or any instrumentation of mucosal surfaces also are likely causes of bacteremia.
The American Heart Association, in conjunction with the American Dental Association, Infectious Disease Society of America, American Academy of Pediatrics, and the American Society for Gastrointestinal Endoscopy, released in December 1997 a suggested guideline of prophylactic treatment for the prevention of bacterial infectious endocarditis.1 These guidelines take into consideration the degree to which the patient’s underlying condition creates a risk of endocarditis, the apparent risk of bacteremia with the procedure, adverse reactions to the particular prophylactic regimen, and cost-benefit aspects.
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Following the recommendations of the American Heart Association, almost all congenital heart defects require prophylaxis. The exceptions to this are bicuspid aortic valve (without regurgitation), mitral valve prolapse (without regurgitation), and ASD. Additional recommendations are that all postoperative patients, irrespective of the adequacy of repair, receive prophylactic measures for six months following the procedure. For patients who must undergo a procedure that poses significant risk of bacteremia and whose need for prophylaxis is unclear, it is better to administer the prophylaxis. These patients should then be referred for evaluation by a cardiologist.
General considerations in choosing a specific antimicrobial for prophylaxis include the most likely organism associated with the expected procedure, recent antimicrobial therapy, and the likelihood of resistant organisms. Antibiotic recommendations are summarized in the Table. For dental procedures, prophylaxis with amoxicillin or ampicillin is recommended where treatment generally is directed toward streptococcal species. The most common organism involved in endocarditis associated with gastrointestinal or genitourinary procedures is Enterococcus faecalis.2,3 Prophylaxis is, therefore, directed toward this species. Recommended regimens include ampicillin and gentamycin for high risk patients and amoxicillin or ampicillin for moderate risk patients.
Patients presenting to the ED with evidence of soft tissue infections such as cellulitis or an abscess should receive appropriate antibiotic coverage prior to manipulations, debridement or incision and drainage. Coverage here should be directed toward staphylococcal and streptococcal species, a first-generation cephalosporin is an appropriate choice. Generally, the most common organisms associated with post-cardiac surgery infectious endocarditis are Staphylococcus aureus, coagulase negative staphylococcus, and diptheriods. No single antibiotic covers these three organisms. Most hospitals have instituted treatment protocols for patients undergoing cardiac surgery based on the organisms typically seen at that institution.
For patients known to culture resistant organisms, antibiotics should be directed based on the known susceptibilities of that organism or likely organisms.
References
1. Dajani AS, Taubert KA, Wilson W, et al. Preventions of bacterial endocarditis: Recommendations by the American Heart Association. JAMA 1997;277:1794-1801.
2. Durack DT. Prevention of IE. N Engl J Med 1995;332:38-44.
3. Steckelberg JM, Wilson WR. Risk factors for infective endocarditis. Infect Dis Clin North Am 1993;7:9-19.
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