Many fewer people will need to receive antibiotics as prophylaxis against infective endocarditis before undergoing dental procedures, according to new guidelines released by the American Heart Association.1 Now, the only patients to receive antibiotics will be those at highest risk, ie, those with a prosthetic heart valve, a history of endocarditis, certain forms of congenital heart disease, or valvulopathy after heart transplantation, and only before certain dental procedures.
Unfortunately, these guidelines are still based largely on expert opinion, with very little hard evidence to show that antibiotic therapy actually prevents infective endocarditis. Nevertheless, the new guidelines appear reasonable, and we believe they should be followed.
A RARE BUT LIFE-THREATENING INFECTION
Infective endocarditis is a rare but life-threatening infection, with an incidence in the United States of 10,000 to 20,000 new cases per year. Mortality rates for both native-valve endocarditis and prosthetic-valve endocarditis range from 20% to 30%.2,3 For the past half-century, antibiotic prophylaxis for dental procedures has been recommended for patients judged to be at risk of infective endocarditis, in hopes of preventing this dreaded infectious disease.
ENDOCARDIAL INJURY, THEN BACTERIAL SEEDING
A combination of events must occur to cause infective endocarditis. First, injury to the endocardial surface induces focal adherence of platelets and fibrin. Then, a bacteremic event seeds this aggregate with microorganisms, attracting more platelets and fibrin, allowing uninhibited microbial growth and the development of an inflammatory plaque or vegetation.
The magnitude and duration of bacteremia that produces this cascade of events is uncertain. Transient bacteremia occurs commonly, not only during procedures that cause trauma to mucosal surfaces or tissue but also with daily activities such as brushing teeth and chewing. The reported incidence of bacteremia during dental intervention ranges from 10% to 100%, and with daily brushing and flossing, from 20% to 68%.1
STAPHYLOCOCCI OVERTAKING VIRIDANS STREPTOCOCCI AS CAUSE
While historically the viridans group of streptococci has been responsible for the largest percentage of cases of both native-valve endocarditis and late-onset prosthetic-valve endocarditis, times have changed. In more recently reported series, Staphylococcus aureus appears more common, and unlikely to be susceptible to antibiotics recommended for dental prophylaxis. Other causative pathogens include coagulase-negative staphylococci, enterococci, gram-negative microorganisms, and fungi.
Previous American Heart Association guidelines4 separated patients into three risk categories for infective endocarditis. High-risk patients were those with prosthetic heart valves, a history of infective endocarditis, complex cyanotic congenital heart disease, or surgically constructed systemic pulmonary shunts. Moderate-risk patients had other congenital cardiac defects, hypertrophic cardiomyopathy, or acquired valvular heart disease including mitral valve prolapse with regurgitation. Negligible-risk patients—ie, most patients—included those with coronary artery bypass grafts, a permanent pacemaker, or mitral valve prolapse without regurgitation. Antibiotic prophylaxis was recommended only for patients in the high-risk and moderate-risk groups.