The new guidelines for preventing infective endocarditis: Controversy over the diminished role of antibiotics

Individuals with congenital heart defects are at an increased risk of developing infective endocarditis – a disease notorious for its morbidity and mortality. Prolonged antibiotic administration is required to treat infective endocarditis; major cardiac sequelae are common after treatment. It is evident that the development of effective measures to prevent the disease would be invaluable for this group of patients. Since 1955, the American Heart Association (AHA) has regularly published and updated guidelines for the prevention of infective endocarditis. Until recently, the cornerstone of these guidelines was antibiotic prophylaxis for most types of heart malformations (not including isolated atrial septal defects) at the time of certain surgical or dental procedures. In 2007, the AHA published guidelines (1) that were dramatically different from the previous ones, excluding approximately 90% of patients for whom antibiotics were previously recommended. Instead, good oral hygiene was emphasized. Given that the AHA's guidelines had been widely accepted in North America for the past several decades and that thousands of doctors, dentists and individuals at risk invested considerable time and money to understand and ensure that the latest antibiotic recommendations were followed, why were the guidelines altered and was this radical change justified? The first comprehensive description of the clinical manifestations of infective endocarditis was given by Sir William Osler, in 1885, when he delivered “The Gulstonian lectures on malignant endocarditis” (2) in London, England, which was based on cases he had witnessed while teaching at Montreal General Hospital affiliated with McGill University (Montreal, Quebec). Maude Abbott, a McGill pathologist and Osler's protégée, authored his Modern Medicine: Its Theory and Practice chapter on congenital cardiac malformations in 1908 (3). In it, she observed that individuals with congenital heart problems were particularly susceptible to infective endocarditis. She recognized the disease's dire consequences, and commented that patients with even the most minor congenital heart lesions often died prematurely of infective endocarditis and its sequelae. Importantly, Abbott also called attention to the importance of ‘careful hygiene’ to prevent endocarditis and improve the long-term prognosis in patients with congenital heart disease. Penicillin was first used to treat infective endocarditis in the early 1940s, with limited success. Efforts, therefore, turned toward preventing the disease. Bacteremias had long been held responsible for causing infective endocarditis. Osler had surmised that in practically all cases, bacteria gained access to the heart through the skin or mucous membranes. Studies in the 1930s and 1940s demonstrated the presence of bacteremias after dental manipulations or extractions. Subsequently, a 1948 study by Hirsch et al (4) showed that a preprocedure dose of penicillin could reduce the risk of bacteremia after a dental extraction. In 1953, Arthur Bloomfield suggested the prophylactic use of penicillin to prevent the development of infective endocarditis due to bacteremias secondary to oral procedures, such as dental extraction (5). Following Bloomfield's lead, in 1955, the AHA proposed the use of a single intramuscular injection of penicillin before operative procedures for patients with rheumatic or congenital heart disease to protect against infective endocarditis (6). Two years later, the AHA switched to a much more aggressive prophylactic regimen without justification. The 1957 recommendation included both oral and intramuscular doses of antibiotics before and after certain dental and surgical procedures, over a time period of five days (7). The AHA admitted that the dosage and duration of treatment were ‘somewhat empirical'. Over the next 40 years, multiple iterations of the antibiotic prophylaxis recommendations were published by the AHA, and there continued to be no conclusive evidence supporting the efficacy of any of the proposed regimens. By 1997, the AHA was recommending only one dose of antibiotics before certain dental or surgical interventions. In a departure from previous guideline statements, and based on a number of illustrative studies, the AHA acknowledged that most cases of infective endocarditis were likely caused by random bacteremias that occured during activities of daily living, such as chewing and tooth brushing, rather than while undergoing a dental procedure or an invasive surgical procedure (8). Evidence continued to mount that bacteremias during dental manipulations represented an infinitesimally small proportion of the bacteremias incurred during a patient's lifetime. In addition, the risk of developing bacterial resistance and the risk of serious allergic reaction to antibiotics, albeit low, began to be considered. Thus, in 2007, the AHA published new guidelines that removed the recommendation for prophylaxis with antibiotics for most patients with congenital heart disease, with the exception of the most complicated or palliated patients with cyanotic congenital heart disease, those with a previous history of endocarditis, those with artificial valves or residual lesions adjacent to prosthetic tissue, and those with valve problems after heart transplant. In these exceptional cases, antibiotic prophylaxis is recommended for dental procedures only, and is no longer recommended before gastrointestinal or genitourinary interventions. Patients with other congenital heart diseases, including all of the most common noncyanotic heart malformations, such as valvular aortic stenosis and ventricular septal defects, should no longer receive antibiotic prophylaxis under the new guidelines. The AHA argued that patients would have to be on continuous antibiotics if they were to be protected from all bacteremias, and that the small number of cases (if any) of infective endocarditis that would be prevented by giving an antibiotic to these patients before an invasive procedure would not warrant the potential expense and risks of giving it. The new 2007 AHA recommendations have now shifted from emphasizing antibiotic prophylaxis to promoting good oral hygiene, harkening back to Maude Abbott's ‘careful hygiene’ of 1908. Multiple studies have demonstrated that patients with bad teeth and gums are more apt to develop bacteremias with organisms capable of causing infective endocarditis. Since 1977, the AHA has encouraged good dental hygiene to reduce potential sources of bacterial seeding (9). The most recent AHA guidelines in 2007 are very explicit about the need for good dental health and encourage improved access to routine dental care to prevent infective endocarditis. Exactly 100 years after Maude Abbott's discussion of ‘careful hygiene’ for patients with congenital heart disease, good oral hygiene has now become the cornerstone for the prevention of infective endocarditis in patients with congenital heart disease. Expert opinion and consensus have been guiding prophylaxis efforts since 1908. Given the lack of evidence-based recommendations, and the demonstration that bacteremias occur often on a daily basis and more commonly in patients with poor teeth and gums, the AHA was entirely justified in 2007 in withdrawing the recommendation of antibiotic prophylaxis for most patients with congenital heart disease, and in encouraging good oral hygiene for all. With the new emphasis on healthy teeth and gums, it will be important to carry these recommendations forward and advocate for accessible and affordable dental care for all children and adolescents in Canada. The AHA has called for further studies to prove the efficacy of preventive measures for any given procedure or patient. The Canadian Paediatric Society will hopefully soon be embarking on a survey of the incidence of infective endocarditis in Canada as part of its surveillance program. The Society is hopeful that data derived from this survey and its follow-up questionnaire will help sort out some of the issues that have left many practitioners uneasy about modifying their former antibiotic prophylaxis practice to conform to the new recommendations of the AHA.

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