Cardiovascular conditions predisposing to infective endocarditis: time to reconsider the current risk classification system?

Infective endocarditis (IE) remains a devastating disease despite continued advances in diagnosis, anti-microbial agents, and surgical therapy. Treatment typically involves a several week course of parenteral antibiotics, and nearly half of cases will require cardiac surgery during the acute to subacute phase. The epidemiology of IE has changed significantly in recent years, a trend characterized by a decrease in the prevalence of rheumatic heart disease, the advancing age of the population, patient co-morbidities, increases in the use of prosthetic heart valve substitutes and cardiac implanted electronic devices (CIEDs), and the worldwide surge in injection drug use. Staphylococcal species are now the most common bacterial pathogens, and many instances of IE occur in the absence of antecedent valvular heart disease. Patient outcomes are highly variable, depending on prompt recognition, early complications, and the timely application of surgery when indicated. Development of effective strategies to prevent IE has been challenged by its relatively low incidence at the population level and the increasing heterogeneity of predisposing conditions that confer risk. Recent guideline recommendations for the use of prophylactic antibiotics to prevent IE have been focused on their delivery to atrisk patients prior to dental/oral surgical procedures associated with transient bacteraemia. As a prevention strategy, they are thus quite narrow in scope and not without controversy. Inability to prove causality, concerns regarding the emergence of antibiotic resistance, and wariness about cost-effectiveness led professional societies and health organizations to re-examine this practice. It has been >10 years since the American Heart Association (AHA), followed in turn by the National Institute for Health and Care Excellence (NICE) and the European Society of Cardiology (ESC), issued restricted recommendations for antibiotic prophylaxis. Two of the three organizations (AHA and ESC) limited antibiotic prophylaxis to ‘highrisk’ patient subsets [e.g. those with prior IE, prosthetic heart valves, or cyanotic congenital heart disease (CHD)], whereas the third (NICE) recommended against the routine use of antibiotics across all patient risk categories. The results of epidemiological studies examining the effects of a reduction in antibiotic prescribing for dental prophylaxis on the incidence of IE have been mixed. It is reasonable to question whether IE risk in the current era can be reliably assigned using outdated historical benchmarks. Accurate risk assessment is essential not only for targeting prevention strategies but also for ensuring best practices and informing the design of future clinical trials. In this issue of the journal, Thornhill et al. provide a contemporary assessment of the relative risks of incident IE from all causes and hospital-related mortality among patients with cardiovascular disease identified as ‘high’ or ‘moderate’ risk by AHA and ESC criteria (see Supplementary table S1 in Thornhill et al. in for definitions) during admission to all English hospitals between January 2000 and March 2008. Individuals were followed for a minimum of 5 years through March 2013. Data were extracted from the Hospital Episode Statistics (HES) registry. The registry, using National Health Service unique patient numbers, captured cases of IE admitted to English hospitals reliably and accurately. The English population in 2008 served as the referent cohort. The study confirmed that the 5-year relative risks of incident IE and in-hospital death following admission with IE are very high among select patient cohorts traditionally considered ‘high risk’, namely those with a previous history of IE or prosthetic or repaired heart valves, CHD, or CHD with palliative shunts/conduits. Five-year risks of IE and related mortality in other patient subgroups, however, varied somewhat from what was expected. For example, patients with CHD repaired with prosthetic material (traditionally considered a