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INTRODUCTION

Infective endocarditis (IE) is thought to result from formation of nonbacterial thrombotic endocarditis (platelets and fibrin) on the surface of a valve or damaged endothelial surface, bacteremia with adherence to the fibrin-platelet matrix, and proliferation of the bacteria within the vegetation. The annual incidence of IE has been increasing from 2000 to 2011 and ranges from 3 to 10 episodes/100,000 population worldwide and 11 to 15/100,000 in the U.S. with a male predominance. Incidence of native-valve IE has decreased, while IE related to prosthetic valves and cardiac devices has increased.

Since 1955 the American Heart Association (AHA) has issued guidelines with various recommendations for prevention of IE with antimicrobial prophylaxis before specific procedures such as dental, gastrointestinal (GI), and genitourinary (GU) procedures in patients considered to be at risk for its development. The underlying principles were that: IE is uncommon but life- threatening and prevention is preferable to treatment; certain underlying cardiac conditions predispose to IE; bacteremia with organisms known to cause IE occurs in association with specific procedures; antimicrobial prophylaxis prevented experimental IE in animals and was thought to be effective in preventing IE in humans undergoing specific procedures. However, incidence and mortality of IE have not decreased in the past 30 years despite prophylaxis, and the guidelines are based on consensus or expert opinion rather than randomized controlled trials (RCT). With the incidence of IE continuing to increase, there have been questions about whether the change in guidelines that resulted in fewer groups of patients receiving prophylaxis was too restrictive. A 2013 Cochrane systematic review concluded that there remained no evidence about whether penicillin prophylaxis is effective or ineffective against IE in people at risk undergoing an invasive dental procedure.1 The authors questioned whether the potential harms and costs of prophylactic antibiotics outweighed any potential benefit. Previous guidelines were complicated, making it difficult for physicians and patients to remember or interpret, resulting in both overuse and underuse of prophylaxis.

This chapter will review and summarize the 2007 AHA guidelines2 (including the 2017 AHA/ACC focused update for the management of patients with valvular heart disease3) and highlight some of the recommendations from other societies, including the European Society of Cardiology (ESC)4 and National Institute for Health and Clinical Excellence (NICE)5 [http://www.nice.org.uk/CG064].6

PATIENT-RELATED RISK FACTORS/CARDIAC CONDITIONS

Conditions identified by the previous AHA guidelines as being associated with an increased risk of IE with a higher lifetime risk compared to individuals with no known underlying cardiac conditions included prosthetic cardiac valves, rheumatic heart disease (RHD), previous IE, congenital heart disease (CHD), and mitral valve prolapse (MVP) with mitral regurgitation.

However, the most recent AHA guidelines (2007) restricted prophylaxis to those patients with the highest risk of adverse outcome from IE who would derive the greatest benefit from its prevention assuming prophylaxis is effective. This high-risk group included patients ...

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