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Infective endocarditis 

Infective endocarditis

Chapter:
Infective endocarditis
Author(s):

James L. Harrison

, Bernard D. Prendergast

, and William A. Littler

DOI:
10.1093/med/9780199204854.003.160902_update_001

Update:

Antimicrobial Chemotherapy (2012), Guidelines for the antibiotic treatment of endocarditis in adults: report of the Working Party of the British Society for Antimicrobial Chemotherapy.

Updated on 29 Oct 2015. The previous version of this content can be found here.
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date: 26 March 2017

Endocarditis predominantly affects the aortic and mitral valves; involvement of the tricuspid valve occurs in approximately one-fifth of cases and pulmonary valve involvement is rare. In the developing world rheumatic heart disease is the most common predisposing factor. In developed countries endocarditis is more common in older people with native valve disease and in patients with prosthetic valves and intracardiac devices (pacemakers and defibrillators). In these countries up to 50% of cases have no predisposing cardiac lesion and more cases are related to intravenous drug abuse and nosocomial infection related to invasive procedures. Mortality remains high (30%) despite advances in antimicrobial therapy and surgery, and at least 50% of cases require valve surgery. Early diagnosis, specialist management, and timely intervention are key to successful outcome.

Clinical features

Presenting symptoms and signs include those of a bacteraemic illness, tissue destruction (heart valve(s) and adjacent structures); phenomena thought to be related to circulating immune complexes, e.g. splinter and conjunctival haemorrhages, Osler’s nodes, Janeway lesions, vasculitic rash, Roth spots, and nephritis; and systemic and septic pulmonary emboli in left- and right-sided lesions respectively.

Blood culture is the most important laboratory investigation, with prolonged incubation requested in circumstances where endocarditis is strongly suspected. Serological tests can aid in the identification of organisms that are difficult to isolate. Echocardiography should be performed as soon as possible when endocarditis is suspected: its principal role is to detect vegetations, but it is not sufficiently sensitive to allow the clinician to exclude the diagnosis confidently on the basis of a negative result. Diagnosis is based on pathological criteria (demonstration of microorganisms by culture or histological examination, or histological evidence of active endocarditis) or—more usually—a combination of major and minor clinical criteria, with the major clinical criteria relating to (1) positive blood cultures of ‘typical’ or ‘consistent’ organisms, and (2) evidence of endocardial involvement detected on physical examination (new murmur) or with echocardiography.

Causes and management

Worldwide the principal causes of endocarditis are viridans streptococci (up to 58%) and Staphylococcus aureus (30% of community-acquired and 46% of hospital-acquired disease) with Streptococcus bovis, enterococcus species, fungi, coagulase-negative staphylococci, and the HACEK group of organisms making up the remainder. However, in developed countries the epidemiological profile has changed in recent decades: rheumatic heart disease is now rare, and with more cases related to prosthetic valves (20% of all cases) device therapy and nosocomial infection, Staph. aureus has overtaken oral streptococci as the most common pathogen.

Best management is provided by a multidisciplinary team involving cardiologists, microbiologists, infectious disease specialists, and cardiac surgeons. Bactericidal antibiotics are the mainstay of treatment. Recommended empirical therapy for the patient with suspected native valve endocarditis is amoxicillin or ampicillin (12 g/day IV in four divided doses) plus gentamicin (1mg/kg body weight IV 8-hourly, modified according to renal function), substituting vancomycin for amoxicillin/ampicillin in patients with penicillin allergy. This should be modified to a definitive antibiotic treatment regimen when the pathogen is known. Surgery is required in about 50% of cases, with the main indications being haemodynamic instability, persistent infection, annular or aortic abscesses, and significant residual valve regurgitation once antibiotic therapy is complete.

Prevention

Until recently, antibiotic prophylaxis in at-risk patients—meaning any with a wide variety of cardiac lesions undergoing a wide variety of dental, medical, and surgical procedures—was accepted as reasonable, but there is no good evidence to support this practice. Recommendations from relevant United Kingdom, European, and American professional bodies are now much more restrictive. National Institute for Health and Clinical Excellence (United Kingdom) guidelines state that antibiotic prophylaxis should only be given to high-risk patients (including those with prosthetic cardiac valves or other prosthetic material within their hearts, previous endocarditis, and some forms of congenital heart disease) if they are undergoing a gastrointestinal or genitourinary procedure at a site where there is suspected infection. Most cardiologists feel that this is too restrictive and prefer European and American guidelines that recommend prophylaxis before dental and nondental procedures for patients at high risk.

When prophylaxis is recommended for dental and other procedures, regimens typically include amoxicillin (or clindamycin if penicillin-allergic), with the addition of gentamicin if risks are thought to be high, and substitution of vancomycin (or teicoplanin) for amoxicillin if the patient is penicillin-allergic (or has taken more than a single dose of penicillin in the previous month).

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