Infective endocarditis

Endocarditis predominantly affects the valves of the left side of the heart: a large autopsy series revealed mitral involvement in 86%, aortic 55%, tricuspid 20%, and pulmonary 1%. In the developing world rheumatic heart disease is the commonest predisposing factor, but in developed countries over 50% of patients have no known pre-existing cardiac lesion.

Clinical features

Presenting symptoms and signs include those of a bacteraemic illness, tissue destruction (heart valve(s) and adjacent structures), systemic or pulmonary embolism, and 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. Right-sided infective endocarditis accounts for only 5% of cases overall, is usually associated with intravenous drug abuse or indwelling intravascular devices, and often causes septic pulmonary emboli that can lead to cavitating pulmonary infarcts.

Investigation and diagnosis—blood culture is the most important laboratory investigation in the diagnosis of endocarditis, 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 by echocardiography.

Causes and management

The causes of endocarditis are viridans streptococci (up to 58%), Staphylococcus aureus (30% of community acquired and 46% of hospital acquired), Streptococcus bovis (up to 12%), enterococcus species (up to 10%), fungal (up to 10%), coagulase-negative staphylococci (5% of native valve endocarditis), the HACEK group of organisms (3%), and others.

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 endocarditis presenting acutely is flucloxacillin (8–12 g/day IV in four to six divided doses) plus gentamicin (1 mg/kg body weight IV 8-hourly, modified according to renal function), and for the patient presenting with a more indolent course is penicillin (7.2 g/day IV in six divided doses) or ampicillin/amoxicillin (2 g IV 6-hourly) plus gentamicin (as above). This should be modified to a definitive antibiotic treatment regimen when the pathogen is known (see text for details). Surgery is required in about 30% of cases during the acute phase and in 20 to 40% of cases thereafter, with the main indications being haemodynamic instability, persistent infection, and annular or aortic abscesses.

Prevention

Until recently, antibiotic prophylaxis in ‘at risk’ patients—meaning any with a wide variety of cardiac lesions undergoing a wide variety of medical/surgical procedures—were accepted as reasonable, but there is no good evidence to support this practice. Recommendations from relevant UK, European and American professional bodies are now much more restrictive. UK (National Institute for Health and Clinical Excellence) guidelines state that antibiotic prophylaxis should only be given to patients at risk 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 which recommend prophylaxis before dental and non-dental procedures for patients at high risk, including those with prosthetic cardiac valves or other prosthetic material within their hearts, previous infective endocarditis, and some forms of congenital heart disease.

When prophylaxis is recommended for dental and other procedures, regimen 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).