Endocarditis

Epidemiology

The incidence of bacterial endocarditis increases from 3/100000 of the population to 10/100000 for people aged over 65 years. Valvular abnormalities, particularly those that damage the endothelial surface by high-velocity jets (audible as a murmur), predispose to a fibrin–platelet deposit. Patients who had endocarditis previously or have prosthetic heart valves are also at risk. An intermittent bacteraemia (e.g. caused by injury or inflammation of the mucosal surfaces in the mouth, gastrointestinal or genitourinary tract) seeds the preformed thrombus, which enlarges to a vegetationStreptococcus viridans, enterococci, Staphylococcus aureus and the so-called HACEK group (oral fastidious Gram-negative rods) have particular affinity for fibrinonectin in the thrombus. Patients in high-risk group, (prosthetic heart valves, congenital heart disease and previous endocarditis) should receive antibiotic prophylaxis on induction for surgery that is potentially contaminated and dirty. Usually amoxicillin and gentamicin is given.

Clinical features

Patients with infective endocarditis present with non-specific symptoms such as fever, night sweats, arthralgias and usually a murmur. Infected valvular vegetations result in local tissue destruction, embolic events and formation of immune complexes. Valve destruction may present as new regurgitation or conduction block. Embolic events lead to the characteristic splinter haemorrhages (Fig. 3.23.1), Janeway lesions and cerebral and pulmonary infarcts. Immunological phenomena comprise painful Osler nodes on fingers, arthritis and glomerulonephritis.

Fig. 3.23.1 Splinters and infarcts produced by embolization in infective endocarditis. (Reproduced with permission from Spicer W J 2008 Clinical microbiology and infectious diseases, 2edn, Churchill Livingstone, Edinburgh.)

Echocardiography (Fig. 3.23.2) is the mainstay of diagnosis. Transthoracic echocardiography (TTE) is less sensitive (70%) than transoesophageal echocardiography (TOE), but more readily availabe in hospitals. Patients with abnormal native valves, prosthetic valves or calcification require TOE for imaging of vegetation or abscesses. Three to six blood cultures should be collected from different venepuncture sites within 24 h (spaced at least 1 h apart) before commencing antibiotic therapy. For the diagnosis of microorganisms that usually do not grow in blood cultures (Coxiella burnetii, Bartonella spp. and Chlamydophila psitacii), serological investigations should be performed. As symptoms are non-specific (Fig. 3.23.3), modified Dukes criteria have been developed to improve the diagnosis by weighting clinical symptoms. Division is made into whether a native or prosthetic valve is involved and the latter by time of onset: early (within 2 months of surgery) or late.