Endocarditis
Endocarditis refers to inflammation of the endocardium, the inner layer of the heart (including the heart valves). Endocarditis can be:
infective (e.g. bacterial, fungal)
non-infective (e.g. Libman-Sacks endocarditis in systemic lupus erythematosus).
The characteristic lesion in endocarditis is the vegetation, a mass of inflammatory material which can include fibrin, platelets, red and white blood cells and (where present) micro-organisms.
INFECTIVE ENDOCARDITIS
In the past, infective endocarditis has been classified as acute or subacute (‘SBE’, subacute bacterial endocarditis) but this terminology is outdated and should no longer be used. Although infective endocarditis is rare (fewer than 10 cases per 100 000 population every year), it is nevertheless a serious and dangerous condition, with a mortality of around 20 per cent even with treatment.
Infective endocarditis starts with organisms reaching the endocardium either via a bacteraemia or directly via surgery or device placement. The organisms adhere to the endocardium, and as they invade the local tissues a vegetation begins to form. Left untreated, they cause local tissue destruction (e.g. valvular regurgitation) and can also lead to abscess and/or fistula formation.
The single most common causative organism is Staphylococcus aureus; other commonly encountered organisms are listed in Table 23.1.
Clinical features of infective endocarditis
The clinical features of infective endocarditis (Table 23.2) can be subtle and sometimes will have been present for several weeks, so a high index of suspicion is needed to avoid missing the diagnosis. Be particularly alert to the possibility of infective endocarditis in those at risk (see above), and/or those with a history of invasive procedures or intravenous drug use.
The Duke (or modified Duke) criteria can be helpful in cases of diagnostic uncertainty (Durack et al. 1994).
Blood cultures are the mainstay of diagnosis, and at least three sets should be taken from different sites at different times. Always perform an echo study in any patient with a positive blood culture for Staphylococcus aureus or for Candida, in view of the likelihood of infective endocarditis with these organisms and the particularly serious consequences that can result. Blood cultures may be negative, even in the presence of infective endocarditis, because of prior antibiotic treatment or the presence of fastidious (difficult to culture) organisms.
Table 23.1 Common causes of infective endocarditis | ||||
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Table 23.2 Clinical features of infective endocarditis | ||||||||||||
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Echocardiography plays a valuable role in identifying:
presence of vegetations
valvular destruction
associated abscess, fistula or perforation.
‘Major’ echo criteria supporting a diagnosis of infective endocarditis are the presence of oscillating structures (vegetations), the presence of an abscess, new valvular regurgitation and dehiscence of a prosthetic valve.
Transthoracic echo (TTE) can, at best, detect vegetations down to a minimum size of 2 mm (and is known to miss the majority of vegetations <5 mm). The superior image quality of transoesophageal echo (TOE) makes it more sensitive and specific than TTE, particularly in cases of prosthetic valve endocarditis and in the detection of abscesses. TTE has an overall sensitivity in detecting vegetations of ≈50 per cent, whereas the sensitivity of TOE is ≥90 per cent.
TTE is an appropriate first-line imaging investigation in suspected infective endocarditis, and is ideally performed within 24 h, but consider TOE in cases where the TTE is negative or inconclusive (particularly if the clinical suspicion of infective endocarditis is high), or where there is a suspicion of prosthetic valve endocarditis, right heart endocarditis or a cardiac abscess. Indeed, TOE should be considered in most adult patients with suspected infective endocarditis, even when the TTE is positive. However, if a good-quality TTE is negative, and the clinical suspicion is low, then it is not usually necessary to proceed to a TOE.
Where the clinical suspicion is high, but an initial scan has been negative, then a repeat TTE/TOE
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