Investigations in suspected infective endocarditis
THE CONTEXT
Investigation identifies the organism, assesses vegetations and valve damage, detects complications, and monitors treatment progress.
Blood cultures
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Blood culture is the pivotal investigation for identifying the organism and guiding antibiotic treatment.
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Collect three to six sets before starting therapy without waiting for episodes of pyrexia. The first two specimens detect bacteraemia in 90% of culture-positive cases.
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Use meticulous aseptic technique and peripheral sampling sites rather than in-dwelling lines. Collecting discrete sets at 30-minute intervals reduces misdiagnosis from contamination with skin commensals.
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A typical organism isolated in more than one culture strongly supports the diagnosis. Both aerobic and anaerobic cultures are required.
Echocardiography
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Perform echocardiography as soon as endocarditis is suspected to detect and follow vegetations, assess valve damage and detect abscesses.
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Transthoracic echocardiography can detect vegetations as small as 2–4 mm; transoesophageal echocardiography can visualise smaller vegetations measuring 1–1.5 mm.
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Transoesophageal echocardiography is particularly valuable for detecting abscesses, imaging prosthetic valves and investigating a negative or unremarkable initial transthoracic study.
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Transthoracic sensitivity is approximately 65%, compared with more than 90% for transoesophageal echocardiography. Abnormal valves can make vegetations difficult to distinguish, and failure to detect vegetations does not exclude endocarditis.
Blood and urine findings
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Inflammatory markers are almost always raised. Elevated CRP and ESR, normocytic normochromic anaemia and leucocytosis are common but not invariable.
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Surveillance CRP is more reliable than ESR for monitoring progress.
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Proteinuria may occur, and non-visible haematuria is usually present.
Electrocardiography and chest imaging
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The ECG may show atrioventricular block due to aortic root abscess formation, or occasionally infarction due to emboli.
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The chest X-ray may show cardiac failure and cardiomegaly.