INFECTIVE ENDOCARDITIS

The true incidence of endocarditis is unknown but it is, at least, 25 cases per million. The formation of an infected vegetation results from an interplay between the host and the microorganism; host mechanisms include phagocytes, antibodies and clotting factors whilst the adherence properties of the microorganisms are crucial. Evidence suggests that for a given species it is the intensity of the bacteraemia rather than its duration that is important. A fever, a murmur (often changing) and embolic phenomena remain the most common clinical features in endocarditis. Endocarditis appears to be rarely associated with HIV infection or the AIDS syndrome. Ninety per cent of positive cultures are obtained from the first two blood samples and 95% of clinically significant bacteria are isolated from blood cultures within 7 days of incubation. Negative cultures in cases of endocarditis with typical features occur in about 5% of cases, the commonest reason being prior antibiotic therapy within 2 weeks of blood cultures being taken. The possibility that the illness is not endocarditis should be considered when cultures are repeatedly negative. A diagnosis of endocarditis cannot be excluded by a negative echocardiogram; the sensitivity of the echocardiogram depends on the size of the vegetation and the time course of the disease. Transoesophageal echos (TOE) are more than twice as sensitive as transthoracic echos and TOE is the preferred approach for suspected mitral prosthetic endocarditis, mitral leaflet perforation, abscess location and right-sided endocarditis. Streptococci remain the commonest bacteria isolated from cases of infective endocarditis, unusual organisms accounting for only 5% of cases. In the treatment of endocarditis, bacteriocidal antibiotics should be used, if possible, and the duration of therapy is dependent on the nature and severity of the infection, the clinical response to treatment and the development of any complications. A cardiac surgeon should always be involved from the outset in the overall management of a case. The main indications for surgery are a failure to maintain haemodynamic stability or a failure to cure sepsis. The link between vegetation size (> 10 mm) and embolization is not strong enough to advocate surgery as an absolute treatment in these circumstances. Of patients with endocarditis, about half were not previously known to be at risk whilst those with prosthetic values are the highest risk category. The essence of good practice is to identify those patients at risk and the procedures known to predispose to endocarditis and give appropriate antibiotic prophylaxis.