Diagnostic value of echocardiography in infective endocarditis: a probabilistic approach

The high sensitivity and specificity of echocardiography in the diagnosis of infective endocarditis have been well established for a number of years. However, little is known yet about the incremental value of this technique over the clinical and serological findings already available in subsets of patients presenting different initial probabilities in infective endocarditis. In this report, sensitivity and specificity of echocardiography were calculated in 173 consecutive patients with suspected infective endocarditis who underwent echocardiography within 5 days following admission. The echocardiogram was considered positive when Duke major criteria were fulfilled. Infective endocarditis was diagnosed in 88 patients, while other illnesses in the remaining 85. The diagnoses were confirmed retrospectively with a follow-up done after at least 3 months, at surgery or during autopsy. Sensitivity and specificity of the echocardiography in this population were 85 and 97% respectively. The initial probabilities of infective endocarditis in patients with different clinical presentations were taken from a thorough review of the literature available in English and from personal research. The positive predictive value of echocardiography is already high or very high even at low or very low levels of initial probability, and this has a strong impact on clinical decisions. In these situations and with intermediate probabilities, a negative echocardiogram would theoretically rule out the disease. However, this result, if considered alone, calls for a careful reassessment of the entire clinical context. As with any other test, when the initial probabilities of infective endocarditis are highest, the incremental value of echocardiography is poor.