The ability of echocardiography to detect left atrial clot is determined by the sophistication of the equipment, the ease with which the left atrium and left atrial appendage can be scanned and the skill and experience of the operator. Historically, at best, the sensitivity of two dimensional transthoracic echocardiography for detecting left atrial thrombus has been of the order of 40–65%, with the left atrial appendage visualised in under 20% of patients even in experienced hands. This compared with a reported sensitivity of 75–95% for visualising left ventricular thrombi from the transthoracic approach. More recent data, from a tertiary referral centre using the new generation transthoracic echocardiography, suggest the left atrial appendage can be adequately imaged in 75% of patients and that within this group 91% of thrombi identified by transoesophageal echocardiography will also be visualised from the transthoracic approach. Although encouraging, the extent to which these figures can be reproduced using similar equipment by the generality of units remains to be established.
Available data for the sensitivity of transoesophageal echocardiography in detecting left atrial and left atrial appendage thrombus consistently report a high positive predictive value. The largest series of 231 patients identified thrombus ranging from 3 to 80mm in 14 patients: compared with findings at surgery this produced a sensitivity of 100%. But these findings need to be interpreted with considerable caution and are unlikely to be applicable to all users of the technique. The study was carried out in a tertiary referral centre with a particular interest and long-standing investment in the technique and the nine observers involved in reporting the data all had extensive experience. Nonetheless, transoesophageal echocardiography is undoubtedly the investigation of choice for imaging the left atrium and left atrial appendage.
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