Left Atrium

Left atrial thrombi occur in the setting of low cardiac output, mitral valvular disease (particularly mitral stenosis), atrial fibrillation, and LA enlargement. Both TTE and TEE can detect thrombi within the main cavity of the left atrium (Fig. 13-131), but TEE is clearly superior for visualizing thrombi within the left atrial appendage.658-660 Since approximately 50 percent of LA thrombi are limited to the appendage, TEE is the diagnostic procedure of choice to detect this lesion.652,661 LA thrombi appear as discrete masses, either fixed or mobile, and are usually of homogeneous echo density659 Fig. 13-52). On TEE, normal pectinate muscular ridges in the appendage must be distinguished from small thrombi. In addition, the left atrial appendage may occasionally be multilobed. Although this anatomic variant may be a risk factor for appendage thrombi, the atrial tissue separating the lobes should not be mistaken for clot.662

Images Left Atrial Thrombus Formation

Figure 13-131: Apical four-chamber image of a large mobile "ball" thrombus (arrow) in the left atrium (LA). LV = left ventricle. (From Blanchard DG, DeMaria AN. Cardiac and extracardiac masses: Echocardiographic evaluation. In: Skorton DJ, Schelbert HR, Wolf GL, Brundage BH, eds. Marcus' Cardiac Imaging, 2d ed. Philadelphia: Saunders; 1996:452-480, with permission.)

Figure 13-131: Apical four-chamber image of a large mobile "ball" thrombus (arrow) in the left atrium (LA). LV = left ventricle. (From Blanchard DG, DeMaria AN. Cardiac and extracardiac masses: Echocardiographic evaluation. In: Skorton DJ, Schelbert HR, Wolf GL, Brundage BH, eds. Marcus' Cardiac Imaging, 2d ed. Philadelphia: Saunders; 1996:452-480, with permission.)

Left atrial thrombi are often accompanied by spontaneous echo contrast (or "smoke") within the LA. This finding, probably produced by transient aggregation of erythrocytes and plasma proteins,663 indicates stagnant blood flow and can occur in any cardiac chamber or the aorta. Left atrial spontaneous echo contrast, like LA thrombus, has been associated with embolic events664,665 and may be a marker of regional prothrombotic activity.666 On 2D imaging, the contrast signals are in constant motion and can be missed if gain settings are inappropriately low.

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