Left atrial appendage: structure, function, and role in thromboembolism

The left atrial appendage (LAA) is derived from the left wall of the primar y atrium, which forms during the fourth week of embryonic development. It h as developmental, ultrastructural, and physiological characteristics distin ct from the left atrium proper. The LAA lies within the confines of the per icardium in close relation to the free wall of the left ventricle and thus its emptying and filling may be significantly affected by left ventricular function. The physiological properties and anatomical relations of the LAA render it ideally suited to function as a decompression chamber during left ventricular systole and during other periods when left atrial pressure is high. These properties include the position of the LAA high in the body of the left atrium; the increased distensibility of the LAA compared with the left atrium proper; the high concentration of atrial natriuretic factor (AN F) granules contained within the LAA; and the neuronal configuration of the LAA. Thrombus has a predilection to form in the LAA in patients with atria l fibrillation, mitral valve disease, and other conditions. The pathogenesi s has not been fully elucidated; however, relative stasis which occurs in t he appendage owing to its shape and the trabeculations within it is thought to play a major role. Obliteration or amputation of the LAA may help to re duce the risk of thromboembolism, but this may result in undesirable physio logical. sequelae such as reduced atrial compliance and a reduced capacity for ANF secretion in response to pressure and volume overload.