الفهرس 
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Abstract
The left atrial appendage (LAA) is derived from the left wall of the primary atrium, which forms during the fourth week of embryonic development. It has developmental, ultrastructural and physiological characteristics distinct from the left atrium proper. 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 The LAA shortens to a greater extent than the rest of the left atrium and has a distinct pattern of contraction. Blood flow within the LAA has been studied with trans-esophageal echocardiography (TEE), which affords good views of the appendage and its orifice. Doppler measured LAA flow in patients with sinus rhythm was initially described as biphasic, but additional emptying and filling waves resulting in quadriphasic appendage flow have been described in 40–70% of patients.
Left atrial appendage dysfunction was found to be an independent predictor of thromboembolism in mitral stenosis (MS).
Echocardiographic studies in patients with non-rheumatic AF demonstrate that more than 90% of atrial thrombi develop in the LAA. Stagnant blood flow in LA is believed to increase the risk of thrombus formation. This in turn leads to a heightened risk of embolic stroke. Echocardiographic criteria for identifying patients at a particular risk are findings of spontaneous echo contrast seen with the transthoracic echocardiogram or peak flow velocities in the LAA of 20 cm/s on a TEE.