The left atrial appendage is the most common site for cardiac thrombus. It is anatomically attached to the left inferior portion of the left atrium and consists of muscular trabeculae. The left atrial appendage does not contribute, to a large degree, to overall cardiac output.
Left atrial appendage thrombus is diagnosed on transesophageal echocardiography, as thoracic views are not adequate to visualize the left atrial appendage. Transesophageal echocardiographic findings of a left atrial appendage thrombus includes direct visualization of a mobile echodensity within the appendage. The echodensity should move independent of the walls of the atrium, which helps to distinguish artifact or trabeculae from thrombus. Pulse wave Doppler can be used in the left atrial appendage to determine the flow velocity. A velocity of < 0.4 m/s indicates a higher risk, in general, of thromboembolism. Cardiac CT can be used, as well.
During atrial fibrillation and atrial flutter, the left atrial appendage loses contractility. This results in decreased flow velocities and rouleaux formation of red blood cells, which is seen as “spontaneous echo contrast” on echocardiography.
If a thrombus in the left atrial appendage embolizes, stroke can occur. Embolism to the lower extremities, kidney, spleen or mesenteric vessels can occur, as well.