[Recent morphofunctional findings on the left atrium: their relations to thromboembolic risk]

In the past, the left atrial appendage has been considered a "useless" structure but associated to thromboembolic complications; its physiologic role is still undefined. Owing to its great distensibility, left atrial appendage positively influences atrial compliance and left ventricular performances. In addition this structure seems to play an important role in circulatory homeostasis by the release of atrial natriuretic factor in response to volume loading and atrial stretch. Transesophageal echocardiography provides a detailed anatomical characterization of this structure and, by means of Doppler flow velocities recordings, supplies relevant functional data. Despite their anatomical contiguity, the left atrium and atrial appendage result from a separate embryonic development; likewise, their function may differentiate. In the left atrial appendage a quadriphasic flow pattern has been described in subjects with sinus rhythm; however, as we reported, in some patients a more complex Doppler pattern can be observed, with an additional systolic forward flow wave which is presumably due to reflection phenomena. In patients with atrial fibrillation, an irregular flow pattern has been detected, which is mostly dependent on the duration of the arrhythmia, the underlying heart disease and the left atrial pressure. By transesophageal echocardiography a clear correlation has been established between the left atrial appendage slow flow and the occurrence of thromboembolic events; however, while waiting data from large studies, stratification of patients according to thromboembolic risk and decisions about anticoagulant prophylaxis should be performed by clinical information and transthoracic echocardiographic findings. No clinical or echocardiographic parameter has been found to be predictive of the thromboembolic events after cardioversion; in this setting the exclusion of atrial or atrial appendage thrombi by transesophageal echocardiography does not rule out the need for anticoagulation in patients with atrial fibrillation undergoing electrical or pharmacological cardioversion.