Left atrial impression: a sign of extra-cardiac pathology.

Compression of the left atrium by extra-cardiac structures is a rare cause of dyspnoea or reduced exercise tolerance and can easily be visualized by transthoracic echocardiography (TTE). An impression of the left atrium visualized by TTE could be the first indication of the presence of a pathological structure dorsal to the left atrium; such a structure can, in time, compress the left atrium. The existence of this phenomenon and its clinical implications will be reviewed. The impressing structures are divided into four anatomic groups: (i) gastrointestinal structures, which are the most common, (ii) mediastinal structures, (iii) aorta and intrapericardial structures, and (iv) pulmonary structures. Explanatory examples of left atrial impression with different causes and various levels of severity are presented.