Prolapsed left atrium behind the left ventricular posterior wall: two dimensional echocardiographic and angiographic features.

Left atrial enlargement can usually be detected accurately using M mode echocardiography. However, in the presence of heart disease, asymmetric enlargement may lead to inaccurate assessment of left atrial size and shape. Pericardial effusion can usually be diagnosed on the basis of characteristic M mode echocardiographic findings. However, false positive patterns sometimes occur with the use of this single dimensional technique. Three patients with a greatly enlarged left atrium are described whose M mode echocardiogram suggested significant posterior pericardial fluid accumulation. In each patient, two dimensional echocardiography detected portions of a huge left atrium that prolapsed behind the left ventricular posterior wall and mimicked an isolated posterior pericardial effusion. In one case a right anterior oblique left ventricular cineangiogram suggested the presence of a ventricular septal defect or a false aneurysm of the left ventricle due to the prolapsed left atrium. Because two dimensional echocardiography can provide accurate spatial orientation with visualization of intracardiac structures in relation to one another in real time, it can identify the presence of left atrial prolapse and play an important role in the differential diagnosis of isolated echo-free spaces behind the left ventricle detected with M mode echocardiography.