Earliest sign of left atrial enlargement

.Left atrial enlargement refers to dilation of the left atrium which occurs from multiple disease states that can chronically increase the left atrial pressure. These include congestive hea failure, cardiomyopathies, congenital hea defects and valvular hea disease In rheumatic mitral valve disease, there may be left atrial enlargement with specific enlargement of the left atrial appendage, first seen as a straightening of the left hea border below the left main bronchus, then as a discrete bulge on the left, immediately below the pulmonary bay and left main bronchus. Ref Robbins 9/e pg 345