Left atrial enlargement
In the general population, obesity appears to be the most important risk factor for LAE. LAE has been found to be correlated to body size, independent of obesity, meaning that LAE is more common in people with a naturally large body size.  Also, a study found that LAE can occur as a consequence of atrial fibrillation (AF), although another study found that AF by itself does not cause LAE. The latter study also showed that the persistent type of AF was associated with LAE, but the number of years that a subject had AF was not.
Obstructive sleep apnea (OSA) may be a cause of LAE in some cases. When an OSA event occurs, there is an attempt to breathe with an obstructed airway and the pressure inside the chest is suddenly lowered. The negative intrathoracic pressure may cause the left atrium to expand and stretch its walls during each OSA event. Over time, the repetitive stretching of the left atrium may result in a persistent left atrial enlargement.
Although other factors may contribute, left atrium size has been found to be a predictor of mortality due to both cardiovascular issues as well as all-cause mortality. Current research suggests that left atrium size as measured by an echo-cardiograph may have prognostic implications for preclinical cardiovascular disease. However, studies that have found LAE to be a predictor for mortality recognize the need for more standardized left atrium measurements than those found in an echo-cardiogram. 
LAE is suggested by an electrocardiogram (ECG) that has a pronounced notch in the P wave. However, if there is atrial fibrillation, a P wave would not be present. In any case, LAE can be diagnosed and measured using an echocardiogram (ECHO).
Characterizing the size of the left atrium according to its volume is preferred over a single linear dimension since enlargement can be different for different directions. For example, because of the smaller distance in the thoracic cavity between the sternum and spine, compared to the other directions, there is less room for enlargement of the left atrium along the anteroposterior axis. By approximating the shape of the left atrium as an ellipsoid, its volume can be calculated from measurements of its dimensions along three perpendicular directions.
Indexing the left atrial volume to body surface area (volume/BSA) is recommended by the American Society of Echocardiography and the European Association of Echocardiography. The values for volume/BSA in the following table are the ones that are the best validated and are the same for both men and women.
|Left Atrium Size||Women||Men|
|BSA, body surface area|
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