A left atrium of 40mm is considered enlarged and should normally be less than 30mm.
There are many factors that affect the size of the left atrium, such as height and race and other physiological factors. However, it is more often associated with disease, such as hypertension, coronary artery disease, heart valve disease such as mitral stenosis or closure insufficiency, in addition, cardiac muscle disease such as dilated cardiomyopathy can also affect the size of the left atrium.
When the left atrium is found to be enlarged on examination, tests such as evaluation of the patient’s heart valves and systolic-diastolic function are also needed to further define the cause.
Patients with mild enlargement and no obvious clinical symptoms can be reviewed periodically. However, when significant enlargement occurs, or when the cause is clearly identified, symptomatic treatment should be based on the cause.