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 heart failure, cardiomyopathies, congenital heart defects and valvular heart disease.
Left atrial enlargement can be diagnosed on the ECG or via echocardiography. When left atrial enlargement occurs, it takes longer for cardiac action potentials to travel through the atrial myocardium, thus the P wave length becomes longer. Thus the criteria for diagnosing LAE on ECG is as follows:
1) The P wave length in lead II greater than 120 milliseconds
2) The downward deflection of the P wave in lead V1 greater than 40 milliseconds in length AND greater than 1 millimeter negative deflection (less than -1 millimeter in amplitude).
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