Right atrial enlargement (RAE):
RAE is synonymous with RVH. The best criterion is a positive component of the P wave in lead V1 OR V2 > 1.5 mm, shown below.

Another criterion is a P wave amplitude in lead II > 2.5 mm. Caveat: A tall, peaked P in lead II may represent RAE, but is more commonly due to either COPD and/or increased sympathetic tone.

Left atrial enlargement (LAE):
The most sensitive lead for the diagnosis of LAE is lead V1, but criteria for lead II are more specific. With LAE, consider: LVH, coronary artery disease, mitral valve disease or cardiomyopathy.

In lead V1, look for a terminal negative wave > 1 mm deep and > 40 msec wide (one small box by one small box in area). In lead II, look for > 40 msec between the first (R) & second (L) atrial components.

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