Electrocardiograms showing atrial enlargement

P wave morphology with atrial enlargement in leads I, II, and V1. The P waves in left atrial enlargement (left panel) are wide (>0.12 seconds) and notched in leads I and II, and the terminal segment has a negative deflection that is deep and delayed in V1. In right atrial enlargement (middle panel), the P wave amplitude is increased (0.28 mV) in lead II. Biatrial enlargement (right panel) has characteristics of both atrial abnormalities: the P wave amplitude (0.22 mV) and duration (0.12 seconds) are increased in lead II, and there is deep terminal negativity in V1.