P wave

The P wave is the first wave of a normal beat. It represents atrial depolarisation.

On a normal ECG, the P wave is positive (upright) in leads I and II, but negative (inverted) in aVR and biphasic in V1. At standard settings, it should be less than 3 mm wide (120 ms), and less than 2.5 mm tall (or <1.5 mm in the chest leads V1-V6).

An abnormal P wave can be caused by atrial enlargement or abnormal rhythms.

P waves are often easiest to see in the inferior leads (II, III and aVF) and lead V1.

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