About P waves

1/ Let’s talk about P waves.

The P wave is the first positive deflection on the EKG and represents atrial depolarization. The first half represents right atrial depolarization and the second half represents left atrial depolarization.

2/ Normal P wave

Criteria

✅ Axis: 0° to +75°.
✅ Amplitude (L leads): <2.5 mm.
✅ Amplitude (P leads): <1.5 mm.
✅ Duration: 0.08 - 0.11 sec. 
✅ Morphology: Upright in I, II, aVF and inverted in aVR. 

3/ Peaked P wave 

The morphology is peaked with amplitude ≥2.5 mm, usually in II, III and aVF. 

The peaked P wave is a typical characteristic of right atrial abnormality/enlargement. 

Causes: PE, COPD, congenital heart disease, pulmonary hypertension, normal variant, others.

4/ Notched P wave

The morphology is notched like an "M" shape. 

If the duration is ≥0.12 sec consider left atrial abnormality/enlargement. 

Causes include: Heart failure, LVH, MI, mitral or aortic valve disease, others.

5/ Inverted P waves

Causes include: 

✅ Ectopic atrial beat or rhythm.
✅ AV junctional premature complex or rhythm.
✅ Lead placement error. 
✅ Dextrocardia. 
✅ Others. 

6/ Retrograde P wave

The impulse can travel backward, in a retrograde fashion, through the atria, producing a retrograde P wave, as long as the impulse penetrate the AV node and depolarize the atria. 

Retrograde P waves can be: 

✅ Before the QRS. 
✅ During the QRS. 
✅ After the QRS. 

Usually inverted in II, III and aVF and upright in aVR and V1.

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The EKGs are courtesy of EKGDX.