The P waves
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.
Normal P wave
✅ 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.
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.
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.
Inverted P waves
Causes include:
✅ Ectopic atrial beat or rhythm.
✅ AV junctional premature complex or rhythm.
✅ Lead placement error.
✅ Dextrocardia.
✅ Others.
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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