Last update: May 2020


  P wave shows atrial depolarization.

  Right atrium depolarizes first since sinoatrial node, the source of sinus impulse, is located in high right atrium.

  Therefore,

- first half of the P wave is formed by depolarization of right atrium and

- second half is formed by depolarization of left atrium.

  During normal sinus rhythm, the P wave is positive (upright) in leads I and II.

  Normal P wave duration (width) is < 120 ms (three small squares).

  Normal P wave amplitude (height) is < 2.5 mm (0.25mV).



Effect of P wave axis on mortality

  Abnormal P wave axis has been reported to be related to mortality.

  A long-term follow-up (median 13.8 years) of 7,5012 individuals from the NHANES III survey has shown that abnormal P wave axis was associated with 55% increase in all-cause mortality, 41% increase in cardiovascular mortality (P wave axis between 0 and +75 degrees was accepted as normal).

  This association of P wave axis and mortality was observed even in patients without COPD.



Absence of P wave is seen in the following:

1. Atrial fibrillation
2. Hyperkalemia
3. Nodal rhythm
4. Sinoatrial exit block


Click here for double P wave (atrial dissociation)


Tall and peaked P waves in right precordial leads (V1-V3) should raise the suspicion of congenital absence of the pericardium.

Reference

  Am J Cardiol 2014;113:372-376.