Cite this article as:
Tessa Davis. Rhythm, Don't Forget the Bubbles, 2014. Available at:

Sinus: atrial depolarisation starts from the sinoatrial node.

This requires:

  1. P wave precedes each QRS complex, with a regular PR interval.
  2. P wave axis is normal (0 ‐ +90) i.e. P wave upright in leads Ι and aVF .

Non‐sinus: some atrial (non‐sinus) rhythms may have P waves in front of every QRS but with an abnormal P axis.