ECG Level 2 Tutorial: Origins of Activity
Tutorial: Origins of Activity
This module will teach how to determine the origins (pacemaker location) of the electrical activity.
How to level up?
Develop your skills by completing our Practice Cases!
Tutorial: Origins of Activity Where are YOU from?
Times Practiced
Cases Completed
1h 24m
Total Time spent
1m 24s
Average Time
Where are YOU from?
Here is a summary of all the rules. Discussions for the practice cases will refer to the rule numbers listed here:
  1. Upright P waves (in lead II) are from the SA node 95% of the time
  2. Inverted P waves are from the atria, AV node, or ventricles
  3. No P waves rules out the SA node
  4. A normal PR interval rules out the AV node
  5. A normal PR interval rules out the ventricle
  6. Wavy baseline with P waves and QRS complexes = no fibrillation
  7. Wavy baseline with no P waves = atrial fibrillation (probably) = atrial origin
  8. Wavy baseline with no QRS complexes = ventricular fibrillation = ventricular origin
  9. Narrow QRS rules out the ventricles
  10. Wide QRS could be caused by diseased purkinje fibers
  11. An atrial rate > 200 rules out the SA node
  12. A ventricular rate > 200 rules out the SA node and atria
  13. More P waves than QRS complexes = conduction block
  14. P waves not all the same size and shape = 2 or more origins for the P waves
  15. P waves + QRS complexes present but absent PR interval = 2 origins

Is your head swimming with all these rules?

Here is your chance to practice. This might be ugly at first so don't panic. Click on the ask/comment button if you need human help. We will try to reply within 12 hours.

Read the discussions carefully for detailed explanations. Every case has a discussion that explains the ECG. Good luck!