ECG Level 2 Tutorial: Origins of Activity
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Tutorial: Origins of Activity
This module will teach how to determine the origins (pacemaker location) of the electrical activity.
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Tutorial: Origins of Activity Upright P waves
Lessons
42
Times Practiced
1284
Cases Completed
1h 24m
Total Time spent
1m 24s
Average Time
Progress
Accuracy
Efficiency
Accuracy
Efficiency
1 The 4 Options The 4 Options
Current lesson 2 Upright P waves Upright P waves
3 PR Interval Rules PR Interval Rules
4 Wavy Baselines Wavy Baselines
5 Narrow QRS Narrow QRS
6 HR > 200 rule HR > 200 rule
7 P wave rules P wave rules
8 Where are YOU from? Where are YOU from?
Upright P waves
Rule: P waves from the SA node are upright

If a P wave comes from the SA node (image below), it will travel "downward" and to the patient's left. When measured in most ECG leads, this will create an upright P wave.
P wave normal depolarization 
upright P waves 


Rule: P waves from the atria are usually inverted

When a P wave comes from the atrium (image below), it will travel upward and often to the patient's right. This will usually (but not always) create an upside down P wave, also called an inverted P wave.
atrial pacemaker and direction of atrial depolarization 
inverted P waves


Rule: P waves from the AV node are inverted

Similarly, when a P wave comes from the AV node (image below), it will also travel upward. This will also create an inverted P wave:
AV node depolarization in atria, direction


Rule: P waves from the ventricle are inverted

This is a rare event. Sometimes with a ventricular origin, the electrical signal can travel in reverse direction through the AV node and cause a P wave. If this happens (again, rare), the P wave will be inverted.


Rule: No P waves rules out SA node and atria

The SA node and atria will both generate P waves when they are the origins of activity. Therefore, no P waves rules out the SA node and atria.
Caution: sometimes P waves are very very hard to see.
Exception to this rule: if you have a wavy baseline (discussed in Lesson #4 ... 2 after this one).


Summary:
  • upright P waves are usually (> 95%) from the SA node
  • inverted P waves are usually (> 95%) from the atria, AV node, or ventricles
  • no P waves rules out SA node and atria
  • P waves that come from the ventricles is a rare event