In this lesson, we will examine the size and shape of the P waves. If the P waves are different shapes, they have different origins.Origin means the location inside the heart that initiates the heartbeat. You could also call it the pacemaker of the heart, but don't confuse this term with an artificial pacemaker.
The most common origin of a P wave is the SA node. So why would a different origin, such as the atrium, create a different sized or shaped P wave?
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I am glad you asked! The answer is that the direction of electrical activity will be different. Remember the vector that is generated by the atrial depolarization that is generated by the SA node? It is moving down as is seen in this image.
If the start of this wave was near the bottom of the atrium, then the wave would travel upwards through the atrium. This would create a different vector, which would create a different shaped (and probably sized) P wave. It might even create an inverted (upside down) P wave.
So what is the take home message here? If all your P waves are the same size and shape, then the origin of these P waves is probably one single origin. If they are different, then the ones that are different probably arose from a different origin.
Here is an example where they are all the same:
How about this one:
Can you see that one P wave is different from the other 4 (this is same ECG simply with blue circle)
In case it is late and your eyes are getting bleary and you can't see the difference, here is a zoomed in view:
How about this one?
The first and 3rd P waves are the same. All others are different. Therefore, there are multiple origins for the P waves.
One detail that might be helpful for you: P waves almost always will have a regular rhythm if they are from the same source/pacemaker. Therefore, an early beat among many regular beats is most likely (> 99% of the time), arising from a different location and as such, will likely have a different size and shape.
Another detail: a P wave superimposed on a T wave will have a different appearance, so it is sometimes a little difficult to determine if the P wave looks different because it truly is different, or if it looks different because of being superimposed.
Please practice P wave size and shape now. This is also a more challenging skill, so be patient as you practice and don't be too frustrated if you make mistakes early in your practice.
