How to Interpret EKG – Part 2

In this second part EKG series we are going to learn about P wave.

P wave is the first wave that forms in an EKG. It is a short burst of energy that represents the contraction of right and left atrium. We will discuss more about how the wave is formed. First, let’s take a look at how a P wave looks.


The Circled Part Represents P Wave

Heart contracts due to depolarization process. Concept of depolarization is little complex. Hence, for the sake of simplicity let’s assume contraction occurs due to electric current (which is similar to depolarization).

This wave of electric current begins at the Sinus Node.


As you can see from the above picture, Sinus Node is situated above Right Atrium. Therefore, when the electric current passes it contracts the Right Atrium first and then Left Atrium.

P wave, therefore, is nothing but contraction of Right Atrium and Left Atrium.

Taking this idea further, we can deduce that first half of P wave represents Right Atrium and second half represents Left Atrium (Sinus Node is situated at top of Right Atrium. Hence, Right Atrium will contract first.)


depiction of right & left atrium within P wave

depiction of right & left atrium within P wave

After P wave there is small pause because it takes time for electric current to reach the ventricles. Once, it reaches the ventricles another lengthy wave called QRS complex is generated which we will discuss in the next part.