ACLS – Einthoven’s Triangle
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Article at a Glance
- Einthoven’s P wave describes the shape of the P wave as the electrical impulse moves along the Lead II axis.
- If the impulse starts in the SA node, it moves from positive to negative, causing a positive P wave.
- If the impulse starts in the AV node, it moves from negative to positive, causing a negative deflection (inverted) P wave.
Einthoven’s Triangle
To understand conduction through the heart and how these tracings occur on our ECG paper, let’s talk about Einthoven’s P wave. Let’s look at Einthoven’s triangle first.
Einthoven’s triangle is an imaginary formation of three limb leads in the shape of a triangle.
In Einthoven’s triangle, the right shoulder is ‘negative, negative,’ and the left foot is ‘positive, positive.’ Make note that anytime the electrical conduction in the heart is moving towards a positive electrode, it will create an upward deflection on the ECG tracing.
When the electrical conduction of the heart moves towards a positive electrode, the ECG tracing will show an upward deflection.
Let’s take a look at Einthoven’s right shoulder and left foot as it compares to a P wave. During the P wave, the conduction starts at the SA node then moves towards the positive electrode.
On the ECG, we can see the P wave is starting to form an upward deflection. As the conduction moves closer to the AV node, the conduction moves slightly back around and up to the AV node. The P wave terminates once the conduction reaches the AV node. In this general conduction pattern, we are moving towards the positive electrode, and then away from it, forming a P wave.
Read: Interpreting an ECG Strip
The conduction moves from the SA node to the AV node during the P wave.
Premature Junctional Complex (PJC)
Next, let’s consider a premature junctional complex (PJC). In a PJC, the conduction starts at the AV node and goes in the opposite direction of normal conduction. That is what creates the inverted P wave during a PJC.
Related Video – One Quick Question: What are PJCs (Premature Junctional Contractions)?
A PJC shows an inverted P wave on the ECG tracing.
It is important to note that the right shoulder ‘negative, negative’ and left foot ‘positive, positive’ concept is lead II on your ECG tracing. We usually use lead II because it most accurately follows the natural conduction pathway of electricity through the heart. Now, lead II is only one, small view of the heart, but it’s a pretty good view.
Now, you should have a better grasp of Einthoven’s triangle and how it can help you better understand the heart’s conduction system.
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Editorial Note
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