The cardiac conduction system a marvel of engineering

The cardiac conduction system is a marvelous system that provides the heart with the organization it needs to be effective. The heart itself is one big battery; every single cell in the heart has the ability to beat independent of each other. So the heart doesn’t need power what it needs is organization. Without organization the heart will beat like a bowl full of jelly as in ventricular fibrillation. What the cardiac conduction system is able to provide is the ability to organize the beats.

The beat or rhythms come from the Sinoatrial node (SA node). This is the starting point for every normal beat. A beat from this location is known as “normal sinus”. When a doctor talks about cardiac ablation it is usually in this location. The SA node is boss and controls most of the beats, but a failure here and the heart doesn’t fail, it has three fail-safe devices. The signal works its way across and down the atria and ends at the Atrioventricular node (AV node). The SA node works at a rate of 60 to 100 beats per minute.

The AV node is a node that separates the atria conduction system from the ventricle conduction system. It is meant as a gateway that allows the atria to fully contract before allowing the electrical signal to enter the ventricles. This ability of the heart helps with cardiac preload and thus helping with cardiac output. It gives the atria one last squeeze and makes sure every last drop of blood is in the ventricles before the final push. A failure of the SA node means the AV node takes over so we’ll refer to it as the second in command, the SA nodes right hand man! The AV node beats at a rate of 40 to 60 beats per minute if it gets no signal from the SA node. As long as the big cheese is in power then the AV node has to do what it is told.

The AV node then deals out the electricity equally to the ventricles via the Bundle of His, into the right and left bundle branches and finally into the purjinke fibers. This finally causes the ventricles to contract to deliver the life blood to all organs including itself. The purjinke fibers are the final fail-safe of the heart. If the SA node fails then the AV node fails then the purjinke fibers take control and beats at a rate of around 30 beats per minute.


The cardiac conduction system is a marvel of engineering specific tracks for the electricity to take and the timing required to allow the heart to beat at its utmost efficiency is just incredible. Not to mention the built in back up system so the heart does not miss a beat. Knowing the rate of each area is important so you know where the problem lies. A heart of 50 is troubling but couple it with the knowledge that the P wave is inverted then you know the beat is not coming from the SA node but the AV node because you know the rate and is most likely an idioventricular rhythm. If you notice the P wave is pretty far from the QRS complex then you might be dealing with first degree AV block . By knowing your cardiac conduction system you and all its nuances you can stop problems before they become deadly rhythms.

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