How an AED Actually Works

Mechanical vs. Electrical – How an AED Actually Works

If you’ve taken a CPR or First Aid course recently you’ve probably noticed a new addition to all of our programs – the Automated External Defibrillator (AED). What exactly this little machine does, and why and when we use it may seem a little overwhelming if you’re new to it, so I thought I’d write a series of posts all about how an AED actually works to help clarify things. Let’s start off by talking about how the heart works.

To understand how the heart works and related it to using the AED, we need to split the heart into two parts – the electrical heart, and the mechanical heart. The mechanical heart is the physical beating of the heart. It is what you feel if you hold your hand over your chest and feel the thump, thump, thump beating of your heart. The thumping you hear and feel is due to valves opening and closing and blood moving from one chamber to another.

The electrical heart is a little more complicated, so let’s break down the components. The sinoatrial node (SA node) is the pacemaker of the heart. It sends out an electrical signal, which is picked up by the atrioventricular node (AV node), where the signal is regulated, and then sent along the purkinje fibers, which causes the heart muscle to contract, creating a heart beat. So essentially the electrical heart drives the mechanical heart, and the SA node sets the pace.

There are four possible rhythms the SA node may be in:

-Normal Sinus Rhythm (NSR), which, if you are alive, breathing, and reading this post, you are most likely in right now!

-Asystole, or a flatline, is when there is no electrical activity and the heart is not beating at all.

-Ventricular fibrillation (V-fib) is an abnormal, uncoordinated electrical rhythm which causes the heart muscle to quiver rather than contracting properly. If V-fib is not corrected quickly it can lead to asystole.

-Ventricular tachycardia (V-tach) is an abnormally fast heart rate which may not allow the heart to pump blood properly, and can lead to V-fib or asystole.

When we put the sticky pads of an AED onto the chest of an unresponsive patient who is not breathing normally, the first thing the machine does is an analysis of what sort of rhythm the electrical heart is in. The AED is unable to detect the presence or absence of a pulse (the mechanical heart). The AED will NOT deliver a shock to anyone who is in a Normal Sinus Rhythm, and it will NOT deliver a shock to anyone who is an asystole. The AED will deliver an electrical shock to a patient who is in ventricular fibrillation, or in pulseless ventricular tachycardia.

What does the shock do? Recall that V-fib and V-tach are both abnormal rhythms which don’t allow the mechanical heart to beat properly. The goal is to re-set the electrical heart. When the AED delivers a shock it causes the heart to go into asystole for a few seconds. That’s right, the shock actually stops the heart. What we hope happens is that when the electrical heart starts back up that the SA node will have reset and will begin sending a normal sinus rhythm once again.

I hope this makes things a little more clear when it comes to the mechanical vs the electrical heart, and what the AED actually does. Next time we’ll dive a little deeper into AED use!

~ Article courtesy of Katie Trant

Interested in learning the practical applications of AED use? Sign up for a CPR or first aid class today!

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