Will An AED Detect a Pulse?
In this blog, we answer the question “Will an AED detect a pulse?” We will also talk about what an AED DOES do, and also what it DOES NOT do. These kind of questions are what we routinely cover in our basic CPR classes. Before we jump into answering this question, let’s do some heart physiology 101.
How does the heart work?
The heart is a big piece of muscle. Inside this muscle are lots of electrical wires. An electrical shock generates at the top of the heart and flows down the wires throughout the rest of the heart.
If you stick your finger in an outlet and get shocked, what happens? You tense up and your muscles contract. That’s exactly what’s happening in the heart. An electrical shock generates in the heart, causing it to contract which pumps the blood through the chambers of the heart and through the rest of the body.
Sometimes, the electrical system in the heart starts to malfunction for various reasons. This can cause the heart to either pump too slow, too fast, and sometimes not at all. When the heart stops pumping, that’s called cardiac arrest. There are 4 cardiac arrest rhythms.
Cardiac Arrest Rhythms
- Ventricular Fibrillation – quivering of the entire heart
- Ventricular Tachycardia – fast heart rate originating from the ventricles
- Asystole – no electrical or mechanical response (the classic flat line)
- Pulseless Electrical Activity – a normal rhythm but no pulse
What Does an AED Do?
An AED or Automated External Defibrillator is a portable electronic device used during CPR. It diagnoses cardiac arrhythmias. Specifically, it detects an arrhythmia called ventricular fibrillation (V-Fib or VF for short). There’s a another arrhythmia found during cardiac arrest called ventricular tachycardia (V-Tach or VT) which a lot of people think an AED can also detect. However, AEDs do not detect V-Tach which we’ll explain why in a little bit.
V-Fib is when the heart’s electrical system is spazzing out. There are multiple electrical currents firing at the same time all over the heart which cause the heart to fibrillate (or quiver). When an AED detects V-Fib, it treats this arrhythmia through the use of defibrillation, also known as electrotherapy, in an attempt to stop, restart, and restore a normal heart rhythm.
What An AED Does Not Do
It is a very useful piece of equipment, but an AED is also basic in the functions it provides. Will an AED detect a pulse? No, it can’t. An AED cannot detect a normal rhythm or pulse. There are so many variations of rhythms, it’s impossible for an AED to detect and accurately diagnose all of them. We still rely on humans to ultimately interpret heart rhythms.
An AED cannot detect a pulse because it is an “ELECTRO-cardiogram“. It only detects electrical impulses. It is not able to detect the physical/mechanical beating of a heart.
There are times when the heart can have electrical impulses going through it but the muscle is completely unresponsive to those electrical currents and is not contracting. One such rhythm is called V-Tach which we mentioned earlier. V-Tach is a rhythm found in both people who have a pulse and do not have a pulse. Since an AED cannot detect pulses, it will not shock V-Tach if it’s detected because it’s unable to determine if it’s truly cardiac arrest or not.
Now, there are very notable websites such as the NIH that will tell you that an AED can shock V-Tach. However, talk to AED manufacturers and they will tell you otherwise. I’m going to get nerdy for a second here and might loose some of you. Hang tight.
Danger of using an AED to shock V-Tach.
V-Tach is a serious problem whether a person has a pulse or not. In fact, as healthcare providers, we shock that rhythm regardless, but we don’t use an AED to do it.
If a person is in cardiac arrest due to pulseless V-Tach, we shock them with a manual defibrillator which means we analyze the rhythm, charge the system, and shock.
If a person is in V-Tach with a pulse, we shock them with a manual defibrillator as well but with one exception. Before charging and shocking the patient, we press a “Sync” button. This tells our defibrillator to sync up with the rhythm and shock only at a specific moment. If we do not sync with the rhythm and shock at the right moment, it can actually have the opposite effect and cause the person to go into cardiac arrest due to something called the R on T phenomenon.
What happens if the AED does not advise a shock?
Just because the AED says “no shock advised” does not mean everything is ok. Just like we said above, there are several rhythms an AED will not shock even though the person is in cardiac arrest. So, if you’re doing CPR and the AED does not advise a shock, that’s not necessarily a good sign.
The AED will tell you to continue doing CPR, and it will reanalyze again in 2 minutes. Once you start CPR and apply an AED, you don’t stop doing CPR unless one of theses things happen.
Remember the American Heart Association says that it is much better to give CPR to a person who doesn’t need it, rather that not give CPR to a person who does need it.
I hope that answers your questions. It’s a simple answer to the question, “Will an AED detect a pules?”, but we want to help people understand the reasoning and not just take the answer for face value.
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