#307 How does an AED work?

How does an AED work? It has sensors to detect the rhythm of the heart and it has a powerful battery to deliver a shock to correct the heart.

AED stands for Automatic External Defibrillator. It is a defibrillator that is automatic. So, let’s start by finding out what a defibrillator is. A defibrillator is a device that restores a regular heartbeat by using an electric current. It is not a device that can restart a stopped heart. Many Hollywood movies show a doctor shouting “clear,” and using the two paddles to shock a flat-lining patient back to life, but this is not true. A defibrillator cannot restart a stopped heart. If someone’s heart has completely stopped, doctors will attempt CPR, and they may inject something like epinephrine. They need to get the heart beating before they can use the defibrillator to try to get it beating in a regular rhythm. A defibrillator is designed to stop the heart beating for long enough for it to start beating properly. Basically, a heart reset.

A defibrillator is used when the heart is beating in an irregular way. This is called cardiac arrhythmia and the heart could be beating too fast or too slow. Because the heart is not beating properly, it is not pumping blood around the body, which is obviously extremely dangerous. When the heart cannot pump blood due to a malfunction in its electrical system, it is called a cardiac arrest. This is very different to a heart attack, which is caused when an artery into the heart is blocked. A defibrillator can help with cardiac arrest, but it cannot help with a heart attack.

Why can’t a defibrillator help with a heart attack? In a heart attack, a blockage in an artery cuts off the blood flow to the heart. The heart itself is not the problem and is trying to beat, it just can’t get the blood in to do its job. A defibrillator would be no use here because the heart is not the problem. In the case of a heart attack, the blockage needs to be cleared. Blood thinners such as aspirin can help. Depending on how big the blockage is, heart attacks are survivable. A defibrillator can help with cardiac arrest. This is usually caused by ventricular fibrillation. The ventricles of the heart start to quiver because of an uneven electrical signal. This stops the heart pumping blood, and the patient can lose consciousness very quickly. The defibrillator fires an electric charge through the heart that stops it beating completely. The charge cancels out all of the uneven electrical signals that were in the heart and allows it to resume beating normally.

The defibrillator was invented in 1899 by two Swiss physiologists. They worked out that applying a small charge to the hearts of dogs caused ventricular fibrillation and applying a larger charge stopped it. In 1933, it was first used in a hospital, but a wire had to be put as close to the heart as possible using a hollow needle. The defibrillator with paddles was invented in 1930, but it wasn’t used in a hospital until 1947, and it only worked during open heart surgery. The closed chest defibrillator was invented in the early 1950s. The AED was invented in the late 1970s.

So, how does an AED work? The idea behind an AED is to improve the chances that a regular member of the public without any training will be able to help someone in the event of a cardiac arrest. Most people know a smattering of first aid, but they probably won’t be able to remember any of it when they are faced with an actual emergency. An AED is designed to remove the panic, help the person doing the helping, and restart the heart if necessary. Before the invention of the AED, it was unlikely that a person undergoing a cardiac arrest would be alive when the emergency services arrived. The goal behind the AED is to keep the patient alive long enough for the professionals to arrive.

AEDs are common these days and many buildings have one. If a person is not breathing and doesn’t have a pulse, grab the closest AED. Once it is switched on, it will start to give instructions. It will tell you to make sure the emergency services have been called. Then it will tell you to attach the paddles to the chest of the patient. It will analyze the patient’s heartbeat and determine if a shock will help. If the patient’s heart has stopped, the AED will not be able to do anything, and it will instruct you on how to do CPR. If it can detect an electrical signal in the heart and if it determines that the heart is beating but in a very irregular way, it will ready an electric charge. It still needs a human to push a button to fire the charge to make sure that other people are not touching the patient.

Studies have shown that survival rates are far greater if someone uses an AED instead of just CPR. This may partly be because the AED gives clear and calm instructions. In the cases where someone applies CPR, unless they are well trained, they won’t be very effective. An AED can increase the ability of someone who is untrained in CPR by giving instructions to follow. However, that being said, there have been a number of recording instances of AEDs malfunctioning and doing more harm than good. Still, the technology hasn’t been around for too long and thanks to the huge jump in the number of available AEDs recently, they will start to improve technologically.

So, how does an AED work? By analyzing the heart of a patient and deciding if an electric charge can reset its rhythm and not by restarting a stopped heart. And this is what I learned today.

Image By Cory, CC BY 2.1 jp, https://commons.wikimedia.org/w/index.php?curid=1050059

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