What is a Defibrillator? How AEDs work and How to use Them

What is a Defibrillator? How AEDs work and How to use Them

Patrick Tigue

Patrick Tigue

Published in MedShop Blog

0 min read

September 30, 2021

What is a Defibrilator?Everyone knows what a defibrillator is. They’re a mainstay of Hollywood drama and a paramedic’s most recognisable tool. They’re also used in hospitals around the world, and even an untrained, non-medical professional can use one to deliver first aid if required. 

However, there’s a lot more to this revolutionary piece of equipment than first meets the eye, and for both experienced medical professionals and the layman alike, it’s worth taking a deeper look into the different types of defibrillator and the functions they perform.

Here then, we explore the questions of exactly what a defibrillator is, when to use one, and how a defib works. Read on to learn more with MedShop.

What is a Defibrillator?

A defibrillator is a device that sends an electrical shock or pulse to the heart in order to restore a normal rhythm. They are used to both prevent and correct abnormal heart rhythms (arrhythmia), and also to restart a heart if it stops  due to sudden cardiac arrest or other heart conditions. The very first defibrillator was demonstrated in 1899 by Frédéric Batelli and Jean-Louis Prévost, two physiologists from the University of Geneva.

Over the next 100 years, defibrillation equipment continued to be developed, with clinical trials delivering fully portable units by the 1960s. After this, implantable defibrillators and wearable devices were developed for patients at high risk of frequent issues with ventricular arrhythmia and atrial fibrillation. These three devices are now standard pieces of medical equipment, used around the world to treat cardiac dysrhythmias, specifically ventricular fibrillation (VF) and non-perfusing ventricular tachycardia (VT).

While each one works in essentially the same way, they each fulfil different roles for patients, healthcare professionals, and the general public. Below, we look at the different types of defibrillator and the normal activities that they are responsible for performing. 

What are The Different Types of Defibrillators?


  • Manual External Defibrillator – MEDs are the most recognisable defibrillators thanks to TV, however, they can only be used by healthcare professionals and are primarily found in hospitals and ambulances. They are used in conjunction with an electrocardiogram (ECG), and the user needs to manually identify whether the patient requires a shock, and then what kind of voltage is required. 


  • Automated External Defibrillator – AEDs use two paddles or sticky pads (electrodes) to deliver an electric shock to restore the natural heart rate in a similar way to MEDs. They were designed to allow anyone to use them in an emergency, and the automated computer analyses the heart rhythm to ascertain whether a shock is required—requiring little to no user input in order to save a patient’s life.


  • Implantable Cardioverter Defibrillator – ICDs are surgically placed within the chest cavity to check and correct arrhythmia. They work in a similar way to pacemakers, however, while pacemakers only deliver low-level shocks, ICD defibrillators are capable of delivering both low- and high-energy shocks.


  • Wearable Cardioverter Defibrillators – Like an ICD, an WCD can deliver both low- and high-energy shocks to the patient. In fact, the only difference is that these devices are attached to the skin with trailing wires connected to a unit that monitors your heart.


What does AED stand for?

As indicated above, AED stands for automated external defibrillator, and for the purposes of this guide, this is the type of defib we will be exploring in greater depth. AEDs are commonly used for out-of-hospital cardiac arrest events, and the "automatic" within the name tells us that no previous knowledge or expertise is required to use one.

How Does an AED Defibrillator Work?

AED defibrillators work by identifying arrhythmia and heart failure using a sophisticated computer and then delivering a shock to return the heart back to its natural rhythm. As suggested by the name, defibrillators stop fibrillation, the “trembling” that someone’s heart muscles may experience during cardiac arrest.

AEDs achieve this by passing an electric current through the heart, shocking it back into rhythm. The sticky pads on an AED form a circuit, allowing electricity to pass through the body without harming it and, when placed correctly, focussing that current directly on the heart.


How to Use an AED?

An AED consists of an analysis unit, or computer, and electrodes that are placed on the body which, when combined measure electrical signals from the heart. To help untrained individuals use AEDs correctly, there will be a diagram and set of instructions on the unit itself, telling you how to turn on the machine and begin the process. All clothing should be removed from the patient’s arms, chest, and abdomen before using the AED, and the pads should always be attached directly to the skin.

Once the pads are stuck to the body, the AED will begin to analyse the heart rhythm of the patient. If the process does not start automatically, then ensure you push the analyse button indicated on the machine. During this process, you should not touch or move the patient.

If the AED determines that a shock is required, you will be instructed to press the button on the unit. Newer units will only shock once, however, older units may shock up to three times, so be certain to read the instructions on the unit itself. More information on how to use an AED defibrillator can be found here.


Where to Find an AED

AEDs have revolutionised the healthcare sector, allowing untrained bystanders to provide lifesaving treatment to anyone who requires it. Today, you will find them located within large public places including:

  • Hospitals and other national institutes of health
  • Schools
  • Community centres
  • Workplaces
  • Business centres
  • Sport centres
  • Gyms
  • Shopping centres
  • Public libraries
  • Zoos


When to Use A Defibrillator

AED defibrillators should be used when a patient is unresponsive and AFTER cardiopulmonary resuscitation (CPR) has been performed. This may be any condition where there is no pulse or response from the patient, however, it is also important to shake or otherwise try to wake up someone who is unresponsive before performing CPR or using an AED defibrillator.


When Not to Use an AED

It’s important to follow the health information and guidance printed on the equipment, and NOT to use an AED, or to be more vigilant in its use, in the following circumstances:

  • Heart Attack – Although the symptoms may be similar to that of cardiac arrest, an AED will not help someone suffering from a heart attack.
  • Water – If the patient is in water or is wet, it is important to remove them and dry them off before using a AED.
  • Medication or Pacemaker ­– If the patient has a medication patch or a pacemaker, it is important to remove the patch and avoid putting the sticky pads directly above the pacemaker.
  • Faulty AED – If the AED has an expiration sticker that has passed, or any part of it looks damaged, then do not use it.

Where to Buy an AED Defibrillator

AED defibrillators are available to buy from recognised medical equipment supply stores in Australia, and Medshop has a broad range of options from which to choose. Whether for your home, your business, or any other public place, we stock everything you need to ensure you have the very best lifesaving equipment to hand.

Explore the range here and contact us to discuss your requirements or if you would like more information on any specific products. Additionally, for more information on other health topics and equipment, check back to the Medshop blog


AED Defibrillator FAQs


  • What are the survival rates for people with heart conditions that require AED application?

Some estimates suggest that the use of AEDs in out-of-hospital cardiac arrest situations double the chances of survival for individuals.

  • Can AED defibrillators damage your heart?

It is highly unlikely that an AED will damage a patient’s heart, as the automated computer, step-by-step visuals, and voice prompts essentially make the process “foolproof”. Even if a patient does not require ventricular fibrillation, an AED will know this and not deliver unneeded shocks or electrical impulses.

  • Can AED defibrillators kill you?

Again, it is highly unlikely that and AED defibrillator will harm or kill a patient. They are designed to only work when required, delivering the required treatment as ascertained by the computer after detecting irregular heartbeats or cardiac arrest.

  • Can anyone use AED defibrillators?

Anyone can use AED defibrillators and they are designed exactly for this purpose. Instructions are included on the units themselves, and there are visual and audio prompts to make their usage even easier.

  • How many volts are in an AED defib?

AEDs deliver anywhere from around 200-1000 volts, with the patient’s heart receiving around 300 joules of electrical energy.

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