How Defibrillators Work – a Complete Guide

The life-saving capabilities of defibrillators are truly remarkable. The chance of surviving sudden cardiac arrest without intervention is just 8%, yet if a defibrillator is used within the first 3-5 minutes of SCA occurring the likelihood of survival is an astonishing 74%.

European data shows that around 60,000 out-of-hospital cardiac arrests occur each year in the UK. Emergency response times can be between 7 and 10 minutes on average – so being able to take swift remedial action for a patient in cardiac arrest can mean the difference between life and death.

Although AEDs are becoming widely available and accessible in an effort to save more lives, many people are still unaware of what they are and how they work.

That’s why we created this accessible and comprehensive guide to Lifeline AEDs – sharing what they are, what they do and how they can be used to save lives.

What is an AED?

An AED (short for Automated External Defibrillator) is a lightweight, portable device that intelligently delivers a shock to the heart to reinstate normal heart rhythm following cardiac arrest. This advanced medical equipment is safe and easy for anyone to operate – as a result, thousands of lives have been saved to date each year.

How do AEDs work?

To understand how AEDs work, first we need to understand what SCA is, and why it occurs.

SCA is caused by problems that affect the electrical behaviour of the heart, resulting in abnormalities and disruptions in heart rhythm. Usually ventricular fibrillation (VF) or arrhythmia cause SCA – but in severe cases the heart and electrical rhythm stop completely, known as cardiac flatline. During cardiac arrest a patient stops breathing and loses consciousness, as blood flow to the brain is affected.

Underlying diagnosed or undiagnosed heart conditions are usually behind SCA – most commonly structural heart disorders such as coronary artery disease.

AEDs work by treating ventricular fibrillation, passing a brief electrical current to enable the body to naturally re-establish a proper heart rhythm.

What happens when we use an AED? 

When we use an AED electrode pads placed directly on the patient’s skin deliver an electrical ‘shock’ to the heart. Unlike manual defibrillators (the ones we commonly see on film and tv, where a medical professional sets the voltage and duration in line with the abnormality in heart rhythm), AEDs automatically diagnose the heart rhythm via technology within the electrodes and administer the appropriate voltage. AEDs deliver instructions to the person using them at all times, so no training, experience or special skill is required.

For this reason AEDs are most commonly used for out-of-hospital cardiac arrests.

Why and when are AEDs used?

AEDs offer a literal lifeline when a person goes into sudden cardiac arrest. Even when below average (in 2020 the average was 7 minutes 19 seconds), emergency response times can sometimes cause ambulance crews to arrive too late in a situation when every second counts. For every minute a person is in SCA their survival rate decreases by 10% – that’s why help from those around a person at the time of SCA can be so crucial.

A British Heart Foundation survey found that just 40% of people would feel confident performing CPR – and only 3% of defibrillators are used outside of a hospital environment. Even when a person isn’t first-aid trained or confident delivering manual CPR, and AED can be used to help save a life. SCA doesn’t discriminate and can affect individuals of all ages regardless of how healthy they may seem.

A defibrillator is most effective when administered within the first minute of a victim collapsing (in these cases the survival rate can be as high as 90%). Having AEDs widely and quickly available in public places such as schools, parks, shopping centres, train stations, venues such as theatres and leisure centres and on aircraft and cruise ships ensures that as many lives as possible can be saved should SCA occur.

Are AEDs easy to use?

Yes! All AEDs come with easy, simple instructions and are specifically designed to be used by anybody. It’s important to call the emergency services in the first instance once you identify that someone is in SCA – call handlers can also help you to use the apparatus and offer additional support and advice whilst you wait for an ambulance to arrive.

Every second counts when a person goes into cardiac arrest. Using an AED within the first few minutes dramatically increases their chances of survival – so it’s important to use an AED confidently and without hesitation.

Common misconceptions

Unfortunately the life-saving abilities of AEDs are often hampered by misconceptions about what they do, how they work and who can (or can’t) use them. Some of the most common misconceptions surrounding AEDs include:

Can an AED shock someone accidentally?

Absolutely not! AEDs automatically detect whether a ‘shockable’ heart rhythm is present – if not, the user can’t administer a shock to the heart.

Are AEDs safe to use on everybody?

AEDs are safe to use on most people – and as above, will only deliver a shock if one is needed. Due to the sudden nature of SCA and requirement for swift action you won’t always know whether there are any issues that could affect the deployment of an AED – but the intelligent technology within an AED will detect if a shock is required, so you can deploy it with confidence.

Do AEDs always work?

Although the life-saving ability of AEDs is truly remarkable and saves many lives each year, it’s important to note that they aren’t a guaranteed cure. When we see defibrillators used in television and film they tend to always work right away – but many cases of SCA can be more complex and need additional treatment or prolonged manual CPR. Some cases can be more complex and require additional or advanced medical care.

AEDs offer the best chance of survival before urgent medical care arrives – so spreading awareness and sharing facts about how they work and how to use them is important.

How to use an AED

AEDs have been specifically designed to be simple and straightforward for anybody to use. No medical training is required – simply unpack the equipment and follow the basic instructions included. If you are on the phone to emergency services, they can also support you with verbal instructions.

1/ Check that the patient is unconscious and determine whether they are breathing or have a pulse

2/ Call the emergency services whilst performing CPR. Ask someone nearby to locate an AED as you do

3/ Peel the electrode pads away from the plastic and place them on the patient’s bare skin. Placement of the pads will be shown in the instructions and may vary due to the age of the patient (read more about using AEDs on infants and children here)

4/ Stop performing CPR momentarily to allow the AED to detect and analyse the patient’s heart rhythm. If the AED is activated it will instruct you to press the shock button, or to step back whilst the shock is delivered automatically. Make sure nobody is touching the patient during this time (If the AED does not indicate that a shock is required continue CPR until the emergency services arrive)

5/ When the AED indicates that it is safe, continue with CPR until the patient shows signs of restored heart function, or until medical help arrives. The AED may indicate that additional shocks are needed.

Find out more about the chain of survival here or contact our team directly on 01709 599 222.


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