Demystifying Defibrillators

With almost 30% of out-of-hospital cardiac arrests occurring in a public place but less than 1 in 10 using a Public Access Defibrillator, we aim to help you understand and access AEDs.

Anyone can experience a cardiac arrest at any time.


Whilst older people are more likely to experience a cardiac arrest, anyone with a heart can be affected.

This is evidenced by the tragic loss of 12-year-old Oliver King in 2011, which has recently led to a government pledge to ensure all state-funded schools in England is to have a defibrillator by summer 2023.

Here, we discuss the importance of AEDs, their use and why proportional availability is needed in the UK as well as in schools.

Emergency Medical Personnel (EMS) attempt to revive almost 40% (approx. 31,000) of the 80,000 out-of-hospital cardiac arrests (OHCA) that English ambulance services encounter each year.

When resuscitation is started, around 30% of patients return to spontaneous circulation by the time the patient is transferred to the hospital, and almost one in ten (9.5%) make it to hospital discharge.

The chain of survival must start with early defibrillation. Quick action with a defibrillator, within 3-5 minutes of collapse, can result in survival rates above 50%.

As the heart rhythm changes over time from a shockable rhythm to a non-shockable rhythm, which is mostly unresponsive to treatment, the efficiency of defibrillation diminishes and the likelihood of survival drops.

The probability of survival to discharge is reduced by 10% for each minute of delay. About 85% of patients who survive an OHCA appear in a shockable rhythm, suggesting that early defibrillation may have a disproportionately positive impact on overall survival.

What is PAD?

Public access defibrillation (PAD) is the term used to describe the use of AEDs by the general public.

While waiting for an ambulance to arrive, PAD programmes gives local people access to this life-saving procedure. ILCOR guidelines and national strategies acknowledge the significance of PAD. However, despite greater attention in the UK on ambulance response times, median waits for cardiac arrest remain around seven minutes, with lengthier times in more remote regions. Yet only a small proportion (~5%) of all UK patients who require resuscitation had received PAD treatment before EMS arrived, leaving a substantial number of patients who could have benefited from PAD.

AEDs are widely available in England, however their distribution is uneven, where populations with the greatest needs have the fewest access points.

Health Inequalities

Cardiovascular disease is the leading cause of premature mortality in disadvantaged communities due to health inequities, and there is a social gradient in mortality from the condition, with more deprived areas having higher mortality rates.

Recent research by Brown, Perkins, Smith as published in the Resuscitation Journal, found that communities of colour, particularly those of African, Asian, and other minorities, have a much higher risk of ill health and early death. In addition to demonstrating that postcode districts with higher percentages of non-white ethnic groups have higher chance of OHCA incidence and lower than average bystander CPR rates, the ERC also found that the South Asian population in London has a high OHCA incidence.

People from mixed and non-white ethnic groups made up a much higher percentage of the population in high risk locations. These demographics recently saw a high incidence of OHCA during the first wave of the Covid-19 epidemic in London. Although the risk of OHCA is higher in these places, research has revealed that AED access is less common there. This shows a clear need for any future CPR training and PAD programmes to be focussed on these areas.

Stronger NHS Action on Health Inequalities

The NHS Long Term Plan acknowledges that addressing health inequalities is a top priority and lays out a strategy for “stronger NHS action on health inequalities,” which includes a commitment to lessen arbitrary differences in performance and access to medical care.

This includes a specific goal to reduce the variation in OHCA results. AED placement in regions where they are most needed is vital, but it is not the only factor to consider if we want to enhance outcomes.

The entire chain of survival must be considered, including early detection, bystander CPR, defibrillation, and post-resuscitation treatment. Additionally, it is crucial to think about the allocation and accessibility of EMS resources, their prompt dispatch, as well as the accessibility of specialised cardiac arrest centres.

Even though residential areas account for roughly 80% of all OHCAs, public access AEDs are less common there.

But they are also disproportionately distributed in wealthier communities with fewer non-white ethnic population percentages. Brown, et. al. state that future PAD initiatives should prioritise regions with a higher likelihood of OHCAs.

If you are a local authority or business that would be interested in hosting a PAD within your community, please contact us.

Common Questions

  • What is an AED?

    An AED is an Automatic External Defibrillator, which you’ll probably recognise as a brightly coloured box that can be found in supermarkets, airports, train and bus terminals, and other high-traffic areas and public places.

  • How an AED Works

    An AED, or automated external defibrillator, speaks to you to instruct you on what to do after automatically detecting if someone is in a shockable rhythm.

    Defibrillators halt the heart rather than restart it, similar to how a computer is restarted. In the end, this enables the pacemaker in the heart to hopefully restart it in a regular rhythm while the individual cardiac cells recharge concurrently.

    If the heart is in an unstable but shockable rhythm, the defibrillator shocks it to halt it, allowing the heart’s internal machinery to restart and, ideally, do so in sinus rhythm (normal beat).

    AEDs are utilised in addition to CPR to save the lives of those experiencing cardiac arrest.

  • Where are Public Access Defibrillators?

    Whilst there is a a need to increase the availability in poorer areas for a fairer chance of an OHCA survival, AEDs are accessible at many sites, including train and tube stations, retail centres, dental and GP offices, sports fields, and leisure facilities, and are available for use by the general public.

    They can be totally automatic or semi-automatic (you still need to hit the shock button when it’s suggested) (the machine shocks automatically when a shock is advised).

  • Why are defibrillators important?

    To have a possibility of saving someone after a cardiac arrest, defibrillators are essential.

    CPR aids in blood circulation, maintaining a enough blood supply for the heart and brain. The AED is required to administer the shock, which will hopefully restore the heart to a healthy rhythm.

    Ventricular fibrillation (VF) is the primary cause of abrupt cardiac arrests. VF is a fast and unpredictable heart rhythm produced by the ventricles of the heart.

    AEDs can only be used on those who are unconscious and not breathing properly. If a person is in a shockable rhythm, such as ventricular fibrillation or ventricular tachycardia, an AED will only allow a shock to be administered. The device will identify the rhythm and advise whether or not a shock is necessary.

  • Chain of Survival

    Knowing the chain of survival and the importance of each step can increase the likelihood of prompt action and survival rates:

    • Early recognition and call for emergency services
    • Early CPR
    • Early Defibrillation
    • Early Advanced Care

Defibrillators Availability Law

2018 saw the first reading of the Defibrillators Availability Bill in Parliament, which not only acknowledges the necessity of AEDs in public areas but also establishes legal requirements for education and training so that people are prepared to utilise them.

CPR has also been made a required subject in the English National Curriculum as of September 2020. Therefore, by the time they graduate from secondary school, every young person in England should be familiar with how to perform CPR and operate a defibrillator. Hopefully, this will significantly increase our survival rates from cardiac arrests that occur outside of a hospital, as it did in Denmark and other Scandinavian nations.

How to use an AED:

When the AED is turned on, it will speak to you and instruct you on what to do.


Immediate Checks and Actions:

  1. Avoid putting yourself at risk.
  2. If there is no response in the patient, yell for assistance, ask a bystander to phone an ambulance, and if available, seek a defibrillator.
  3. Make sure the airway is open and monitor breathing.
  4. If there are less than two breaths in a ten-second interval and the casualty doesn’t appear to be breathing regularly, you must begin doing CPR.
  5. If there is a nearby AED, call 999/112 and obtain it as soon as you can.
  6. If you can, ask a bystander to alert the authorities that the victim is unresponsive and not breathing. You should hurry to fetch the AED in the interim. Maintain CPR whilst waiting for the defibrillator.


Defibrillators are made to be simple to use. Even though you have never received training, you should make every effort because it will explain how to use itself as it goes along.

  1. Start by activating it. Depending on the machine, this is typically accomplished by lifting the lid or depressing a prominent button.
  2. If you’re not by yourself, have someone perform CPR while the other attaches the leads to the AED (if necessary).
  3. Ensure the chest is dry (and use the razor to shave if excessively hairy as the pads need to stick to the skin).
  4. Following the instructions on the package, carefully peel each pad off its backing and set it on the dry chest.
  5. Position a pad just below the victim’s right collarbone.
  6. Place the second pad over the victim’s lower ribs on their left side.
  7. The cardiac beat will be examined by the AED.
  8. When the AED instructs you, stop CPR.
  9. Verify that nobody is touching the victim.

If the machine says a shock is advised:

  1. Verify that no one is touching the casualty throughout the entire length of their body.
  2. Then shout “stand clear” loudly.
  3. As instructed, press the flashing shock button (fully automated AEDs will do this automatically if a shock is advised).
  4. Keep performing CPR as instructed by the machine.
  5. Continue to perform 30 compressions to every two breaths.
  6. Unless they begin to regain consciousness and breathe regularly, do not stop to check on them – keep going.
  7. Every 2 minutes, the gadget will re-evaluate their heart rhythm and, if necessary, recommend another shock.

If no shock is recommended, keep performing CPR and follow instructions.

  • Persist until assistance arrives. If the victim begins to breathe regularly and begins to regain consciousness, stop performing CPR.
  • Every 2 minutes, the AED will check their cardiac rhythm again and, if necessary, recommend an electric shock.
  • Current CPR Guidance is 30 compressions followed by two rescue breaths constitute CPR. Repeat.
  • If there are multiple rescuers, they alternate every few minutes.

Things to remember about AEDs

  • Defibrillators are easy to use

    The machine will speak to you and guide you what to do step-by-step.

  • You do not have to be medically trained to use them

    AEDs are designed to be used by members of the public.  CPR is a trained skill and should be used in conjunction with a defibrillator, but using an AED is not a skill and can be used by anyone.

  • You are not jump-starting a stopped heart, you are stopping an irregular heartbeat

    Contrary to popular belief, defibrillators do not jump-start a stopped heart, they actually stop an irregular heartbeat so the heart can “restart” itself.

    The AED will not allow you to administer a shock if the heart doesn’t need it, so apply the pads and turn on the machine – you will increase their chances of survival by up to 74% if this is done within 3 minutes.  This drops by 10% for every minute delayed.

  • AEDs are safe for use on children

    Ideally, you would use child/paediatric pads, but if the child is unconscious and not breathing, adult pads would suffice and you would use the defibrillator the same way you would on an adult.

    Adult pads would be placed one on the front of the chest and one on their back and CPR would start with 5 rescue breaths.

  • Don’t wait for the ambulance!

    Unless the overstretched, busy ambulance service can get to the patient within 3 minutes*, they cannot improve the chance for survival more than a member of the public can by using an AED whilst waiting for them.

    *Current average wait time is 8-11 minutes

Accessing PAD - Public Access Defibrillators

Whilst most out-of-hospital cardiac arrests occur in the home, it’s not practical for every home to have one. But, with local access to a PAD, even home-based victims can improve their chances of survival if there is a person present who is able to obtain a local AED.

Improving public access to Defibrillators will benefit everyone, particularly those in high-occurrence, low-survival areas.

If you are a school, community group or local business who would like to invest in a defibrillator for your community, please visit our defibrillators page or contact us where we will be happy to help you.