Frequently Asked Questions

What is Sudden Cardiac Arrest (SCA)?

A Sudden Cardiac Arrest is a condition that occurs when the heart unexpectedly stops pumping.  Each year out of hospital SCA strikes approximately 60,000 people in the UK. Unfortunately, less than 10% survive, often because help cannot reach them in time.  SCA is not gender or age specific.  The symptoms for a sudden cardiac arrest are most often immediate and without warning: 

  • Suddenly collapsing
  • Lack of pulse
  • Not breathing
  • Unconscious


Is sudden cardiac arrest (SCA) the same as a heart attack?

No.  A heart attack occurs when a blood vessel feeding the heart itself is blocked by plaque or a blood clot.  The longer the blood flow is interrupted, the more extensive the damage done.  The majority of people who have a heart attack survive the first attack.  However, a heart attack can possibly lead to a cardiac arrest.

Sudden cardiac arrest involves problems with the heart’s electrical system which can cause it to stop beating entirely.  When that happens, blood flow to the rest of the body is interrupted and the person passes out.  Defibrillation is the only known treatment for this condition.

Basically, a heart attack is about a person’s blood circulation, whilst a cardiac arrest is about the person’s electrical system.


What causes a Sudden Cardiac Arrest?

The direct cause of a sudden cardiac arrest is an irregular heart rhythm that leads to a decrease in blood pressure and pulse.  The more indirect environmental factors that can heighten the risk of having a SCA, however, are:

  • A history of heart disease in the family
  • Smoking
  • High blood pressure
  • High cholesterol
  • Obesity or being overweight
  • Diabetes
  • Excessive drinking of alcohol
  • An inactive or sedentary lifestyle


What is an Automated External Defibrillator (AED)?

A defibrillator is a life-saving device used to treat Sudden Cardiac Arrest (SCA), a condition that occurs when the heart unexpectedly stops pumping due to a sudden knock or an underlying medical condition.  When a defibrillator analyses the heart rhythm and recognises an abnormal rhythm, it will decide whether a shock is required to be delivered or not.  A defibrillator is also known as an automated external defibrillator (AED) or simply a ‘defib’. 

Basically, a defibrillator’s job is to ‘restart’ the heart by giving a burst of electric energy, re-establishing the electrical pulses and allowing the heart to beat again. 


What are Public Access Defibrillators (PADs)

Public Access Defibrillators are AEDs for use by members of the public.  AEDs have been provided in many public locations.  They are meant to be used by members of the public if they witness a cardiac arrest.

How does a defibrillator work?

A defibrillator delivers a set amount of electrical shock to the heart after it analyses the heart rhythm.  It determines whether a shock is required to the heart via adhesive electrode pads attached to the person’s chest.  The shock delivered by a defibrillator interrupts the chaotic rhythm of the heart and gives the heart the chance to return to its normal rhythm.

Do I need training to use a defibrillator?

Anyone can use a defibrillator (AED), they are designed for the lay person. Clear, spoken instructions and visual illustrations guide users through the process.  AEDs calculate their own electro-static shock and determine when a shock needs to be delivered, taking the pressure away from the person delivering medical care.  When an emergency occurs, a defibrillator must be used straight away without waiting for professional help which is why they are designed with the user in mind so that anyone can deliver care.  However, attending a short training or awareness course in CPR and defibrillation will no doubt give the user that extra confidence.  The British Heart Foundation has an excellent short video on defibrillation that you might want to see … Click here

Are defibrillators (AEDs) safe to use?

Modern AEDs are very reliable and will not allow a shock to be given unless it is needed.  They are extremely unlikely to do any harm to a person who has collapsed in suspected SCA.  They are safe to use and present minimal risk to the userYou should, however, not touch the person when the shock is delivered.  These features make them suitable for use by members of the public even without any training.


Is it safe to use a defibrillator if the patient is lying on a wet or metal surface?

Yes, it is usually safe to use a defibrillator on an individual who is lying on a metallic,wet or other conductive surface.  If the self-adhesive pads are applied correctly, and provided there’s no direct contact between the user and the patient when the shock is delivered, there is no direct pathway that electricity can take that would cause the user to experience a shock.  If the patient is wet, their chest should be dried so that the self-adhesive AED pads will stick properly.

Is it safe to use a defibrillator on a child?

Yes; defibrillators can be used on children.  Smaller special infant/child pads that attenuate the current delivered during defibrillation should be used on children aged between 1 and 8 years if they are available. However, in an emergency, if an AED with adult pads is the only device available, then these should be used.  It is recommended when using adult pads on small children to place the pads on the front of the chest and on the back, to lessen the impact of the shock.  It is not recommended that you use a defibrillator on infants younger than 1 year.


Is it safe to use a defibrillator on a pregnant woman?

Yes; defibrillators can be used on pregnant women without causing harm to the child.  In fact, fibrillation of the heart can be extremely dangerous for unborn children so it is important to act quickly.


What if I attached the defibrillator to a conscious person; can I harm them?

The defibrillator will not deliver a shock unless it detects a shockable rhythm, e.g. the heart is not beating regularly.  Therefore, you cannot do any harm to a person if you attach a defibrillator.  In fact, modern defibrillators will also advise whether you are carrying out CPR correctly (e.g., fast enough or hard enough).


What are the benefits of using an AED during a SCA?

Without defibrillation the chance of survival is less than 3%; with defibrillation this can rise to about 75%.  However, time is of the essence; the intervention of a defibrillator should take place within 5 minutes.  For every minute that passes the chance of survival is reduced by 10 – 15%.   


Can a heart stop beating after a defibrillator has got it beating again? How would I know?

Once a shock is delivered, the defibrillator will continue to monitor the person’s heart rhythm.  For this reason you should leave the pads attached until a medical professional attends the patient.  If the heart stops beating again, it will advise that a shock is required.  Follow the prompts given by the defibrillator. 

Why don’t I just wait until an ambulance arrives?

For every minute that passes the chance of survival is reduced by 10 – 15%.  Therefore, defibrillation is most effective when carried out as quickly as possible in the first five minutes after a cardiac arrest.  Ambulances are targeted within the UK to respond to ‘red calls’ (emergency calls) within 8 minutes – often they take longer.  If you wait for an ambulance the likelihood is that the patient will die.  If you have access to a defibrillator you are the patient’s best hope of survival. However, you should always call for an ambulance in the event of an emergency.


What maintenance does a defibrillator require?

All AEDs perform self-maintenance checks on a daily, weekly and monthly basis to ensure that they are ready for use.  In the event that the machine fails part of the test, it will ‘beep’ to alert you that there is a fault.  Some modern defibrillators will advise the person responsible for it through software media. Batteries should last 5 years if not used and the pads should be replaced after use.    


How do you use a defibrillator?

Defibrillators (AEDs) are designed for use by anyone, with clear written and verbal instructions, AEDs are cleverly manufactured to walk anyone step by step through the process of delivering emergency care.  Many defibrillators have impressive features such as increasing the volume by monitoring background noise and giving prompts when someone is delivering the correct care.  Inside AEDs you will find step by step instructions which show how to set the equipment up and with AEDs being automatic, they will also administer the shock for you.

Is CPR effective on its own (When should it be used)?

No; CPR will not save the life of a sudden cardiac arrest sufferer on its own.  CPR helps to circulate a small amount of blood to the vital organs, thus prolonging the dying process until a defibrillator arrives to attempt to resuscitate the patient.

CPR should be used as soon as it is discovered that a patient has no pulse, to help to keep the blood flowing round the body and should be continued until the defibrillator arrives.  From then on, the defibrillator will instruct you on what to do, including when to perform CPR.

How do I use a Defibrillator?

Almost all modern defibrillators are equipped with voice and/or visual commands on how to use.  Once you have ascertained that the person is likely to have had a cardiac arrest (no pulse, unresponsive, unconscious, not breathing) you should:

  • Call an ambulance
  • Begin CPR at a rate of 2 breaths and 30 chest compressions.
  • Locate a defibrillator
  • Turn on the defibrillator
  • Apply the pads:
    • First check the pads are attached to a cable, plugged into the defibrillator
    • Ensure the patient is bare-chested (even females)
    • Attach the adhesive pads to the patient’s chest in the appropriate locations
  • Follow the instructions of the AED very clearly.

How do I know where to find a Public Access Defibrillator (PAD)? 

PADs are increasingly being placed in public places and buildings.  They are usually in a yellow and/or green cabinet.  Heartbeat Trust UK is leading a national campaign to introduce greater signage to defibrillator locations.  Look out for the green heart logos with a shock/pulse line within it.


Where can I get defibrillator awareness training?

Heartbeat Trust UK works with its partners to deliver free CPR and defibrillator awareness training within the community.  These are usually short 1 hour sessions.  Please contact us if you are interested in receiving such training.  In the meantime, we can highly recommend a short video (about 4 minutes) prepared by the British Heart Foundation:   


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