Automated External Defibrillators (AED)

Introduction

In the UK, like many other countries, Heart Disease is the number one killer. Most of these deaths happen with little or no warning and the most common cause is Sudden Cardiac Arrest (SCA) where the heart rhythm is disturbed. The most common heart disturbance is ventricular fibrillation (VF) and it is dangerous because it cuts off the blood supply to the brain and other vital organs.

  Normal Heart Rhythm

   Heart in Ventricular Fibrillation

Within the heart, the ventricles are the chambers that pump blood from the heart into the blood vessels. The blood supplies oxygen and other nutrients to organs, cells and other structures. If these structures are starved of blood, they start to shut down or fail. If the blood flow is not restored quickly, permanent brain damage or death is the result.

SCA can often be treated by applying an electric shock to the chest, a procedure called defibrillation which generally restores normal heart rhythm. Early defibrillation is the key to surviving SCA.

Most patients in a hospital coronary care unit who experience SCA survive because defibrillation is performed almost immediately. However outside of a hospital setting, the situation is reversed depending upon how swiftly the Emergency Services arrive on the scene.  It is generally accepted that for every one minute the person remains in VF without defibrillation, the chances of a successful resuscitation drop by almost 10%. After 10 minutes, the chances of survival are near zero.

Cardiopulmonary Resuscitation (CPR) does provide temporary artificial breathing and circulation as it can deliver a limited amount of blood and oxygen to the brain until a defibrillator becomes available.

However, defibrillation is the only effective way to resuscitate a victim of SCA.
 

Chain of Survival and the Role of the Emergency Services

The Chain of Survival is a series of actions that when performed together, gives the SCA victim the greatest chance of survival. The steps are:

• Early Access:  Early access means alerting the Emergency Services through a 999 call immediately and stating the victim is unconscious and not breathing.
• Early CPR:  Performing CPR is essential to resuscitation from SCA as it buys time before defibrillation is available. The mouth to mouth breathing and chest compressions help oxygenated blood flow to the victim’s brain, lungs and other organs. Appropriate Oxygen therapy during CPR is an effective way of increasing the oxygen in the blood flow.
• Early Defibrillation: This is the most significant link in the chain and is the only action that can restore the hearts disturbed rhythm to normal.
• Early Advanced Care:  Paramedics from the emergency services provide this care which includes basic life support, defibrillation, administration of cardiac drugs and the insertion of endotracheal breathing tubes.  This type of care can help the heart maintain a normal rhythm on the way to the hospital where a more definitive diagnostic evaluation can occur.
   

Manual Defibrillation

Manual defibrillation is a complex skill and in a hospital environment, requires the operator to interpret ECG heart rhythms and understand the abnormalities that require defibrillation and which ones do not.

In the 1970’s, defibrillators began to be used outside the hospital environment by carefully trained paramedics. This was a significant step in increasing the chance of survival of SCA victims. However the inherent delay in getting a paramedic to a SCA victim within the first critical minutes still means that many SCA victims die. 

Automated External Defibrillators (AEDs)

In the mid 1980’s a new generation of computerised defibrillators became available. These AEDs are capable of analysing a victim’s heart rhythm and automatically delivering an appropriate defibrillation shock with minimal input from the operator. It also means that the operator of an AED does not necessarily need to understand or interpret ECG rhythms. Modern AEDs are not expensive, are easy and safe to use and will not deliver a shock unless it is appropriate.

Despite these advances, the problem still remains of the need to get a defibrillator to the victim within those first critical few minutes.

Public Access Defibrillators (PADs)

The recognition that AEDs are extremely easy to use has led to the concept of placing them in public places. The provision of AEDs in airports, railway stations, sports facilities and where large numbers of people congregate is a developing programme and in the UK, many thousands have been deployed. In the ideal situation, members of staff and first aiders would be trained to use the AED and CPR techniques.  Whilst training is recommended, operating an AED with its clear spoken commands can be undertaken by untrained members of the public.

In the UK, many Community First Responders are trained and equipped with AEDs and in some very remote areas where a timely paramedic response is difficult, local initiatives have funded AEDs within the community and trained a number of villagers on the chain of survival including how to operate the AED.

The North Gloucestershire ICD Support Group AED Project

In 2007, the N Glos ICD group combined with Cleeve Vale Rotary Club to raise funds and initiate a project to place AEDs in locations that could save lives. The first phase of the project is now complete with life saving facilities being provided at Cleeve School near Cheltenham. A full write up of what has been achieved can be viewed by clicking here.

Comments to  webmaster@icd-gloucestershire.org.uk