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Automated External Defibrillators (AED)

What is an automated external defibrillator (AED)?

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Although advances in emergency cardiac care continue to improve the chances of surviving cardiac arrest, cardiac arrest remains a leading cause of death in many parts of the world.

Each year, almost 350,000 Americans die from heart disease. Half of these will die suddenly, outside of the hospital, because their heart stops beating. Most of these deaths occur with little or no warning, from a syndrome called sudden cardiac arrest. The most common cause of sudden cardiac arrest is a disturbance in the heart rhythm called ventricular fibrillation.

Ventricular fibrillation is dangerous because it cuts off blood supply to the brain and other vital organs.

  • The ventricles are the chambers that pump blood out of the heart and into the blood vessels. This blood supplies oxygen and other nutrients to organs, cells, and other structures.
  • If these structures do not receive enough blood, they start to shut down, or fail.
  • If blood flow is not restored immediately, permanent brain damage or death is the result.

Ventricular fibrillation often can be treated successfully by applying an electric shock to the chest with a procedure called defibrillation.

  • In coronary care units, most people who experience ventricular fibrillation survive, because defibrillation is performed almost immediately.
  • However, the situation is just the opposite when cardiac arrest occurs outside a hospital setting. Unless defibrillation can be performed within the first few minutes after the onset of ventricular fibrillation, the chances for reviving the person (resuscitation) are very poor.
  • For every minute that goes by that a person remains in ventricular fibrillation and defibrillation is not provided, the chances of resuscitation drop by almost 10 percent. After 10 minutes, the chances of resuscitating a victim of cardiac arrest are near zero.

Cardiopulmonary resuscitation, usually known as CPR, provides temporary artificial breathing and blood circulation.

  • 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 ventricular fibrillation.

Chain of Survival

CPR is one link in what the American Heart Association calls the "chain of survival." The chain of survival is a series of actions that, when performed in sequence, will give a person having a heart attack the greatest chance of survival.

  • The first link in the chain of survival is immediate recognition of cardiac arrest and activation of the emergency response system by calling 911 (check your community plan, some communities require dialing a different number).
  • The next link in the chain of survival is to perform early CPR, with an emphasis on chest compressions until a defibrillator becomes available.
  • Following early CPR, the next link is to provide rapid defibrillation. In many areas of the country, simple, computerized defibrillators, known as automated external defibrillators, or AEDs, may be available for use by the lay public or first person on the scene.
  • Once the EMS unit arrives, the next link in the chain of survival is effective advanced life support care. This involves administering medications, using special breathing devices, and providing additional defibrillation shocks if needed.


Manual defibrillation, which is the traditional form of defibrillation performed by health care professional, is a complex skill.

  • First, the operator must have the ability to interpret an electrocardiogram (EKG, ECG) heart rhythms.
  • The operator also needs to be able to recognize what ECG abnormalities require defibrillation and which ones do not. (For example, a person with a "flat line" ECG would not require, or benefit from, defibrillation.)
  • The operator needs to know how to manually operate the particular model of defibrillator that is available.

Originally, defibrillators were used only in hospitals.

  • As the units became more portable, and as early EMS systems began to develop in the United States in the early 1970s, defibrillators began to be used outside the hospital by carefully trained and supervised paramedics.
  • This was a significant step forward in increasing the chance of survival from out-of-hospital cardiac arrest. Rather than transporting the victim to a defibrillator, the defibrillator was transported to the victim.

Because of the delay inherent in getting an ambulance to the cardiac arrest victim within those critical first few minutes, many people continued to die from ventricular fibrillation.

Medically Reviewed by a Doctor on 9/28/2016

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