What is an automated external defibrillator?

The automated external defibrillator (AED) is a computerized medical device. It has adhesive pads that are put on the chest. These allow an electrical current to pass through to the heart. This can help reset the heart's normal electrical current. A normal, regular or organized electrical rhythm through the heart is needed for the muscle to contract and pump blood to the body.

When a person is in cardiac arrest, they may have one of these problems:

• No electrical current.

• A rapid rhythm that doesn't allow for the heart pumping chambers to fill the right way (ventricular tachycardia).

• A disorganized electrical rhythm or current that doesn't allow the heart muscle to contract and circulate blood to the body (ventricular fibrillation).

Ventricular fibrillation and ventricular tachycardia can be stopped with an electric shock to bring back normal heart rhythm and circulation to the body. This is called either cardioversion or defibrillation.

An AED can check a person's heart rhythm through monitors that are in the defibrillator pads. This means you don't have to be a trained expert to recognize irregular heart rhythms to save someone's life when you use an AED. The AED can detect a rapid or irregular heart rhythm that needs a shock. And it can tell the rescuer when a shock is needed. The AED uses voice prompts, lights, and text messages to tell the rescuer the steps to take.

AEDs are very accurate. And they're easy to use. There are a lot of different brands of AEDs. But the same basic steps apply to all of them. The American Heart Association doesn't recommend a specific model.

Do you need training to use an AED?

No. Most anyone with or without a medical background can learn to use an AED or place the pads in the right way and give a shock by following the AED's prompts. In most cases, people learn to use an AED in a course that also teaches CPR. The AED will tell a rescuer to push the defibrillate button if cardiac arrest is from an abnormal heart rhythm that could respond to a shock. (Not all rhythms will.) This could be either ventricular fibrillation or ventricular tachycardia. Ventricular fibrillation is the most common heart-rhythm problem in someone who has sudden cardiac arrest.

Won't the cost of devices like AEDs keep them out of most places?

No. The cost of AEDs has gone down a lot in the past few years. Many AEDs and the replacement parts cost about $1,500 to $2,000.

Are AEDs really needed in places other than hospitals?

The rate of sudden cardiac death can be reduced by placing AEDs in the community and by teaching people how to use them. Seconds and minutes count when cardiac arrest occurs. The chance of survival goes down for every minute that goes by without this type of help.

Is an AED useful for all types of cardiac arrest?

No. Other abnormal rhythms can't be treated with an AED. This includes having a very slow heart rate or no electrical rhythm at all. When a user puts the AED's electrodes or pads on a person's chest, the device checks whether their heart needs to be shocked or not. Then the AED will instruct the rescuer about the next steps. Many of the newer models talk the rescuer through the steps. They automatically give the shock if needed.

Do AEDs mean CPR is no longer needed?

Absolutely not. Both are needed to correctly resuscitate someone having a cardiac arrest. An AED can bring back a normal heart rhythm in certain cases. Chest compressions in CPR are used to help keep blood flowing through the heart and the body. CPR can double the chances of survival when done the right way when a person has collapsed and just before an AED gives a shock. CPR should be started while someone else gets the AED.

Does research back the community use of AEDs?

Yes. One study looked at the survival rates of people who had sudden cardiac arrest from ventricular fibrillation in casinos and got AED treatment from security staff. There was a 75% survival rate for people who got their first shock within 3 minutes. This is compared to a 50% survival rate for those shocked after more than 3 minutes.