AED is the acronym for Automated External Defibrillator. AEDs have revolutionized the way we think of and perform CPR. There are now laws regulating the placement of AEDs in public places such as airports, and they are being carried by police officers, firemen and EMTs everywhere.
A person's heartbeat is regulated by the transmission of electrical impulses from a small region of the right atrium, called the sinoatrial (SA) node. This node sends out electrical impulses that control the contraction of first the atria of the heart, then the ventricles, moving blood through the lungs to get oxygenated, then to the body.
When cardiac arrest occurs, it is fairly uncommon that there is no electrical activity going on in the heart, medical shows notwithstanding... "He's flatlining!! Shock him!!". Actually, what usually occurs when a person has no pulse is that the electrical activity of the heart has become disorganized, so that the heart muscle is no longer contracting effectively and rhythmically. There are several different types of electrical rhythm disturbances, called arrhythmias. Only a few of them, however, will respond to defibrillation. The most common of these are ventricular fibrillation, or V-fib, and ventricular tachycardia, or V-tach.
Defibrillation is the applying of an electrical shock to the heart muscle in order to stop the disorganized electrical activity and allow the heart to resume its normal rhythm. By itself, CPR very, very rarely will revive a person in cardiac arrest, and the sooner defibrillation is used, the better the patient's outcome will be.
Before AEDs, the people who could defibrillate were doctors and paramedics, because they had the necessary training to identify rhythms that could or could not be shocked successfully. However, since the development of the AED, anyone who can read and follow directions can defibrillate a cardiac arrest patient, significantly increasing their chance of survival. The patient's chance of survival decreases tremendously with even a short delay between occurrence of the arrest and defibrillation, even if CPR is being performed.
The AED is a defibrillator that includes a processor capable of analyzing the patient's electrical rhythm and determining whether it is shockable. AEDs can be either semi-automatic or shock-advisory defibrillators, which require the operator to press a button to deliver the shock when the machine tells them to, or fully automatic defibrillators, which deliver the shock themselves. Both types of defibrillator have a voice system which will speak instructions such as "attach pads to patient" "stand away from the patient" "shock advised" or "shock not indicated; resume CPR" "shocking" "check pulse" and "resume CPR". The device basically talks the rescuer through the necessary actions.
The AED is responsible for many saved cardiac arrest patients; it has become the new standard of care in First Aid and Emergency Care for the pulseless patient.
Information taken from personal experience, inservices, articles I've read in the past I can no longer find, and Emergency Care, 9th Ed., by Limmer, O'Keefe, Grant, Murray and Bergeron, edited by Edward T. Bickinson, M.D., FACEP, published by Brady/Prentice Hall Health. ISBN # 0-13-015794-5