AEDs are lightweight, portable devices containing a battery, capacitors, and electronic circuitry to analyze the cardiac rhythm and inform the operator when a defibrillation shock is needed. The adhesive electrode pads that are placed on the victim’s chest are used to monitor the heart rhythm and to deliver a shock when needed. These devices have been shown to be extremely safe and have neither delivered any inappropriate shocks to patients nor caused harm to users or bystanders. They are highly accurate in detecting life-threatening heart rhythms and are effective in delivering shock therapy.
Laypersons trained in the use of an AED may go for many months or even years without operating an AED. Individuals not trained in AED use may find themselves needing to provide assistance to a victim of cardiac arrest. Because of these considerations, operation of the AED has been made straightforward to ensure timely delivery of a life-saving shock. After the AED is turned on, self-adhesive electrode pads are applied to the chest wall, as shown in the Figure. When activated, an automated voice inside the AED guides the user through several simple steps. The heart rhythm is automatically interpreted by the AED, and the voice prompt recommends either that a shock be delivered by pushing a button on the device or that monitoring be continued without a shock. AEDs have been designed to markedly reduce the time to defibrillation and minimize the need for training. One study of a mock cardiac arrest showed that the average time to defibrillation from arrival at the scene was only 90 seconds for a group of untrained sixth-grade students compared with 67 seconds for trained emergency medical technicians and paramedics.