Automated external defibrillator

When and why AEDs are used

Sudden cardiac arrest (SCA) typically results from an abrupt failure of the heart’s electrical system, most often ventricular fibrillation or pulseless ventricular tachycardia. These rhythms are potentially reversible with rapid defibrillation. Because survival from a shockable arrest declines quickly—by roughly ten percent for every minute without treatment—timely access to an AED can be lifesaving. For this reason AEDs are commonly placed where many people gather or where emergency medical services may arrive slowly.

How an AED works

Most AEDs operate in a similar sequence: the rescuer exposes the victim’s bare chest, applies adhesive electrode pads, and follows voice and visual instructions. The device automatically analyses the heart rhythm and advises whether a shock is indicated. Semi-automatic units require the user to press a button to deliver the shock; fully automatic units will deliver the shock without further action by the rescuer. Many AEDs also provide CPR prompts, a metronome for compression rate, and built-in safety checks to prevent shocks when they are not required.

Components, maintenance and special features

• Electrode pads: single-use adhesive pads that sense electrical activity and deliver the shock; pads have an expiration date and must be replaced after use.
• Battery and electronics: most AEDs perform periodic self-tests and display status indicators; batteries and pads should be checked according to manufacturer guidance.
• User interface: voice prompts, lights and symbols simplify use; pediatric pads or attenuators are available for children in many models.
• Enclosures and access: public AEDs are often mounted in cabinets; some cabinets are locked and may be opened with a code provided by emergency dispatch when the caller requests it.

Placement, programs and registries

Public access defibrillation programs deploy AEDs in airports, train stations, schools, sports facilities, workplaces and other high-traffic areas to reduce time to treatment. Many emergency medical services and community programs maintain registries of publicly accessible AEDs so dispatchers can direct callers to the nearest device or alert volunteer responders carrying an AED. Placement strategies consider likely response times and population density to maximize the chance that an AED will be on scene before professional teams arrive.

Training, legal protection and community impact

Although AEDs are user-friendly, short training courses increase confidence and effectiveness by teaching pad placement, CPR coordination and device operation. Many jurisdictions offer Good Samaritan protections or specific statutes covering bystander use of AEDs to encourage intervention. Research on public access defibrillation has shown substantially improved outcomes when bystanders apply an AED early; some series report median survival rates around forty percent when a public AED is used promptly.

Limitations and practical advice

AEDs are intended for victims in cardiac arrest and are not appropriate for conscious people with a pulse. Rescuers should perform high-quality CPR until an AED is available and follow emergency dispatch instructions. Regular program maintenance—checking pad expiry, battery status and cabinet accessibility—keeps devices ready. When in doubt, emergency dispatchers can provide guidance, including codes for secured cabinets, and direct rescuers to nearby devices.

For background on defibrillation technology see defibrillator. For general medical emergency guidance consult local medical emergency resources. Examples of public placement include hubs such as airports. Regional program information is available in some countries, for example the United Kingdom. Outcome studies and systematic reviews are discussed in cardiac arrest studies, and statistical measures used in reports are explained in sources on median and related terms.