An automated external defibrillator or AED is a portable electronic device that automatically diagnoses the potentially life threatening cardiac arrhythmias of ventricular fibrillation and ventricular tachycardia in a patient, and is able to treat them through defibrillation, the application of electrical therapy which stops the arrhythmia, allowing the heart to reestablish an effective rhythm.
AEDs are designed to be simple to use for the layman, and the use of AEDs is taught in many first aid, first responder and basic life support (BLS) level CPR classes.
Unlike regular defibrillators, an automated external defibrillator requires minimal training to use. It automatically diagnoses the heart rhythm and determines if a shock is needed. Automatic models will administer the shock without the user's command. Semi-automatic models will tell the user that a shock is needed, but the user must tell the machine to do so, usually by pressing a button. In most circumstances, the user cannot override a "no shock" advisory by an AED. Some AEDs may be used on children - those under 55 lbs (25 kg) in weight or under age 8. If a particular model of AED is approved for pediatric use, all that is required is the use of more appropriate pads. Some organizations, such as the American Heart Association, recommend that if pediatric AED pads are not available, adult pads should be used to determine if the child is in a shockable rhythm. There is insufficient evidence to suggest that a child, in a shockable cardiac arrest, can be "hurt" by an adult defibrillation energy setting.
All AEDs approved for use in the United States use an electronic voice to prompt users through each step. Because the user of an AED may be hearing impaired, many AEDs now include visual prompts as well. Most units are designed for use by non-medical operators. Their ease of use has given rise to the notion of public access defibrillation (PAD), which experts agree has the potential to be the single greatest advance in the treatment of out-of-hospital cardiac arrest since the invention of CPR.
Automated external defibrillators are now easy enough to use that most states in the United States include the "good faith" use of an AED by any person under the Good Samaritan laws."Good faith" protection under a Good Samaritan law means that a volunteer responder (not acting as a part of one's occupation) cannot be held civilly liable for the harm or death of a victim by providing improper or inadequate care, given that the harm or death was not intentional and the responder was acting within the limits of their training and in good faith. In the United States, Good Samaritan laws provide some protection for the use of AEDs by trained and untrained responders. AEDs create little liability if used correctly; NREMT-B and many state EMT training and many CPR classes incorporate or offer AED education as a part of their program. In addition to Good Samaritan laws, Ontario, Canada also has the "Chase McEachern Act (Heart Defibrillator Civil Liability), 2007 (Bill 171 – Subsection N)", passed in June, 2007,which protects individuals from liability for damages that may occur from their use of an AED to save someone's life at the immediate scene of an emergency unless damages are caused by gross negligence.