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How an AED Analyzes the Heart Rhythm

How an AED Analyzes the Heart Rhythm - Departments & Programs, UW Health, Ambulatory Education, CPR, Automated External Defibrillator (AED) Training (All Ages)


An AED contains a computer chip that analyzes the rate, size, and pattern of the victim's heart rhythm. AEDs are very accurate for use with person over the age of 1. The device is used to administer an electric shock through the chest wall to the heart. Audible and/or visual prompts guide the user through the process. If a shockable rhythm is identified (either V-fib or V-tach) the AED will tell the operator. The AED electrodes have two functions:

All AEDs must charge before they can deliver a shock. Most AEDs charge automatically. Others require that you press a charge button.  The operator will generally press a button to deliver the SHOCK.  However there are some AEDs that are fully automated and will automatically deliver the shock.

Another computer chip inside the defibrillator interprets or analyzes the victim's heart rhythm through adhesive electrodes (some AED models require you to press an ANALYZE button). The computer analyzes the heart rhythm and advises the operator whether a shock is needed. AEDs advise a shock only to ventricular fibrillation and fast ventricular tachycardia. The electric current is delivered through the victim's chest wall through adhesive electrode pads.  If the AED advises “no shock”, it has not detected a shockable rhythm.