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U.S. Department of Health and Human Services

Medical Devices

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What is an External Defibrillator?

External defibrillators are life-saving devices designed to restore normal heart rhythms at the time of sudden cardiac arrest. They are designed to deliver electrical energy to the heart.The term “external defibrillator” is generally used to refer to any device that operates outside the body and delivers energy through paddles or electrode pads for the purposes of restoring normal heart rhythm.

Automated external defibrillators (AEDs) can be semi-automated or fully automated. Semi-automated defibrillators analyze the heart’s rhythm, and if an abnormal rhythm is detected that requires a shock, then the device prompts the rescuer to press a button to deliver a defibrillation shock. Fully automated defibrillators deliver a defibrillation shock if commanded by the device software without help from the user. AEDs are used by trained users, first responders, and by untrained bystanders. They are used in homes and are increasingly found in public places such as airports, hotels, schools, and sports facilities.

Monitor/Defibrillators are more complex devices that can include the ability to monitor different kinds of bodily functions such as blood oxygen level, pulse, and heart rhythm. These devices deliver external cardiac pacing and external defibrillation either manually. Some have automatic function like AEDs. The monitor/defibrillators are used by medical professionals and are found mostly in hospitals and emergency medical systems.

Manual external defibrillators are used with (or have built-in) an electrocardiogram (EKG) display to diagnose the rhythm of the heart. Manual external defibrillators have no automatic function to assess and treat rhythms. On the basis of the diagnosis, the clinician determines the energy level to be delivered to the patient. These devices are used predominantly in hospitals and on some ambulances.

Wearable external defibrillators are vest-like devices that continuously monitor the patient’s rhythm to identify changes that require a defibrillation shock. If a shock is needed, alarms are sounded. If the patient fails to respond to the alarms because of loss of consciousness from the rhythm changes, the system delivers a life-saving shock.