An Automated External Defibrillator, or AED, is a portable medical device used when a person has sudden cardiac arrest. It checks the heart's electrical rhythm and can deliver a controlled electric shock if the rhythm is shockable. AEDs matter because rapid defibrillation can greatly improve the chance of survival.
They are designed so trained rescuers and ordinary bystanders can use them with voice prompts and visual instructions.
The AED uses adhesive electrode pads to sense electrical signals from the heart through the chest. Its internal computer analyzes the rhythm and decides whether a shock is advised, most often for ventricular fibrillation or pulseless ventricular tachycardia. If a shock is needed, the device charges a capacitor and releases stored electrical energy across the chest to help reset chaotic heart activity.
CPR, calling emergency services, and following AED prompts all work together to support the person until advanced care arrives.
Key Facts
- Sudden cardiac arrest is an electrical problem where the heart stops pumping blood effectively.
- AED stands for Automated External Defibrillator.
- Energy delivered by many adult AED shocks is about 120 J to 200 J, depending on the device.
- Electrical energy stored in a capacitor is E = 1/2 C V^2.
- Current through the chest depends on resistance by Ohm's law: I = V/R.
- Use the AED as soon as it arrives, keep doing CPR when prompted, and make sure nobody touches the person during analysis or shock.
Vocabulary
- Automated External Defibrillator
- A portable device that analyzes heart rhythm and can deliver an electric shock to treat certain life threatening rhythms.
- Defibrillation
- Defibrillation is the delivery of an electric shock intended to stop chaotic heart electrical activity so a normal rhythm can return.
- Electrode pads
- Electrode pads are sticky conductive pads placed on the chest to detect heart signals and deliver the shock.
- Ventricular fibrillation
- Ventricular fibrillation is a dangerous rhythm where the lower chambers of the heart quiver instead of pumping blood.
- Capacitor
- A capacitor is an electrical component that stores charge and energy before releasing it quickly during an AED shock.
Common Mistakes to Avoid
- Touching the person during rhythm analysis or shock delivery is wrong because movement can confuse the AED and a shock can pass through someone in contact with the patient.
- Placing pads too close together is wrong because the current may not pass through enough of the heart to be effective.
- Stopping CPR for a long time while setting up the AED is wrong because blood flow to the brain and heart falls quickly during interruptions.
- Using an AED only after a professional arrives is wrong because AEDs are built for bystanders and earlier shocks are linked to better survival.
Practice Questions
- 1 An AED delivers 150 J of energy in a shock. If the shock lasts 0.010 s, what is the average power delivered during the shock?
- 2 A capacitor inside an AED has a capacitance of 160 microfarads and is charged to 1500 V. Using E = 1/2 C V^2, how much energy is stored in the capacitor?
- 3 Explain why an AED tells rescuers not to touch the person while it analyzes the rhythm and again before it delivers a shock.