What does an AED (Defribrillator) test for before it delivers a shock

1. What the Automated External Defribrillator (AED) is actually “looking for”
It analyses the heart rhythm to detect shockable rhythms, primarily:

• Ventricular fibrillation (VF) – chaotic, disorganised electrical activity
• Pulseless ventricular tachycardia (VT) – very fast rhythm with no effective pumping

These are the rhythms where a shock can help “reset” the heart.

2. “No shock advised” doesn’t mean the situation isn’t critical
The AED won’t shock for non-shockable rhythms like:

• Asystole (flatline)
• Pulseless electrical activity (PEA)

But in those cases, high-quality CPR is the treatment, not electricity.

3. The “charging” and safety process
Correctly described—modern AEDs:

• Charge automatically when a shock is advised
• Prompt rescuers to stand clear to avoid interference and accidental shock
• Some models deliver the shock automatically

4. Why the “clear” step matters
It’s not just about safety—movement or contact can interfere with rhythm analysis, so clearing ensures accuracy as well as protection.

5. Self-testing and readiness
Most AEDs run regular self-checks (battery, circuitry, pads). That’s why you’ll often see a status light indicating “ready.”

Bottom line:
AEDs are designed to reduce human error—they only deliver shocks when a shockable rhythm is detected, and they guide the rescuer step by step. They will not shock a normal heart rhythm or a flatline.