⚡ Automated External Defibrillator (AED)

🫀 Conditions the device treats

An AED is used in life-threatening cardiac arrhythmias leading to sudden cardiac arrest — which is not the same as a heart attack. The rhythms treated are usually limited to:

In both shockable arrhythmias, the heart is electrically active but cannot pump blood effectively. VT causes extremely fast beats → inefficient pumping → degenerates into VF. In VF, chaotic electrical activity prevents ventricular contraction. Without treatment, VF eventually degrades to asystole (flatline).

AEDs are not designed to shock asystole — no positive outcome. Survival in asystole depends on high-quality CPR and cardiac stimulants to re-establish a shockable rhythm. CPR before defibrillator arrival is imperative.

⏱️ Effect of delayed treatment

Uncorrected VT, VF, or asystole rapidly cause irreversible brain damage and death. After 3–5 minutes in cardiac arrest, irreversible brain damage may begin. For each minute without defibrillation:

• First 3 minutes: survival decreases by 7% per minute
• Beyond ~3 minutes: survival decreases by 10% per minute

📋 Requirements & training

AEDs are designed for laypersons. Studies show sixth-grade students can deliver shocks within 90 seconds (trained operators ~67 sec). Manual defibrillators require advanced ECG interpretation.

⚠️ Safety precautions

• Remove metal underwire bras and torso piercings to avoid interference / arcing (Mythbusters confirmed fire risk only in unusual conditions).
• Ideal to have AED training, but Chicago’s Heart Start program: 11 survivors out of 18 treatable arrests, 6 treated by bystanders with no prior training.

🌍 Placement & availability

Public access AEDs are found in shopping centers, offices, transport hubs, gyms. Universal AED sign (ISO 7010 E010) indicates location. Home AEDs are increasing, but training is encouraged.

Typical AED kit includes: face shield, nitrile gloves, trauma shears, towel, razor for hairy chests.

🔧 Preparation & maintenance

Check before duty: battery expiration, electrode pad expiration date, self-test indicator. Most units have voice prompts, visual displays and event memory (ECG + audio).

⚙️ Mechanism of operation

“Automatic” because the unit autonomously analyzes cardiac rhythm. Electrode pads are placed on bare chest → device analyzes electrical output. If shockable rhythm (VF/VT), it charges internal capacitor and instructs user to deliver shock (semi-auto requires button press). Most AEDs now use biphasic waveform (120–200 joules) instead of older monophasic (360–400 J), improving efficacy and reducing myocardial injury & burns.

📍 Geolocation & mapping

OpenStreetMap tag: emergency=defibrillator. Visible signage and public registries help first responders locate nearest AED.

🧑‍🤝‍🧑 Ease of use & pediatric application

Voice and visual prompts guide user. Pediatric pads or attenuator for children <8 years or <55 lbs (25 kg). Studies show public access defibrillation is associated with ~40% median survival in out-of-hospital cardiac arrests when used by lay first responders.

⚖️ Legal & reliability insights

Good Samaritan laws (most US states, Canada’s “Chase McEachern Act”) protect lay rescuers from civil liability when using AED in good faith, without gross negligence.

However, reliability concerns exist: FDA reclassified AEDs as Class III (premarket approval) due to >750 deaths (2004–2009) linked to component failures/design errors. February 2015: FDA requires rigorous PMA applications to ensure safety of batteries, pads, and pediatric accessories.

Despite challenges, AEDs dramatically improve survival when properly maintained and deployed. User cannot override “no shock” advisory, ensuring safety.

🔬 Historical note

First commercial AEDs: monophasic, high-energy. Modern biphasic devices deliver lower energy with superior termination of VF and shorter recovery.