Compared with an external AED, an automatic implanted defibrillator (AICD) has which characteristic?

• A. Higher energy output
• B. Lower energy output
• C. Similar energy output
• D. No energy output

Answer: (B)

The key idea is that energy needs differ because of where the shock is delivered. An implanted defibrillator sits right against the heart and delivers current directly through the heart tissue via its leads. That close, direct path means we can terminate dangerous rhythms with much less energy, minimizing collateral damage to surrounding tissues. External AEDs have to push current through the chest wall and across a larger distance, dealing with higher impedance, so they require substantially more energy to achieve defibrillation. In practice, implanted devices deliver relatively low-energy shocks (often in the 20–40 joule range), whereas external defibrillators deliver much higher energies.