What is the initial energy dose for cardioversion in atrial fibrillation?

• A. 100 J
• B. 125 J
• C. 150 J
• D. 200 J

Answer: (B)

When converting atrial fibrillation with a shock, you deliver a synchronized cardioversion so the energy hits the heart at the right moment in the rhythm. Modern biphasic defibrillators have a typical starting energy around 125 joules for atrial fibrillation. This dose is high enough to reliably cardiovert many patients while minimizing unnecessary tissue damage compared with higher levels. If the rhythm doesn’t convert, you follow the device’s protocol and move to the next dose (often higher, such as 150–200 J, depending on the machine and guidelines).

Other options aren’t as appropriate for the initial shock: 100 J is usually on the lower end and may be less reliably effective on many biphasic devices, while 150 J or 200 J are commonly used for subsequent attempts or specific device guidelines rather than the standard first dose.