Which energy level is appropriate for defibrillation in unstable polymorphic ventricular tachycardia?

• A. 100 joules
• B. 200 joules
• C. 50 joules
• D. 360 joules

Answer: (B)

When a patient is in a shockable, unstable ventricular tachyarrhythmia, the goal is to deliver a defibrillating shock that reliably terminates the abnormal rhythm and restores a perfusing rhythm. For modern biphasic defibrillators, the standard initial energy for defibrillation in this situation is 200 joules. This dose provides a strong enough pulse to stop the reentrant or focal activity causing the VT without unnecessarily increasing myocardial injury. If the first shock doesn’t terminate the rhythm, subsequent shocks are delivered at higher energies as guided by the device and protocol (often 300–360 J), with monophasic devices typically delivering 360 J as the initial dose.

It’s important to distinguish defibrillation from synchronized cardioversion. If the patient has a pulse but is unstable, synchronized cardioversion is used, starting around 100 J and escalating as needed, rather than defibrillation. In the specific context of unstable polymorphic VT, the 200 J energy level aligns with defibrillating a shockable rhythm when the patient is nonperfusing or not responding to initial therapy.