In which of the following arrhythmias is immediate synchronized cardioversion indicated?

A. Unstable SVT

B. Multifocal Atrial Tachycardia (MAT)

C. Ventricular Fibrillation

D. Atrial Fibrillation

E. Accelerated Idioventricular Rhythm

Answer: Unstable SVT

Synchronized cardioversion is a shock timed with the QRS complex to avoid the R on T phenomenon that can lead to Ventricular Fibrillation. Defibrillation (unsynchronized cardioversion) is indicated for ventricular fibrillation, pulseless ventricular tachycardia and unstable polymorphic ventricular tachycardia. Accelerated Idioventricular Rhythm (AIVR) is seen after myocardial reperfusion resulting in a regular wide complex rhythm that can be distinguished from Ventricular Tachycardia by a slower rate (40-120 bpm); do not treat, generally benign. Synchronized cardioversion is not recommended for MAT as it can increase the automaticity; treat the underlying cause, most commonly COPD, and control the rate.