Which of the following arrhythmias requires synchronized shocks?

Synchronized shocks are a critical intervention in certain arrhythmias to restore normal heart rhythm while minimizing the risk of inducing ventricular fibrillation. In the case of ventricular tachycardia, synchronized cardioversion is necessary because it allows the shock to be delivered during a specific point in the cardiac cycle, ensuring that it is effective and reducing the chance of causing more harm.

Ventricular tachycardia can sometimes be stable, and in these instances, synchronized cardioversion is preferred over unsynchronized shocks. When a shock is synchronized, it is timed to occur just after the R wave on the ECG, which corresponds to the phase of the heartbeat that is least likely to trigger a dangerous rhythm like ventricular fibrillation.

In contrast, other arrhythmias listed, like ventricular fibrillation, require unsynchronized shocks, as the chaotic electrical activity does not allow for effective synchronization. Atrial fibrillation can also be treated with synchronized shocks depending on the clinical context, but the focal question regarding which specifically requires synchronization points specifically to ventricular tachycardia. Bradycardia, while it can be serious, typically would be managed with medications or pacing rather than synchronized shocks.