**Core Concept**
Wolff-Parkinson-White (WPW) syndrome is a rare heart condition characterized by the presence of an accessory electrical pathway between the atria and ventricles, leading to an abnormal heart rhythm. Atrial fibrillation in WPW syndrome poses a high risk of ventricular fibrillation and cardiac arrest.

**Why the Correct Answer is Right**
In patients with WPW syndrome and atrial fibrillation, the goal is to eliminate the accessory pathway to prevent the abnormal conduction of impulses. **Procainamide** is the drug of choice for this purpose because it can effectively block the accessory pathway, thereby preventing the transmission of impulses from the atria to the ventricles. Procainamide works by inhibiting the sodium channels in the accessory pathway, which leads to a reduction in the conduction velocity and eventually, the elimination of the accessory pathway.

**Why Each Wrong Option is Incorrect**
**Option A:** **Digoxin** is not the drug of choice in WPW syndrome with atrial fibrillation because it does not effectively eliminate the accessory pathway and can even increase the risk of ventricular fibrillation.
**Option B:** **Beta blockers** can be used to control heart rate in WPW syndrome but are not effective in eliminating the accessory pathway and preventing the transmission of impulses from the atria to the ventricles.
**Option C:** **Amiodarone** is a powerful antiarrhythmic medication but is not the first-line treatment for WPW syndrome with atrial fibrillation.

**Clinical Pearl / High-Yield Fact**
In WPW syndrome, the accessory pathway can be eliminated using **electrical cardioversion** or **catheter ablation**. These procedures are often performed under sedation and are highly effective in preventing the transmission of impulses from the atria to the ventricles.

**Correct Answer:** D. Procainamide.