Random fact that I learnt today!
If a patient with WPW syndrome develops symptomatic atrial fibrillation, what is the drug of choice?
Answer is procainamide.
Stable patients suspected of having WPW with atrial fibrillation should not receive agents that predominantly block atrioventricular conduction, but they may be treated with procainamide or ibutilide.
Because if you block the AV node using beta blockers, calcium channel blockers or digoxin, you will favour conduction to the accessory pathway. This will worsen the arrhythmia.
That's why, in stable patients, chemical cardioversion is preferred.
If instability is present, electrical cardioversion is required.
Related post: Supraventricular tachycardia mnemonic