Which drug is NOT typically used to cardiovert atrial fibrillation back to normal sinus rhythm?

Aspirin is not used to cardiovert atrial fibrillation back to normal sinus rhythm because it is an antiplatelet medication that functions primarily to prevent blood clot formation, rather than directly affecting the heart's rhythm. In the context of atrial fibrillation, the goal is to restore the normal electrical activity of the heart.

The other options listed are all antiarrhythmic drugs used in the management of atrial fibrillation. Amiodarone, Flecainide, and Ibutilide are all capable of converting atrial fibrillation to sinus rhythm through different mechanisms. Amiodarone is particularly effective due to its multi-channel blockade properties, while Flecainide and Ibutilide also work on specific ion channels to restore normal rhythm. Therefore, the use of these medications is relevant to the treatment of atrial fibrillation, making aspirin the clear choice that does not fit this purpose.