62. Why must an AV nodal blocking agent be used with a class 1C antiarrhythmic drug?

Class IC antiarrhythmic drugs include flecainide and propafenone. These agents must be used in combination with an AV blocking agent in order to prevent rapid atrial fibrillation or atrial flutter conduction (1:1 conduction) through the AV node resulting in very fast ventricular rates if a breakthrough episode occurs since they also act to increase AV nodal conduction.