Functional description of antiarrhythmic drugs. Class 1a-block sodium channels (quinidine, procainamide, disopyramide); class 1b-reduce phase 0 or maximum upstroke velocity of action potential (lidocaine, phenytoin, tocainide); class 2-block sympathetic activity (beta blockers such as propranoiol); class 3-prolong duration of action potential (bretylium, amiodarone); class 4-inhibit flow of slow inward current (verapamil).