Which of the following antiarrhythmic drugs can decrease the slope of Phase 0 and prolong the action potential duration?: (A) Lignocaine, (B) Propanolol, (C) Quinidine, (D) Adenosine
Answer is C. Na+ channel blockers reduce the slope of phase 0 whereas K+ channel blockers prolong the APD. Both of these propeies are present in class Ia antiarrhythmics like quinidine and procainamide.