Class I Antiarrhythmics and their Key Pharmacologic Properties



Class IA = Quinidine, Procainamide, Disopyramide ("Quarter PounDer")

Class IB = Lidocaine, Tocainide, Mexiletine, Phenytoin ("Lettuce, Tomato, Mayo, Pickle")

Class IC = Flecainide, Propafenone ("Fries Please")



Block fast Na+ channels that are responsible for the rapid depolarization (phase 0) of fast-response cardiac action potentials. This type of action potential is found in non-nodal cardiomyocytes. This decreases conduction velocity in non-nodal tissue and serves as an important mechanism for suppressing tachyarrhythmias.

  • Slows depolarization, results in wide QRS on EKG

  • Na+ channel blockade: IC > IA > IB

Some increase the effective refractory period (ERP) due to their actions on K+ channels involved in phase 3 repolarization of action potentials.

  • Prolongs repolarization and refractory period, results in prolonged QT on EKG

  • Increasing the ERP: IA > IC > 1B (decreases)



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