Which of the following describes the four main classes of antiarrhythmic drugs?

• A. I sodium channel blockers; II beta-blockers; III potassium channel blockers; IV calcium channel blockers
• B. I potassium channel blockers; II calcium channel blockers; III beta-blockers; IV sodium channel blockers
• C. I beta-blockers; II sodium channel blockers; III calcium channel blockers; IV potassium channel blockers
• D. I calcium channel blockers; II potassium channel blockers; III sodium channel blockers; IV beta-blockers

Answer: (A)

The four main antiarrhythmic classes are defined by their primary target in the heart: Class I are sodium channel blockers, Class II are beta-adrenergic blockers, Class III are potassium channel blockers that prolong repolarization, and Class IV are calcium channel blockers. This option correctly matches that scheme: sodium channel blockers as Class I, beta-blockers as Class II, potassium channel blockers as Class III, and calcium channel blockers as Class IV. This classification helps explain how each class affects cardiac electrical activity—sodium channel blockers slow conduction, beta-blockers reduce automaticity and AV-node conduction, potassium channel blockers extend the action potential and QT interval, and calcium channel blockers decrease calcium entry affecting nodal conduction and the plateau phase. While some drugs have multiple actions, the primary grouping follows this four-class structure, which is why this choice best fits.