Verapamil belongs to which class of antiarrhythmic drugs?

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

Answer: (A)

Verapamil is a Class IV antiarrhythmic, which are calcium channel blockers. They block L-type calcium channels in cardiac tissue, especially in the AV node, reducing calcium influx. This slows conduction through the AV node and increases the nodal refractoriness, helping to control rapid ventricular rates in atrial tachyarrhythmias. This mechanism is distinct from the other classes: Class I drugs are sodium channel blockers that mainly affect ventricular depolarization; Class II agents are beta-blockers that lower heart rate by reducing sympathetic drive; Class III drugs are potassium channel blockers that prolong repolarization and the QT interval.