Which drug is an example of a Class IV antiarrhythmic (calcium channel blocker)?

• A. Diltiazem
• B. Amiodarone
• C. Lidocaine
• D. Propranolol

Answer: (A)

Class IV antiarrhythmics are calcium channel blockers that primarily slow conduction through the AV node by blocking L-type calcium channels. This reduces AV nodal conduction velocity and increases the nodal refractory period, which helps control heart rate during atrial tachyarrhythmias such as atrial fibrillation or flutter with rapid ventricular response. Diltiazem is a nondihydropyridine calcium channel blocker that acts on cardiac tissue to slow AV conduction and lower heart rate, making it a textbook example of a Class IV agent.

The other drugs listed do not belong to this class. Amiodarone is mainly a Class III agent (potassium channel blockade with many other effects), Lidocaine is a Class Ib sodium channel blocker used for ventricular arrhythmias, and Propranolol is a Class II beta-blocker that reduces AV conduction via adrenergic blockade.