Which of the following is a beta-blocker used as an antiarrhythmic (Class II)?

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

Answer: (B)

Beta-adrenergic blockade is what Class II antiarrhythmics rely on. By blocking beta receptors in the heart, these drugs dampen sympathetic stimulation, slow the pace of the SA node, and slow conduction through the AV node, which helps prevent or terminate tachyarrhythmias driven by adrenergic activity.

Metoprolol fits here as a beta-1 selective blocker. It mainly affects the heart, reducing heart rate and AV nodal conduction, lowering automaticity, and helping control tachyarrhythmias such as atrial fibrillation or flutter and certain re-entrant rhythms. This makes it the typical choice for Class II antiarrhythmic therapy.

Lidocaine acts on sodium channels and is focused on ventricular arrhythmias (Class IB), not a beta-blocker. Amiodarone has strong effects across multiple channels and mainly acts as a Class III antiarrhythmic, with beta-blocking properties but not its primary mechanism. Diltiazem is a calcium channel blocker (Class IV) and slows AV nodal conduction without being a beta-blocker.