Which of the following is a drug-related cause of bradycardia?

• A. Nitroglycerin
• B. Beta-blockers or calcium channel blockers
• C. Atropine
• D. Adrenaline

Answer: (B)

Drug-induced bradycardia happens when medicines dampen the heart’s electrical activity or slow its conduction. The best answer is drugs that blunt the heart’s rate control: beta-blockers and non-dihydropyridine calcium channel blockers. Beta-blockers reduce the SA node’s automaticity and slow AV nodal conduction by blocking adrenergic receptors, which lowers the heart rate and can lead to bradycardia, especially in older patients or those with underlying conduction issues. Calcium channel blockers like verapamil or diltiazem directly slow AV nodal conduction, also risking bradycardia.

Nitroglycerin mainly causes vasodilation and often triggers reflex tachycardia rather than bradycardia. Atropine counteracts bradycardia by blocking parasympathetic effects and raises heart rate. Adrenaline tends to increase heart rate and contractility, not cause bradycardia.