Which agent is a first-line treatment for bradycardia and certain toxic emergencies?

• A. Digoxin
• B. Atropine sulfate
• C. Calcium chloride
• D. Magnesium sulfate

Answer: (B)

Atropine sulfate is used because it blocks muscarinic receptors on the heart, removing the parasympathetic (vagal) influence that slows the heartbeat. By inhibiting this vagal tone, the SA node fires more readily and the AV node conducts more effectively, causing the heart rate to rise and improving cardiac output in symptomatic bradycardia.

In toxic emergencies like organophosphate poisoning, excess acetylcholine overstimulates muscarinic receptors and drives bradycardia and other secretory effects; atropine reverses these muscarinic effects, helping to restore heart rate and stabilize the patient.

Other agents don’t fit this role: digoxin can cause bradycardia and is not a treatment for it; calcium or magnesium are reserved for specific overdose or electrolyte situations (such as calcium channel blocker overdose or torsades de pointes) and are not first-line treatments for general bradycardia.