In atrial fibrillation with rapid ventricular response due to hyperthyroidism, which rate-controlling agent is most appropriate?

• A. Calcium channel blocker
• B. Beta-blocker
• C. Digoxin
• D. Amiodarone

Answer: (B)

In thyrotoxic atrial fibrillation with rapid ventricular response, the heart is rowing under high sympathetic drive, so the aim is to slow the AV nodal conduction quickly while also dampening the excess thyroid state. A beta-blocker fits this best because it directly reduces the ventricular rate by blocking adrenergic input at the AV node, which slows conduction. In addition, nonselective beta-blockers like propranolol can decrease the peripheral conversion of T4 to the more active T3, helping address the thyrotoxic state as part of initial management.

Calcium channel blockers can slow the AV node as well, but they don’t mitigate the thyroid excess and may worsen hypotension or heart failure in some patients. Digoxin often has a limited effect in hyperthyroidism due to increased clearance and persistent adrenergic stimulation. Amiodarone can treat AF but carries a risk of worsening thyroid dysfunction because of its iodine content and can complicate thyroid disease management.

So, using a beta-blocker provides the fastest, most comprehensive rate control in this scenario.