In a patient with stable narrow-complex supraventricular tachycardia, what is the first-line pharmacologic therapy?

• A. Amiodarone
• B. Adenosine
• C. Diltiazem
• D. Cardioversion

Answer: (B)

Adenosine is the drug of choice for terminating stable narrow-complex SVT because it transiently blocks AV nodal conduction, interrupting the reentrant circuit that typically involves the AV node. Its effects are incredibly rapid and short-lived, so a quick IV push can stop the tachycardia within seconds and reveal the patient’s underlying rhythm, with minimal downstream effects once the drug wears off. If adenosine doesn’t work or isn’t suitable, calcium channel blockers like diltiazem or beta blockers can be used for rate control, and synchronized cardioversion is reserved for instability; amiodarone is generally considered for other tachyarrhythmias rather than first-line treatment of stable narrow-complex SVT, making adenosine the best initial pharmacologic option.