In an infant with supraventricular tachycardia, after unsuccessful vagal stimulation, which drug should be given first?

• A. Adenosine
• B. Digoxin
• C. Verapamil
• D. Esmolol

Answer: (A)

Adenosine is used first because it acts very quickly to interrupt the AV node’s conduction, which is usually the part of the reentrant circuit driving SVT in infants. Its ultra-short half-life means it terminates the tachycardia with minimal delay and minimal ongoing effects if it fails, making it ideal for an acute, unstable-appearing rhythm in a small child. It’s given as a rapid IV bolus with a saline flush, and the dose can be repeated if there’s no response.

Digoxin has slower onset and is not for abrupt termination of an acute SVT. Verapamil and esmolol can depress cardiac function and blood pressure in infants and are not preferred as first-line agents for acute termination, especially after vagal maneuvers fail. Adenosine directly targets the AV node, which is typically the key to stopping AV nodal–dependent SVT, making it the best initial pharmacologic choice.