Adenosine is most reliably used to terminate tachycardias that depend on which structure?

• A. Atrial tachycardia
• B. AV node-dependent tachycardia (such as AVNRT)
• C. Ventricular tachycardia
• D. Sinus tachycardia

Answer: (B)

Adenosine works by briefly blocking conduction through the AV node and increasing its refractory period. Tachycardias that depend on the AV node as part of their reentrant circuit—most classically AV nodal reentrant tachycardia—are terminated because the circuit can no longer propagate past the AV node. In contrast, atrial tachycardias originate above the AV node and ventricular tachycardias originate in the ventricles, so their maintenance doesn’t rely on AV nodal conduction; adenosine may slow conduction briefly but typically does not terminate them. Sinus tachycardia is a normal rate response and is not a reentrant tachycardia through the AV node, so it is not reliably terminated by adenosine.