A patient with a history of SVT who failed vagal maneuvers is given a drug that acutely terminates the arrhythmia by slowing conduction through the AV node. Which drug is the first-line choice?

A patient with a history of SVT who failed vagal maneuvers is given a drug that acutely terminates the arrhythmia by slowing conduction through the AV node. Which drug is the first-line choice?

• A. Atropine
• B. Amiodarone
• C. Amlodipine
• D. Adenosine

Answer: (D)

Adenosine is the drug of choice for acutely terminating AV-nodal dependent SVT because it works directly on the AV node to interrupt the reentrant circuit that underlies most of these tachycardias. It acts very quickly by binding A1 receptors in the AV node, opening potassium channels, hyperpolarizing nodal cells, and transiently blocking conduction. This brief AV nodal block usually resets the rhythm to sinus or a slower rate within seconds, and its effects wear off almost as fast due to an ultra-short half-life, limiting systemic impact. In this situation, where vagal maneuvers have failed, adenosine offers a rapid, targeted way to stop the arrhythmia with minimal toxicity. By contrast, atropine aims to increase heart rate via the SA node and is not effective for AV-nodal reentry. Amiodarone can terminate some SVTs but is not first-line for AV node–dependent tachycardias and has a longer onset. Amlodipine slows AV conduction as a rate-control measure but does not reliably terminate the tachycardia acutely. Adenosine’s precise action on the AV node, combined with its transient, rapid effect, makes it the best initial choice.

Adenosine is the drug of choice for acutely terminating AV-nodal dependent SVT because it works directly on the AV node to interrupt the reentrant circuit that underlies most of these tachycardias. It acts very quickly by binding A1 receptors in the AV node, opening potassium channels, hyperpolarizing nodal cells, and transiently blocking conduction. This brief AV nodal block usually resets the rhythm to sinus or a slower rate within seconds, and its effects wear off almost as fast due to an ultra-short half-life, limiting systemic impact.

In this situation, where vagal maneuvers have failed, adenosine offers a rapid, targeted way to stop the arrhythmia with minimal toxicity. By contrast, atropine aims to increase heart rate via the SA node and is not effective for AV-nodal reentry. Amiodarone can terminate some SVTs but is not first-line for AV node–dependent tachycardias and has a longer onset. Amlodipine slows AV conduction as a rate-control measure but does not reliably terminate the tachycardia acutely. Adenosine’s precise action on the AV node, combined with its transient, rapid effect, makes it the best initial choice.