If vagal maneuvers fail and the rhythm is regular, what is the next drug to administer?

• A. Amiodarone
• B. Adenosine
• C. Synchronized cardioversion
• D. Magnesium sulfate

Answer: (B)

When a patient has a regular narrow-complex tachycardia and vagal maneuvers haven’t converted the rhythm, the aim is to transiently block conductions through the AV node to stop the tachycardia. Adenosine is the drug of choice here because it temporarily blocks AV nodal conduction for a few seconds, which can interrupt AV node–dependent reentrant circuits (like AVNRT or AVRT) and often restore normal rhythm quickly.

Administer it as a rapid IV push, then immediately flush with saline. If there’s no response, a second, higher dose can be given. Because of its very short half-life, it acts quickly and then wears off, minimizing overall impact if tolerated well. If the patient becomes unstable or the rhythm persists despite adenosine, synchronized cardioversion is the next step.

Amiodarone is more commonly used for stable ventricular tachycardias or polysystolic/irregular tachycardias, not first-line for a regular SVT after vagal maneuvers. Magnesium sulfate targets specific situations like torsades de pointes or true magnesium deficiency. Cardioversion is reserved for instability or when drug therapy fails.