In the Stable Tachycardia Narrow Complex with regular rhythm, what is the first pharmacologic intervention after maneuvers?

• A. Adenosine 6 mg rapid IVP/IO
• B. Amiodarone 150 mg
• C. Lidocaine 1 mg/kg
• D. Magnesium sulfate 2 g

Answer: (A)

The key idea is that for a stable, narrow-complex SVT with a regular rhythm, the first drug to try after maneuvers is adenosine. Adenosine rapidly blocks AV nodal conduction, which often interrupts the re-entrant circuit that sustains the tachycardia and can briefly reveal the underlying atrial activity. Its ultra-short half-life means it acts quickly and then disappears, allowing a swift assessment of the rhythm once it’s terminated or paused. Administer as a rapid IV bolus, typically 6 mg, followed by a swift saline flush; if there’s no response, a second dose of 12 mg can be given. Be prepared for a brief pause in conduction, flushing, chest tightness, or lightheadedness—these are expected and usually transient. If adenosine is ineffective, not tolerated, or contraindicated, consider alternatives like amiodarone, lidocaine, or magnesium, but they are not the first choice for this situation.