In a patient with paroxysmal supraventricular tachycardia unresponsive to Valsalva maneuvers, which measure is next most appropriate for conversion?

• A. Carotid sinus massage
• B. Adenosine bolus
• C. Lidocaine bolus
• D. Cardioversion

Answer: (B)

The key idea is that when a stable patient has PSVT that doesn’t respond to vagal maneuvers, the best next step is a rapid-acting drug that pauses AV nodal conduction to interrupt the reentrant circuit. Adenosine does this by briefly blocking the AV node, which is central to most AV nodal-dependent SVTs. The effect is almost instantaneous and extremely short-lived, so a rapid IV bolus with saline flush is given first (typically starting with 6 mg, then 12 mg if needed; a third dose may be given if still not converted). Most patients convert within seconds to a normal rhythm, and the drug wears off quickly without lasting effects, allowing continuous monitoring for any recurrence.

If adenosine fails or the patient is unstable, synchronized cardioversion becomes the next step. Other options like lidocaine are aimed at ventricular arrhythmias and aren’t effective for PSVT, and carotid sinus massage is a vagal maneuver with variable success and carries risks in certain patients, making adenosine the preferred immediate pharmacologic choice in this scenario.