In stable patients with suspected SVT, which interventions are recommended?

• A. Observation only
• B. IV lidocaine as first-line
• C. Vagal maneuvers and adenosine administration
• D. Immediate synchronized cardioversion

Answer: (C)

In stable SVT, the focus is to terminate the tachycardia safely using fast-acting, noninvasive measures. Vagal maneuvers—such as bearing down (Valsalva) or carotid sinus massage when there are no carotid artery disease concerns—aim to boost parasympathetic tone and slow conduction through the AV node. Many reentrant SVTs rely on the AV node for their circuit, so this can stop the tachycardia or at least reveal the underlying rhythm.

If vagal maneuvers don’t work, giving adenosine intravenously is the next best step. Adenosine briefly blocks AV nodal conduction, which can terminate the tachycardia and often helps diagnose the mechanism by revealing the atrial rhythm. Its very short duration makes it ideal for a controlled, reversible interruption of the SVT.

Lidocaine is not appropriate here because it targets ventricles, not AV nodal–dependent SVT, and would not terminate the rhythm. Immediate synchronized cardioversion is reserved for unstable patients with SVT (signs of poor perfusion, chest pain, or altered mental status). Observation alone won’t terminate an ongoing SVT in a stable patient, so active measures are preferred.