What is the first line treatment for narrow complex SVT?

• A. Vagal maneuvers
• B. Atrial pacing
• C. AV nodal blockade with adenosine
• D. Electrical cardioversion

Answer: (C)

When a patient has stable narrow-complex SVT, the main goal is to interrupt the reentrant circuit with techniques that slow conduction through the AV node. The first step is vagal maneuvers (like Valsalva or carotid sinus massage, if not contraindicated). These nondrug techniques increase parasympathetic tone and can terminate the tachycardia by slowing AV nodal conduction.

If vagal maneuvers do not restore sinus rhythm, the next step is a rapid IV dose of adenosine. Adenosine transiently blocks AV nodal conduction, which often terminates AV nodal–dependent tachycardias such as AVNRT and AVRT and also helps reveal the underlying rhythm. Its effect is very short-lived, making it ideal for acute termination and for diagnostic clarity without a prolonged pause in heart rhythm.

Electrical cardioversion is reserved for patients who are unstable or when pharmacologic therapy fails or is contraindicated. Atrial pacing isn’t a first-line option in the initial stable setting.

So, while vagal maneuvers are the initial approach, adenosine is the primary pharmacologic agent used if rapid termination is needed after maneuvers or if pharmacologic management is preferred in that clinical scenario.