An alert 66-year-old patient with a history of cardiovascular disease develops a narrow-complex tachycardia; which intervention is indicated first?

An alert 66-year-old patient with a history of cardiovascular disease develops a narrow-complex tachycardia; which intervention is indicated first?

• A. Adenosine
• B. Synchronized cardioversion
• C. Carotid sinus massage
• D. Lidocaine

Answer: (A)

The important concept here is that stable narrow-complex tachycardia is most effectively treated first with a rapid-acting AV nodal blocker to interrupt the reentrant circuit. Adenosine does exactly that: it temporarily blocks conduction through the AV node, which commonly terminates AV-node–dependent supraventricular tachycardias (like AV nodal reentry or AVRT) and often reveals the underlying rhythm. Its onset is very fast and its half-life is extremely short, so if the rhythm doesn’t convert, any adverse effects wear off quickly and you can retry or move on to the next step. In a patient with cardiovascular disease who is hemodynamically stable, adenosine is preferred over synchronized cardioversion, which is reserved for those who are unstable or not responding to pharmacologic therapy. Vagal maneuvers such as carotid sinus massage carry additional risks in older adults with vascular disease and are not reliably first-line in this scenario. Lidocaine targets ventricular arrhythmias and would not terminate a narrow-complex SVT. If adenosine terminates the tachycardia, you’ve confirmed an AV-node–dependent SVT and can continue monitoring. If there’s no response, or if there are contraindications, you would consider alternatives based on stability and rhythm characteristics.

The important concept here is that stable narrow-complex tachycardia is most effectively treated first with a rapid-acting AV nodal blocker to interrupt the reentrant circuit. Adenosine does exactly that: it temporarily blocks conduction through the AV node, which commonly terminates AV-node–dependent supraventricular tachycardias (like AV nodal reentry or AVRT) and often reveals the underlying rhythm. Its onset is very fast and its half-life is extremely short, so if the rhythm doesn’t convert, any adverse effects wear off quickly and you can retry or move on to the next step.

In a patient with cardiovascular disease who is hemodynamically stable, adenosine is preferred over synchronized cardioversion, which is reserved for those who are unstable or not responding to pharmacologic therapy. Vagal maneuvers such as carotid sinus massage carry additional risks in older adults with vascular disease and are not reliably first-line in this scenario. Lidocaine targets ventricular arrhythmias and would not terminate a narrow-complex SVT.

If adenosine terminates the tachycardia, you’ve confirmed an AV-node–dependent SVT and can continue monitoring. If there’s no response, or if there are contraindications, you would consider alternatives based on stability and rhythm characteristics.