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Atrial Tachycardia — EECC MCQ

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ModerateArrhythmia & ElectrophysiologyAtrial TachycardiaEECC

A 50-year-old man presents with a regular narrow-complex tachycardia at 180 bpm. Adenosine 12 mg IV is administered. The tachycardia transiently slows revealing a 2:1 relationship between atrial and ventricular activity, then resumes at 180 bpm once adenosine wears off. What is the most likely diagnosis?

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Correct answer: C — Atrial tachycardia with 2:1 AV conduction, unmasked by adenosine

Adenosine causes transient AV block, which helps distinguish the mechanism of narrow-complex tachycardias. In AVNRT and AVRT, adenosine typically terminates the tachycardia by blocking conduction through the AV node (an essential part of the re-entrant circuit). In atrial tachycardia, the atrial mechanism continues despite AV block — adenosine 'unmasks' the underlying atrial activity by slowing ventricular response, revealing the true atrial rate with 2:1 or higher-degree AV block. This continuation of tachycardia despite AV block is diagnostic of atrial tachycardia. Management includes rate control or rhythm control with catheter ablation of the atrial focus.

Reference: ESC (2019): Guidelines on SVT Management