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Atrial Flutter 2:1 Recognition — EECC MCQ

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EasyArrhythmia & ElectrophysiologyAtrial Flutter 2:1 RecognitionEECC

A 55-year-old man presents to the emergency department with palpitations and a regular narrow-complex tachycardia at 150 bpm. What diagnosis should always be considered when the ventricular rate is exactly 150 bpm?

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Correct answer: E — Atrial flutter with 2:1 AV conduction — the atrial rate in typical flutter is approximately 300 bpm, and with 2:1 conduction the ventricular rate is characteristically ~150 bpm; adenosine may unmask flutter waves

A regular narrow-complex tachycardia at approximately 150 bpm should always raise suspicion for atrial flutter with 2:1 AV block. Typical (CTI-dependent) atrial flutter has an atrial rate of approximately 300 bpm; with 2:1 conduction, the ventricular rate is ~150 bpm (the 'tell-tale' rate). Flutter waves (sawtooth pattern, best seen in leads II, III, aVF, and V1) may be obscured at 2:1 conduction. Adenosine transiently increases AV block, revealing the underlying flutter waves without terminating the arrhythmia (unlike AVNRT/AVRT where adenosine terminates the tachycardia). Treatment: electrical cardioversion (most effective), ibutilide, or catheter ablation of the cavotricuspid isthmus (CTI ablation — >95% success rate, curative for typical flutter).

Reference: ESC (2019): SVT Guidelines; ESC (2024): AF Guidelines