Atrial flutter with 2:1 conduction sits at close to 150 beats per minute and stays there. That fixity is the diagnostic feature. Sinus tachycardia varies with position, anxiety, pain and time; fibrillation is irregular; flutter at 2:1 is metronomic, because the atrial rate is fixed at around 300 and the ratio is fixed at two.
So when a monitor shows 148 to 152 for an hour without drifting, stop treating the number and look for flutter waves. They are frequently invisible in the leads you glance at. Slow the ventricular rate transiently — vagal manoeuvre or adenosine — and the atrial activity appears. Look at leads II, III, aVF and V1; the sawtooth is often clearest in the inferior leads and the discrete atrial deflection clearest in V1.
The cost of missing it is that the patient is treated for sinus tachycardia, the underlying cause is hunted for, and an arrhythmia with an anticoagulation decision and a highly effective ablation goes unnamed.
- A ventricular rate parked at about 150 with no variation is flutter until proven otherwise.
- Use adenosine diagnostically with a continuous rhythm strip running — the recording is the point, not the response.
- Check V1 for discrete atrial deflections when the inferior leads are equivocal.
- Once flutter is named, the CHA2DS2-VA score and an ablation discussion both follow; neither happens if it is filed as sinus tachycardia.
Why it matters
Flutter misread as sinus tachycardia sends the team looking for a cause of tachycardia instead of making an anticoagulation and ablation decision.
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