Atrial flutter ECG recognition: the sawtooth pattern
Atrial flutter is a macro-reentrant atrial arrhythmia producing a distinctive sawtooth baseline pattern — organized atrial activity at approximately 250–350 bpm. The flutter waves are continuous, regular, and saw-toothed, most prominent in the inferior leads (II, III, aVF) and V1.
Conduction ratios determine the ventricular rate. In typical 2:1 flutter, every other flutter wave conducts: atrial rate 300 → ventricular rate 150 bpm. 4:1 flutter produces ventricular rate 75 bpm. Variable block (2:1 and 4:1 alternating) produces irregular ventricular response mimicking AFib — measure the flutter-to-QRS timing to differentiate.
Key recognition feature: QRS morphology is normal and narrow (unless bundle branch block exists). The QRS rides on the continuous flutter wave baseline. Identifying the flutter-wave frequency (measure F-F interval) confirms atrial rate and rules out AFib.
Atrial flutter vs atrial fibrillation: the clinical distinction
Atrial flutter and AFib are both supraventricular arrhythmias and require similar anticoagulation assessment — but their ECG recognition and some management details differ. Flutter: organized sawtooth flutter waves at fixed rate (~300/min), often regular ventricular response (unless variable block). AFib: chaotic fibrillatory baseline, always irregularly irregular ventricular response, no organized P waves.
Adenosine differentiates them when in doubt: adenosine transiently blocks AV conduction, slowing the ventricular rate and revealing the underlying atrial activity. In flutter, the sawtooth pattern becomes unmistakable. Adenosine does not terminate flutter — it only unmasks it. Treatment is synchronized cardioversion for unstable flutter or rate control with antiarrhythmics for stable flutter.