atrial flutter
If atrial fibrillation is chaotic noise, atrial flutter is a fast but tidy loop — like a single electrical wave chasing its own tail around a fixed racetrack in the atrium. The most common form circles the right atrium roughly 300 times a minute, producing a very regular, organized atrial rhythm rather than the disorganized quiver of fibrillation.
Because the AV node cannot pass every one of those rapid impulses, it lets through only a fraction — often one in two, giving a heart rate near 150 beats per minute. On the ECG this looks like a regular “sawtooth” pattern of flutter waves, especially in the lower leads, a hallmark that separates it from fibrillation.
Atrial flutter carries a similar stroke risk to fibrillation and is managed with the same attention to anticoagulation. Its great advantage is that the re-entry circuit is usually predictable, so catheter ablation — burning a small line across the circuit — cures the typical form in the large majority of patients.
An ECG showing a regular rate of 150 with sawtooth waves in the inferior leads prompts referral for catheter ablation of the right-atrial circuit, after which the patient's flutter does not recur.
Typical atrial flutter has a predictable circuit, making it especially curable by ablation.
A regular tachycardia at almost exactly 150 beats per minute should always raise suspicion of atrial flutter with 2:1 conduction, where alternate flutter waves are hidden inside the QRS complexes.