Atrial flutter is classified as a regular rhythm. The upper chambers of the heart beat very rapidly, typically around 300 beats per minute, but in an organized, repeating pattern. This regularity is actually where the name comes from: early researchers coined “flutter” to describe the rapid but regular contractions they observed, distinguishing them from the chaotic, irregular contractions seen in atrial fibrillation.
That said, the pulse you actually feel can sometimes be regular or slightly irregular, depending on how the signal travels from the upper chambers to the lower chambers. Understanding why requires a closer look at what’s happening electrically in the heart.
Why the Atrial Rhythm Is Regular
In atrial flutter, an electrical signal gets caught in a loop, circling around the same path in the right upper chamber of the heart over and over again. Because the loop follows a fixed circuit (usually around the tricuspid valve), each lap takes roughly the same amount of time. This produces a very predictable atrial rate, typically between 240 and 400 beats per minute.
On an ECG, this shows up as a distinctive “sawtooth” pattern: smooth, repeating waves with no flat baseline between them. These waves are evenly spaced, reflecting that regular circuit. This is one of the clearest visual differences between flutter and fibrillation, where the baseline looks chaotic and disorganized.
How the Pulse Can Sometimes Feel Irregular
Here’s where it gets nuanced. The upper chambers may be firing at 300 beats per minute, but the lower chambers (the ventricles, which actually pump blood to your body) can’t keep up with that pace. A built-in gatekeeper called the AV node blocks some of those signals from reaching the ventricles. How many signals get through determines the heart rate you actually feel at your wrist.
When the AV node blocks signals in a fixed, consistent ratio, the resulting pulse is regular. The most common pattern is 2:1 block, meaning every other signal gets through, producing a steady ventricular rate around 150 beats per minute. A 4:1 ratio would give you a rate around 75, which can look deceptively normal.
The pulse becomes irregular when that blocking ratio changes. If the AV node sometimes lets every other beat through and sometimes lets only every third or fourth beat through, the ventricular rhythm becomes uneven. This is called variable block, and it can make atrial flutter look and feel more like atrial fibrillation to the person experiencing it. The key distinction is that the underlying atrial rhythm itself remains regular. The irregularity is happening at the gatekeeping level, not in the electrical circuit.
How Flutter Differs From Fibrillation
Atrial fibrillation and atrial flutter are closely related conditions, and many people experience both. But they behave quite differently in terms of regularity. In atrial fibrillation, the upper chambers don’t follow any organized pattern at all. They quiver chaotically, sending random, disorganized signals to the ventricles. The result is a rhythm that’s “irregularly irregular,” meaning there’s no discernible pattern to the heartbeat.
In atrial flutter, by contrast, the upper chambers follow a single organized circuit. Even when the ventricular response varies, there’s usually some underlying structure to the rhythm. A clinician reading an ECG can spot the difference by looking at the atrial activity itself: the neat sawtooth waves of flutter versus the messy, erratic baseline of fibrillation.
The two conditions frequently coexist. Someone diagnosed with atrial flutter often has episodes of atrial fibrillation as well, which is one reason doctors monitor for both.
Types of Atrial Flutter
Atrial flutter is divided into two main categories based on where the electrical circuit runs. Typical flutter (sometimes called CTI-dependent flutter) uses a well-defined path around the tricuspid valve in the right atrium. It produces the classic sawtooth ECG pattern and is the more common form. An older classification system labeled this “type I,” though that terminology is no longer used in current guidelines.
Atypical flutter follows a different circuit, sometimes in the left atrium. It often develops after a prior heart procedure, particularly ablation for atrial fibrillation. Atypical flutter can look less obviously regular on an ECG and is generally harder to treat.
Stroke Risk and Treatment
Because atrial flutter involves the upper chambers beating abnormally, blood can pool and form clots, raising the risk of stroke. Research shows that stroke patterns differ somewhat between flutter and fibrillation. In one study comparing the two, strokes caused by flutter were more often the small-vessel “lacunar” type (47% of flutter strokes versus 14% with fibrillation), while fibrillation-related strokes were more frequently caused by larger clots traveling from the heart.
Regardless of these differences, current guidelines from the American Heart Association recommend that people with atrial flutter receive blood-thinning medication based on their overall stroke risk, just as they would for atrial fibrillation. This is partly because the two rhythms so often coexist, and partly because flutter itself carries meaningful clot risk.
For typical atrial flutter specifically, catheter ablation (a procedure that disrupts the electrical circuit causing the flutter) has a high success rate and low recurrence rate, making it a common first-line treatment. Atypical flutter is more technically challenging to ablate. After ablation for flutter, continued monitoring and often continued blood thinners are recommended, since atrial fibrillation may still develop independently.