Distinguishing Atrial Flutter vs. Atrial Fibrillation on the ECG
Atrial flutter (AFL) and atrial fibrillation (AFib) are two of the most common supraventricular arrhythmias.
Correctly differentiating them is important because:
Typical atrial flutter has a high success rate with catheter ablation
Atypical flutter and atrial fibrillation require different ablation strategies
Rhythm interpretation can guide anticoagulation, rate control, and EP referral
This page outlines ECG characteristics, diagnostic tips, and examples.
Primary References:
Atrial Flutter
Atrial flutter is usually a macro–reentrant circuit in the right atrium, producing rapid, regular atrial depolarizations.
Key ECG Features
Atrial rate ~300 bpm (range 200–400 bpm)
Ventricular rate ~150 bpm with 2:1 AV conduction
Regular rhythm
Absence of P waves
Saw-tooth “flutter waves” (F-waves) in inferior leads: II, III, aVF
F-wave polarity pattern:
Types of Atrial Flutter
Typical (Type I): Cavotricuspid isthmus (CTI) dependent; highly ablation-curable
Atypical (Type II): Non-CTI circuits (left atrial, postoperative, scar-related); variable ECG morphology
Atypical flutter may appear irregular if AV conduction varies, mimicking AFib.
Atrial Fibrillation
Atrial fibrillation is characterized by chaotic, disorganized atrial activation.
Key ECG Features
No distinct P waves
Atrial rate: 400–600 bpm
Ventricular rhythm is “irregularly irregular”
Variable R-R intervals
“Fibrillatory (f) waves” present, low amplitude
Coarse AF: f-wave amplitude > 0.5 mm (can mimic flutter)
ECG signs supportive of AFib:
Highly variable AV conduction
Baseline undulations without repeating pattern
Absence of consistent flutter waves
Distinguishing Atrial Flutter vs Atrial Fibrillation
| Feature | Atrial Flutter | Atrial Fibrillation |
| Rhythm | Regular (unless variable block) | Irregularly irregular |
| Atrial rate | ~300 bpm | 400–600 bpm |
| Baseline | Saw-tooth flutter waves | Chaotic, uneven baseline |
| P waves | None | None |
| F waves | Organized, repetitive | Disorganized, variable |
| R-R interval | Regular with fixed block (e.g., 2:1) | Irregular, unpredictable |
| Typical lead patterns | II, III, aVF (saw-tooth) | No consistent morphology |
| Response to vagal maneuvers | May increase AV block → reveals flutter waves | Minimal organized effect |
| Ablation success | High in typical flutter | Lower in AFib |
| Anticoagulation | Required if persistent or risk factors | Required based on CHA₂DS₂-VASc |
Special Case: Coarse Atrial Fibrillation
Sometimes AFib produces large amplitude f-waves (>0.5 mm), creating confusion with atypical flutter.
How to differentiate:
AFib: Lacks regularity; waveforms vary beat-to-beat
Flutter: Organized, consistent F-wave pattern
AFib: Atrial rate typically faster (400–600 bpm)
Flutter: Atrial rate 200–400 bpm, usually near 300
Flutter shows stable repeating morphology
AFib does not
Practical Tips for Distinguishing AFL vs AFib
Look in inferior leads (II, III, aVF) where flutter waves are most pronounced
Check lead V1, where flutter often appears positive (typical)
Assess regularity of the R-R interval
Perform manual caliper measurement of the flutter cycle length (~200 ms)
In uncertain cases, try:
Sample ECG Images
Typical Atrial Flutter (2:1 Conduction)
Atrial Fibrillation (Irregularly Irregular Rhythm)
Coarse Atrial Fibrillation (Flutter Mimic)
Key Takeaways
Atrial flutter has an organized, repeating pattern, usually around 300 bpm.
Atrial fibrillation shows disorganized atrial activity with irregularly irregular ventricular response.
Coarse AFib may resemble flutter but lacks stable morphology.
Typical flutter is highly curable with ablation; AFib treatment is more complex.
Using leads II, III, aVF, and V1 greatly improves diagnostic accuracy.
When uncertain, evaluate rhythm regularity, flutter cycle length, and use AV nodal slowing if appropriate.