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:

• AHA/ACC/HRS Atrial Fibrillation Guidelines
• LITFL ECG Library – Flutter & Fibrillation
• StatPearls: Atrial Flutter

Atrial flutter is usually a macro–reentrant circuit in the right atrium, producing rapid, regular atrial depolarizations.

• 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:
  • Typical (Counterclockwise) Flutter:
    • Negative flutter waves in II, III, aVF
    • Positive flutter waves in V1
  • Reverse (Clockwise) Flutter:
    • Positive in II, III, aVF
    • Negative in V1

• 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 is characterized by chaotic, disorganized atrial activation.

• 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

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

• 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:
  • Adenosine (if safe) → reveals flutter waves by slowing AV node
  • Vagal maneuvers → may expose flutter waves

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• 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.