- Atrial flutter is a type of supraventricular tachycardia caused by a macro-re-entry circuit in the right atrium.
- The re-entry circuit results in an atrial rate of 200-400 bpm (typically 300 bpm).
- Ventricular rate is determined by the AV conduction ratio — commonly referred to as the “degree of AV block” (NB. This term is slightly misleading as the AV block is a physiological response to the rapid atrial rates; these patients usually have no evidence of AV block at normal heart rates)
- The commonest AV conduction ratio is 2:1 — i.e. the ventricular rate is half the atrial rate (= 150 bpm).
- Higher-degree AV blocks can occur — usually due to medications or underlying heart disease — resulting in lower rates of ventricular conduction, e.g. 3:1 or 4:1 block.
- Atrial flutter with 1:1 conduction can occur due to sympathetic stimulation or in the presence of an accessory pathway (especially if AV-nodal blocking agents are administered to a patient with WPW).
- Atrial flutter with 1:1 conduction is associated with severe haemodynamic instability and progression to ventricular fibrillation.
Latest classification of atrial flutter is based on anatomical identification and direction of reentry circuit, as described below.
Typical Atrial Flutter (Common, or Type I Atrial Flutter)
Involves the inferior vena cava – tricuspid isthmus in the reentry circuit. Can be further classified based on the direction of the circuit:
- Anticlockwise Reentry
- Commonest form of typical atrial flutter 90% cases
- Positive flutter waves in V1
- Negative flutter waves in leads II,III, aVF
- Clockwise Reentry (Reversed Typical Atrial Flutter)
- Wide negative flutter waves in V1
- Positive flutter waves in leads II, III, aVF
Atypical atrial flutter (Uncommon, or Type II Atrial Flutter)
- Does not fulfil criteria for either type of typical atrial flutter.
- Often associated with higher atrial rates and rhythm instability.
- Less amenable to treatment with ablation.
- Regular rhythm in presence of fixed AV block.
- Ventricular rate ~150 bpm in presence of 2:1 AV block.
- Flutter waves / ‘saw-tooth pattern’ best seen in leads II, III, aVF and V1.
- Flutter wave morphology depending on type of atrial flutter (see above).
- QRS complexes usually < 120 ms unless pre-existing bundle branch block, accessory pathway, or rate related aberrant conduction.
- Variable AV block will result in an irregular rhythm.
- Absence of an isoelectric baseline.
- Atrial flutter is closely related to atrial fibrillation in both causes and symptoms.
- Atrial flutter is usually paroxysmal but may be chronic (in which case it may lead to tachycardia-dependent cardiomyopathy).
- Symptoms of atrial flutter can include dizziness, palpitations, dyspnoea, and chest pain.
- Acute treatment of atrial flutter involves either rate or rhythm control (rhythm control is more likely to be successful).
- Long term cure requires ablation of the tricuspid isthmus to interrupt the re-entry circuit.
- Atrial flutter should be considered in all regular narrow complex tachycardia with a ventricular rate of ~150 bpm.
- Vagal manoeuvres may help differentiate sinus tachycardia from atrial flutter. In atrial flutter vagal manoeuvres may be ineffective or result in a rapid decrease in rate allowing flutter waves to be more easily seen.
- In atrial flutter with variable block the R-R distances will be multiples of each other unlike atrial fibrillation in which no relationship exists e.g. assuming atrial rate of 300bpm the R-R distance in 2:1 block is 400ms, in 3:1 block 600ms, in 4:1 block 800ms.
- Flutter waves may be more easily appreciated by turning the ECG upside-down.
Atrial flutter with variable block:
- Flutter waves are clearly visible — there is a “sawtooth” baseline most evident in leads II, III, aVF and V1.
- The morphology is typical for an anticlockwise re-entry circuit — the flutter waves are upgoing in V1, downgoing in lead II.
- There is a varying relationship between the flutter waves and QRS complexes (variable AV block).
- The relatively slow ventricular rate suggests treatment with AV-nodal blocking drugs.
Atrial flutter with 2:1 block:
- There is a narrow complex tachycardia at 150 bpm.
- There are no visible P waves.
- There is a sawtooth baseline in V1 with flutter waves visible at 300 bpm.
- Elsewhere, flutter waves are concealed in the T waves and QRS complexes.
- The heart rate of 150 bpm makes this flutter with a 2:1 block.
NB. Flutter waves are often very difficult to see when 2:1 block is present.
- Suspect atrial flutter with 2:1 block whenever there is a regular narrow-complex tachycardia at 150 bpm — particularly when the rate is extremely consistent.
- In contrast, the rate in sinus tachycardia typically varies slightly from beat to beat, while in AVNRT/AVRT the rate is usually faster (170-250 bpm).
- To tell the difference between these rhythms, try some vagal manoeuvres or give a test dose of adenosine — AVNRT/AVRT will often revert to sinus rhythm, whereas slowing of the ventricular rate will unmask the underlying atrial rhythm in sinus tachycardia and atrial flutter.
Atrial flutter with 3:1 block:
- Negative flutter waves at ~ 300bpm are best seen in the inferior leads II, III and aVF (= anticlockwise pattern).
- There is a 3:1 relationship between the flutter waves and the QRS complexes, resulting in a ventricular rate of 100 bpm.
Atrial flutter with 4:1 block
- Flutter waves are visible at a rate of ~ 260 bpm.
- Upright in V1-2, inverted in II, III and aVF (= anticlockwise circuit).
- There is a 4:1 relationship between the flutter waves and QRS complexes, resulting in a ventricular rate of ~ 65 bpm.
Atrial flutter with variable block (clockwise type):
- Positive flutter waves in lead II suggest the presence of a clockwise re-entry circuit (= uncommon variant).
Atrial flutter with a variable block:
- Another good ECG example of flutter with a variable block and typical anticlockwise morphology.
- ECG BASICS – Waves, Intervals, Segments and Clinical Interpretation
- ECG CLINICAL CASES – Your favourite ECG’s placed in clinical context with a challenging Q&A approach
- ECG and Cardiology Eponymous Syndromes – Cheats guide to eponymous emancipation
- ECG Reference Sites on the WEB – the best of the rest
- Surawicz B, Knilans TK. Chou’s Electrocardiography in Clinical Practice. 6th Edition. Saunders Elsevier 2008.
- Chan TC, Brady WJ, Harrigan RA, Ornato JP, Rosen P. ECG in Emergency Medicine and Acute Care. Elsevier Mosby 2005.
- Brady WJ, Truwit JD. Critical Decisions in Emergency & Acute Care Electrocardiography. Wiley Blackwell 2009.
- Saoudi N, Cosío F, Waldo A, Chen SA, Iesaka Y, Lesh M, Saksena S, Salerno J, Schoels W; Working Group of Arrhythmias of the European of Cardiology and the North American Society of Pacing and Electrophysiology. A classification of atrial flutter and regular atrial tachycardia according to electrophysiological mechanisms and anatomical bases; a Statement from a Joint Expert Group from The Working Group of Arrhythmias of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology. Eur Heart J. 2001 Jul;22(14):1162-82. PMID: 11440490 Full Text
- Wells JL Jr, MacLean WA, James TN, Waldo AL. Characterization of atrial flutter. Studies in man after open heart surgery using fixed atrial electrodes. Circulation. 1979 Sep;60(3):665-73. PMID: 455626 Full Text