When evaluating an atrial arrhythmia, one of the most common clinical challenges is determining whether the patient is experiencing atrial fibrillation (AFib) or atrial flutter. Both conditions involve rapid heart rhythms originating in the atria, yet they differ in the organization and regularity of the electrical impulses, which has important diagnostic, treatment, and prognostic implications. Understanding these differences is crucial in the context of Atrial Arrhythmias: Is it Fibrillation or Flutter?
Atrial Fibrillation (AFib)
- Mechanism and Electrical Activity: In AFib, electrical impulses in the atria are highly disorganized. Instead of a single dominant pacemaker (like the sinoatrial node), multiple abnormal foci fire erratically throughout the atria, resulting in a chaotic, fibrillatory state. This disorganization means that the atrial muscle fibers quiver rather than contract in a coordinated manner.
- ECG Findings: You will typically see an irregularly irregular rhythm with no distinct P waves on the ECG. Instead, the baseline is often filled with erratic, irregular fibrillatory waves. The R-R intervals (the time between ventricular beats) vary in an unpredictable manner.
- Clinical Implications: Because the atria do not contract effectively, blood can pool and form clots, increasing stroke risk. The ventricular rate may also be highly variable, which sometimes results in symptoms like palpitations, fatigue, or even a rapid, uncontrolled heart rate that can compromise cardiac output.
- AF can be categorized as follows:
- Paroxysmal (e.g., self-terminating or intermittent) AF – a rhythm that ends spontaneously or with intervention within seven days of onset.
- Persistent AF – does not self-terminate within seven days. Episodes require pharmacologic or electrical cardioversion to convert back to NSR.
- Long-standing AF – AF that has lasted longer than 12 months.
- Permanent AF – rhythm can’t be converted to NSR; patient and clinician decide together that they will no longer attempt to control the rhythm.
Atrial Flutter
- Mechanism and Electrical Activity: Atrial flutter, on the other hand, is characterized by a more organized electrical circuit within the atria. Generally, this organized reentrant circuit fires very rapidly (often between 250 to 350 beats per minute), but because of the “block” at the atrioventricular (AV) node, not all of these impulses are conducted to the ventricles.
- ECG Findings: The hallmark of atrial flutter on an ECG is the “sawtooth” pattern—regular, repetitive, and uniform flutter waves, especially visible in the inferior leads such as II, III, and aVF. The conduction ratio (commonly 2:1) means that, for example, even if the atria contract at 300 beats per minute, the ventricles may only conduct about 150 beats per minute in a regular pattern. This often leads to a regular or even a consistently rapid ventricular response.
- Clinical Implications: Although atrial flutter is more organized, it can also lead to decreased cardiac efficiency and presents a risk for thromboembolic complications. However, the regularity and pattern often make management strategies (such as rate control or electrical cardioversion) more straightforward.
- Atrial flutter can be categorized as follows:
- Typical atrial flutter – involves a reentry circuit of impulses across the cavo-tricuspid isthmus (CTI) in the right atrium. The impulses travel in a counterclockwise direction creating a “sawtooth” appearance of the P waves on ECG. The signals can also travel in a clockwise direction, called reverse typical atrial flutter, and in rare cases, the signals can travel in both directions.
- Atypical atrial flutter – the CTI is not involved, instead any region of the right or left atria, around areas of scar tissue due to heart disease or surgical/ablation procedures, can cause an abnormal circuit of impulses.
Symptoms
People with AFib or atrial flutter may not experience any symptoms. If symptoms do occur, they are similar:
| Symptom | Atrial fibrillation | Atrial flutter |
| rapid pulse rate | usually rapid | usually rapid |
| irregular pulse | always irregular | can be regular or irregular |
| dizziness or fainting | yes | yes |
| palpitations (feeling like the heart is racing or pounding) | yes | yes |
| shortness of breath | yes | yes |
| weakness or fatigue | yes | yes |
| chest pain or tightness | yes | yes |
| increased chance of blood clots and stroke | yes | yes |
Distinguishing AFib from Atrial Flutter
| Characteristics of atrial fibrillation and atrial flutter | ||
| Atrial fibrillation | Atrial flutter | |
| Rhythm | Irregularly irregular | Regular/organized or irregular |
| Rate | Atrial – indiscernibleVentricular – typically rapid, 100 to 175 beats per minute (bpm) if uncontrolled | Atrial – 240 to 340 bpm Ventricular – typically rapid, 150 bpm |
| P wave | No distinct P waves, instead “fibrillatory” baseline | Appear in a “sawtooth” pattern (also called F or “flutter” waves) in leads II, III, aVFAtrial to ventricular ratio – 2:1, 3:1, 4:1 |
| PR interval | Indeterminate (no P waves) | Indeterminate (no P waves) |
| QRS complex | Normal (0.6-0.10 seconds) | Normal (0.6-0.10 seconds) |
| Signs and symptoms | May be asymptomatic in either AF or atrial flutter. Symptoms usually mild in atrial flutter. Palpitations. Fatigue. Dyspnea with exertion Chest Pain. Syncope. Dizziness | |
| Complications | Transient ischemic attack. Stroke. Heart failure. Thromboembolism. Bleeding with anticoagulation | |
| Management | Calcium channel blocker or beta blocker for ventricular rate control or an antiarrhythmic for rhythm control. Anticoagulant therapy to prevent stroke | |
| Potential procedures | Radiofrequency ablation of AV node with pacemaker implantation. Electrical synchronized cardioversion. Pharmacologic cardioversion | |
Atrial Flutter Leading to Atrial Fibrillation
When comparing atrial flutter vs. AFib, atrial flutter is considered a less severe heart condition than AFib. However, without treatment, people with atrial flutter can develop AFib as their heart weakens from the stress of beating too fast for too long. Research indicates AFib rarely develops without being preceded by atrial flutter.13
In some people, atrial flutter coexists with AFib (alternating from one to the other). In a study of adult patients in Finland with atrial flutter and atrial fibrillation, the following was reported:14
- 80% of those diagnosed with atrial flutter also had AFib
- 20% of those diagnosed with AFib patients also had atrial flutter
Treatment Differences Between Atrial Flutter vs. Fibrillation
While there are some treatment differences between atrial flutter vs. fibrillation, the goals of treating these conditions include the following:2
- Controlling your heart rate
- Restoring the normal rhythm of your heart rate
- Preventing blood clots to reduce your risk of stroke
Factors such as your age, your level of fitness, and other medical conditions are used to create a personalized plan of treatment. This can be achieved through the use of medication, devices, and/or surgery.
Why the Distinction Matters
- Stroke Risk and Management: While both conditions require attention regarding stroke prevention, the approaches to set anticoagulation and rhythm control might differ.
- Treatment Options: Decision-making regarding rate versus rhythm control strategies and the types of medications used (or the consideration of electrical cardioversion and ablation procedures) can be influenced by the type of atrial arrhythmia present.
- Prognostic Considerations: Patients with atrial flutter sometimes later develop atrial fibrillation, and vice versa, making close follow-up essential.
REFERENCES
- Nall, R. (2024, April 5). Atrial flutter vs. atrial fibrillation. Healthline. https://www.healthline.com/health/atrial-flutter-vs-atrial-fibrillation
- Sgreccia D, Manicardi M, Malavasi VL, et al. Comparing outcomes in asymptomatic and symptomatic atrial fibrillation: a systematic review and meta-analysis of 81,462 patients. J Clin Med. 2021;10(17):3979. doi:10.3390/jcm10173979
- Kumar, K. (2023, October 31). Atrial fibrillation: Overview and management of new-onset atrial fibrillation. UpToDate. https://www.uptodate.com/contents/atrial-fibrillation-overview-and-management-of-new-onset-atrial-fibrillation
- Phang, R. & Prutkin, J.M. (2024, March 7). Overview of atrial flutter. UpToDate. https://www.uptodate.com/contents/overview-of-atrial-flutter
- Aro A, Eyob-Fesseha H, Haukka J, et al. How often atrial flutter and atrial fibrillation coexist? Results from a large nationwide ECG-based study. Europace. 2023;25(Suppl 1):euad122.037. doi:10.1093/europace/euad122.037
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