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# Atrial fibrillation and atrial flutter

- ECG tracing

The upper chambers beat chaotically (fibrillation) or in a fast loop (flutter); the ECG shows it, and both raise the risk of clots and stroke.

Updated Nov 13, 2026

## Key points

- AF: irregularly irregular RR intervals, no P waves, fine or coarse fibrillatory waves best seen in V1, usually narrow QRS.
- Typical flutter: sawtooth flutter waves at about 300/min, negative in II, III and aVF and positive in V1; no isoelectric baseline between them.
- A regular narrow tachycardia at about 150/min is atrial flutter with 2:1 block until proven otherwise.
- Irregular, very fast (over 200/min) and broad, changing QRS complexes suggest AF with pre-excitation (WPW): AV-node blockers are dangerous.
- Unstable patient: synchronised cardioversion; stable: rate or rhythm control, and decide on anticoagulation by stroke risk (CHA2DS2-VASc), not by the rhythm type.

On this page

- The basics Key points
- What it is
- How to recognise it
- Why it happens
- Step by step
- Atrial fibrillation and atrial flutter side by side.
- Next step
- Memory aid
- Elsewhere in DurgiPedia

- Clinical Differential and pitfalls

- Study Test yourself

- Connections Connections

## What it is

Atrial fibrillation (AF) is the commonest sustained arrhythmia. The atria are activated chaotically at about 350–600 times a minute, so there is no organised P wave, and the AV node lets impulses through at random: the ventricular rhythm is irregularly irregular. Atrial flutter is a single, organised macro-reentrant circuit, in its typical form running around the right atrium through the cavotricuspid isthmus at about 250–350 a minute; it draws regular «sawtooth» flutter waves and the AV node usually conducts every second wave (2:1), giving a regular ventricular rate close to 150 a minute. Both lose the atrial contribution to filling and let blood stagnate, above all in the left atrial appendage, so both carry a risk of thrombus and stroke and are anticoagulated by the same rules. On the ECG the questions are always the same: is the rhythm regular or irregular, are there P waves, flutter waves or fibrillatory waves, how fast is the ventricular response, and is the QRS narrow or broad. The bedside questions follow: is the patient stable, how long has it lasted, what triggered it and how high is the stroke risk.

## How to recognise it

- AF rhythm: irregularly irregular, with no repeating pattern of RR intervals; measure several intervals across the long rhythm strip.
- AF atrial activity: no P waves; an undulating baseline of fibrillatory (f) waves, coarse or so fine it looks almost flat, clearest in V1 and II.
- AF ventricular rate: under 60/min is slow AF, 60–100/min controlled, over 100/min AF with rapid ventricular response.
- AF QRS: narrow (under 120 ms) unless there is a bundle branch block, rate-related aberrancy or an accessory pathway.
- Flutter atrial activity: regular flutter (F) waves at about 250–350/min (typically 300), with no flat line between them, best in II, III, aVF and V1.
- Typical (counterclockwise) flutter: F waves negative in the inferior leads and positive in V1; clockwise flutter gives the reverse polarity.
- Flutter ventricular rate: a fixed ratio gives a regular rhythm (2:1 about 150/min, 4:1 about 75/min); variable block makes it irregular.
- Turning the paper upside down or looking at the inferior leads often shows the sawtooth more clearly than the upright view.

## Why it happens

- AF is usually triggered by rapid firing from muscle sleeves in the pulmonary veins and kept going by multiple wandering wavelets or rotors in a stretched, fibrosed atrium.
- The AV node conducts some impulses and blocks others in a random way, which is why the ventricular rhythm has no pattern.
- Typical flutter is one large reentrant loop around the tricuspid annulus; its fixed path and timing produce identical, regular F waves.
- The AV node cannot conduct 300 impulses a minute, so it blocks in a ratio; 2:1 is the commonest, giving a rate near 150/min.
- Common substrates and triggers: hypertension, heart failure, valve disease (above all mitral), ischaemic heart disease, hyperthyroidism, alcohol, sepsis, surgery, lung disease and older age.
- Loss of atrial contraction and stasis in the left atrial appendage allow thrombus, which can embolise to the brain or limbs.

## Step by step

- Look at the rhythm strip first — irregularly irregular RR intervals point to AF; regular ones to flutter with fixed block or another rhythm.
- Search for P waves in II and V1 — none plus a wavy baseline means AF; regular sawtooth waves mean flutter.
- Count the atrial rate if waves are visible — about 300/min means flutter; 100–250/min with distinct P waves suggests atrial tachycardia.
- Count the ventricular rate — it sets urgency and tells you whether rate control is needed.
- Measure the QRS — broad complexes need an explanation: bundle branch block, aberrancy or pre-excitation.
- In a regular rate near 150/min, look for a second flutter wave hidden in the QRS or the T wave — 2:1 flutter is easily read as sinus tachycardia.
- Look for other clues — ST changes, left ventricular hypertrophy or a delta wave on a previous sinus ECG change the plan.

## Atrial fibrillation and atrial flutter side by side.

| Feature | Atrial fibrillation | Atrial flutter (typical) |
| --- | --- | --- |
| Atrial activity | No P waves; chaotic fibrillatory waves | Regular sawtooth flutter waves |
| Atrial rate | About 350–600/min, not countable | About 250–350/min, typically 300 |
| Ventricular rhythm | Irregularly irregular | Regular with fixed block; irregular with variable block |
| Usual ventricular rate untreated | Variable, often 100–180/min | About 150/min with 2:1 block |
| Best leads | V1 and II | II, III, aVF and V1 |
| Mechanism | Pulmonary vein triggers and multiple wavelets | Single right atrial macro-reentry through the cavotricuspid isthmus |

## Differential and pitfalls

- Multifocal atrial tachycardia is also irregular, but each QRS has a P wave, with at least three different P shapes; it is common in lung disease.
- Sinus rhythm with frequent atrial ectopic beats is irregular but has P waves before most complexes.
- Very regular «AF» with a slow rate suggests complete heart block with an escape rhythm, for example in digoxin toxicity.
- Tremor, shivering or a loose electrode can mimic fibrillatory or flutter waves; look at the patient and at other leads.
- Treat a broad irregular tachycardia with QRS shapes that keep changing as possible pre-excited AF: avoid AV-node blockers such as adenosine, verapamil, diltiazem, beta-blockers and digoxin.
- Rate-related ST depression during fast AF is common and does not by itself mean an acute coronary syndrome; recheck once the rate is controlled.

## Next step

- Unstable (shock, syncope, ischaemic chest pain, acute heart failure): call a senior and arrange synchronised cardioversion at once.
- Stable: control the rate with a beta-blocker or a non-dihydropyridine calcium channel blocker (digoxin in heart failure or low activity); a senior decides on rhythm control.
- Cardioversion when onset is over 48 hours or unknown needs prior anticoagulation or a transoesophageal echo to exclude atrial thrombus.
- Score the stroke risk (CHA2DS2-VASc) and the bleeding risk, and start long-term anticoagulation as guidelines set; flutter follows the same rules as AF.
- Look for the cause: electrolytes, thyroid function, kidney function, alcohol, infection and an echocardiogram for valve disease and ventricular function.
- Refer to cardiology for follow-up; typical flutter responds very well to catheter ablation of the cavotricuspid isthmus.

## Memory aid

«150 and regular? Think flutter»: a regular narrow tachycardia at about 150/min hides a second flutter wave until you prove otherwise.

## Test yourself

Think of the answer, then tap the question to see it.

## A 70-year-old with palpitations: narrow QRS, rate 130/min, RR intervals all different, no P waves, wavy baseline in V1. What is the rhythm?

Atrial fibrillation with rapid ventricular response: irregularly irregular rhythm without P waves and with fibrillatory waves. Assess stability, control the rate and assess stroke risk for anticoagulation.

## A regular narrow-complex tachycardia at exactly 150/min shows negative sawtooth waves in II, III and aVF. What is it?

Typical atrial flutter with 2:1 AV block: atrial rate about 300/min, ventricular rate half of it. One flutter wave is often hidden in the QRS or T wave.

## Why is adenosine useful in a regular narrow tachycardia at 150/min when flutter is suspected?

It blocks the AV node briefly; the ventricular rate falls and the flutter waves become visible. It confirms the diagnosis but does not end the flutter. Record a rhythm strip while giving it.

## Which ECG finding in AF makes AV-node blocking drugs dangerous, and why?

An irregular, very fast rhythm with broad, varying QRS complexes suggests pre-excited AF (WPW). Blocking the AV node pushes conduction down the accessory pathway and can trigger ventricular fibrillation.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/clinical-skills/atrial-fibrillation-and-atrial-flutter/)

## Elsewhere in DurgiPedia

- [ECG basics: waves, intervals and leads](https://durgical.com/en/physiology/ecg-basics-waves-intervals-and-leads/)
- [How arrhythmias arise](https://durgical.com/en/physiology/how-arrhythmias-arise/)
- [The cardiac conduction system](https://durgical.com/en/physiology/the-cardiac-conduction-system/)
- [Arterial pulse: rate, rhythm and amplitude](https://durgical.com/en/clinical-exam/arterial-pulse-rate-rhythm-and-amplitude/)
- [Cardiac monitoring at the bedside: leads, alarms and rhythm changes to report](https://durgical.com/en/nursing/cardiac-monitoring-at-the-bedside-leads-alarms-and-rhythm-changes-to-report/)

## Connections

## Related 9

- [Reading an ECG step by step](https://durgical.com/en/clinical-skills/reading-an-ecg-step-by-step/)
- [Narrow-complex tachycardia (SVT)](https://durgical.com/en/clinical-skills/narrow-complex-tachycardia/)
- [Sinus rhythm, sinus tachycardia, bradycardia and arrhythmia](https://durgical.com/en/clinical-skills/sinus-rhythm-sinus-tachycardia-bradycardia-and-arrhythmia/)
- [Pre-excitation: Wolff–Parkinson–White](https://durgical.com/en/clinical-skills/pre-excitation-wolff-parkinson-white/)
- [Defibrillation and synchronised cardioversion](https://durgical.com/en/clinical-skills/defibrillation-and-synchronised-cardioversion/)
- [Vagal manoeuvres and carotid sinus massage](https://durgical.com/en/clinical-skills/vagal-manoeuvres-and-carotid-sinus-massage/)
- [Thyroid function tests](https://durgical.com/en/clinical-skills/thyroid-function-tests/)
- [Echocardiography: transthoracic and transoesophageal](https://durgical.com/en/clinical-skills/echocardiography-transthoracic-and-transoesophageal/)
- [Holter and ambulatory blood-pressure monitoring](https://durgical.com/en/clinical-skills/holter-and-ambulatory-blood-pressure-monitoring/)

## Related conditions 8

- [Atrial fibrillation](https://durgical.com/en/conditions/atrial-fibrillation/)
- [Atrial flutter](https://durgical.com/en/conditions/atrial-flutter/)
- [Ischaemic stroke](https://durgical.com/en/conditions/ischaemic-stroke/)
- [Mitral stenosis](https://durgical.com/en/conditions/mitral-stenosis/)
- [Heart failure](https://durgical.com/en/conditions/heart-failure/)
- [Graves disease (hyperthyroidism)](https://durgical.com/en/conditions/graves-disease/)
- [Wolff-Parkinson-White syndrome](https://durgical.com/en/conditions/wolff-parkinson-white-syndrome/)
- [Digoxin toxicity](https://durgical.com/en/conditions/digoxin-toxicity/)

## In Pharmacology 11

- [Beta blockers](https://durgical.com/en/pharmacology/classes/beta-blockers/)
- [Metoprolol](https://durgical.com/en/pharmacology/metoprolol/)
- [Diltiazem](https://durgical.com/en/pharmacology/diltiazem/)
- [Verapamil](https://durgical.com/en/pharmacology/verapamil/)
- [Digoxin](https://durgical.com/en/pharmacology/digoxin/)
- [Amiodarone](https://durgical.com/en/pharmacology/amiodarone/)
- [Flecainide](https://durgical.com/en/pharmacology/flecainide/)
- [Adenosine](https://durgical.com/en/pharmacology/adenosine/)
- [Direct oral anticoagulants (DOACs)](https://durgical.com/en/pharmacology/classes/direct-oral-anticoagulants/)
- [Warfarin](https://durgical.com/en/pharmacology/warfarin/)
- [Heparins](https://durgical.com/en/pharmacology/classes/heparins/)

[← All clinical skills](https://durgical.com/en/clinical-skills/)

Educational content; it does not replace supervised hands-on training, your institution's protocols or a prescriber's order. A procedure is learnt with a teacher and done only once you are trained to do it.

Sources: [Atrial Fibrillation](https://www.ncbi.nlm.nih.gov/books/NBK526072/) (StatPearls (NCBI Bookshelf), 2026); [Atrial Flutter](https://www.ncbi.nlm.nih.gov/books/NBK540985/) (StatPearls (NCBI Bookshelf), 2022).

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/clinical-skills/atrial-fibrillation-and-atrial-flutter/