PassFinals
Cardiovascular

Atrial Fibrillation

Disorganised atrial electrical activity abolishes coordinated atrial contraction, so the atrioventricular node is bombarded irregularly and blood stagnates in the left atrial appendage.

Definition

A supraventricular arrhythmia with uncoordinated atrial activation and ineffective atrial contraction, diagnosed on a 12-lead ECG showing irregular RR intervals with no consistent P waves. It is classified as paroxysmal, persistent or permanent by how it behaves over time.

Epidemiology

AF is the commonest sustained cardiac arrhythmia and becomes more prevalent with age. Important associations include hypertension, coronary and valvular disease, heart failure, obesity, obstructive sleep apnoea, diabetes, hyperthyroidism, alcohol, chronic kidney disease and acute illness. Paroxysmal episodes may be asymptomatic.

Pathophysiology

Triggers, often arising near the pulmonary veins, interact with atrial stretch, fibrosis and electrical remodelling to sustain disorganised activation. Remodelling is progressive, which is why AF tends to become more persistent over time and why early rhythm control is considered in selected patients.

First principles

Disorganised atrial activation creates an irregular ventricular rhythm

Rapid, spatially disorganised atrial activation removes consistent P waves and bombards the atrioventricular node with variably timed impulses. The node conducts an unpredictable subset, so RR intervals have no repeating pattern. The rhythm is therefore irregularly irregular unless complete atrioventricular block, ventricular pacing or another process regularises it.1

Loss of atrial systole and a fast rate both reduce cardiac output

Coordinated atrial contraction normally tops up ventricular filling, and losing it matters most in a stiff or impaired ventricle. A rapid ventricular response shortens diastole further and may provoke myocardial ischaemia, pulmonary oedema or shock. Sustained poor rate control can cause a reversible tachycardia-induced cardiomyopathy.1

Stroke risk is scored separately from symptoms, and the score decides one thing

Ineffective left-atrial contraction promotes appendage thrombus, and that risk persists because atrial fibrillation recurs silently after cardioversion or ablation. CHA2DS2-VASc estimates a person's yearly risk of stroke from atrial fibrillation. It decides one thing: whether to offer lifelong anticoagulation. Two components score 2 each: age 75 or over, and previous stroke, transient ischaemic attack or thromboembolism. Six score 1 each: congestive heart failure or left-ventricular dysfunction, hypertension, diabetes, vascular disease, age 65 to 74, and female sex. The maximum is 9.1,2

A bleeding score changes what you fix, not whether you anticoagulate

ORBIT estimates a person's yearly risk of major bleeding on an anticoagulant. It does not decide whether to anticoagulate; it decides which bleeding risks you correct first. Its components are older age, reduced haemoglobin or haematocrit or a history of anaemia, previous bleeding, impaired renal function and antiplatelet treatment. NICE then names the modifiable targets: uncontrolled hypertension, poor INR control, concurrent antiplatelets, selective serotonin reuptake inhibitors or non-steroidal anti-inflammatory drugs, harmful alcohol and reversible anaemia.1,3

Rate control, rhythm control and anticoagulation answer different questions

Rate control accepts ongoing atrial fibrillation and limits ventricular conduction. Rhythm control tries to restore and hold sinus rhythm, for symptoms or haemodynamics. Anticoagulation prevents thromboembolism and follows the stroke score, not whether the patient feels the arrhythmia or looks to be in sinus rhythm afterwards.1

Duration changes the safe cardioversion pathway

Cardioversion can embolise pre-existing atrial thrombus, and atrial stunning persists after sinus rhythm returns. NICE therefore allows either strategy when onset is definitely under 48 hours, and uses rate control when onset is over 48 hours or uncertain. Planned cardioversion then waits for at least 3 weeks of therapeutic anticoagulation, unless a transoesophageal-echocardiography-guided strategy is used. Instability caused by the rhythm overrides the delay.1,4

Presentation

Atrial fibrillation may be found incidentally or cause palpitations, breathlessness, fatigue, dizziness, chest discomfort or reduced exercise tolerance. Confirm it on a 12-lead ECG showing irregular RR intervals without consistent P waves. Then decide immediately whether the rhythm is causing life-threatening instability.1,4,5,6

Cardinal features

  • An irregularly irregular pulse with variable pulse volume
  • Palpitations, breathlessness, fatigue, dizziness, presyncope or chest discomfort when the ventricular response compromises output
  • An ECG with irregular RR intervals and no consistent P waves
  • An incidental asymptomatic finding, or first presentation with stroke, systemic embolism or heart failure

Red flags

  • Shock or impaired organ perfusion attributable to the tachyarrhythmia
  • Syncope with severe or ongoing hypotension
  • Myocardial ischaemia or severe heart failure with pulmonary oedema caused by the rhythm
  • Immediately after return of spontaneous circulation with a persisting tachyarrhythmia
  • An irregular broad-complex tachycardia with varying QRS morphology: possible pre-excited AF
  • New focal neurological deficit: activate the acute stroke pathway rather than starting anticoagulation for AF

Investigations

12-lead ECG

Confirm atrial fibrillation, measure rate and QRS width, and look for ischaemia, pre-excitation, conduction disease or another atrial rhythm. A pulse check or a consumer single-lead trace can raise suspicion but does not replace the diagnostic 12-lead ECG.

Expected finding: Irregular RR intervals with no consistent P waves. The QRS complex, the ventricular part of the trace, is usually narrow (under 0.12 seconds) unless there is aberrancy, bundle branch block, ventricular pacing or pre-excitation.

1,4,5

Ambulatory ECG monitoring when paroxysmal AF is suspected

Use a 24-hour ambulatory monitor when asymptomatic episodes are suspected, or when symptomatic episodes are less than 24 hours apart. If episodes are more than 24 hours apart, choose a longer monitor, an event recorder or other ECG technology matched to symptom frequency.

Expected finding: Intermittent ECG-confirmed atrial fibrillation, correlated with symptoms or detected asymptomatically

1

Blood tests directed at triggers and prescribing safety

Check FBC, renal function including creatinine clearance, electrolytes with magnesium, thyroid function, glucose and liver tests. Creatinine clearance and body weight are not optional here: they set the direct oral anticoagulant dose.

Expected finding: A reversible precipitant such as sepsis, anaemia or thyrotoxicosis, or a renal, hepatic or weight finding that changes anticoagulant dose and monitoring

1,7

Echocardiography, transthoracic first

Obtain transthoracic echocardiography (TTE) when a baseline study matters for long-term management, when cardioversion or rhythm control is being considered, or when structural or functional heart disease is suspected. Reserve transoesophageal echocardiography (TOE) for a specialist TOE-guided cardioversion strategy or when TTE is inadequate.

Expected finding: Left-atrial enlargement, valve disease or ventricular dysfunction on TTE. TTE cannot exclude left-atrial-appendage thrombus; on TOE, absence of thrombus permits specialist-led early cardioversion

1

CHA2DS2-VASc and ORBIT scoring

Score CHA2DS2-VASc in symptomatic or asymptomatic paroxysmal, persistent or permanent AF, in atrial flutter, and where risk of recurrence continues after cardioversion or ablation. Score ORBIT when starting or reviewing anticoagulation.

Expected finding: A documented stroke-prevention decision, plus a plan for blood pressure, anaemia, alcohol, interacting medicines and anticoagulation control

1,2,3

Management

StepDetailSource
Assess stability and treat reversible causesUse ABCDE (airway, breathing, circulation, disability, exposure). Monitor ECG, blood pressure and oxygen saturation, give oxygen only if saturation is below 94%, obtain intravenous access and record a 12-lead ECG. Correct hypoxia, sepsis, electrolyte disturbance, acute coronary syndrome, pulmonary embolism, thyrotoxicosis or alcohol-related illness.4Resuscitation Council UK, Adult tachyarrhythmia algorithm V3, March 2026
Decide whether the rhythm is causing a life-threatening featureThe five life-threatening features are shock, syncope with severe or ongoing hypotension, myocardial ischaemia, severe heart failure with pulmonary oedema, and immediately after return of spontaneous circulation. Ask whether the AF is causing the feature, not merely accompanying it.4Resuscitation Council UK, Adult tachyarrhythmia algorithm V3, March 2026
Cardiovert immediately when AF is causing instabilityCall senior, anaesthetic and resuscitation help. Perform synchronised cardioversion without delaying to achieve anticoagulation, up to 3 attempts. For AF, Resuscitation Council UK supports an initial synchronised shock at the defibrillator's maximum output rather than escalating energies. Give sedation or anaesthesia if the conscious patient can tolerate the delay.1,8,4NICE NG196 recommendation 1.8.1; Resuscitation Council UK, Adult advanced life support Guidelines 2025 and Adult tachyarrhythmia algorithm V3
If 3 shocks fail and the patient is still unstableGive amiodarone 300 mg intravenously over 10 to 20 minutes, or procainamide 10 to 15 mg/kg (maximum 1 g) over 20 minutes, then repeat the synchronised shock with expert help. Procainamide availability varies between UK hospitals; the algorithm names both.4Resuscitation Council UK, Adult tachyarrhythmia algorithm V3, March 2026, unstable box
Decide between rate control and rhythm controlNICE recommendation 1.7.1 makes rate control first line except in 5 situations: a reversible cause for the AF; heart failure thought to be primarily caused by the AF; new-onset AF; atrial flutter suitable for an ablation strategy; and rhythm control judged more suitable on clinical grounds.1NICE NG196 recommendation 1.7.1
Prescribe rate control with a real doseNICE offers a standard beta-blocker, meaning any except sotalol, or diltiazem or verapamil, choosing on symptoms, rate, comorbidity and preference. A worked example is metoprolol 50 mg orally 2 to 3 times daily, titrated to 300 mg daily. Intravenously, up to 5 mg at 1 to 2 mg/minute, repeated after 5 minutes, to a total of 10 to 15 mg.1,9NICE NG196 recommendation 1.7.2; BNF metoprolol tartrate monograph, arrhythmias
Calcium-channel blockers and digoxin for rate controlVerapamil 5 to 10 mg by slow intravenous injection over 2 minutes, or 3 minutes if elderly, with a further 5 mg after 5 to 10 minutes if needed; orally 40 to 120 mg 3 times daily. Digoxin loading 0.75 to 1.5 mg orally in divided doses over 24 hours, then 125 to 250 micrograms daily.10,11UK Summary of Product Characteristics for Verapamil 2.5 mg/ml Solution for Injection sections 4.1 and 4.2; BNF digoxin monograph
Rate-control choices that depend on the ventricle and the renal functionThe acute algorithm allows a beta-blocker, verapamil, diltiazem or digoxin above an ejection fraction of 40%, and only a beta-blocker or digoxin below 40%. In suspected acute decompensated heart failure, seek senior input before a beta-blocker and do not use a calcium-channel blocker.4,1Resuscitation Council UK, Adult tachyarrhythmia algorithm V3; NICE NG196 recommendations 1.7.3 and 1.8.3
Rate-control safety rules, monotherapy and combinationsBoth drugs slow the same node, so stacking them intravenously is a listed contraindication: never follow an intravenous beta-blocker with intravenous verapamil. Digoxin only slows conduction at rest, which is why it suits a sedentary person with non-paroxysmal AF. NICE permits any 2 of a beta-blocker, diltiazem and digoxin, and bars amiodarone from long-term rate control at recommendation 1.7.6.10,1,11UK Summary of Product Characteristics for Verapamil Injection sections 4.3 and 4.5; NICE NG196 recommendations 1.7.4 to 1.7.6
Time cardioversion around anticoagulationDefinite onset under 48 hours allows either strategy. NICE still expects oral anticoagulation if sinus rhythm is not restored within that period, if recurrence risk is high, or if the stroke score indicates it. Over 48 hours or uncertain: rate control, and delay planned cardioversion until 3 weeks of therapeutic anticoagulation, or use a TOE-guided strategy.1NICE NG196 recommendations 1.8.2, 1.8.6, 1.8.9, 1.8.10 and 1.7.18
Choosing the cardioversion method, and the 24-hour divergenceBeyond 48 hours NICE prefers electrical to pharmacological cardioversion. If a drug is used, NICE offers flecainide or amiodarone without structural or ischaemic heart disease, and amiodarone when structural disease is present. Divergence note: NICE sets 48 hours as the cardioversion branch point, while the acute algorithm prompts anticoagulation beyond 24 hours. They govern different decisions.1,4,12NICE NG196 recommendations 1.7.16, 1.8.5 and 1.7.9; Resuscitation Council UK, Adult tachyarrhythmia algorithm V3
Score stroke and bleeding risk, then set the thresholdThe threshold is a score of 2 or more, at which NICE offers a direct-acting oral anticoagulant (DOAC). A man scoring 1 is a 'consider' rather than an 'offer'. At the bottom of the scale sits a genuine no-treatment group: under 65 with sex as the only risk factor, meaning 0 in men and 1 in women.1,2NICE NG196 recommendations 1.6.3, 1.6.4 and 1.6.7
Prescribe the DOAC, and know the criteria that reduce the doseApixaban 5 mg twice daily. Reduce to 2.5 mg twice daily if at least 2 of these apply: age 80 years or over, weight 60 kg or less, serum creatinine 133 micromol/litre or more. Rivaroxaban 20 mg once daily with food, reduced to 15 mg once daily at creatinine clearance 15 to 49 mL/minute. Avoid both below 15 mL/minute.7,13BNF apixaban and rivaroxaban monographs, non-valvular atrial fibrillation indication
The renal floor, and the remaining two DOACsSevere renal impairment overrides the counting rule: apixaban drops to 2.5 mg twice daily at clearance 15 to 29 mL/minute whatever the age or weight. Edoxaban halves from 60 mg to 30 mg once daily on any one of: clearance 15 to 50 mL/minute, weight 60 kg or less, or ciclosporin, dronedarone, erythromycin or ketoconazole.7,13,14BNF apixaban and rivaroxaban monographs, renal impairment; UK Summary of Product Characteristics for Lixiana (edoxaban) section 4.2
When a vitamin K antagonist is the answer insteadA vitamin K antagonist is the fallback when a DOAC is contraindicated, not tolerated or unsuitable. A mechanical valve or moderate-to-severe mitral stenosis is exactly that: edoxaban is not recommended in either; apixaban is contraindicated with a prosthetic valve. Warfarin is 5 to 10 mg on day 1, then 3 to 9 mg daily at the same time each day.1,14,7,15NICE NG196 recommendation 1.6.5; UK Summary of Product Characteristics for Lixiana (edoxaban) section 4.4; BNF apixaban and warfarin sodium monographs
Judge warfarin control by numbers, not impressionsCalculate time in therapeutic range at each visit, excluding the first 6 weeks and using a maintenance period of at least 6 months. Reassess anticoagulation if it is under 65%. Also reassess after 2 INR values above 5, or 1 above 8, or 2 below 1.5, within 6 months.1,15NICE NG196 recommendations 1.6.10 and 1.6.11
The anticoagulation rules candidates get wrongDo not offer aspirin monotherapy solely for stroke prevention in AF. Do not withhold anticoagulation because of age or falls alone. A high ORBIT score directs you to correct modifiable bleeding risks, not to withhold. Do not stop anticoagulation because sinus rhythm has returned: the score applies to the continuing risk of recurrence.1,3NICE NG196 recommendations 1.6.14, 1.6.8, 1.2.3 and 1.2.1
Heparin at first presentation, and acute strokeIn new-onset AF on no or subtherapeutic anticoagulation, offer heparin at initial presentation unless contraindicated, continued until risks are assessed and antithrombotic treatment started. NICE names no agent or dose; a treatment-dose low molecular weight heparin example is enoxaparin 1.5 mg/kg subcutaneously every 24 hours. Heparin does not replace emergency cardioversion; it accompanies it.1,16NICE NG196 recommendation 1.8.8; BNF enoxaparin sodium monograph, treatment of deep-vein thrombosis
If the presentation is an acute stroke, the stroke pathway takes overDo not apply the generic AF instruction. NICE advises against routine anticoagulation as treatment for acute stroke, and in disabling ischaemic stroke with AF gives aspirin 300 mg for the first 2 weeks before anticoagulation is considered. The stroke team sets antithrombotic timing.1,6NICE NG196 recommendation 1.9.1; NICE NG128, anticoagulation treatment for other comorbidities
Recognise pre-excited AF before giving an atrioventricular-nodal blockerAn irregular, very rapid broad-complex tachycardia with varying QRS morphology may be pre-excited AF. Verapamil is contraindicated because conduction across the accessory pathway increases and ventricular tachycardia may be precipitated; digoxin is contraindicated for the same reason. The current acute route is procainamide or synchronised cardioversion. Amiodarone is not among the listed options.10,11,4,5UK Summary of Product Characteristics for Verapamil Injection section 4.3; BNF digoxin monograph, contra-indications; Resuscitation Council UK, Adult tachyarrhythmia algorithm V3; 2019 ESC SVT Guideline section 10.2
Escalate to cardiology for long-term rhythm controlNICE sets the referral interval at 4 weeks from failed treatment or recurrence after cardioversion. Long-term rhythm control starts with a standard beta-blocker other than sotalol. The specialist then adds two options you will not choose yourself. Left-atrial catheter ablation, when drug treatment fails or is unsuitable; left atrial appendage occlusion, only where anticoagulation cannot be used.1NICE NG196 recommendations 1.5.1, 1.7.10, 1.7.19, 1.6.18 and 1.6.19
Plan disposition, driving and reviewKeep the patient on cardiac monitoring after acute treatment, and record an ECG afterwards to document the rhythm and catch a post-cardioversion bradycardia. Admission is driven by instability, an uncontrolled rate, acute heart failure or ischaemia, pre-excitation, a treatment complication or diagnostic uncertainty. Document the anticoagulation decision and the rate or rhythm plan, then review anticoagulation at least annually.1NICE NG196 recommendation 1.6.17
DrivingThe DVLA (Driver and Vehicle Licensing Agency) counts AF as an arrhythmia. Group 1: no driving for at least 4 weeks if it has caused or may cause incapacity; notify the DVLA. Other catheter ablation: at least 2 days, no need to notify. Group 2 needs 3 months free of incapacitating arrhythmia and an ejection fraction of at least 40%.17DVLA, Assessing fitness to drive: cardiovascular disorders, Arrhythmias and Successful catheter ablation tables, last updated 7 November 2025

Illustrations

ECG in atrial fibrillation12-lead ECG showing irregular RR intervals and no consistent P waves. A broad or varying QRS morphology should prompt assessment for aberrancy, bundle branch block or pre-excitation rather than being assumed to be uncomplicated AF.CardioNetworks: [ ], Wikimedia Commons · CC-BY-SA-3.0
Chaotic atrial activation and appendage stasisDiagram linking disorganised atrial activation to an irregular ventricular response, loss of atrial systole and left-atrial-appendage stasis.PassFinals · original
Rate, rhythm and stroke-prevention decisionsFlow diagram separating haemodynamic stabilisation, rate or rhythm control, and the independent anticoagulation decision.PassFinals · original

Differentials

Atrial flutter with variable block

Flutter has organised atrial activity, often with sawtooth waves; variable atrioventricular block can make the ventricular rhythm irregular and mimic AF.

Multifocal atrial tachycardia

An irregular rhythm with at least three distinct P-wave morphologies and an isoelectric baseline, often during severe pulmonary illness.

Frequent atrial ectopy

Premature abnormal P waves interrupt an otherwise organised sinus rhythm rather than producing continuously absent P waves.

Pre-excited atrial fibrillation

An irregular, very rapid broad-complex rhythm with varying QRS morphology; an emergency, because atrioventricular-nodal blockers may accelerate accessory-pathway conduction.

Complications

  • Ischaemic stroke, transient ischaemic attack and systemic embolism
  • Acute or chronic heart failure and pulmonary oedema
  • Tachycardia-induced cardiomyopathy
  • Myocardial ischaemia, syncope or shock during a rapid ventricular response
  • Bleeding related to anticoagulation
  • Bradycardia or pauses from sinus-node disease or rate-control treatment

Prognosis

Prognosis depends on age, comorbidity, ventricular function and stroke risk. Anticoagulation substantially reduces embolic risk when indicated, and treating blood pressure, weight, alcohol and sleep apnoea reduces recurrence. AF commonly returns after cardioversion or ablation, so surveillance and risk reassessment continue.

Guidelines

  • Atrial fibrillation: diagnosis and management (NG196) (NICE, 2021)
  • Adult tachyarrhythmia algorithm V3 (Resuscitation Council UK, 2026)
  • Adult advanced life support Guidelines (Resuscitation Council UK, 2025)
  • 2019 ESC Guidelines for supraventricular tachycardia (European Society of Cardiology, 2019)

References

  1. NICE, Atrial fibrillation: diagnosis and management (NG196)Published 27 Apr 2021 | Updated 30 Jun 2021
  2. CHA2DS2-VASc Score for Atrial Fibrillation Stroke Risk, the calculation tool linked from NICE NG196 recommendation 1.2.1 (MDCalc)
  3. ORBIT Bleeding Risk Score for Atrial Fibrillation, the calculation tool linked from NICE NG196 recommendation 1.2.2 (MDCalc)
  4. Resuscitation Council UK, Adult tachyarrhythmia algorithm V3 (Updated March 2026)
  5. 2019 ESC Guidelines for the management of patients with supraventricular tachycardia, European Heart Journal full text (Eur Heart J 2020;41(5):655, doi:10.1093/eurheartj/ehz467)Published 31 Aug 2019
  6. NICE, Stroke and transient ischaemic attack in over 16s: diagnosis and initial management (NG128)Published 1 May 2019 | Updated 13 Apr 2022
  7. BNF, Apixaban, non-valvular atrial fibrillation dose, renal impairment and contra-indications. Verbatim extract at reports/textbook-source-packs/batch03/apixaban.md (British National Formulary)
  8. Resuscitation Council UK, Adult advanced life support Guidelines (Resuscitation Guidelines 2025)Published 27 Oct 2025
  9. BNF, Metoprolol tartrate, indications and dose: arrhythmias. Verbatim extract at reports/textbook-source-packs/batch07/metoprolol-tartrate.md (British National Formulary)
  10. Summary of Product Characteristics, Verapamil 2.5 mg/ml Solution for Injection (electronic medicines compendium)Updated 28 Oct 2025
  11. BNF, Digoxin, indications and dose for atrial fibrillation or flutter, and contra-indications. Verbatim extract at reports/textbook-source-packs/batch06/digoxin.md (British National Formulary)
  12. BNF, Flecainide acetate, indications and dose. Verbatim extract at reports/textbook-source-packs/batch07/flecainide-acetate.md (British National Formulary)
  13. BNF, Rivaroxaban, non-valvular atrial fibrillation dose and renal impairment. Verbatim extract at reports/textbook-source-packs/batch03/rivaroxaban.md (British National Formulary)
  14. Summary of Product Characteristics, Lixiana 60 mg film-coated tablets (edoxaban) (electronic medicines compendium)Updated 26 Sept 2025
  15. BNF, Warfarin sodium, indications and dose. Verbatim extract at reports/textbook-source-packs/batch03/warfarin-sodium.md (British National Formulary)
  16. BNF, Enoxaparin sodium, treatment doses. Verbatim extract at reports/textbook-source-packs/batch02/enoxaparin-sodium.md (British National Formulary)
  17. DVLA, Assessing fitness to drive: cardiovascular disorders (DVLA guidance for medical professionals)Published 11 Mar 2016 | Updated 7 Nov 2025

Evidence checked: 2026-08-08

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.