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Atrial fibrillation (AFib)

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Atrial fibrillation (AFib)

Atrial fibrillation (AFib) is a common type of abnormal heart rhythm in which the upper chambers of the heart (the atria) beat in a rapid, uncoordinated way. This causes the heartbeat to become irregular.

ICD-10

I24.9

Specialty

Cardiology

Onset

Acute

Reviewed

June 2026

On This Page

Overview

Atrial fibrillation (AFib) is the most common sustained abnormal heart rhythm. In AFib, the upper chambers of the heart (atria) beat very rapidly and irregularly, causing the heart rhythm to become irregularly irregular.

Etiology & Risk Factors

The exact cause of atrial fibrillation (AFib) is unknown. However, several underlying conditions and reversible triggers are associated with its development.

Reversible causes for Atrial fibrillation (AFib)

  • Hyperthyroidism (thyrotoxicosis)
  • Electrolyte imbalances
  • Cardiothoracic surgery
  • Myocarditis
  • Pericarditis
  • Myocardial infarction
  • Alcohol use
  • Excess caffeine
  • Fever
  • Recreational or pharmacologic drug use
  • Pulmonary embolism
  • Other triggers of tachycardia (e.g., pain, hypovolemia, anemia)

-Approximately 15% of people with AFib have no identifiable risk factors (idiopathic or “lone” AFib).

Risk Factors ;

Common reversible causes

  • Hyperthyroidism
  • Electrolyte abnormalities
  • Myocardial infarction, myocarditis, or pericarditis
  • Alcohol or excess caffeine
  • Pulmonary embolism
  • Fever, pain, hypovolemia, or anemia
  • Cardiothoracic surgery

Major Risk Factors for Atrial fibrillation (AFib)

  • Advanced age
  • Hypertension
  • Diabetes mellitus
  • Obesity
  • Obstructive sleep apnea (OSA)
  • Coronary artery disease (CAD)
  • Valvular heart disease (especially mitral valve disease)
  • Heart failure
  • Hyperthyroidism
  • Chronic lung disease (e.g., COPD)
  • Excessive alcohol use (“holiday heart syndrome”)

Pathophysiology

Pathophysiology of Atrial Fibrillation (AFib)

  • AFib is a supraventricular arrhythmia with rapid, disorganized electrical activity in the atria.
  • The exact mechanism is not fully understood, but contributing factors include:
    • Atrial dilation or hypertrophy due to volume overload or hemodynamic stress
    • Atrial ischemia
    • Inflammation of the atrial myocardium
    • Abnormal ion conduction in atrial tissue

Mechanism

  1. Atrial fibrillation (AFib) is triggered by:
    • Rapid electrical impulses from automatic foci near the pulmonary vein ostia (left atrium) or fibrotic atrial tissue.
    • Less commonly, pre-excitation through an accessory pathway (e.g., WPW syndrome).
  2. Atrial fibrillation (AFib) is maintained by:
    • Re-entry circuits and/or rapid ectopic firing.
    • Enlarged or diseased atria make these abnormal circuits more likely.
  3. Atrial remodeling:
    • Electrical changes occur within hours.
    • Persistent AFib leads to atrial fibrosis and dilation over months.
    • These changes make AFib more likely to continue (“AFib begets AFib”).

Effects

  • Rapid, ineffective atrial contraction → blood stasis in the atria → thrombus formation → increased risk of stroke and systemic thromboembolism.
  • Irregular conduction through the AV node → irregular ventricular rhythm and often tachycardia.

Clinical Presentation

  1. Symptoms (stable Atrial fibrillation AFib)

    • Often asymptomatic
    • Palpitations
    • Fatigue
    • Dyspnea (shortness of breath)
    • Lightheadedness
    • Syncope
    • Signs of underlying heart disease (e.g., murmur from mitral stenosis)

    Features of Unstable Atrial fibrillation (AFib)

    • Ischemic chest pain
    • Altered mental status
    • Pulmonary edema
    • Acute heart failure
    • Cardiogenic shock

    Complications at Presentation

    • Stroke or TIA (most important)
    • Acute left heart failure with pulmonary edema
    • Other thromboembolic events (e.g., renal, splenic, intestinal, or limb infarction)
    • Tachycardia-induced cardiomyopathy

History Taking

  • Palpitations
  • Shortness of breath
  • Chest pain
  • Dizziness or lightheadedness
  • Syncope (fainting)
  • Fatigue
  • Onset and duration of symptoms
  • Previous episodes of AFib
  • History of heart disease, hypertension, thyroid disease, or sleep apnea
  • Recent illness, surgery, alcohol/caffeine intake, or stimulant/drug use
  • Current medications (especially anticoagulants and rate/rhythm-control drugs)

-Red Flags for Atrial fibrillation (AFib)

  • Chest pain (possible myocardial ischemia)
  • Syncope
  • Altered mental status
  • Severe shortness of breath or pulmonary edema
  • Signs of acute heart failure
  • Cardiogenic shock or hemodynamic instability
  • Symptoms of stroke/TIA (sudden weakness, facial droop, speech difficulty)

Physical Examination

  • Vital signs
    • Heart rate (tachycardia or, rarely, bradycardia)
    • Blood pressure
    • Oxygen saturation
  • Pulse
    • Irregularly irregular pulse (hallmark finding)
    • Apical pulse deficit
  • Cardiovascular examination
    • Irregular heart rhythm on auscultation
    • Murmurs suggesting underlying valvular disease (especially mitral valve disease)
  • Respiratory examination
    • Signs of pulmonary edema (crackles)
  • Neurologic examination
    • Assess for focal neurological deficits suggestive of stroke or TIA
  • Assess for heart failure
    • Peripheral edema
    • Signs of acute heart failure or cardiogenic shock

Investigations

  • 12-lead ECG (first-line)
    • Irregularly irregular rhythm
    • No discernible P waves
  • Cardiac rhythm monitoring (Holter/event monitor) if paroxysmal AFib is suspected and ECG is nondiagnostic

Blood tests

  • CBC – anemia, infection
  • Electrolytes – Na⁺, K⁺, Mg²⁺, Ca²⁺
  • Renal and liver function tests
  • Thyroid function tests (TFTs) – screen for hyperthyroidism

Cardiac imaging

  • Transthoracic echocardiogram (TTE)
    • Assess cardiac function
    • Detect structural heart disease (e.g., mitral valve disease)
    • Assess atrial enlargement
  • Transesophageal echocardiogram (TEE) (before cardioversion in selected patients)
    • Detect left atrial thrombus
    • Assess safety of rhythm control

Additional investigations (when indicated)

  • Chest X-ray (evaluate cardiopulmonary disease)
  • CT pulmonary angiography if pulmonary embolism is suspected

Diagnosis

Atrial Fibrillation · Diagnostic Criteria

12-Lead ECG — Diagnostic Features All 3 required for diagnosis
P waves
Absent / chaotic
No distinct P waves; replaced by irregular fibrillatory (f) waves at 350–600 bpm. Best seen in V1 and II.
RR intervals
Irregularly irregular
No fixed pattern between QRS complexes. This is the hallmark finding — even a single regular RR interval argues against AF.
QRS complex
Narrow (<120 ms)
Usually narrow unless aberrant conduction (BBB, WPW, or pre-excitation). Wide QRS AF = suspect WPW → do NOT give AV nodal blockers.
Pattern Duration / definition Spontaneous termination Management implication
First detected First diagnosed episode regardless of symptoms or duration — Establish rhythm; anticoagulate; investigate cause
Paroxysmal Self-terminating, usually <48 h (up to 7 days) Yes — within 7 days Rate or rhythm control; CHA₂DS₂-VASc for OAC
Persistent Lasts >7 days or requires cardioversion to terminate No Rhythm control preferred; anticoagulate ≥4 weeks before cardioversion
Long-standing persistent Continuous AF >12 months; rhythm control still attempted No Consider ablation; strict anticoagulation
Permanent AF accepted by patient and physician; no rhythm control attempted No Rate control only; lifelong anticoagulation
Diagnostic workup — ESC 2020
Mandatory investigations
12-lead ECG — confirm AF, assess rate, QRS width, ischaemia
Echocardiography (TTE) — LV function, valve disease, LA size, thrombus
Blood: FBC, U&E, TFTs, LFTs, coagulation, fasting glucose, HbA1c
CHA₂DS₂-VASc score — anticoagulation decision
HAS-BLED score — bleeding risk assessment
Selective / additional
Holter monitor / prolonged ECG — if paroxysmal AF suspected
TOE (TEE) — exclude LA appendage thrombus before cardioversion if AF >48h
Exercise ECG — rate response assessment; exclude ischaemia as trigger
Sleep study — if OSA suspected (common reversible trigger)
Chest X-ray — cardiac silhouette, pulmonary congestion, lung pathology
Differential diagnosis — irregular rhythm on ECG
Atrial Flutter with variable block
Sawtooth flutter waves (F) — 300 bpm; 2:1, 3:1, or 4:1 block
Key distinction: flutter waves are regular; RR may be irregular but organised. Best seen in II, III, aVF and V1.
Multifocal Atrial Tachycardia (MAT)
≥3 distinct P-wave morphologies; irregular RR; rate >100 bpm
P waves ARE present (unlike AF). Common in COPD, hypoxia, hypomagnesaemia. Treat underlying cause.
Frequent PACs / PVCs
Normal sinus rhythm with premature beats causing irregular RR
P waves present before each sinus beat. PACs: narrow; PVCs: wide and bizarre. No fibrillatory baseline.
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Management of Atrial fibrillation (AFib)

1. Assess hemodynamic stability

  • Unstable AFib (e.g., hypotension, shock, acute heart failure, pulmonary edema, ischemic chest pain, altered mental status)
    • Immediate synchronized electrical cardioversion
    • Start anticoagulation if indicated, but do not delay emergency cardioversion
  • Stable AFib
    • Confirm diagnosis with ECG
    • Evaluate for structural heart disease (TTE)
    • Identify and treat reversible causes

2. Rate control

  • Goal: Control ventricular rate and relieve symptoms
  • First-line:
    • Beta-blockers
    • Nondihydropyridine calcium channel blockers

3. Rhythm control

  • Restore and maintain sinus rhythm with:
    • Electrical cardioversion
    • Antiarrhythmic drugs (e.g., flecainide, propafenone, amiodarone)
    • Catheter ablation

    • 4. Treat underlying causes

      • Correct reversible triggers (e.g., hyperthyroidism, electrolyte abnormalities, alcohol use)
      • Manage cardiovascular risk factors and comorbidities

5. Anticoagulation : As Follows:

Atrial Fibrillation · CHA₂DS₂-VASc Score

Letter Risk factor Definition / threshold Points
C
 Congestive Heart Failure Signs/symptoms of HF or reduced LVEF (<40%) — includes HFpEF if symptomatic +1
H
 Hypertension Resting BP >140/90 mmHg on ≥2 occasions, or on antihypertensive therapy +1
A₂
 Age ≥ 75 years High-risk age threshold — counts double due to markedly increased stroke risk +2
D
 Diabetes mellitus Fasting glucose >7 mmol/L (>125 mg/dL) or on oral hypoglycaemic / insulin therapy +1
S₂
 Stroke / TIA / thromboembolism Prior ischemic stroke, TIA, or systemic thromboembolism — strongest individual predictor +2
V
 Vascular disease Prior MI, peripheral artery disease, or aortic plaque on imaging +1
A
 Age 65–74 years Intermediate age risk — scores 1 point (age ≥75 scores 2 points separately) +1
Sc
 Sex category (female) Female sex — risk modifier only; does not trigger anticoagulation alone (score must be ≥2 in females, ≥1 in males from other factors) +1
Maximum score = 9. Score is sex-adjusted: female sex adds 1 point but anticoagulation is only indicated when ≥1 additional risk factor is present.
Annual stroke risk by score
Score 0 (M) / 1 (F)
~0%
No anticoagulation needed
Score 1 (M) / 2 (F)
~1.3%
Consider anticoagulation (physician discretion)
Score 2–4
2–4%
Anticoagulation recommended
Score ≥5
>6%
High risk — anticoagulation strongly indicated
ESC 2020 — Clinical action by score
Score
0 in males / 1 in females
No antithrombotic therapy recommended. Reassess periodically as new risk factors may develop.
Score
1 in males / 2 in females
Consider OAC. Weigh stroke risk vs. bleeding risk (HAS-BLED). Shared decision-making with patient.
Score
≥2 in males / ≥3 in females
OAC recommended. Prefer DOAC over warfarin:
Apixaban Rivaroxaban Dabigatran Edoxaban

Complications of Atrial fibrillation (AFib)

  • Thromboembolic events (most important)
    • Stroke/TIA
    • Renal infarction
    • Splenic infarction
    • Intestinal ischemia
    • Acute limb ischemia
  • Acute left heart failure → pulmonary edema
  • Tachycardia-induced cardiomyopathy

Prognosis of Atrial fibrillation (AFib)

  • Generally good with appropriate treatment, especially with good rate/rhythm control and anticoagulation when indicated.
  • The major determinant of prognosis is the risk of thromboembolic complications, particularly ischemic stroke.
  • Prognosis is influenced by:
    • Underlying heart disease and comorbidities
    • Adequate rate or rhythm control
    • Adherence to anticoagulation and other therapies
    • Correction of reversible risk factors

Key Points / Clinical Pearls of Atrial fibrillation (AFib)

  • Most common sustained cardiac arrhythmia.
  • ECG: Irregularly irregular rhythm with absent P waves.
  • Classic physical finding: Irregularly irregular pulse.
  • Many patients are asymptomatic; common symptoms are palpitations, dyspnea, fatigue, dizziness, and syncope.
  • Greatest complication: Ischemic stroke due to atrial thrombus formation.
  • Diagnosis: 12-lead ECG; echocardiography evaluates structural heart disease.