Atrial fibrillation

Definition

Atrial fibrillation is a rapid, irregularly irregular atrial rhythm. The atria no longer contract in an organized way; the AV node is bombarded with numerous electrical impulses and conducts them inconsistently. This produces an irregularly irregular ventricular rhythm, usually in the tachycardic range.

Classification

Types by course

• Paroxysmal: lasts less than one week and ends spontaneously or is terminated; episodes may recur
• Persistent: continuous for longer than one week
• Long-standing persistent: longer than one year, but sinus rhythm can still be restored
• Permanent: can no longer be converted to sinus rhythm, or a decision has been made not to attempt this
• Lone atrial fibrillation: without an identifiable cause in people younger than 60 years

Occurrence & epidemiology

Atrial fibrillation is one of the most common arrhythmias. Its frequency rises with age; men are affected more often than women. The lifetime risk is about 25 % for men and 20 % for women. Atrial fibrillation is responsible for about 20–25 % of all strokes.

Aetiopathogenesis

Most common causes: arterial hypertension, coronary artery disease, cardiomyopathies, valvular heart disease (mitral stenosis, mitral and tricuspid regurgitation), hyperthyroidism and binge drinking ("holiday heart"). Less common causes: pulmonary embolism, atrial septal defect and other congenital heart defects, COPD, sleep apnea, myocarditis and pericarditis.

Mechanism: early in the course, focal automaticity and micro-reentry dominate, mainly arising from muscular sleeves in the pulmonary veins. Electrical and structural remodeling of the atria then promotes functional reentrant circuits and rotors; the longer fibrillation persists, the more stable it becomes.

Because atrial contraction is absent, thrombi form, predominantly in the left atrial appendage (about 90 % of left atrial thrombi in nonvalvular atrial fibrillation). Loss of atrial contraction can reduce cardiac output at normal heart rate by as much as 20 %.

Clinical features

• Often asymptomatic; otherwise palpitations, chest discomfort, weakness, light-headedness, effort intolerance and dyspnea, particularly with a very rapid ventricular rate (often 140–160/min)
• Findings: irregularly irregular pulse, loss of a waves in the jugular venous pulse, pulse deficit (apical rate faster than the rate palpated at the wrist)
• Thromboembolism: stroke and systemic emboli to the gut, kidneys, limbs or eyes, sometimes as the first manifestation
• Heart failure, especially with a rapid ventricular rate or pre-existing reduced pump function; with sustained tachycardia, tachycardia-induced cardiomyopathy
• In pre-excitation (Wolff-Parkinson-White syndrome), atrial fibrillation may present with wide QRS complexes and a very high ventricular rate.

Diagnosis

ECG

• Absence of P waves
• Fibrillatory (f) waves between the QRS complexes, irregular in timing and morphology, at rates above 300/min; usually best seen in V1 and not apparent in all leads
• Irregularly irregular R-R intervals; usually narrow QRS complexes
• Aberrantly conducted beats after a long-short R-R sequence (Ashman phenomenon), typically with right bundle branch block morphology, can mimic ventricular extrasystoles.

Further tests

• Ambulatory ECG or event recorder when paroxysmal atrial fibrillation is suspected
• Thyroid function tests (hyperthyroidism as a cause), plus electrolytes
• Transthoracic echocardiography: structural heart disease (e.g. left atrial enlargement, wall motion abnormalities, valve disease, cardiomyopathy)
• Transesophageal echocardiography: thrombi in the atrial appendage, which are often not visible transthoracically
• Stroke risk: risk factors such as older age, hypertension, diabetes mellitus, left ventricular dysfunction and previous thromboembolism are included in scores such as the CHA₂DS₂-VA(Sc) score.

CHA₂DS₂-VA score (ESC 2024)

• Change 2024: female sex removed as Sc point.
• Point values: C 1 + H 1 + A₂ (≥ 75) 2 + D 1 + S₂ 2 + V 1 + A (65–74) 1.

Keep learning in the app

Further reading (open access)

1. MSD Manual Professional: Atrial Fibrillation
2. StatPearls: Atrial Fibrillation
3. MSD Manual Professional: Overview of Arrhythmias
4. The 2024 European Society of Cardiology Atrial Fibrillation Guidelines: A Moving Goalpost (Eur Cardiol 2025, PMC11865665)

Cross-references