Atrial fibrillation (AF) is a supraventricular tachyarrhythmia characterised by uncoordinated atrial electrical activation and consequently ineffective atrial mechanical contraction 1,2. It affects 2–4% of adults globally (rising to >10% in individuals aged ≥80 years) and increases the risk of cardioembolic ischaemic stroke five-fold 1,2.

1. Etiology & Risk Factors (PIRATES Mnemonic)

  • Pulmonary disease: pulmonary embolism, COPD, obstructive sleep apnoea (OSA), pneumonia.
  • Ischaemic & Structural Heart Disease: coronary artery disease, HFrEF/HFpEF, hypertensive heart disease (most common population attributable risk factor).
  • Rheumatic & Valvular Heart Disease: mitral stenosis and mitral regurgitation causing left atrial dilatation.
  • Alcohol & Acute triggers: acute alcohol binge ("holiday heart syndrome"), sepsis, post-cardiothoracic surgery, electrolyte derangements (hypokalaemia, hypomagnesaemia).
  • Thyrotoxicosis: overt or subclinical hyperthyroidism (Graves' disease / toxic multinodular goitre).
  • Elderly age & Genetic channelopathies.
  • Sick sinus syndrome (tachy-brady syndrome).

2. Pathophysiology & Temporal Classification

Ectopic focal discharges arising most commonly from the myocardial sleeves of the pulmonary veins (85–90% of paroxysmal AF) initiate multiple re-entrant wavelets across a fibrotic, dilated left atrium ("AF begets AF"). Loss of coordinated atrial contraction eliminates the late diastolic "atrial kick" (reducing left ventricular filling by 15–25%, especially detrimental in mitral stenosis and diastolic dysfunction) and promotes blood stasis within the left atrial appendage (LAA), where >90% of non-valvular AF thrombi form 1,2.

Pathophysiological Mechanism — Atrial fibrillation 1 Pulmonary Vein Ectopic Triggers + Atrial Structural Remodelling Hypertension, heart failure, mitral valve disease, thyrotoxicosis, or alcohol ('holiday heart') stretch left atrium 2 Chaotic Multiple Micro-Reentrant Wavelets (350–600 bpm) Disorganised atrial depolarisation replaces sinoatrial (SA) node pacemaker; absent P waves & f-waves on ECG 3 Decremental Variable AV Nodal Conduction Irregularly irregular ventricular response (typically 110–160 bpm untreated) + loss of 'atrial kick' (20% cardiac output) 4 Left Atrial Appendage (LAA) Blood Stasis (Virchow's Triad) Thrombus formation in LAA → 5× increased risk of cardioembolic ischaemic stroke & systemic arterial embolism
  • Paroxysmal AF: self-terminating or cardioverted within 7 days of onset (usually <48 hours).
  • Persistent AF: continuous AF sustained beyond 7 days (including episodes terminated by cardioversion after ≥7 days).
  • Long-standing Persistent AF: continuous AF lasting >12 months where a rhythm-control strategy is still pursued.
  • Permanent AF: AF accepted by both patient and clinician where no further attempts to restore sinus rhythm are planned.

3. Clinical Presentation & Physical Examination

  • Symptoms: palpitations, exertional dyspnoea, fatigue, presyncope, chest discomfort, or completely asymptomatic ("silent AF" first detected after a cryptogenic stroke).
  • Bedside Examination Findings:
    • Irregularly irregular pulse in both rate and volume, with an apical-radial pulse deficit (some early ventricular contractions generate insufficient stroke volume to transmit a peripheral radial pulse).
    • Absent a wave on jugular venous pressure (JVP) waveform due to loss of right atrial contraction.
    • Variable intensity of the first heart sound (S1) and absence of a fourth heart sound (S4).

4. Diagnostic Workup & Interpretation

Investigation Expected Clinical Finding & Diagnostic Purpose
12-Lead ECG (Gold Standard) 1. Absence of distinct P waves · 2. Chaotic baseline fibrillatory f waves (350–600/min, best seen in V1) · 3. Irregularly irregular RR intervals · 4. Narrow QRS complex (<120 ms) unless pre-existing bundle branch block, rate-related aberrancy (Ashman phenomenon), or accessory pathway (WPW).
Thyroid Function Tests (TSH, Free T4) Mandatory in all new-onset AF to exclude occult thyrotoxicosis.
Serum Electrolytes (K⁺, Mg²⁺, Ca²⁺), Renal & Liver Function Correct K⁺ >4.0 mmol/L and Mg²⁺ >0.9 mmol/L; calculate Cockcroft-Gault Creatinine Clearance (CrCl) for accurate DOAC dosing.
Transthoracic Echocardiography (TTE) Assess Left Ventricular Ejection Fraction (LVEF — determines whether calcium channel blockers or flecainide are safe), left atrial volume index, and valvular heart disease.
Transoesophageal Echocardiography (TOE / TEE) Gold standard for visualising the Left Atrial Appendage (LAA) to exclude intracardiac thrombus prior to urgent cardioversion when AF duration is >48 hours.

5. Stroke Risk Stratification — CHA₂DS₂-VASc Score

Clinical Risk Factor Points & Anticoagulation Threshold
C — Congestive heart failure (or LVEF ≤40%) +1 point
H — Hypertension (or on antihypertensive therapy) +1 point
A₂ — Age ≥75 years +2 points
D — Diabetes mellitus +1 point
S₂ — Prior Stroke, TIA, or systemic thromboembolism +2 points
V — Vascular disease (prior MI, peripheral arterial disease, or aortic plaque) +1 point
A — Age 65–74 years +1 point
Sc — Sex category (Female — note: 2024 ESC Guidelines use sex-neutral CHA₂DS₂-VA) +1 point (modifier only if ≥1 other risk factor present)
Oral Anticoagulation Decision Score 0 (men) / 1 (women): No anticoagulation · CHA₂DS₂-VA ≥1: Consider DOAC · CHA₂DS₂-VA ≥2: Class I recommendation for lifelong DOAC (or Warfarin INR 2.0–3.0 if moderate-to-severe mitral stenosis or mechanical heart valve).

6. Differential Diagnosis of Irregular Tachycardia (2-Column Comparison Table)

Arrhythmia Distinguishing ECG & Clinical Features
Atrial Flutter with Variable AV Block Regular "sawtooth" flutter F-waves (atrial rate ~300 bpm, negative in II, III, aVF and positive in V1) with variable 2:1, 3:1, or 4:1 AV conduction creating an irregular ventricular rhythm.
Multifocal Atrial Tachycardia (MAT) Irregularly irregular rhythm with ≥3 distinct P-wave morphologies and varying PR/PP intervals; strongly associated with severe COPD and theophylline toxicity.
Frequent Premature Atrial Contractions (PACs) Underlying sinus rhythm with visible sinus P waves interrupted by early abnormal P' waves.

7. Management & Treatment Protocol (ESC / NICE / AHA Guidelines)

  • Step 1: Emergency Haemodynamic Assessment:
    • If haemodynamically unstable (shock, syncope, acute pulmonary oedema, ongoing myocardial ischaemia): perform immediate synchronised DC cardioversion (120–200 J biphasic) + IV unfractionated heparin or LMWH 1,2.
  • Step 2: Rate Control vs Rhythm Control in Stable Patients:
    • First-line Rate Control (Target resting HR <110 bpm lenient, or <80 bpm if symptomatic):
      • LVEF ≥40%: Cardioselective Beta-blocker (Bisoprolol 2.5–10 mg OD or Metoprolol) OR Non-dihydropyridine Calcium Channel Blocker (Diltiazem MR or Verapamil — contraindicated in HFrEF LVEF <40%) 1,2.
      • LVEF <40% (HFrEF) or sedentary elderly: Beta-blocker ± Digoxin (loading 500 mcg then 62.5–250 mcg OD; monitor renal function and K⁺).
    • Rhythm Control (Cardioversion & Catheter Ablation):
      • Indicated for symptomatic patients, younger patients, first-episode AF, or tachycardia-induced cardiomyopathy.
      • Pharmacological Cardioversion (<48h onset): Flecainide (class IC — only if structurally normal heart and no ischaemic heart disease; "pill-in-the-pocket" 200–300 mg PO with a beta-blocker to prevent 1:1 atrial flutter) OR IV Amiodarone (300 mg IV over 1h then 900 mg over 23h — safe in structural heart disease/HFrEF) 1,2.
      • Pulmonary Vein Isolation (PVI) Catheter Ablation: superior to antiarrhythmic drugs for maintaining sinus rhythm in paroxysmal/persistent AF and improves survival in AF with HFrEF (CASTLE-AF trial).
  • Step 3: Long-Term Stroke Prevention (Anticoagulation):
    • Direct Oral Anticoagulants (DOACs — First-line): Apixaban (5 mg BD; reduce to 2.5 mg BD if ≥2 of: age ≥80 yrs, weight ≤60 kg, creatinine ≥133 µmol/L), Rivaroxaban (20 mg OD with food), Dabigatran, or Edoxaban.
    • Valvular AF Exception: Patients with mechanical prosthetic heart valves or moderate-to-severe rheumatic mitral stenosis MUST receive a Vitamin K Antagonist (Warfarin, target INR 2.0–3.0 or 2.5–3.5 per valve type) — DOACs are contraindicated in this group.