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Rhythm

Atrial fibrillation

Content last updated · 1 min read ·

This is the date the draft was written, not a medical review date.

Atrial fibrillation is the commonest sustained arrhythmia: disorganised atrial activity with an irregularly irregular ventricular response. It carries a risk of stroke and, if rapid or prolonged, of heart failure.

ECG criteria

  • Irregularly irregular RR intervals with no repeating pattern.
  • No distinct P waves; the baseline shows fine or coarse fibrillatory activity (f waves).
  • Ventricular rate variable, often about 110 to 160 beats/min if untreated (slow with AV nodal disease or drugs).
  • QRS usually narrow, unless a bundle branch block, aberrancy or pre-excitation is present.
  • Atrial rate about 350 to 600 beats/min, rarely identifiable on the surface ECG.

Mechanism

Multiple re-entrant wavelets and rapid focal triggers, classically from the pulmonary veins, produce chaotic atrial activation without effective atrial contraction. The AV node filters these impulses irregularly, giving the irregular ventricular response; atrial stasis predisposes to thrombus formation.

Common causes

  • Hypertension, valvular disease (especially mitral), heart failure, coronary artery disease.
  • Hyperthyroidism, alcohol (including binge drinking), obesity, sleep apnoea.
  • Acute illness: sepsis, pulmonary embolism, post-operative states.
  • Age and chronic kidney or lung disease; some cases are idiopathic (lone AF).

Management principles

Management rests on three principles: assess stroke risk and decide on anticoagulation, control the ventricular rate or restore sinus rhythm (rate versus rhythm control), and treat precipitating causes and comorbidities. Haemodynamically unstable patients follow the local advanced life support protocol; follow local guidelines such as those of the ESC.

High-level principles for study. Treatment decisions follow local guidelines and the clinical situation.

Pitfalls and mimics

  • Coarse fibrillation, tremor or muscle artefact can mimic flutter waves or P waves; check several leads and a rhythm strip.
  • Very rapid AF with a wide complex may look like ventricular tachycardia; the irregularity is the clue, and pre-excited AF is a special danger.
  • A regularised ventricular rate in AF suggests complete block, digoxin toxicity or junctional rhythm.

Practise in the ECG trainer — Recognise this pattern on generated tracings.

References

  1. 2020 ESC Guidelines for the diagnosis and management of atrial fibrillation developed in collaboration with the European Association for Cardio-Thoracic Surgery (EACTS). European Society of Cardiology (2020) — Tier 2 (guidelines / primary literature)
  2. Wagner GS, Strauss DG. Marriott's Practical Electrocardiography. Wolters Kluwer, 12th edition (2013) — Tier 3 (textbook)
  3. Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine. Elsevier, 12th edition (2022) — Tier 3 (textbook)

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