Clinical meaning
Atrial fibrillation is the most common sustained cardiac arrhythmia. It is caused by chaotic, disorganized electrical activity originating from multiple ectopic foci and wavelets of re-entry in the atrial myocardium. This results in rapid, irregular atrial depolarization at rates of 350–600 impulses per minute. Because the AV node cannot conduct all impulses, ventricular response is irregularly irregular, typically 100–180 bpm if untreated. Atrial remodeling (electrical and structural) perpetuates AFib: sustained rapid atrial rates shorten the atrial refractory period and promote fibrosis, making spontaneous conversion less likely over time — 'AFib begets AFib.' Loss of organized atrial contraction eliminates the atrial kick, reducing cardiac output by 15–25%. Blood stasis in the left atrial appendage creates a high-risk environment for thrombus formation. Stroke risk is assessed using the CHA₂DS₂-VASc score: Congestive heart failure (1), Hypertension (1), Age ≥75 (2), Diabetes (1), Stroke/TIA/thromboembolism history (2), Vascular disease (1), Age 65–74 (1), Sex category female (1). A score ≥2 in males or ≥3 in females generally warrants anticoagulation. AFib is classified as paroxysmal (self-terminating within 7 days), persistent (lasting >7 days, requires intervention to terminate), long-standing persistent (>12 months), or permanent (accepted, rhythm control abandoned).