Clinical meaning
Multiple re-entrant circuits fire simultaneously throughout the atria at rates of 350-600 per minute. The atria quiver instead of contracting effectively. The AV node acts as a gatekeeper, allowing only some impulses through, producing an irregularly irregular ventricular response. Without effective atrial contraction, blood pools in the atria, dramatically increasing the risk of mural thrombi. If a thrombus dislodges, it can embolize to the brain causing stroke — A-fib is responsible for approximately 15-20% of all ischemic strokes.
Exam relevance
Risk factors: - Hypertension (most common cause) - Heart failure - Valvular heart disease (especially mitral stenosis) - Age over 65 - Obesity - Obstructive sleep apnea - Hyperthyroidism - Binge alcohol use (Holiday Heart Syndrome) - Pulmonary embolism - Post-cardiac surgery - Chronic lung disease
Diagnostics: - ECG: absent P waves replaced by chaotic fibrillatory baseline - Irregularly irregular R-R intervals (hallmark finding) - Narrow QRS complexes (unless aberrant conduction) - Check TSH to rule out thyrotoxicosis - Echocardiogram to assess atrial size, ventricular function, and valvular disease - CHA2DS2-VASc score to assess stroke risk and guide anticoagulation