Atrial Fibrillation: A Comprehensive Guide
What is Atrial Fibrillation?
Atrial fibrillation (AFib) is the most common sustained cardiac arrhythmia, affecting over 6 million Americans. It's characterized by chaotic, disorganized atrial electrical activity where multiple electrical impulses fire simultaneously, causing the atria to quiver rather than contract effectively.
ECG Characteristics
Primary Features:
- Irregularly Irregular Rhythm - The hallmark of AFib with completely unpredictable R-R intervals
- Absent P Waves - Normal P waves are replaced by fibrillatory waves
- Fibrillatory (f) Waves - Fine, irregular baseline oscillations best seen in leads V1 and II
- Narrow QRS Complexes - Typically normal duration unless bundle branch block coexists
- Variable Ventricular Rate - Usually 100-180 bpm when untreated
Rate Classification:
- Slow AFib: 100 bpm (uncontrolled)
Clinical Significance
Hemodynamic Impact:
- Loss of Atrial Kick: Reduces cardiac output by 20-30%
- Reduced Diastolic Filling: Particularly problematic in heart failure
- Tachycardia-Induced Cardiomyopathy: Can develop with prolonged rapid rates
Thromboembolic Risk:
- Blood stasis in left atrial appendage increases clot formation
- 5-fold increased stroke risk compared to sinus rhythm
- Risk stratified using CHA₂DS₂-VASc score
Management
Immediate Assessment:
- Hemodynamic stability (BP, mental status, chest pain)
- Stroke risk calculation (CHA₂DS₂-VASc score)
- Rate vs rhythm control strategy
Treatment:
- Rate Control: Beta-blockers, calcium channel blockers, digoxin
- Rhythm Control: Antiarrhythmics, cardioversion, ablation
- Anticoagulation: Based on stroke risk (DOAC or warfarin)
Key Points
- AFib = irregularly irregular rhythm without P waves
- Always assess hemodynamic stability
- Stroke prevention is critical
- New-onset <48h may allow cardioversion
- Chronic AFib needs anticoagulation consideration
