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atrial fibrillation ECG pattern
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Here is a comprehensive overview of Atrial Fibrillation (AF) on ECG.
ECG Features of Atrial Fibrillation
(Table 18-8, Tintinalli's Emergency Medicine)
| Feature | Detail |
|---|---|
| P waves | Absent — replaced by flat or chaotic baseline (fibrillatory f-waves) |
| Baseline | Irregular oscillations, most prominent in lead V1 |
| Ventricular rhythm | Irregularly irregular — no repeating pattern to R-R intervals |
| QRS complexes | Narrow (normal) — unless pre-existing BBB or pre-excitation syndrome |
| Ventricular rate | Typically 120–170 bpm (unmedicated); can exceed 200 bpm with accessory pathways |
Classic ECG Examples of AF
Three examples of AF with irregular ventricular response (from Tintinalli's):
(A) Rapid, chaotic baseline with fast ventricular response
(B) Clearly irregular R-R intervals in lead II, no P waves
(C) Slower ventricular rate — note the variable spacing between QRS complexes
And a 12-lead ECG demonstrating classic AF with a single PVC:
Key features visible: absent P waves, irregular R-R intervals, narrow QRS complexes, one wide PVC beat.
Mechanism
- Chaotic, disorganized electrical activity in the atria fires at rates >600 bpm
- The AV node acts as a "gatekeeper" — its refractory period limits ventricular response to ~120–170 bpm
- Because conduction is random, ventricular rhythm is never regularly irregular — it is truly random
How to Distinguish from Similar Rhythms
| Rhythm | Key Difference |
|---|---|
| Atrial Flutter | Regular sawtooth flutter waves ~300 bpm; ventricular rhythm often regular (2:1 block → ~150 bpm) |
| Multifocal Atrial Tachycardia (MAT) | ≥3 distinct P wave morphologies; P waves are present; often confused with AF |
| AF + BBB | Wide QRS complexes; can mimic VT |
| AF + WPW | Very rapid rate (>200 bpm), delta waves, wide bizarre QRS |
Clinical Significance
Common causes:
- Ischemic heart disease / valvular disease (most common)
- Congestive cardiomyopathy, myocarditis
- Thyrotoxicosis
- Alcohol binge ("holiday heart")
- Blunt chest trauma
Consequences of AF:
- Loss of atrial kick — reduces ventricular filling, can precipitate heart failure
- Rapid ventricular rate — impairs coronary and systemic perfusion
- Thromboembolism — blood stagnates in the left atrial appendage → clot → stroke
ED Management (Key Principles)
Three pillars of AF management:
- Rate control — beta-blockers, calcium channel blockers, digoxin
- Rhythm conversion — cardioversion (electrical or pharmacological) if <48 hrs or anticoagulated ≥3–4 weeks
- Anticoagulation — use CHADS₂ or CHA₂DS₂-VASc score to risk-stratify
- <12 hrs AF: ~0.3% embolic risk on conversion
- 12–48 hrs: ~1%
-
48 hrs: elevated across all groups — anticoagulate 3–4 weeks before conversion
Sources: Tintinalli's Emergency Medicine (Tbl 18-8), Guyton & Hall Medical Physiology, Harrison's Principles of Internal Medicine 22E
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