ECG reference
AFib · Flutter · SVT.
Three fast, narrow rhythms. One quick decision tree.
| Atrial fibrillation | Atrial flutter | SVT (AVNRT) | |
|---|---|---|---|
| Rhythm | Irregularly irregular | Regular (fixed conduction) | Regular |
| Rate | Variable, often 110–180 | ~150 (2:1) or ~100 (3:1) | 150–220 |
| P waves | Absent — chaotic baseline | Sawtooth flutter waves | Absent or buried in T |
| QRS | Narrow (unless aberrancy) | Narrow | Narrow |
| Onset | Gradual | Gradual | Abrupt |
Prehospital treatment
AFib / Flutter (stable)
- Rate control: diltiazem 0.25 mg/kg IV.
- Consider anticoagulation risk if new-onset.
- Transport for definitive rhythm/rate control.
SVT (stable)
- Vagal maneuvers (Valsalva, modified Valsalva).
- Adenosine 6 → 12 → 12 mg IV.
- Continuous ECG through conversion.
Any of them — unstable
- Synchronized cardioversion.
- AFib: 120–200 J biphasic.
- Flutter/SVT: 50–100 J biphasic.
Trap to avoid
A regular narrow tachy at exactly 150 bpm — think atrial flutter with 2:1, not just SVT. Vagal maneuvers or adenosine will slow conduction and reveal the sawtooth pattern.
Frequently asked
- How do I tell atrial fibrillation from SVT?
- AFib is irregularly irregular with no P waves. SVT is a fast, narrow-complex, perfectly regular tachycardia — usually 150–220 bpm — often with hidden P waves in the T wave.
- What is the classic flutter rate?
- Atrial rate ~300 with a 2:1 conduction → ventricular rate ~150. Sawtooth flutter waves best seen in II, III, aVF.
- When do I cardiovert vs use adenosine?
- Cardiovert any unstable tachyarrhythmia (hypotension, altered mental status, chest pain, signs of shock). Adenosine is for stable, regular, narrow-complex SVT.
- Why avoid adenosine in atrial fibrillation with WPW?
- Adenosine can block AV nodal conduction and push all impulses down the accessory pathway, causing very fast ventricular rates or VF. Cardiovert instead.
Drill dysrhythmias