Tachyarrhythmias
Atrial flutter
Sawtooth flutter waves at about 300 per minute, usually conducted 2:1 to give a ventricular rate near 150.
What you see
- Regular narrow complex tachycardia, characteristically at almost exactly 150 bpm.
- Sawtooth flutter waves at ~300 per minute, best seen in II, III, aVF and V1.
- No isoelectric baseline between flutter waves in typical, counterclockwise flutter.
- Conduction ratios step in whole numbers: 2:1 gives 150, 3:1 gives 100, 4:1 gives 75.
Why it looks like that
A macro-re-entrant circuit inside the right atrium, passing through the cavotricuspid isthmus. Because the circuit is anatomically fixed, the atrial rate is remarkably constant at around 300, and the AV node divides it down.
What to do
- Anticoagulate exactly as for atrial fibrillation — the stroke risk is the same.
- Cavotricuspid isthmus ablation is highly effective and is first-line for symptomatic typical flutter.
- Rate control is often difficult; cardioversion needs less energy than AF (50–100 J).
The trap
Any regular narrow complex tachycardia at 150 should prompt a hunt for flutter waves. Vagal manoeuvres or adenosine will not usually terminate flutter, but they slow AV conduction long enough for the sawtooth to become obvious — which is diagnostic, not a failed treatment.
More in tachyarrhythmias
Atrial fibrillation
Irregularly irregular narrow complexes with no P waves and a wandering baseline.
AV nodal re-entrant tachycardia
Regular narrow complex tachycardia around 180 with P waves hidden inside or just after the QRS.
Monomorphic ventricular tachycardia
Broad, regular, identical complexes — assume VT in any broad complex tachycardia until you have proved otherwise.
Torsades de pointes
Polymorphic VT twisting around the baseline, on a background of a long QT.