ECG rhythms Atrial and supraventricular
Atrial flutter ECG
Atrial flutter with 4:1 conduction. Regular flutter waves at about 300/min run without a flat baseline between them, and every fourth one conducts, giving a regular ventricular rate of about 75/min.
A 30-second recording of the heart model, played in real time. Run live starts the engine itself with this rhythm.
Computed by the TracingsMD heart model (Junkers engine): simulated for education, not a patient recording and not for diagnosis.
Measured on this recording
| Ventricular rate | 75/min |
|---|---|
| PR | — |
| QRS | 84 ms |
| QT | Not assessable in this rhythm |
| QTc (Bazett) | Not assessable in this rhythm |
| QTc (Fridericia) | Not assessable in this rhythm |
What it is
A large re-entry circuit in the atria. In typical flutter the circuit is in the right atrium: the wave travels around the tricuspid annulus (the valve ring), through the cavotricuspid isthmus, at about 300/min, giving sawtooth F waves (flutter waves) that are best seen in II, III, aVF and V1. The AV node most often conducts every second wave (2:1 ≈ 150/min), sometimes every fourth (4:1 ≈ 75/min) or a variable number.
How to read this strip
| Rate | Atrial about 300/min; ventricular about 75/min. |
|---|---|
| Rhythm | Regular. |
| P waves | No P waves; continuous, evenly spaced flutter waves with no flat baseline between them, best seen in the long gaps between QRS complexes. |
| PR | Not applicable. |
| QRS | Narrow. |
| QT | Hard to measure because flutter waves overlap the T wave. |
Causes
- Structural heart disease and heart failure.
- Chronic lung disease.
- After cardiac surgery.
- Hyperthyroidism, alcohol.
- Often coexists with atrial fibrillation.
What to consider
- A regular narrow tachycardia at about 150/min should always raise suspicion of flutter with 2:1 conduction.
- 1:1 conduction (a ventricular rate of about 200–300/min, often with a wide QRS) can occur with sympathetic stimulation, or when class IC drugs slow the flutter enough for the AV node to conduct every wave—so an AV-nodal blocker is given with them. It is dangerous.
- Stroke risk and anticoagulation are assessed as for atrial fibrillation.
- Vagal maneuvers or adenosine can briefly increase the AV block and reveal the F waves; they help the diagnosis but do not end flutter.
- Typical flutter is usually cured by catheter ablation of the cavotricuspid isthmus, although many patients later develop atrial fibrillation.
Key point
At 2:1 conduction the ventricular rate is about 150/min: one flutter wave hides in the QRS and the other only dents the end of the T wave — suspect flutter in any regular narrow tachycardia near 150/min, and look for the waves when the ratio changes.
Not to be confused with
- Sinus rhythm — Sinus rhythm has one P wave before each QRS and a flat baseline between beats. Here the baseline never settles: identical atrial waves run continuously between the QRS complexes.
- Atrial fibrillation — AF has irregular RR intervals and no organized atrial activity. Here the atrial waves are identical and evenly spaced, and the RR intervals are regular.
- Multifocal atrial tachycardia (simulator) — MAT is irregular, with P waves of at least three shapes separated by a flat baseline, at a rate above 100/min. Here the atrial waves are uniform and continuous and the rate is normal.