A 17 yo male patient presents to the pediatric emergency department with chest pain. Pain is only mild to moderate. Dizziness is not reported. However, he felt palpitations. Symptom onset was 20 hours ago.
His ECG reveals the following:
ECG shows ventricular rate of 80 bpm. Atrial rate is 320 bpm. P waves are negative in inferior leads (II/III/aVF) and show a classical "saw-tooth pattern". The latter describes P wave morphology in atrial flutter, where the initial part of the P wave shows a slurred downstroke and rapid terminal upstroke. The morphology of flutter waves differs with regard to location and direction of the reentry circuit.
Most commonly, atrial flutter circuits exist around the tricuspid annulus. Typical atrial flutter appears as either a counterclockwise (common typical, negative P waves inferior leads) or clockwise (uncommon typical, positive P waves inferior leads) reentry circuit around the tricuspid valve.
Typical atrial flutter is dependent on the cavo-tricuspid isthmus (CTI). The CTI serves as a critical structure for conduction in typical atrial flutter, and ablation of the CTI usually terminates the arrhythmia by eliminating the substrate for the reentry circuit.
Hints to quickly spot AFL on an ECG:
- Ventricular rate 150 bpm (in adults):
usually the time it takes for the electrical wavefront to encircle the tricuspid valve takes about 200ms (more or less), leading to an atrial rate of 300 bpm. Most commonly AFL appears as a 2:1 blocked rhythm, typically yielding a ventricular rate of 150 bpm. In pediatric patients higher atrial rates and varying degrees of block must be taken into account!
- Saw-Tooth pattern inferior (II/III/aVF):
may not always be present. Morphology depends on location and direction of reentry circuit.
- Regular R-R intervals:
Usually R-R intervals are quite regular in AFL, which is incontrast to atrial fibrillation. Hoever, varying degrees of AV block may lead to R-R interval variation!