Radiofrequency catheter ablation of atrial flutter circuits.

Common atrial flutter is due to reentrant activation of the right atrium, rotating around anatomic structures and areas of functional block, in counterclockwise direction in the frontal plane. The myocardium between the inferior vena cava and the tricuspid valve is critical to close the activation circuit, and ablation of this isthmus by catheter-delivered radiofrequency can interrupt flutter, and eventually destroy the circuit, preventing recurrence of the arrhythmia. Flutter interruption does not mean complete isthmus ablation, and the procedure endpoint is to attain flutter non-inducibility, and isthmus block. Despite non-inducibility, flutter may recur, and new procedures may be needed for complete ablation. Atrial fibrillation can occur in up to 35% of the cases during follow-up but is generally well controlled with drugs that were ineffective against flutter before ablation. Some atypical atrial flutters show circular right atrial activation, using the same circuit in a clockwise direction, and these can also be interrupted by ablation of the inferior vena cava-tricuspid valve isthmus. Other atypical flutters can have different anatomic substrates in the right or left atrium, and mapping has to define specific isthmuses as ablation targets in each case. Left atrial flutter remains inaccessible to ablation.