Atrial flutter update.

Typical atrial flutter has long been considered a reentrant arrhythmia, but it is only recently that the full structure of the right atrial circuit was understood, leading to de devise of ablation techniques. Recognition of the role of functional block, based on anisotropic conduction was crucial to understanding of the flutter circuit. Anisotropy at the terminal crest creates a line of block that, with the orifices of superior and inferior vena cava, constitutes the posterior boundary of the flutter circuit. The anterior boundary is the tricuspid ring, and the circuit is a ring of myocardium made by the septal and anterior right atrial walls, linked on top by the right atrial roof and inferiorly by the inferior vena cava-tricuspid ring isthmus. This isthmus, a relatively narrow part of the circuit, has become the established target for typical flutter ablation. Complete, bidirectional isthmus block is the final goal of flutter ablation. This has to be assessed, after flutter interruption, by pacing both sides of the ablation line while recording electrogram sequences from the opposite right atrial wall and the isthmus itself. Success is great in terms of prevention of flutter recurrence, however a 30% incidence of atrial fibrillation during follow-up casts a large shadow on long-term prognosis. Understanding of the myocardial abnormalities underlying atrial flutter and fibrillation will be necessary to improve this long-term outlook.