RADIOFREQUENCY ABLATION OF ATRIAL-FLUTTER

Activation mapping in common atrial butter has shown circular (reentra nt) activation of the right atrium around anatomic structures and area s of functional block. The direction of rotation is counterclockwise ( in a frontal view), and in the low right atrium the myocardium between the inferior vena cava (IVC) and the tricuspid valve (TV) is critical to close the activation circle. The circuit can be interrupted by rad iofrequency ablation of the myocardium between the TV and the IVC, and , in some cases, by ablation between the coronary sinus and TV. Flutte r interruption does not mean complete isthmus ablation, as it may rema in inducible, requiring further ablation. Despite attaining noninducib ility, flutter may recur, and new procedures may be needed for complet e ablation. Atrial fibrillation occurs in up to 30% of the cases durin g follow-up but is generally well controlled with antiarrhythmic drugs that were ineffective in treating flutter before ablation. Some nonco mmon atrial flutters show circular right atrial activation in a revers ed (clockwise) direction, with the same critical areas in the low righ t atrium, and in these isthmus ablation is effective. Other noncommon flutters have different substrates in the right or left atrium, and ma pping has to define specific critical isthmuses as ablation targets in each case. Left atrial flutter circuits remain inaccessible to ablati on.