LINEAR ABLATION OF THE ISTHMUS BETWEEN THE INFERIOR VENA-CAVA AND TRICUSPID ANNULUS FOR THE TREATMENT OF ATRIAL-FLUTTER - A STUDY IN THE CANINE ATRIAL-FLUTTER MODEL

Background The isthmus between the inferior vena cava and the tricuspid annulus has been shown to be involved in the reentry circuit of common atrial flutter. The effects of radiofrequency catheter ablation of this isthmus were examined in the canine model of atrial flutter due to reentry around the tricuspid annulus. Methods and Results A model of atrial flutter was prepared in 11 of 14 dogs by creating intercaval and connected transverse lesions (Y-shaped lesion). Bipolar electrodes were attached at 24 atrial sites, and computer-assisted mapping was performed. Stable atrial flutter with a cycle length of 133+/-11 ms was repeatedly induced by rapid atrial pacing in all dogs, and atrial mapping revealed reentry around the tricuspid annulus including the isthmus. In 6 dogs, the isthmus was ligated during atrial flutter (mechanical ablation). In the other 5 dogs, a 7F large-tip electrode catheter was placed at the isthmus under a fluoroscopic control. Radiofrequency energy (25 W for 30 s) was delivered to three sequential sites from the tricuspid annulus to the inferior vena cava to ablate the isthmus linearly. Atrial flutter was terminated in all dogs after mechanical and radiofrequency ablation of the isthmus and was not induced again. Atrial pacing from the posterior left atrium during sinus rhythm demonstrated intra-atrial conduction block at the isthmus after ablation. Pathological examination of the isthmus showed transmural myocardial damage. Conclusions Linear radiofrequency ablation of the isthmus can induce intra-atrial conduction block and is effective as a curative therapy for atrial flutter when the reentry circuit involves the isthmus.