PROGRESSIVE ANTERIOR ABLATION IN THE CORONARY SINUS REGION - EVIDENCETO SUPPORT THE PRESENCE OF A SLOW PATHWAY INPUT IN NORMAL-PATIENTS

Background AV node modification is an emerging approach to rate contro l in patients with medically refractory atrial fibrillation. The mecha nism of benefit of this procedure is not completely understood. Method s and Results Twenty-two patients (age, 65 +/- 11 years; 16 women) wit h medically refractory paroxysmal atrial fibrillation referred for com plete AV node ablation underwent serial ablations beginning at the lev el of the coronary sinus os progressing in a superior and anterior dir ection toward the His bundle. Serial atrial extrastimulus testing was performed to determine the effect of the progressive posteroseptal abl ation in the region of the coronary sinus on the AV node antegrade ref ractory curve. Two of 22 patients had antegrade dual AV node pathways before ablation. Three patterns of response to serial ablation were no ted. In 10 patients (45%), loss of the terminal portion of the AV node antegrade refractory curve occurred without evidence of fast pathway injury. In 7 patients (32%) the curve was shifted upward and to the le ft, consistent with nonspecific AV node damage. In 5 patients (23%), n o effect could be attained before induction of complete AV block at su perior and anterior ablation sites. Clinical variables and site of abl ation did not predict response to serial ablations. Conclusions These data suggest that the mechanism of benefit of AV node modification in this population may be through elimination of ''slow pathway'' tissue in half of patients and nonspecific injury in the remainder. Modificat ion without complete AV block may not be possible in a minority of pat ients, as the response to progressive ablation appears to be ''all or none'' conduction.