CATHETER-INDUCED MECHANICAL CONDUCTION BLOCK OF RIGHT-SIDED ACCESSORYFIBERS WITH MAHAIM-TYPE PREEXCITATION TO GUIDE RADIOFREQUENCY ABLATION

Background Accessory pathways originating at the tricuspid annulus tha t exhibit decremental antegrade conduction properties (Mahaim-type pre excitation) are amenable to radiofrequency (RF) current catheter ablat ion. However, a reliable and reproducible strategy for mapping and abl ation of these fibers is lacking. Methods and Results Eleven patients with preexcited atrioventricular tachycardia involving a decrementally conducting antegrade accessory pathway underwent complete electrophys iological evaluation and subsequent attempts at RF catheter ablation. Mechanical conduction block at the subannular level of the atrial inpu t to the accessory fiber was induced by catheter manipulation in 8 pat ients, in 2 of them during atrial fibrillation. RF current was deliver ed, after resumption of preexcitation, to the site of mechanical block during atrial pacing (n=6) or atrial fibrillation (n=2) and eliminate d the accessory pathway in all 8 patients. In another patient, mechani cal block was not observed, but ablation of the atrial accessory fiber insertion was achieved at the subannular level during atrioventricula r tachycardia. The anatomic site of ablation along the tricuspid annul us was anterolateral (n=1), lateral (n=3), or posterolateral (n=5). Fa ilures were encountered in the first patient of the series in whom abl ation attempts were directed at the ventricular insertion of the acces sory fiber and in a patient in whom ablation of the atrial insertion w as attempted at the supraannular level. Recurrence of preexcitation wi thin 12 hours was observed in 5 of 6 patients in whom ablation had bee n achieved during atrial pacing. Eventually successful repeat sessions were performed the following day using a simplified ablation approach . Thus, a median of 5 RF pulses (range, 1 to 26) per accessory fiber e liminated conduction in 9 (82%) of the 11 patients in 1.9+/-0.9 sessio ns. During a follow-up of 9.5+/-2.3 months, preexcitation recurred in 1 patient. Conclusions The atrial origin of accessory connections with Mahaim-type preexcitation is apparently confined to the anterolateral -to-posterolateral region of the tricuspid annulus. Mechanical conduct ion block in the atrial input to the accessory fiber induced at the su bannular level by catheter manipulation provides an optimal marker to locate the ablation site, even during atrial fibrillation. To expose e arly recurrence of antegrade accessory pathway conduction, intermitten t atrial pacing in the 12 hours after ablation is advisable; in cases of recurrence, a repeat procedure can readily be performed using just the ablation catheter advanced to the target site at the tricuspid ann ulus.