NEW OBSERVATIONS ON DECREMENTAL ATRIOFASCICULAR AND NODOFASCICULAR FIBERS - IMPLICATIONS FOR CATHETER ABLATION

Introduction: The purpose of this study was to characterize the anatom y and physiology of accessory pathways that exhibit anterograde decrem ental conduction. Results: Among 100 consecutive patients with an acce ssory pathway undergoing electrophysiological study, six individuals w ith decremental anterograde accessory pathway conduction were identifi ed. Anterograde accessory pathway effective refractory periods and con duction curves were assessed by atrial extrastimulus testing. Atrial p ace mapping and ventricular activation sequence mapping were used to d efine accessory pathway origin and insertion. Surgical ablation (N = 1 ) or radiofrequency catheter ablation (N = 3) was performed based on a ccessory path way anatomy as determined during electrophysiological st udy. Four of 6 patients had gaps in anterograde accessory pathway cond uction. Two patients had evidence of functional longitudinal dissociat ion in the accessory pathway. Five of 6 patients had atriofascicular f ibers with an atrial rather than AV nodal site of origin of their decr ementally conducting accessory pathway and with distal insertions in t he right bundle branch. Among these five patients, a right posterior a trial origin was nearly as common as a right anterior atrial origin. O ne patient had a true nodofascicular fiber that arose from the AV node , inserting distally into the left bundle branch. Conclusion: Most acc essory path ways with anterograde decremental conduction arise from th e right anterior or right posterior atrium, not the AV node. A gap in anterograde accessory path way conduction and functional longitudinal dissociation are common in such accessory pathways, Surgical or cathet er ablation of such pathways is effective when directed at the atrial origin of the accessory pathway. True nodofascicular fibers arising fr om the AV node are rare. These may insert distally in the left ventric le. Catheter ablation of She proximal origin of such fibers is likely to result in complete AV block.