New observations on decremental atriofascicular and nodofascicular fibers: implications for catheter ablation

The purpose of this study was to characterize the anatomy and physiology of accessory pathways that exhibit anterograde decremental conduction.

Among 100 consecutive patients with an accessory pathway undergoing electrophysiological study, six individuals with decremental anterograde accessory pathway conduction were identified. Anterograde accessory pathway effective refractory periods and conduction curves were assessed by atrial extrastimulus testing. Atrial pace mapping and ventricular activation sequence mapping were used to define accessory pathway origin and insertion. Surgical ablation (N = 1) or radiofrequency catheter ablation (N = 3) was performed based on accessory pathway anatomy as determined during electrophysiological study. Four of 6 patients had gaps in anterograde accessory pathway conduction. Two patients had evidence of functional longitudinal dissociation in the accessory pathway. Five of 6 patients had atriofascicular fibers with an atrial rather than AV nodal site of origin of their decrementally conducting accessory pathway and with distal insertions in the right bundle branch. Among these five patients, a right posterior atrial origin was nearly as common as a right anterior atrial origin. One patient had a true nodofascicular fiber that arose from the AV node, inserting distally into the left bundle branch.

Most accessory pathways with anterograde decremental conduction arise from the right anterior or right posterior atrium, not the AV node. A gap in anterograde accessory pathway conduction and functional longitudinal dissociation are common in such accessory pathways. Surgical or catheter ablation of such pathways is effective when directed at the atrial origin of the accessory pathway. True nodofascicular fibers arising from the AV node are rare. These may insert distally in the left ventricle. Catheter ablation of the proximal origin of such fibers is likely to result in complete AV block.