Intermittent fixed preexcitation: What is the mechanism?

The pre-excited complex may be observed with conduction over the NV, AV, NF, or AF pathways. FV-AP are extremely rare preexcitation variants which have distinctive ECG and electrophysiological features. These fibers take off from the His bundle and the fascicles to the superoseptal location (right ventricular anteroseptum or midseptum). Therefore, they show overlapping characteristics with both anteroseptal and mid-septal AV-AP on surface ECG. These pathways should be ruled out from classical AV-APs before attempting catheter ablation, as FV-APs do not participate in the AVRT circuit and are not associated with rapid antegrade conduction.