Response to letter regarding article, "variable clinical features and ablation of manifest nodofascicular/ventricular pathways".

BACKGROUND Manifest nodofascicular/ventricular (NFV) pathways are rare. METHODS AND RESULTS From 2008 to 2013, 4 cases were identified with manifest NFV pathways from 3 centers. The clinical findings and ablation sites are reported. All 4 cases presented with a wide complex tachycardia but with different QRS morphologies. Case 1 showed a left bundle branch block/superior axis, case 2 showed a right bundle branch block/inferior axis, case 3 showed a left bundle branch block/inferior axis, and case 4 showed a narrow QRS tachycardia and a wide complex tachycardia with a left bundle branch block/inferior axis. Three of the 4 tachycardias had atrioventricular dissociation ruling out extranodal accessory pathways, including atriofascicular pathways. Programmed extrastimuli showed evidence of a decremental accessory pathway in 3 of the 4 cases. Coexisting tachycardia mechanisms were seen in 3 of the 4 cases (atrioventricular nodal reentry tachycardia [2] and atrioventricular reentrant tachycardia [1]). Ablation in the slow pathway region eliminated the NFV pathway in 3 (transient in 1) with the other responding to surgical closure of a large atrial septal defect. The NFV pathway was a critical part of the tachycardia circuit in 1 and proved to be a bystander in the other 3 cases. CONCLUSIONS Manifest NFV pathways presented with variable QRS expression dependent on the ventricular insertion site and often coexisted with other tachycardia mechanisms (atrioventricular nodal reentry tachycardia and atrioventricular reentrant tachycardia). In most cases, the atrial insertion of the pathway was in or near the slow pathway region. The NFV pathways were either critical to the tachycardia circuit or served as bystanders.