Clinical and electrophysiological characteristics of fasciculoventricular fibers in children

Introduction Fasciculoventricular (FV) fiber is a rare cause for ventricular preexcitation. It is usually described as an innocent bystander pathway. There is only limited data on FV fiber in children. Hence we evaluated the clinical and electrophysiological features of FV fiber in a group of 11 children. Methods and results Of 215 children with manifest preexcitation who had electrophysiological studies at the University of Miami, 11 (5.1%) had characteristics of FV fiber. FV fiber was not directly responsible for any arrhythmias in these children. Three children had supraventricular tachycardia due to associated left sided Kent fiber and FV fiber was identified after the ablation of Kent fiber. One child had associated hypertrophic cardiomyopathy, another child had atrial septal defect and a third child had ventricular septal defect. The electrophysiological testing of FV fiber revealed AH interval of 40–95 ms and H-delta interval of 15–40 ms. Mapping study showed that the FV fiber was located on the right side of the heart in all patients: right anteroseptal in 9, right midseptal in 1 and it could not be mapped well in 1 as the delta wave was intermittent. We identified a discrete FV fiber depolarization spike in 9 patients, with a local FV fiber depolarization to delta wave interval of 5–20 ms (11 + 4 ms). Conclusion FV fiber is an uncommon cause for ventricular preexcitation in children and it can be associated with other conduction abnormalities and heart defects. FV fibers are commonly located at the right anteroseptal region and are not usually involved in any tachycardia. Discrete local FV fiber potential can be identified during electrophysiological testing of these patients.