The heterogeneous nature of atrioventricular conduction tissues in tetralogy of Fallot demonstrated by hierarchical phase-contrast tomography.

OBJECTIVES

Postoperative arrhythmias are frequent after tetralogy of Fallot (ToF) repair, yet anatomic substrate and preventive strategies remain poorly defined. Using hierarchical phase-contrast tomography (HiP-CT), the atrioventricular conduction system in pediatric ToF specimens was investigated nondestructively and in 3-dimensions (3D).

METHODS

Eighteen whole-heart specimens (11 ToF, 7 controls) were imaged at the European Synchrotron Radiation Facility. Segmentation and 3D renderings demonstrated gross morphology. Morphology, size, depth, and course of the nonbranching bundle and right bundle branch (RBB) were quantified using custom computational pipelines. Segmentations were visualized in VheaRts, a Unity3D-based XR platform.

RESULTS

The ToF conduction system was more draped than in controls, bilaterally spanning the septum, resembling early embryonic architecture. The RBB was variable in origin, course, and morphologic structure with significantly smaller indexed cross-sectional area in native ToF versus controls (0.05 ± 0.20 vs 0.50 ± 0.20 mm2, P = .005). One anomalous fasciculo-ventricular connection and 6 dead-end tracts were found. Regions at surgical risk included the posterior-inferior margin of the ventricular septal defect and the septal crest along its nadir. The superior margin of the ventricular septal defect at its intersection with the aortic root was free of conduction tissue. The HiP-CT to virtual reality pipeline enabled interactive 3D visualization of conduction pathways relative to key structures.

CONCLUSIONS

This first pediatric cardiac HiP-CT series reveals a broader anomalous conduction complex in ToF, including variable RBB origin and hypoplasia, providing insight into preoperative vulnerability, arrhythmia, and surgical risk.