Related Experiment Video
Updated: Aug 6, 2026
Estimating Bilateral Atrial Function by Cardiovascular Magnetic Resonance Feature Tracking in Patients with Paroxysmal Atrial Fibrillation
Published on: July 20, 2022
Unraveling the enigmatic morphology of the atrioventricular conduction axis using hierarchical phase-contrast
Abdullah Almehandi1, Kan Yan Chloe Li1, Joseph Brunet2
1Centre for Morphology and Structural Heart Disease, UCL Institute of Cardiovascular Disease, London, United Kingdom.
Insights
Hierarchical Phase-Contrast Tomography (HiP-CT) reveals the 3D structure of the atrioventricular (AV) conduction axis in adult hearts. This advanced imaging clarifies the AV node, bundle, and branches, aiding electrophysiology and interventions.
Area of Science:
- Cardiac Anatomy
- Medical Imaging
- Electrophysiology
Background:
- The 3D structure of the atrioventricular (AV) conduction system is not fully understood.
- Traditional histology lacks spatial context for complex cardiac structures.
- Hierarchical Phase-Contrast Tomography (HiP-CT) offers high-resolution, non-destructive 3D virtual histology.
Purpose of the Study:
- To characterize the 3D morphology of the adult human AV conduction axis.
- To investigate the relationship between the AV conduction axis and surrounding cardiac structures.
- To utilize HiP-CT for detailed anatomical analysis.
Main Methods:
- Five adult human hearts were scanned using HiP-CT at high resolution (20 microns and 6.51 microns).
- The AV conduction axis was segmented and reconstructed in 3D.
- Morphological measurements and anatomical landmark analysis were performed.
Main Results:
- HiP-CT successfully visualized the AV node, non-branching bundle, and branching components.
- The non-branching bundle length averaged 6.31 mm, with variations noted.
- A consistent branching pattern (left bundle broader than right) and additional pathways were observed.
- Cardiomyocyte alignment transitions were identified from the AV node to the bundle.
Conclusions:
- HiP-CT provides unprecedented high-resolution 3D visualization of the human AV conduction axis.
- The study revealed morphological details and variability within the AV conduction system.
- Findings enhance understanding of structure-function relationships for clinical electrophysiology and interventions.
Background:
The 3-dimensional (3D) architecture of the atrioventricular (AV) conduction axis and its relationship to surrounding cardiac structures remain incompletely understood. Standard histology provides cellular detail but struggles to demonstrate spatial arrangement and connectivity within the intact heart. Hierarchical phase-contrast tomography (HiP-CT) overcomes this by enabling nondestructive, high-resolution 3D virtual histology.
Objectives:
We aimed to characterize the 3D morphology of the adult human AV conduction axis and its relationship to key anatomic landmarks using HiP-CT.
Methods:
5 adult human hearts (mean donor age 81.6 years) underwent HiP-CT at the European Synchrotron Radiation Facility. Whole-heart scans were acquired at 20-micron isotropic resolution, with targeted imaging of the AV conduction axis at 6.51 microns. The axis was segmented in multiple orthogonal planes, reconstructed in 3D, and measured.
Results:
HiP-CT distinguished the compact AV node, nonbranching bundle, and branching components. Nonbranching bundle length ranged from 2.49 to 8.80 mm (mean 6.31 mm). In all hearts, the axis branched first into a broad left bundle, followed by a cord-like right bundle branch. Additional superior septal pathways were identified in 4 hearts. Orthogonal sections showed a transition from interwoven cardiomyocytes in the node to parallel alignment in the insulated nonbranching bundle. A line from the anteroseptal commissure of the tricuspid valve to the medial papillary muscle reliably located the nonbranching bundle.
Conclusion:
HiP-CT provides high-resolution 3D visualization of the AV conduction axis in adult hearts, revealing its morphology and variability. These findings offer new insights into structure-function correlations relevant to clinical electrophysiology and interventional procedures.
