Defining myocardial fiber bundle architecture in atrial digital twins

TL;DR

This study introduces a novel atrial Laplace-Dirichlet-Rule-Based Method (LDRBM) for prescribing highly detailed myofiber orientations and providing robust regional annotation in bi-atrial morphologies of any complexity, and demonstrates that the novel LDRBM outperforms current state-of-the-art fiber models.

Abstract

A key component in developing atrial digital twins (ADT) - virtual representations of patients' atria - is the accurate prescription of myocardial fibers which are essential for the tissue characterization. Due to the difficulty of reconstructing atrial fibers from medical imaging, a widely used strategy for fiber generation in ADT relies on mathematical models. Existing methodologies utilze semi-automatic approaches, are tailored to specific morphologies, and lack rigorous validation against imaging fiber data. In this study, we introduce a novel atrial Laplace-Dirichlet-Rule-Based Method (LDRBM) for prescribing highly detailed myofiber orientations and providing robust regional annotation in bi-atrial morphologies of any complexity. The robustness of our approach is verified in eight extremely detailed bi-atrial geometries, derived from a sub-millimiter Diffusion-Tensor-Magnetic-Resonance Imaging (DTMRI) human atrial fiber dataset. We validate the LDRBM by quantitatively recreating each of the DTMRI fiber architectures: a comprehensive comparison with DTMRI ground truth data is conducted, investigating differences between electrophysiology (EP) simulations provided by either LDRBM and DTMRI fibers. Finally, we demonstrate that the novel LDRBM outperforms current state-of-the-art fiber models, confirming the exceptional accuracy of our methodology and the critical importance of incorporating detailed fiber orientations in EP simulations. Ultimately, this work represents a fundamental step toward the development of physics-based digital twins of the human atria, establishing a new standard for prescribing fibers in ADT.

Figures (23)

• Figure 1: Schematic representation of the atrial LDRBM in a real bi-atrial geometry (derived from the DTMRI human atrial fiber dataset pashakhanloo2016myofiber).
• Figure 2: Schematic representation of the measurement procedure exploiting the LDRBM reference axis system to asses the local myocardial fiber angle in each atrial bundles across eight human bi-atrial geometries embedded with DTMRI fiber data pashakhanloo2016myofiber.
• Figure 3: Bundles subdivision performed by the bi-atrial LDRBM for the DTMRI dataset geometries: (a) anterior view; (b) posterior view; (c) box-plots showing the bundle parameter variation for the left atrium (LA), right atrium (RA) and inter-atrial connections (IC); standard deviatian (SD) values of the bundle parameters, with SD color-coded on a scale from minimal (0) to maximal (0.32) values (see also Figure \ref{['fig:fiber_bundles']} and Tables \ref{['tab:tau_bundles_BIA']}$-$\ref{['tab:tau_bundles_RA']}).
• Figure 4: Measuring procedure applied to the eight geometries of DTMRI fiber dataset: streamlines represent DTMRI fiber directions, showing the measured angle $\alpha$ relative to LDRBM axis system. Anterior (a) and posterior (b) views.
• Figure 5: Comparison between the atrial LDRBM fibers and the DTMRI data, across eight DTMRI geometries. Glyph-rendered fiber vector fields are reported for each geometry (Geo 1$-$8), displayed in anterior (top) and posterior (bottom) views. The function diff, computed as $\text{diff}(\boldsymbol{x}) = 1 - |\boldsymbol{f}_\text{DTMRI}(\boldsymbol{x}) \cdot \boldsymbol{f}_\text{LDRBM}(\boldsymbol{x})|$, highlights the differences between LDRBM and DTMRI fibers, see also Figures \ref{['fig:fibers_LDRBM_epi']}$-$\ref{['fig:fibers_LDRBM_endo']}.