Image-Based Model of Atrial Anatomy and Electrical Activation: A Computational Platform for Investigating Atrial Arrhythmia

Abstract

Computer models provide a powerful platform for investigating mechanisms that underlie atrial rhythm disturbances. We have used novel techniques to build a structurally-detailed, image-based model of 3-D atrial anatomy. A volume image of the atria from a normal sheep heart was acquired using serial surface macroscopy, then smoothed and down-sampled to 50 μm(3) resolution. Atrial surface geometry was identified and myofiber orientations were estimated throughout by eigen-analysis of the 3-D image structure tensor. Sinus node, crista terminalis, pectinate muscle, Bachman's bundle, and pulmonary veins were segmented on the basis of anatomic characteristics. Heterogeneous electrical properties were assigned to this structure and electrical activation was simulated on it at 100 μm(3) resolution, using both biophysically-detailed and reduced-order cell activation models with spatially-varying membrane kinetics. We confirmed that the model reproduced key features of the normal spread of atrial activation. Furthermore, we demonstrate that vulnerability to rhythm disturbance caused by structural heterogeneity in the posterior left atrium is exacerbated by spatial variation of repolarization kinetics across this region. These results provide insight into mechanisms that may sustain paroxysmal atrial fibrillation. We conclude that image-based computer models that incorporate realistic descriptions of atrial myofiber architecture and electrophysiologic properties have the potential to analyse and identify complex substrates for atrial fibrillation.

Three‐dimensional Integrated Functional, Structural, and Computational Mapping to Define the Structural “Fingerprints” of Heart‐Specific Atrial Fibrillation Drivers in Human Heart Ex Vivo

“…The computed atrial wall thickness in the left atrial appendage was found to be affected by the extremely complex and trabecular atrial anatomy,30 and thus wall thickness of the left atrial appendage was not reported. The atrial cellular activation model is based on a simplified Fenton‐Karma model, not biophysics‐based cellular models10, 12 for the sake of computational efficiency, although it was validated by optical mapping data in this study and widely used by us15, 27 and others 28. Additionally, because of a single uniform cellular model used across the atria in the computer model, APDs in some regions (eg, distal side of PV sleeves) may not match well between modeling and optical mapping.…”

“…The first complete quantitative description of whole intact sheep atria myofiber architecture was done using serial surface imaging and 3D structure tensor analysis 15, 27. The structure tensor approach was extended to explanted human atria imaged by our recent studies using CE‐MRI,8 and micro–computed tomography19 proved to be as robust an approach as diffusion tensor imaging 20.…”

“…The spread of electrical activation in the realistic 3D human atrial geometry can be simulated by solving the cardiac monodomain equation using a voxel‐based finite difference solver 10, 27. In this study, we have adapted the simplified 3‐current Fenton‐Karma cellular activation models to recreate the optically recorded regional conduction velocities and action potential durations (APDs) in the PLA region from the same heart, which was then applied across both atria of the model (Figure 8).…”

Changes in Global and Regional Mechanics Due to Atrial Fibrillation: Insights from a Coupled Finite-Element and Circulation Model

“…Another limitation is the use of a simplified fiber structure. Zhao and coworkers have recently incorporated their detailed atrial fiber orientation data directly into electrophysiologic models 38 , while other groups have utilized rule-based algorithms to generate detailed atrial fiber structures 8 ; incorporating similarly detailed fiber geometries into our FEM could potentially improve the accuracy of predictions in some regions. More broadly, the model presented here was constructed and validated using data from paroxysmal AF, a relatively mild form of the disease characterized by intermittent bouts of fibrillation; we chose to focus on these patients because it was possible to obtain MRI and hemodynamic data during periods when the atrium was not actively fibrillating.…”

“…Published anatomic 17 and histologic 38 studies suggest that muscle fiber orientations in the left atrium do not vary smoothly from region to region or across the thickness of the wall as in the left ventricle. Furthermore, these studies show that fibers are oriented close to the circumferential or longitudinal direction in many regions of the atrium.…”