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Development of an anatomically detailed MRI-derived rabbit ventricular model and assessment of its impact on simulations of electrophysiological function.

Bishop MJ, Plank G, Burton RA, Schneider JE, Gavaghan DJ, Grau V, Kohl P - Am. J. Physiol. Heart Circ. Physiol. (2009)

Bottom Line: Simulation results were compared with those from a simplified model built from the same images but excluding finer anatomical features (vessels/endocardial structures).Postshock, these differences resulted in the genesis of new excitation wavefronts that were not observed in more simplified models.In conclusion, structurally simplified models are well suited for a large range of cardiac modeling applications.

View Article: PubMed Central - PubMed

Affiliation: University of Oxford Computing Laboratory, Parks Road, Oxford OX1 3QD, UK. martin.bishop@comlab.ox.ac.uk

ABSTRACT
Recent advances in magnetic resonance (MR) imaging technology have unveiled a wealth of information regarding cardiac histoanatomical complexity. However, methods to faithfully translate this level of fine-scale structural detail into computational whole ventricular models are still in their infancy, and, thus, the relevance of this additional complexity for simulations of cardiac function has yet to be elucidated. Here, we describe the development of a highly detailed finite-element computational model (resolution: approximately 125 microm) of rabbit ventricles constructed from high-resolution MR data (raw data resolution: 43 x 43 x 36 microm), including the processes of segmentation (using a combination of level-set approaches), identification of relevant anatomical features, mesh generation, and myocyte orientation representation (using a rule-based approach). Full access is provided to the completed model and MR data. Simulation results were compared with those from a simplified model built from the same images but excluding finer anatomical features (vessels/endocardial structures). Initial simulations showed that the presence of trabeculations can provide shortcut paths for excitation, causing regional differences in activation after pacing between models. Endocardial structures gave rise to small-scale virtual electrodes upon the application of external field stimulation, which appeared to protect parts of the endocardium in the complex model from strong polarizations, whereas intramural virtual electrodes caused by blood vessels and extracellular cleft spaces appeared to reduce polarization of the epicardium. Postshock, these differences resulted in the genesis of new excitation wavefronts that were not observed in more simplified models. Furthermore, global differences in the stimulus recovery rates of apex/base regions were observed, causing differences in the ensuing arrhythmogenic episodes. In conclusion, structurally simplified models are well suited for a large range of cardiac modeling applications. However, important differences are seen when behavior at microscales is relevant, particularly when examining the effects of external electrical stimulation on tissue electrophysiology and arrhythmia induction. This highlights the utility of histoanatomically detailed models for investigations of cardiac function, in particular for future patient-specific modeling.

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Tetrahedral finite-element rabbit ventricular mesh. A: visualization of the final ventricular finite-element mesh from a standard anterior view (left) along with cuts along the frontal (middle) and transveral (right) planes to expose endocardial structures. B: highlighted region from an exposed clipping plane in a posterior view demonstrating the level of detail in the finite-element mesh on the endocardial surfaces. C: cut along a frontal clipping plane in a posterior view showing the tagged structures of the papillary muscles (green) and valves or cordae tendinae (blue). Note that the valves do not retain their in vivo shape due to the preparation of the heart. D: simplified rabbit ventricular finite-element model shown from a standard anterior view (left) along with cuts along frontal (middle) and transverse (right) clipping planes. The helix angle α and vectors z, u, v, and af (defining the global apex-base, transmural, circumferential, and fiber directions, respectively) were used in the calculation of fiber orientation explained in Incorporation of Fiber Orientation Information.
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Figure 4: Tetrahedral finite-element rabbit ventricular mesh. A: visualization of the final ventricular finite-element mesh from a standard anterior view (left) along with cuts along the frontal (middle) and transveral (right) planes to expose endocardial structures. B: highlighted region from an exposed clipping plane in a posterior view demonstrating the level of detail in the finite-element mesh on the endocardial surfaces. C: cut along a frontal clipping plane in a posterior view showing the tagged structures of the papillary muscles (green) and valves or cordae tendinae (blue). Note that the valves do not retain their in vivo shape due to the preparation of the heart. D: simplified rabbit ventricular finite-element model shown from a standard anterior view (left) along with cuts along frontal (middle) and transverse (right) clipping planes. The helix angle α and vectors z, u, v, and af (defining the global apex-base, transmural, circumferential, and fiber directions, respectively) were used in the calculation of fiber orientation explained in Incorporation of Fiber Orientation Information.

Mentions: Figure 4 shows the final ventricular mesh. Here, and throughout, Meshalzyer software (carp.meduni-graz.at/) was used for finite-element visualization. Figure 4A shows a standard anterior view of the outer (epicardial) surface of the mesh (left) along with cuts along both frontal (middle) and transverse (right) clipping planes to expose transmural and endocardial structures. Notable features include the large blood vessels close to the epicardial surface and within the midmyocardium as well as the papillary muscles and valves. Figure 4B shows a zoomed-in region of the interior of the LV (in a posterior to frontal view), where the triangular faces of the intracellular finite-element mesh are shown in blue, highlighting the level of detail with which the complex endocardial surfaces are defined. Finally, segmentation tags that were used to label the different regions in the heart were directly transferred from the regular image stack to the unstructured grid. These tags can be subsequently used to define electrophysiological properties on a per region basis. Figure 4C shows tagged structures such as the papillary muscles (green) and valves or cordae tendinae (blue) in a cut along a frontal clipping plane (posterior view) to enable the visualization of important endocardial structures. For the computation of electrical activity within the ventricles, an additional high-resolution mesh was constructed in which the valves were removed from the tagged image stack before meshing, as the valves are considered electrically silent. This mesh is available for download via the online Supplemental Material.


Development of an anatomically detailed MRI-derived rabbit ventricular model and assessment of its impact on simulations of electrophysiological function.

Bishop MJ, Plank G, Burton RA, Schneider JE, Gavaghan DJ, Grau V, Kohl P - Am. J. Physiol. Heart Circ. Physiol. (2009)

Tetrahedral finite-element rabbit ventricular mesh. A: visualization of the final ventricular finite-element mesh from a standard anterior view (left) along with cuts along the frontal (middle) and transveral (right) planes to expose endocardial structures. B: highlighted region from an exposed clipping plane in a posterior view demonstrating the level of detail in the finite-element mesh on the endocardial surfaces. C: cut along a frontal clipping plane in a posterior view showing the tagged structures of the papillary muscles (green) and valves or cordae tendinae (blue). Note that the valves do not retain their in vivo shape due to the preparation of the heart. D: simplified rabbit ventricular finite-element model shown from a standard anterior view (left) along with cuts along frontal (middle) and transverse (right) clipping planes. The helix angle α and vectors z, u, v, and af (defining the global apex-base, transmural, circumferential, and fiber directions, respectively) were used in the calculation of fiber orientation explained in Incorporation of Fiber Orientation Information.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2822578&req=5

Figure 4: Tetrahedral finite-element rabbit ventricular mesh. A: visualization of the final ventricular finite-element mesh from a standard anterior view (left) along with cuts along the frontal (middle) and transveral (right) planes to expose endocardial structures. B: highlighted region from an exposed clipping plane in a posterior view demonstrating the level of detail in the finite-element mesh on the endocardial surfaces. C: cut along a frontal clipping plane in a posterior view showing the tagged structures of the papillary muscles (green) and valves or cordae tendinae (blue). Note that the valves do not retain their in vivo shape due to the preparation of the heart. D: simplified rabbit ventricular finite-element model shown from a standard anterior view (left) along with cuts along frontal (middle) and transverse (right) clipping planes. The helix angle α and vectors z, u, v, and af (defining the global apex-base, transmural, circumferential, and fiber directions, respectively) were used in the calculation of fiber orientation explained in Incorporation of Fiber Orientation Information.
Mentions: Figure 4 shows the final ventricular mesh. Here, and throughout, Meshalzyer software (carp.meduni-graz.at/) was used for finite-element visualization. Figure 4A shows a standard anterior view of the outer (epicardial) surface of the mesh (left) along with cuts along both frontal (middle) and transverse (right) clipping planes to expose transmural and endocardial structures. Notable features include the large blood vessels close to the epicardial surface and within the midmyocardium as well as the papillary muscles and valves. Figure 4B shows a zoomed-in region of the interior of the LV (in a posterior to frontal view), where the triangular faces of the intracellular finite-element mesh are shown in blue, highlighting the level of detail with which the complex endocardial surfaces are defined. Finally, segmentation tags that were used to label the different regions in the heart were directly transferred from the regular image stack to the unstructured grid. These tags can be subsequently used to define electrophysiological properties on a per region basis. Figure 4C shows tagged structures such as the papillary muscles (green) and valves or cordae tendinae (blue) in a cut along a frontal clipping plane (posterior view) to enable the visualization of important endocardial structures. For the computation of electrical activity within the ventricles, an additional high-resolution mesh was constructed in which the valves were removed from the tagged image stack before meshing, as the valves are considered electrically silent. This mesh is available for download via the online Supplemental Material.

Bottom Line: Simulation results were compared with those from a simplified model built from the same images but excluding finer anatomical features (vessels/endocardial structures).Postshock, these differences resulted in the genesis of new excitation wavefronts that were not observed in more simplified models.In conclusion, structurally simplified models are well suited for a large range of cardiac modeling applications.

View Article: PubMed Central - PubMed

Affiliation: University of Oxford Computing Laboratory, Parks Road, Oxford OX1 3QD, UK. martin.bishop@comlab.ox.ac.uk

ABSTRACT
Recent advances in magnetic resonance (MR) imaging technology have unveiled a wealth of information regarding cardiac histoanatomical complexity. However, methods to faithfully translate this level of fine-scale structural detail into computational whole ventricular models are still in their infancy, and, thus, the relevance of this additional complexity for simulations of cardiac function has yet to be elucidated. Here, we describe the development of a highly detailed finite-element computational model (resolution: approximately 125 microm) of rabbit ventricles constructed from high-resolution MR data (raw data resolution: 43 x 43 x 36 microm), including the processes of segmentation (using a combination of level-set approaches), identification of relevant anatomical features, mesh generation, and myocyte orientation representation (using a rule-based approach). Full access is provided to the completed model and MR data. Simulation results were compared with those from a simplified model built from the same images but excluding finer anatomical features (vessels/endocardial structures). Initial simulations showed that the presence of trabeculations can provide shortcut paths for excitation, causing regional differences in activation after pacing between models. Endocardial structures gave rise to small-scale virtual electrodes upon the application of external field stimulation, which appeared to protect parts of the endocardium in the complex model from strong polarizations, whereas intramural virtual electrodes caused by blood vessels and extracellular cleft spaces appeared to reduce polarization of the epicardium. Postshock, these differences resulted in the genesis of new excitation wavefronts that were not observed in more simplified models. Furthermore, global differences in the stimulus recovery rates of apex/base regions were observed, causing differences in the ensuing arrhythmogenic episodes. In conclusion, structurally simplified models are well suited for a large range of cardiac modeling applications. However, important differences are seen when behavior at microscales is relevant, particularly when examining the effects of external electrical stimulation on tissue electrophysiology and arrhythmia induction. This highlights the utility of histoanatomically detailed models for investigations of cardiac function, in particular for future patient-specific modeling.

Show MeSH
Related in: MedlinePlus