Abstract
BackgroundAccurate interpretations of cardiac functions require precise structural models of the myocardium, but the latter is not available always and for all species. Although scaling or substitution of myocardial fiber information from alternate species has been used in cardiac functional modeling, the validity of such practice has not been tested.MethodsFixed mouse (n = 10), rabbit (n = 6), and sheep (n = 5) hearts underwent diffusion tensor imaging (DTI). The myocardial structures in terms of the left ventricular fiber orientation helix angle index were quantitatively compared between the mouse rabbit and sheep hearts.ResultsThe results show that significant fiber structural differences exist between any two of the three species. Specifically, the subepicardial fiber orientation, and the transmural range and linearity of fiber helix angles are significantly different between the mouse and either rabbit or sheep. Additionally, a significant difference was found between the transmural helix angle range between the rabbit and sheep. Across different circumferential regions of the heart, the fiber orientation was not found to be significantly different.ConclusionsThe current study indicates that myocardial structural differences exist between different size hearts. An immediate implication of the present findings for myocardial structural or functional modeling studies is that caution must be exercised when extrapolating myocardial structures from one species to another.
Highlights
Accurate interpretations of cardiac functions require precise structural models of the myocardium, but the latter is not available always and for all species
By characterizing the anisotropy of water diffusion exerted by the molecular environment, cardiovascular magnetic resonance (CMR) diffusion tensor imaging (DTI) [14] has emerged as a viable alternative with the advantages of being non-destructive, relatively convenient, and inherently 3D
Myocardial fiber orientations obtained in representative mouse, rabbit and sheep heart specimens are visualized in Figure 3, which consists of falsecolor-coded fiber orientation helix angle maps, and fiber orientations of the same short-axis slice rendered as cylindrical rods viewed obliquely from an elevated angle
Summary
Accurate interpretations of cardiac functions require precise structural models of the myocardium, but the latter is not available always and for all species. Scaling or substitution of myocardial fiber information from alternate species has been used in cardiac functional modeling, the validity of such practice has not been tested. Because structures of the myocardium such as the fiber orientation play a deterministic role in its material properties and functional behaviours, accurate simulations of cardiac functions require precise anatomical models of the myocardium. Anatomy-based models of the myocardium have been used in computational studies of both electrophysiology [1,2] and mechanics [3,4,5] of the heart. Despite the significance of the information, measuring myocardial fiber orientation can be difficult, the key challenges being the small size (notably for the mouse) and availability of specimens (for humans). Applications of DTI on the human heart are largely limited to in vivo studies [16,17,18], which, due to technical limitations, continue to have relatively low spatial resolution and measurement quality
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