Assessing the impact of fiber orientation in myocardial passive stiffness estimation

Left ventricular passive myocardial stiffness is a valuable biomarker for early dectection of heart failure. Patient-specific finite element models are promising non-invasive tools for estimating this stiffness, using an inverse optimization approach. Implementation of the model requires the definition of cardiac fiber orientation. Traditionally, a linear helix angle distribution from 60◦ at endocardium to−60◦ at epicardium, with zero transverse angle, is assumed. However, in-vivo Diffusion Tensor Imaging (DTI) offers more accurate, patient-specific fiber data, though full integration of personalized fiber architecture remains challenging. This study investigates how fiber orientation affects myocardial stiffness estimation. Three patient-specific models were developed to assess mechanical behavior during passive inflation and to estimate stiffness through inverse optimization. Variations in helix angle range, both globally and by cardiac sector, were tested, as well as changes in transmural distribution and non-zero transverse angles. Additionally, in-vivo DTI data from single slices were wrapped onto the models to compare mechanical responses. This study revealed an increase in stress and strain values caused by more circularly-aligned fibers, and change in the ventricular motion during inflation. No cardiac sector stood out for greater or lesser impact. Transverse angle showed minimal impact. Stiffness estimates showed clear variations between DTI-slice-based reconstructions, but no significant difference with the reference orientation. Deviations observed with estimates during exercise are comparable to those at rest. These findings are intended to guide the selection of an appropriate fiber modeling strategy, balancing ease of implementation with accuracy of stiffness estimate, and improve the biomarker’s clinical utility.