How to choose myofiber orientation in a biventricular finite element model?

Biventricular (BiV) finite element (FE) models of cardiac electromechanics are evolving to a state where they can assist in clinical decision making. Carefully designed patient-specific geometries are combined with generic myofiber orientation data, because of lack of accurate techniques to measure myofiber orientation. However, it remains unclear to what extent the assumption of a generic myofiber orientation influences predictions on cardiac function from BiV FE models. As an alternative approach, it was suggested to let the myofiber orientation adapt in response to fiber cross-fiber shear. The aim of this study was to investigate to what extent variations in myofiber orientation as induced by adaptive myofiber reorientation caused variations in global stroke work in a BiV FE model and whether the adaptation model could be used as an alternative approach to prescribe the myofiber orientation in these models. An average change in myofiber orientation over an angle of about 8., predominantly in transmural direction, resulted in a 91% increase of LV and 20% increase of RV stroke work. These findings indicate the importance for a more thorough effort to address a realistic myofiber orientation. The currently used model for adaptive myofiber reorientation seems a useful approach to prescribe the myofiber orientations in BiV FE models.