Unraveling changes in myocardial contractility during human fetal growth: A finite element analysis based on in vivo ultrasound measurements

Knowledge of normal fetal heart (FH) performance and development is crucial for evaluating and understanding how various congenital heart lesions may modify heart contractility during the gestational period. However, since biomechanical models of FH are still lacking, structural approaches proposed to describe the mechanical behavior of the adult human heart cannot be used to model the evolution of the FH. In this paper, a finite element model of the healthy FH wall is developed to quantify its mechanical properties during the gestational period. An idealized thickwalled ellipsoidal shape was used to model the left ventricle (LV). The diastolic LV geometry was reconstructed from in vivo ultrasound measurements performed on 24 normal FHs between 20 and 37 weeks of gestation. An anisotropic hyperelastic constitutive law describing the mechanical properties of the passive and active myocardium was used. The evolution of the mechanical properties of the normal LV myocardium during fetal growth was obtained by successfully fitting the ejection fraction predicted by the model to in vivo measurements. We found that only the active tension varies significantly during the gestational period, increasing linearly from 20 kPa (at 20 weeks) to 40 kPa (at 37 weeks of gestation). We propose a possible explanation of the increasing force-generating ability of the myocardial tissue during fetal heart development based on a combination of myocyte enlargement, differentiation, and proliferation kinetics.