Diffusion MRI tractography of the developing human fetal heart

Area of Science:

• Cardiovascular Development
• Biomedical Imaging
• Cardiac Anatomy

Background:

• The human heart exhibits a complex 3D myocardial fiber pattern.
• The developmental timing of this anisotropic pattern in fetal life is not well understood.
• The structural maturity of the heart at birth requires further investigation.

Purpose of the Study:

• To characterize the evolution of cardiac fiber architecture in the developing human fetal heart.
• To utilize diffusion tensor MRI (DTI) tractography for this investigation.
• To determine when fetal hearts develop anisotropy and if they are structurally mature at birth.

Main Methods:

• Diffusion tensor MRI (DTI) tractography was applied to human fetal hearts (10-19 weeks gestation).
• Control hearts included a neonate and an adult.
• Myocardial anisotropy was quantified using the fractional anisotropy (FA) index, and fiber tracts were generated.

Main Results:

• Fetal hearts were highly isotropic with poorly resolved tracts from 10-14 weeks gestation.
• Anisotropy development, similar to adult hearts, was observed between 14-19 weeks.
• By 19 weeks, coherent fiber tracts were resolved, but the myocardium remained weakly anisotropic with a low FA and no discernible sheet structure.

Conclusions:

• The human fetal heart is largely isotropic until 14-19 weeks gestation, followed by cardiomyocyte self-alignment into tracts.
• This alignment process occurs 2-3 months after cardiac contraction onset and may be crucial for cardiomyocyte maturation.
• DTI did not reveal a connective tissue scaffold guiding this development; the sheet structure matures late in gestation and postnatally.