Development of the fetal myocardium and changes in myocardial fibers orientation

Figures

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  Fig 1. Sagittal slices for assessment of layer thickness and fiber’s orientation. On the top, specimen in a 16 weeks of gestation fetus: the longitudinal endocardial layer is well represented (yellow line), the radial fibers are about 40% of the total wall thickness (red line), while the longitudinal epicarial layer was thin. The epicardial longitudinal layer progressively increased over the gestational weeks (in the middle, 27 weeks of gestation fetus, bottom, 40 weeks of gestation fetus).

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  Fig 2. The ventricular myocardium was divided into seven layers to model the transmural variation of fiber orientation (A). Each layer contains fibers oriented according to the angles measured by histology across the myocardium thickness (b1: epicardial layer, b2: mesocardium, b3: endocardial layer). Since fiber angles vary with gestational age, three models were developed for 20, 30 and 40-week-old fetuses (see Figs 7 and 8).

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  Fig 3. Speckle tracking echocardiography. On the top, left ventricular strain curves. Bottom, plots of endocardial longitudinal strain values (a), epicardial longitudinal strain values (b), and epicardial to endocardial longitudinal strain ratio (c) at different gestational ages.

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  Fig 4. On the top, strain rate curves with S, E and A peaks. Bottom, strain rate plots at different gestational ages: systolic peak (a), early diastolic peak (b), active atrial contraction peak (c) and early diastolic to atrial contraction peak ratio (d).

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  Fig 5. Left ventricular end diastolic diameter (a), left ventricular wall thickness (as mean of basal septum and basal lateral wall end diastolic thickness) (b), and left ventricular end diastolic volume (c) [in logarithmic scale] at different gestational ages.

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  Fig 6. Relative wall thickness of endocardial (a), epicardial (b) and mesocardium (c) by histological evaluation. The proportion of trabeculated myocardium (d) remained unchanged during gestational age.

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  Fig 7. Endocardial to epicardial wall thickness ratio by histology. There was a progressive increase over gestational weeks (GW).

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  Fig 8. Changes in fibers’ angulation during gestational age based on histology. The myocardium was divided in seven layers. Layers from 1 to 3 (dashed lines) represent endocardial layers, layer 4 (continue line) is the mesocardial layer, the layers 5 to 7 (dotted lines) become epicardial layer.