Purpose: To investigate postnatal development of left ventricular (LV) cardiac function and myocardium structure.
Materials and methods: In vivo cardiac MR and ex vivo diffusion tensor imaging (DTI) were performed in normal Sprague-Dawley rats at postnatal day 2, 4, 7, 14, 21, 28, and 56 (N = 6 per group).
Results: Morphologically, LV size increased with age. Functionally, stroke volume and cardiac output increased. Heart rate increased gradually and became stable after day 14. On average, ejection fraction increased within the first 4 days, decreased at day 7, gradually increased until day 21, and became stable afterward. Structurally, double-helical myocardial structure was found as early as day 2. Myocardial fiber parameters, described by fractional anisotropy, mean apparent diffusion coefficient, and axial diffusivity, increased within the first 4 days. Then radial diffusivity increased until day 7 while other parameters decreased up to day 56.
Conclusion: Postnatal heart development was documented by MRI. DTI findings are in agreement with the two known stages of early postnatal growth: hyperplasia and hypertrophy. These results can serve as the baselines for study of postnatal heart developmental abnormalities. They also demonstrate the ability of DTI to reveal microstructural alterations in myocardium.
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