MR study of postnatal development of myocardial structure and left ventricular function.

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. (c) 2009 Wiley-Liss, Inc.