Abstract 19328: Postnatal Formation of Myocardial Laminar-Sheet Architecture in New Born Pig Hearts
Myocardial fiber and laminar sheet architecture is a critical determinant of coordinated cardiac contractile function. We hypothesized that myofiber and sheets may reorganize after birth to accommodate programmed perinatal adaptations of cardiac function. Isolated fixed pig hearts at postnatal day 1, day 5, day 14, and adulthood (n = 5 for each group) were acquired for diffusion-weighted magnetic resonance imaging to determine cardiomyocyte fiber angle and sheet structure in the left ventricular free wall using previously reported methods. Finally, hearts were prepared for histology analysis of sheet architecture. A progressive increase in left ventricular wall thickness occurred from day 1 (4.8±0.2 mm) to adulthood (22±4 mm, p < 0.05). However, the transmural distribution of helix angle (fiber architecture) was comparable at all ages (p = N.S.). In contrast, fractional anisotropy decreased progressively from day 1 (0.71±0.05) to adulthood (0.28 ±0.29, p < 0.05), which was caused by increased cross-fiber water diffusivity (0.25 ± 0.04 μm2/ms at day 1 vs. 0.55±0.05 μm2/ms at day 5, p < 0.05). The expected laminar sheet cleavage (white spaces) was not detectable at day 1, but became visually appreciable after day 5 (Figure ). In summary, the helical myofiber architecture appeared well developed at birth but unchanged thereafter. However, the higher order laminar sheet architecture did not emerge until after birth. The postnatal formation of laminar sheets appears to play a critical role in physiological remodeling of new born hearts to accommodate the an abrupt increase of left ventricular workload after the closing of patent ductus arteriosus and foramen ovale, which bypassed the right ventricular output to systemic circulation in prenatal hearts. .
- © 2012 by American Heart Association, Inc.