Region-Specific Microstructure in the Neonatal Ventricles of a Porcine Model

Abstract

The neonate transitions from placenta-derived oxygen, to supply from the pulmonary system, moments after birth. This requires a series of structural developments to divert more blood through the right heart and onto the lungs, with the tissue quickly remodelling to the changing ventricular workload. In some cases, however, the heart structure does not fully develop causing poor circulation and inefficient oxygenation, which is associated with an increase in mortality and morbidity. This study focuses on developing an enhanced knowledge of the 1-day old heart, quantifying the region-specific microstructural parameters of the tissue. This will enable more accurate mathematical and computational simulations of the young heart. Hearts were dissected from 12, 1-day-old deceased Yorkshire piglets (mass: 2.1-2.4 kg, length: 0.38-0.51 m), acquired from a breeding farm. Evans blue dye was used to label the heart equator and to demarcate the left and right ventricle free walls. Two hearts were used for three-dimensional diffusion-tensor magnetic resonance imaging, to quantify the fractional anisotropy (FA). The remaining hearts were used for two-photon excited fluorescence and second-harmonic generation microscopy, to quantify the cardiomyocyte and collagen fibril structures within the anterior and posterior aspects of the right and left ventricles. FA varied significantly across both ventricles, with the greatest in the equatorial region, followed by the base and apex. The FA in each right ventricular region was statistically greater than that in the left. Cardiomyocyte and collagen fibre rotation was greatest in the anterior wall of both ventricles, with less dispersion when compared to the posterior walls. In defining these key parameters, this study provides a valuable insight into the 1-day-old heart that will provide a valuable platform for further investigation the normal and abnormal heart using mathematical and computational models.

Effect of myofibre architecture on ventricular pump function by using a neonatal porcine heart model: from DT-MRI to rule-based methods

“…It is expected that there are differences in myofibre structure between the porcine heart and the canine heart, but this is difficult to assess as we do not have measured DT-MRI fibre structure for the porcine heart. However, despite the species difference, we find that the mapped canine myofibre structure agrees well with other studies in terms of mean values [6,23,25] (table 1). For instance, Ahmad et al [25] measured myofibre rotation angles in LV free wall of neonatal hearts (anterior 51.1 ± 3.8°to −51.1 ± 3.8°and posterior 40.2 ± 2.9°to −40.2 ± 2.9°).…”

“…However, despite the species difference, we find that the mapped canine myofibre structure agrees well with other studies in terms of mean values [6,23,25] (table 1). For instance, Ahmad et al [25] measured myofibre rotation angles in LV free wall of neonatal hearts (anterior 51.1 ± 3.8°to −51.1 ± 3.8°and posterior 40.2 ± 2.9°to −40.2 ± 2.9°). Sack et al [6] reported fibre rotation angles for a normal adult porcine heart based on DT-MRI measurements (endocardium: 66.5 ± 16.6°, epicardium: −37.4 ± 22.4°).…”

“…When normalized by n f , the ratio between the sheet-normal and myofibre direction is 41%, which agrees with the ratio reported by Lin & Yin (40%) [38]. We further calculate the dispersion parameters from a recent study on neonatal porcine heart by Ahmad et al [25], n f = 0.68 and n n = 0.32 with nearly negligible n s ≈ 0.0009, again very close to our values in this study. We are not aware of any available experimental measurements for estimating n n and n s in the myocardium.…”

Current Understanding of the Biomechanics of Ventricular Tissues in Heart Failure

“…Sacks et al reported that the canine RV had greater anisotropy than the LV [17]. Similarly, Ahmad et al found that the neonatal porcine RV had significantly greater anisotropy than the LV in different anatomic regions [89]. However, Javani et al reported that the ovine LV was more anisotropic than the RV [44].…”

Modelling of fibre dispersion and its effects on cardiac mechanics from diastole to systole

“…Micro-structurally informed constitutive modelling in soft tissue has attracted tremendous interest in this area since its introduction in the 1970s [7]. With advanced imaging techniques, such as diffusion tensor magnetic resonance imaging, detailed three-dimensional (3D) fibre distribution for the whole organ, such as the heart, can be acquired in ex/in vivo [8,9]. Existed measurements have shown that fibres in myocardium are dispersed in space with a predominant mean fibre direction [8,10].…”