Cardiac multi-scale investigation of the right and left ventricle ex vivo: a review

The heart is a complex multi-scale system composed of components integrated at the subcellular, cellular, tissue and organ levels. The myocytes, the contractile elements of the heart, form a complex three-dimensional (3D) network which enables propagation of the electrical signal that triggers the contraction to efficiently pump blood towards the whole body. Cardiovascular diseases (CVDs), a major cause of mortality in developed countries, often lead to cardiovascular remodeling affecting cardiac structure and function at all scales, from myocytes and their surrounding collagen matrix to the 3D organization of the whole heart. As yet, there is no consensus as to how the myocytes are arranged and packed within their connective tissue matrix, nor how best to image them at multiple scales. Cardiovascular imaging is routinely used to investigate cardiac structure and function as well as for the evaluation of cardiac remodeling in CVDs. For a complete understanding of the relationship between structural remodeling and cardiac dysfunction in CVDs, multi-scale imaging approaches are necessary to achieve a detailed description of ventricular architecture along with cardiac function. In this context, ventricular architecture has been extensively studied using a wide variety of imaging techniques: ultrasound (US), optical coherence tomography (OCT), microscopy (confocal, episcopic, light sheet, polarized light), magnetic resonance imaging (MRI), micro-computed tomography (micro-CT) and, more recently, synchrotron X-ray phase contrast imaging (SR X-PCI). Each of these techniques have their own set of strengths and weaknesses, relating to sample size, preparation, resolution, 2D/3D capabilities, use of contrast agents and possibility of performing together with in vivo studies. Therefore, the combination of different imaging techniques to investigate the same sample, thus taking advantage of the strengths of each method, could help us to extract the maximum information about ventricular architecture and function. In this review, we provide an overview of available and emerging cardiovascular imaging techniques for assessing myocardial architecture ex vivo and discuss their utility in being able to quantify cardiac remodeling, in CVDs, from myocyte to whole organ

Quantification of the detailed cardiac left ventricular trabecular morphogenesis in the mouse embryo

During embryogenesis, a mammalian heart develops from a simple tubular shape into a complex 4-chamber organ, going through four distinct phases: early primitive tubular heart, emergence of trabeculations, trabecular remodeling and development of the compact myocardium. In this paper we propose a framework for standardized and subject-independent 3D regional myocardial complexity analysis, applied to analysis of the developmentevolution of the mouse left ventricle. We propose a standardized subdivision of the myocardium into 3D overlapping regions (in our case 361) and a novel visualization of myocardial complexity, whereupon we: 1) extend the fractal dimension, commonly applied to image slices, to 3D and 2) use volume occupied by the trabeculations in each region together with their surface area, in order to quantify myocardial complexity. The latter provides an intuitive characterization of the complexity, given that compact myocardium will tend to occupy a larger volume with little surface area while high surface area with low volume will correspond to highly trabeculated areas. Using 50 mouse embryo images at 5 di erent gestational ages (10 subjects per gestational age), we demonstrate how the proposed representation and complexity measures describe the developmentevolution of LV myocardial complexity. The mouse embryo data was acquired using high resolution episcopic microscopy. The complexity analysis per region was carried out using: 3D fractal dimension, myocardial volume, myocardial surface area and ratio between the two. The analysis of gestational ages was performed on embryos of 14.5, 15.5, 16.5, 17.5 and 18.5 embryonic days, and demonstrated that the regional complexity of the trabeculations increases longitudinally from the base to the apex, with a maximum around the middle. The overall complexity decreases with gestational age, being most complex at 14.5. Circumferentially, at ages 14.5, 15.5 and 16.5, the trabeculations show similar complexity everywhere except for the anteroseptal and inferolateral area of the wall, where it is smaller. At 17.5 days, the regions of high complexity become more localized towards the inferoseptal and anterolateral parts of the wall. At 18.5 days, the high complexity area exhibits further localization at the inferoseptal and anterior part of the wall.B. Paun is supported by the grant FI-DGR 2014 (2014 FI B01238) from the Generalitat de Catalunya. The research leading to these results has received funding from the EU FP7 for research, technological development and demonstration under grant agreement VP2HF (no. 611823) and from the Spanish Ministry of Economy and Competitiveness (grant TIN2011-28067, TIN2014-52923-R, the Maria de Maeztu Units of Excellence Programme MDM-2015-0502) and FEDER. C. Butakoff is supported by the grant from the Fundació La Marató de TV3 (20154031), Spain. The HREM datasets used in this manuscript were provided and collected by Dr. T. J. Mohun, Emily Hardman and Fabrice Prin from the Francis Crick Institute, London

Quantification of the detailed cardiac left ventricular trabecular morphogenesis in the mouse embryo

During embryogenesis, a mammalian heart develops from a simple tubular shape into a complex 4-chamber organ, going through four distinct phases: early primitive tubular heart, emergence of trabeculations, trabecular remodeling and development of the compact myocardium. In this paper we propose a framework for standardized and subject-independent 3D regional myocardial complexity analysis, applied to analysis of the developmentevolution of the mouse left ventricle. We propose a standardized subdivision of the myocardium into 3D overlapping regions (in our case 361) and a novel visualization of myocardial complexity, whereupon we: 1) extend the fractal dimension, commonly applied to image slices, to 3D and 2) use volume occupied by the trabeculations in each region together with their surface area, in order to quantify myocardial complexity. The latter provides an intuitive characterization of the complexity, given that compact myocardium will tend to occupy a larger volume with little surface area while high surface area with low volume will correspond to highly trabeculated areas. Using 50 mouse embryo images at 5 di erent gestational ages (10 subjects per gestational age), we demonstrate how the proposed representation and complexity measures describe the developmentevolution of LV myocardial complexity. The mouse embryo data was acquired using high resolution episcopic microscopy. The complexity analysis per region was carried out using: 3D fractal dimension, myocardial volume, myocardial surface area and ratio between the two. The analysis of gestational ages was performed on embryos of 14.5, 15.5, 16.5, 17.5 and 18.5 embryonic days, and demonstrated that the regional complexity of the trabeculations increases longitudinally from the base to the apex, with a maximum around the middle. The overall complexity decreases with gestational age, being most complex at 14.5. Circumferentially, at ages 14.5, 15.5 and 16.5, the trabeculations show similar complexity everywhere except for the anteroseptal and inferolateral area of the wall, where it is smaller. At 17.5 days, the regions of high complexity become more localized towards the inferoseptal and anterolateral parts of the wall. At 18.5 days, the high complexity area exhibits further localization at the inferoseptal and anterior part of the wall.B. Paun is supported by the grant FI-DGR 2014 (2014 FI B01238) from the Generalitat de Catalunya. The research leading to these results has received funding from the EU FP7 for research, technological development and demonstration under grant agreement VP2HF (no. 611823) and from the Spanish Ministry of Economy and Competitiveness (grant TIN2011-28067, TIN2014-52923-R, the Maria de Maeztu Units of Excellence Programme MDM-2015-0502) and FEDER. C. Butakoff is supported by the grant from the Fundació La Marató de TV3 (20154031), Spain. The HREM datasets used in this manuscript were provided and collected by Dr. T. J. Mohun, Emily Hardman and Fabrice Prin from the Francis Crick Institute, London

Quantifying heart development

This thesis presents a series of papers on quantified heart development. It contains an atlas of human embryonic heart development, covering the first 8 weeks after conception. This atlas gives graphs of growth in size and volume of the various cardiac compartments. Such measures are still scarce in literature as illustrated in a review about ventricular wall development. The atlas also shows that by quantification of growth, new insights in developmental processes, such as sinus venosus incorporation can be gained. It, together with a series of ventricular wall growth curves covering foetal development, illustrates that a hypertrabeculated ventricle is the result of differential growth rather than a failure of compaction as has been presumed to underlie left ventricular non-compaction cardiomyopathy. Additionally, this thesis shows that trabecular myocardium is not necessarily weaker or ill-adapted to force generation compared to the compact wall as is assumed to be the case in aforementioned cardiomyopathy. Furthermore, quantification of atrioventricular canal growth on foetal ultrasounds lend support to the theory that aberrant atrioventricular canal development can lead to tricuspid valve agenesis. Finally, this thesis shows that there is a role for comparative anatomy, in a broader sense than just mouse and chicken, in understanding mammalian and human heart development by comparing a series of bird hearts from different species