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

Abstract

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.

Keywords: Ventricular architecture; cardiomyocytes; cardiovascular imaging; multi-scale imaging; myocardium.

Figure 1

Spatial resolution of multi-scale cardiovascular imaging modalities, from animal to subcellular level. MRI, magnetic resonance imaging; micro-CT, micro-computed tomography; nano-CT, nano-computed tomography; X-PCI, X-ray phase contrast imaging. This figure was created using Servier Medical Art templates, which are licensed under a Creative Commons Attribution 3.0 Unported License; https://smart.servier.com.

Figure 2

Multi-scale imaging and analysis of cardiac tissue. (A) Schematic representation of multi-scale synchrotron-based acquisition pipeline. Synchrotrons generate coherent and brilliant X-ray beams, whose energy can be selected with a monochromator. The X-ray beam is then controlled and shaped by a shutter and slits to minimize the radiation deposited on the sample. After interacting with the rotating sample, X-rays are first detected by a low-resolution microscope. Then, regions of interested will be selected from such low-resolution scan and the microscope will be automatically displaced to allow measurements with a high-resolution microscope, thus achieving multi-scale imaging without sample manipulation; (B) diagram showing the multi-scale quantitative image analysis. Low-resolution data is used to extract information on the macro-structure of the heart, such as the trabeculations, vasculature or myocyte orientation. High-resolution data is, in turn, used to analyze micro-structural components such as the collagen matrix, micro-vasculature or even individual myocytes.