Novel micro-computed tomography contrast agents to visualise the human cardiac conduction system and surrounding structures in hearts from normal, aged, and obese individuals

The cardiac conduction system (CCS) regulates electrical impulses across the heart and cardiac arrhythmias cause structural remodelling of the CCS. Since its discovery over a century ago, the precise anatomy and differences between the human CCS in healthy, aged, and obese human hearts has remained relatively unknown. Using iodine potassium-iodide (I 2 KI) and graphene oxide (GO) as contrast agents for high-resolution micro-computed tomography (micro-CT), we explored and identified the anatomies of whole healthy, aged, and obese hearts, including their CCS. Human specimens were obtained from 5 post-mortem hearts, under local ethical rules and stored in the Dobrzynski laboratory, under the Human Tissue Act 2004. Specimens were stained with I 2 KI or GO contrast agents before scanning with micro-CT. Data obtained from micro-CT was uploaded onto Amira v6.5 software for analysis, 3-dimensional reconstructions, and segmentation of relevant structures. Following micro-CT analyses, tissue blocks were cryosectioned and stained for histological assessments. There are obvious anatomical structural differences between the healthy, aged and obese hearts. Compared to the healthy heart, the aged heart and obese heart had larger chambers; thicker myocardial walls; thicker blood vessels; more extensive nodal regions and connective tissue; more epicardial fat; and fewer Purkinje fibres. Our use of I 2 KI and GO as contrast agents for high-resolution micro-CT scanning contribute to - and expands - the current understanding of CCS structural variations between healthy, aged and obese human hearts.These current and novel techniques can have key impacts on our anatomical understandings for current treatments for cardiovascular disease and the development of mathematical models of aged and diseased hearts. Thus ultimately aiding in the reduction of cardiac morbidities and reduction of patient death rate. • Graphene oxide is a novel contrast agent for high-resolution micro-computed tomography scanning to visualise fat within and surrounding cardiac tissue. • Iodine potassium-iodide is a contrast agent for high-resolution micro-computed tomography scanning to various structures within and around cardiac tissue. • 3-dimensional reconstruction and segmentation of whole hearts, blood vessels and other relevant structures from the normal, aged, and obese hearts showed interesting anatomical differences. • Compared to the healthy heart, the aged heart and obese heart had larger chambers; thicker myocardial walls; thicker blood vessels; more extensive nodal regions and connective tissue; more epicardial fat; and fewer Purkinje fibres. • Number of coronary arteries reduces in the aged and obese hearts, and their thickness increases, compared to the normal hearts'.