Links between wall shear stress topological skeleton and imaging markers of early atherosclerosis at the carotid artery

Cardiovascular diseases are still the leading cause of death globally. Atherosclerosis, one of the most diffused, consists in the formation of plaques between intima and media layers of the vessel wall. Since this disease develops silently until the vessel lumen is severely narrowed, it is capitally important predicting its onset, which depends on systemic, biological and hemodynamical factors. In particular, haemodynamics and geometry play a localizing role in atherosclerotic lesion formation. In fact, in the arterial tree, atherosclerotic plaques tend to develop at specific sites, characterized by complex geometries and complex blood flow patterns. One of these preferential sites is the carotid artery bifurcation. For many years, low and oscillatory Wall Shear Stress (WSS) acting on the endothelial cells have been recognized as the main indices of disturbed flow promoting atherosclerosis onset and progression; however, this theory has been recently questioned: new studies highlight how low and oscillatory WSS are significant, but only moderate predictors of plaques localization. In this context, new indicators have been explored: among them, WSS topological skeleton descriptors are receiving increasing interest. The WSS topological skeleton is composed by fixed points and contraction/expansion regions linking fixed points. The interest in WSS topological skeleton analysis arises from its ability to reflect cardiovascular complexity, with direct links to flow features known to be associated with adverse vascular biological events. The aim of this study is to explore if and how these new topological indicators are linked to the imaging markers of early atherosclerosis at the carotid artery, for the purpose of understanding whether they could be attainable in predicting the onset of this disease. To do that, 45 ostensibly healthy carotid bifurcation models were considered, on which computational fluid dynamics (CFD) simulations were performed. The variability of the WSS contraction/expansion action along the cardiac cycle and the WSS fixed point residence time were quantified using the WSS topological shear variation index (TSVI) and the WSS Fixed Point Weighted Residence Time (RT∇xfp), respectively. the analysis has been complemented through the evaluation of the Time Averaged Wall Shear Stress (TAWSS), whose correlation with atherosclerosis is well-established. In particular, areas of the luminal surface exposed to high TSVI (TSVA), high fixed point weighted residence time (wRTA) and low TAWSS (LSA) were computed; different combinations of thresholds and surface of interest have been used. Bivariate analysis among haemodynamic variables and imaging markers showed significant correlations between WSS topological skeleton descriptors (TSVA, wRTA) and wall thickness in common carotid artery, so as between LSA and contrast enhancement on internal carotid artery. The results of this study therefore support the association between WSS topological skeleton and markers of vascular disease, making a contribution in understanding the connection between TSVI, RT∇xfp and clinical observations.