P858High endothelial shear stress and local Reynolds number are associated with lipid growth of coronary plaques

Background Local haemodynamic disturbances in coronary blood flow are associated with abnormal endothelial shear stress (ESS) and progressive atherosclerosis. However, standard techniques to estimate ESS lack the diagnostic specificity necessary for future clinical utility. Possible improvements include use of a more realistic non-Newtonian model of blood, which may provide more accurate ESS measurements and is further able to detect local variations in blood viscosity. Purpose To compare accuracy of ESS generated by Newtonian versus non-Newtonian rheological models to detect coronary plaque progression. To investigate local Reynolds number (ReL), a viscosity-based haemodynamic metric calculated by the non-Newtonian model, as an independent marker of plaque progression. Methods Sixteen patients with non-culprit plaques completely visualised in serial optical coherence tomography (OCT) imaging were identified. Plaques were analysed in 0.2mm intervals at each timepoint for lipid and calcium arc. Computational fluid dynamic simulations were performed using Newtonian and non-Newtonian models to calculate ESS, whereas ReL was calculated by the non-Newtonian simulations. Each haemodynamic index was compared to interval changes in lipid and calcium using multivariate regression. Results In total, 894 matched arterial segments from baseline and follow up imaging were analysed. In the Newtonian results, baseline segments exposed to ESS>1.7Pa had a 12.5° increase in lipid arc (95% CI 2.2° to 22.8°, p=0.018) while segments exposed to ESS<1.1Pa had an 8.1° decrease in calcium (95% CI −14.0° to −2.2°, p=0.007). In the non-Newtonian results, baseline regions exposed to ESS>2.2Pa had a 14.4° increase in lipid (95% CI 4.2° to 24.7°, p=0.006) while areas with ESS<1.4Pa had an 8.7° decrease in calcium (95% CI −14.6° to −2.8°, p=0.004). Baseline regions exposed to ReL<34 showed an average 11.9° increase in lipid arc (95% CI 0.6° to 23.2°, p=0.039). Regions exposed to ReL>55 had an average increase in lipid arc of 26.6° (95% CI 14.5° to 38.6°, p<0.001). Conclusions Both Newtonian and non-Newtonian rheological models show that high ESS is associated with increased lipid while low ESS is associated with decreased calcium. ReL is independently associated with interval increases in lipid arc, suggesting a mechanistic role of local blood viscosity in lipid accumulation. ReL may serve as a novel haemodynamic marker of plaque progression.