Improvement in local haemodynamics 5 years after implantation of a coronary bioresorbable scaffold: a pulsatile non-Newtonian shear stress analysis

A 3.0 × 18 mm Absorb bioresorbable vascular scaffold (Abbott Vascular, Santa Clara, CA, USA) was implanted in the left circumflex coronary artery of patient with stable angina pectoris. Optical coherence tomography (OCT) revealed a well-expanded and apposed scaffold (pullback speed: 18 mm/s, acquisition rate: 180 frames/s). A patient-specific 3D geometry of the scaffolded lumen was generated by fusing OCT with coronary angiography. Pulsatile computational fluid dynamic (CFD) simulations were carried out by solving the Navier–Stokes equations. Blood was modelled as non-Newtonian fluid. Endothelial shear stress (ESS) at lumen and scaffold surfaces was calculated as product of local blood viscosity and near-wall velocity gradient. During low-coronary flow in systole, low-ESS predominates (PanelsA and C) whereas at peak diastolic flow the vessel is exposed to high-ESS (PanelsB and D). Irrespective of systolic or diastolic phase, the post-implantation vessel appears highly corrugated with an alternans of high-ESS on top of the struts and low-ESS between struts (PanelsA and B), that has been associated with blood micro-recirculation, fibrin deposition, and platelet aggregation. By 5 years, heterogeneity in ESS has largely dissipated (PanelsC and D, see Supplementary data online, Videos S1) while ESS distribution narrows and becomes more homogenous in both systole and diastole (PanelE). Histograms depicting the overall percent area of the simulated vessel exposed to varying levels of ESS during each of the studied flow conditions and time-points (PanelE) demonstrate that vessel exposure to very low and very high ESS decreases, leading to an overall increase in mid-range values of ESS generally considered to be more physiologic.