Investigating the impact of coronary stent design on near-wall and intravascular hemodynamic features linked to In-Stent Restenosis in idealized curved computational models of coronary arteries

Atherosclerosis is a cardiovascular disease predominantly affecting older individuals in Western countries. It consists of a progressive chronic inflammation of the arterial walls, culminating in the formation of plaques with thickening of the intima and narrowing, or even occlusion, of the lumen. This may result in reduced blood supply downstream of the lesion, with risks of necrosis, ischemia, and myocardial infarction. A fairly common and efficient method to treat this condition is percutaneous coronary intervention, a minimally invasive revascularization technique, with stent implantation. In detail, stent is a hollow cylindrical device with a metal/polymeric mesh structure that, thanks to its mechanical properties, helps keep the vessel open, counteracting stenosis and restoring a stable physiological lumen diameter for normal blood flow. Based on their material properties, coronary stents are classified in Bare Metal Stents (BMS) or Drug-Eluting Stents (DES). Despite the advancements in coronary stent technology and design, in-stent restenosis (ISR) remains a major complication still affecting the long-term postoperative outcomes . In detail, previous studies have demonstrated a relationship between local hemodynamic alteration and the pathophysiological mechanisms leading to ISR, identifying the wall shear stress (WSS) as the main biomechanical marker/predictor of stent failure risk. Additionally, helical flow (HF) has been hypothesized to have a relevant impact on vascular disease, by mitigating flow disturbances at the arterial wall and suppressing WSS disturbances. In this scenario, this thesis work focuses on analyzing the impact of the designs of 12 commercial coronary stents on both near-wall and intravascular hemodynamics. To do that, existing 3D geometries of commercial coronary stents (2 BMS, 10 DES) with a uniform thickness of 80 µm, were virtually placed in an idealized curved model of left anterior descending coronary artery, with a curvature radius of 14.84 mm. Twelve unsteady-state simulations were performed to simulate blood flowing in each stented model. The hemodynamic-related risk of ISR was evaluated in terms of (i) canonical WSS-based descriptors (i.e., time-averaged WSS - TAWSS, oscillatory shear index - OSI, relative residence time - RRT), (ii) variation in WSS contraction/expansion action over the cardiac cycle (i.e., topological shear variation index - TSVI), and (iii) HF descriptors (i.e., local normalized helicity - LNH, h index). Overall, repetitive patterns of WSS divergence were observed at the luminal stented surface, with a WSS contraction/expansion action proximal/distal to each stent strut, confirming previous evidence. Independent of stent design, risky values of WSS-based descriptors were located nearby stent struts and links, with design Taxus Libertè exhibiting the worst near-wall hemodynamic performance (lowest TAWSS and highest TSVI values). Conversely, the Cypher design exhibited the best near-wall hemodynamic performances. As for intravascular hemodynamics, comparable values of helicity intensity and balance of counter-rotating helical flow structures emerged among all the investigated coronary stent designs, when focusing on the whole vascular domain. In conclusion, this study suggests a negligible impact of coronary stent design on intravascular hemodynamics, pointing out the potential of the available stent dataset for benchmarking purposes in the development of innovative stent designs and assessing patient-specific risk of ISR.