Hemodynamic analysis of a novel bioresorbable scaffold in porcine coronary artery model.

BACKGROUND: The shear stress distribution assessment can provide useful insights for the hemodynamic performance of the implanted stent/scaffold. Our aim was to investigate the effect of a novel bioresorbable scaffold, Mirage on local hemodynamics in animal models. METHOD: The main epicardial coronary arteries of 7 healthy mini-pigs were implanted with 11 Mirage Microfiber sirolimus-eluting Bioresorbable Scaffolds (MMSES). Optical coherence tomography (OCT) was performed post scaffold implantation and the obtained images were fused with angiographic data to reconstruct the coronary artery anatomy. Blood flow simulation was performed and Endothelial Shear Stress(ESS) distribution was estimated for each of the 11 scaffolds. ESS data were extracted in each circumferential 5-degree subunit of each cross-section in the scaffolded segment. The generalized linear mixed-effect analysis was implemented for the comparison of ESS in two scaffold groups; 150-µm strut thickness MMSES and 125-µm strut thickness MMSES. RESULTS: ESS was significantly higher in MMSES (150 µm) [0.85(0.49-1.40) Pa], compared to MMSES (125 µm) [0.68(0.35-1.18) Pa]. Both MMSES (150 µm) and MMSES (125 µm) revealed low recirculation zone percentages per luminal surface area [3.17% ± 1.97% in MMSES (150 µm), 2.71% ± 1.32% in MMSES (125 µm)]. CONCLUSION: Thinner strut Mirage scaffolds induced lower shear stress due to the small size vessels treated as compared to the thick strut version of the Mirage which was implanted in relatively bigger size vessels. Vessel size should be taken into account in planning BRS implantation. Small vessels may not get benefit from BRS implantation even with a streamlined strut profile. This pilot study warrants comparative assessment with commercially available bioresorbable scaffolds.

Strut protrusion and shape impact on endothelial shear stress: insights from pre-clinical study comparing Mirage and Absorb bioresorbable scaffolds.

Protrusion of scaffold struts is related with local coronary flow dynamics that can promote scaffold restenosis and thrombosis. That fact has prompted us to investigate in vivo the protrusion status of different types of scaffolds and their relationship with endothelial shear stress (ESS) distributions. Six Absorb everolimus-eluting Bioresorbable Vascular Scaffolds (Absorb, Abbott Vascular) and 11 Mirage sirolimus-eluting Bioresorbable Microfiber Scaffolds (Mirage, Manli Cardiology) were implanted in coronaries of eight mini pigs. Optical coherence tomography (OCT) was performed post-scaffold implantation and obtained images were fused with angiographic data to reconstruct the three dimensional coronary anatomy. Blood flow simulation was performed and ESS distribution was estimated for each scaffold. Protrusion distance was estimated using a dedicated software. Correlation between OCT-derived protrusion and ESS distribution was assessed for both scaffold groups. A significant difference was observed in the protrusion distances (156 ± 137 µm for Absorb, 139 ± 153 µm for Mirage; p = 0.035), whereas difference remained after adjusting the protrusion distances according to the luminal areas. Strut protrusion of Absorb is inversely correlated with ESS (r = -0.369, p < 0.0001), whereas in Mirage protrusion was positively correlated with EES (r = 0.192, p < 0.0001). Protrusion distance was higher in Absorb than in Mirage. The protrusion of the thick quadratic struts of Absorb has a tendency to lower shear stress in the close vicinity of struts. However, circular shape of the less thick struts of Mirage didn't show this trend in creating zone of recirculation around the struts. Strut geometry has different effect on the relationship between protrusion and shear stress in Absorb and Mirage scaffolds.

Assessment of the hemodynamic characteristics of Absorb BVS in a porcine coronary artery model.

BACKGROUND AND AIM: Local hemodynamic changes are one of the main factors that determine the vessel wall biological response after stent/scaffold implantation. Computational fluid dynamic studies provide an opportunity to investigate the rheological effects of implanted stent/scaffold. The aim of this study was to assess the local hemodynamic microenvironment in scaffolded segments in porcine coronary models. METHODS: In six epicardial coronary arteries of healthy mini-pigs, six Absorb bioresorbable vascular scaffolds (Absorb BVS) were implanted. Optical coherence tomography(OCT) was performed after scaffold implantation and the images were fused with the angiographic data to reconstruct the three-dimensional coronary artery anatomy. Blood flow simulations were performed, and endothelial shear stress(ESS) distribution was estimated for each scaffolded segment. In a linear mixed-effect model, the contributing factors for low (<1.0Pa) ESS levels were assessed. At 30-day post-implantation, histopathological assessment was performed at 2 scaffolds. RESULTS: In scaffolded segments, the median ESS was 0.57 (IQR: 0.29-0.99) Pa. In linear mixed-effect analysis, cross-section area was associated with low shear stress levels. In scaffolded segments, the percentage of the recirculation zone per scaffolded luminal surface was 3.26±2.07%. At 30-day histopathological assessment of implanted vessel segments revealed minimal injury score, minimal neointimal inflammation and minimal adventitial inflammation scores with moderate endothelial coverage. Fibrin accumulation was seen at 95.69±2.47% of the struts. CONCLUSION: The thick rectangular strut design of the Absorb BVS incited flow disruptions with low shear stress inducing fibrin accumulation. CFD assessment can be used to guide improvements in the scaffold design for a more "hemo-compatible" geometry.