Early strut protrusion and late neointima thickness in the Absorb bioresorbable scaffold: a serial wall shear stress analysis up to five years

The aim of the study was to evaluate the effect of strut protrusion (SP) on wall shear stress (WSS) and neointimal growth (NG) one and five years after implantation of an Absorb bioresorbable vascular scaffold.Eight patients were selected from a first-in-man study. Following three-dimensional (3D) reconstruction of coronaries, WSS was quantified using Newtonian steady-flow simulation in each cross-section at 5° subunits (sectors) of the circumferential luminal surface. At one year, neointimal thickness (NT) was measured by optical coherence tomography (OCT) and correlated to WSS and SP post procedure. Median SP was 112.9 (90.8, 133.1) µm post implantation. Post procedure, a logarithmic inverse relationship between SP and post-implantation WSS (r=-0.425, p<0.001; correlation coefficients in a range from -0.143 to -0.553) was observed, whereas a correlation between baseline logarithm-transformed WSS (log-WSS) and NT (r=-0.451, p<0.001; correlation coefficients ranged from -0.140 to -0.662) was documented at one year. Mixed-effects analysis between baseline log-WSS and NT at follow-up yielded a slope of 30 µm/ln Pascal (Pa) and a y-intercept of 98 µm. As a result of NG, median flow area decreased from 6.91 (6.53, 7.48) mm2 post implantation to 5.65 (5.47, 6.02) mm2 at one-year follow-up (p=0.01) and to 5.75±1.37 mm2 at five-year follow-up (p=0.024). However, the vessel surface exposed to low WSS (<1 Pa) decreased significantly post procedure (42%) to one year (35.9%) and five years (15.2%) (p-overall <0.0001).SP disturbs laminar flow, creates regions of low WSS (<1.0 Pa) that are associated with NG and lumen area reduction. Low WSS post implantation reduced significantly at long-term follow-up. Thin struts with effective embedment would substantially reduce NG and accelerate homogenisation of WSS towards physiological values.