P5631The impact of plaque type on strut embedment/protrusion and shear stress distribution in bioresorbable scaffold

Background and aim

Scaffold design and plaque characteristics influence implantation outcomes and local flow dynamics in treated coronary segments. Our aim is to assess the impact of strut embedment/protrusion of bioresorbable scaffold on local shear stress distribution in different atherosclerotic plaque types.

Method

Fifteen Absorb everolimus-eluting Bioresorbable Vascular Scaffolds were implanted in human epicardial coronary arteries. Optical coherence tomography (OCT) was performed post-scaffold implantation and strut embedment/protrusion were analyzed using a dedicated software. OCT data was fused with angiography to reconstruct three-dimensional coronary anatomy. Blood flow simulation was performed and wall shear stress (WSS) was estimated in each scaffolded surface and the relationship between strut embedment/protrusion and WSS was evaluated.

Results

There were 9083 struts analysed. Ninety-seven percent of the struts (n=8840) were well apposed and 243 (3%) were malapposed. At cross-section level (n=1289), strut embedment was significantly increased in fibroatheromatous plaques (76±48μm) and decreased in fibro-calcific plaques (35±52 μm). Compatible with strut embedment, WSS was significantly higher in lipid-rich fibroatheromatous plaques (1.50±0.81Pa), whereas significantly decreased in fibro-calcified plaques (1.05±0.91Pa). After categorization of WSS as low (<1.0 Pa) and normal/high WSS (≥1.0 Pa), the percent of low-WSS in the plaque subgroups were 30.1%, 31.1%, 25.4% and 36.2% for non-diseased vessel wall, fibrous plaque, fibro-atheromatous plaque and fibro-calcific plaque, respectively (p-overall<0.001).

Table 1. Cross-section level Embedment/Protrusion and WSS according to the plaque type Plaque type Embedment depth (μm) Protrusion distance (μm) WSS (Pa) Non-atherosclerotic intimal thickening/normal vessel wall (n=2275) 47±34*Δ¥ 123±34¶Ξπ 1.44±0.9解 Fibrous (n=4191) 53±40*#& 118±38¶Ψ‡ 1.24±0.78αθ∞ Fibroatheromatous (n=2027) 76±48#ΦΔ 94.6±46Ω†Ψπ 1.50±0.81Σ§α Fibro-calcific (n=590) 35±52&Φ¥ 139±50‡†Ξ 1.05±0.91∞£Σ For embedment: *p=0.09, #p<0.001, &p<0.001, Φp<0.0001, Δp<0.0001, ¥p<0.0001. For protrusion: ¶p=0.74, Ξp<0.0001, πp<0.0001, Ψp<0.0001, ‡p<0.0001, †p<0.0001. For WSS: θp<0.001, §p=0.06, £p<0.0001, αp<0.0001, ∞p<0.0001, Ωp<0.0001. n=total strut number in each plaque type, p-values come from mixed-effects regression analysis.

Conclusion

The composition of the underlying plaque influences strut embedment which seems to have effect on WSS. The struts deeply embedded in lipid-rich fibroatheromas plaques resulted in higher WSS compared to the other plaque types.

P5629The effect of strut protrusion on local shear stress and neointimal hyperplasia

Objective

To evaluate effect of strut protrusion (SP) on wall shear stress (WSS) and neointimal growth (NG) 1 and 5 year after implantation of Absorb scaffold.

Method

8 patients were selected from Absorb Cohort B. After 3-dimensional reconstruction of coronaries, WSS was quantified using Newtonian steady flow simulation (Figure). At 1-year neointimal thickness (NT) was measured by optical coherence tomography and correlated to WSS and SP post-procedure.

Results

Median SP was 112.9 (90.8, 133.1) μm. A logarithmic (log) inverse relationship between SP and post-procedure WSS (r=−0.425 p<0.001 correlation coefficients range: −0.143 to −0.553) was observed whereas a correlation between baseline log transformed WSS and NT (r=−0.451 p<0.001 correlation coefficients range: −0.140 to −0.662) was documented at 1 year. Mixed effects analysis between baseline log transformed WSS and NT at follow up yielded a slope of 30 μm/ln Pascal (Pa) and a y-intercept of 98 μm. As result of NG, flow area decreased from 6.91 (6.53, 7.48) mm2 post-implantation to 5.65 (5.47, 6.02) mm2 at 1 year (p=0.01) and to 5.75±1.37 mm2 at 5 years (p=0.024). Vessel surface with low WSS (<1 Pa) decreased from post-procedure (42%) to 1 year (35.9%) and 5 years (15.2%) (p-overall<0.0001).

Conclusion

SP disturbs laminar flow, creates region of low WSS that is mechanistically associated with NG and lumen area reduction. This observation would suggest thin strut with effective embedment would reduce NG and improve WSS towards physiological values.

Comparative radiopacity of conventional and full-contour Y-TZP ceramics

The purpose of this study was to evaluate the radiopacity of different yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) ceramics used in the fabrication of fixed dental prostheses. Disk-shaped specimens (N=120, n=30 per group) were fabricated with thicknesses of 0.3, 0.5, and 1 mm from the following four Y-TZP ceramics: Cercon ht (Degudent) (CZ), Prettau (Zirkonzahn) (ZZ), Alliance (Kuraray Noritake Dental) (NA), and Ice Zirkon (Zirkonzahn) (ICE). The optical densities of each material were measured from radiographic images, and each material (N=1) were characterized by using XRD and SEM. The results were analyzed with oneway analysis of variance and the Tukey-Kramer test (α=0.05). In the case of the ICE and NA specimens, the radiopacity significantly differed with thickness (p<0.05). However, the radiopacities of 0.5- and 0.3-mm-thick CZ and ZZ specimens were not significantly different (p>0.05). Full-contour Y-TZP materials have higher radiopacities than those of the conventional Y-TZP materials in decreased thicknesses.

Comparative radiopacity of bone graft materials

The aim of this study was to investigate the radiopacity of bone graft materials (BGMs) in comparison with bovine mandibular cortical bone and human dentine. Eight samples of each material (8 mm in diameter and 3 mm in thickness) were prepared from Dexabone(®) (DB), Bio - Oss(®) (BO), 4BONE SBS (4B), KASIOS(®) TCP (KA), S.C. PONETI (PO), and Apatite-Wollastonite (AW). The optical densities of each material, along with one tooth section (human canine tooth 1 mm slice), bovine mandibular cortical bone (BC) samples, and an aluminum step wedge, were measured from radiographic images using a transmission densitometer. The data were analyzed by nonparametric one-way ANOVA (Kruskal-Wallis) and Duncan's multiple range tests for post hoc comparison (α = 0.05). BC and AW had statistically lower optical density values than BO, 4B and human dentine (p < 0.05). Among BGMs, AW (3.681 ± 0.409 mm eq Al) had the highest radiopacity values whereas BO (1.925 ± 0.176 mm eq Al) had the lowest one. The radiopacity values of DB and KA did not reveal a statistically significant difference when compared with other materials (p > 0.05). The radiopacity of all BGMs investigated seemed to be too low to be detected radiographically when placed in the mandibular cortical bone.

New power loss optimized Fontan connection evaluated by calculation of power loss using high resolution PC-MRI and CFD

A new blood vessel configuration was invented to optimize blood flow efficiency and reduce the power loss in the Fontan connection. The current preferred Fontan configuration, the total cavopulmonary connection (TCPC), usually connects the venae cava (VC) to the pulmonary arteries (PA), bypassing the right ventricle. The new connection, called OptiFlo, has two vertical inlets, which both bifurcate then merge into one another to form two horizontal outlets. One of the preliminary configurations of the new OptiFlo model was used for a comparison experiment between computational fluid dynamics (CFD) and high resolution phase contrast magnetic resonance imaging (PC-MRI) with a voxel resolution of 0.23 mmx0.23 mmx0.25 mm. The thin slice thickness was achieved using the ACGI interpolation technique we have used in other applications before. The 2D PC-MRI velocity vectors were mapped into a CFD grid, enabling direct CFD and MRI data comparisons. The mean squared difference was found between the two dataset Using the viscous power dissipation function we calculated the power loss for both CFD and MRI data. The power losses, calculated with the viscous power dissipation function, were 0.66 mW for CFD and 0.46 mW for the PC-MRI data.