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Bioabsorbable polymer scaffolds are designed to break down slowly and are eventually absorbed by the body. Optical coherence tomography (OCT) imaging is used to evaluate scaffold structural integrity after implantation, however the ability of OCT to detect fracture in bioresorbable scaffolds is unknown.. In this preclinical analysis, strut stacking and strut fracture were evaluated in the Absorb Bioresorbable Vascular Scaffold (BVS; Abbott Vascular, Santa Clara, CA) using in vivo OCT assessment and verified by a high-resolution smart vision system on explanted scaffolds.
Nine animals were implanted with 2 or 3 scaffolds in non-injured coronary arteries; RCA, LCx, or LAD, one scaffold per vessel (N=23); 11 were implanted in 4 animals for 30 days (d) and 12 were implanted in 5 animals for 90d. The BVS scaffolds were deployed following the manufacturer’s Instructions for Use, targeting an inner diameter:artery ratio of 1.1 based on qualitative coronary angiography (QCA). All animals underwent angiography and OCT assessment immediately post implant, and at 14d and 30d. The 90d cohort also underwent angiography and OCT assessment at 60d and 90d. At termination, arterial tissue was dissected to the level of the tunica intima. The scaffolds were examined using a high-resolution smart vision system which generated a 2-dimensional (2D) planar image of the geometry of each scaffold. Scaffolds were loaded on a translucent mandrel that evenly disperses transmitted light, and rotational images were captured using the Visicon Measurement System (Napa, CA) yielding a 2D image allowing precise evaluation of strut fracture.
There were no clinical observations attributed to BVS implantation in any animal. All implanted animals survived until scheduled euthanasia. OCT analysis revealed stacked struts in 8.7% of scaffolds (2/23) at 14 days, 21.7% (5/23) of scaffolds at 30 days, and 33.3% of scaffolds (4/12) at 60 d and 90 d after implantation. Evaluation of the true scaffold images using Visicon found strut fracture in 36.3% of scaffolds at 30 d (4/11) and 91.7% of scaffolds at 90 d (11/12).
In vivo OCT analysis was suitable for evaluation of stacked struts with BVS, but did not accurately capture all fractures compared to high resolution visual examination of explanted devices. Strut fracture through 90 d after implantation of BVS was more accurately assessed with a smart vision.