Spatial Distribution and Temporal
نویسندگان
چکیده
he Abbott Vascular bioresorbable vascular scaffold (BVS) (Santa Clara, CA, USA) consists of a semicrystalline poly(L-lactide) (PLLA) backbone and conformal coating of amorphous poly(D,L-lactide) (PDLLA) and the antiproliferative agent, everolimus. The molecular weight of the BVS polymers is degraded primarily through hydrolysis of the ester bonds present in each monomer subunit. Crystalline residues with a characteristic dimension less than 2 μm are phagocytosed by macrophages. Ultimately, PLLA and PDLLA degrade to lactate, which is metabolised via the Krebs’ cycle and other metabolic pathways,1 similarly to other biodegradable polymers.2 Complete polymer resorption occurs approximately 2 years after implantation.3,4 The BVS is laser-cut from a single piece of polymer tubing and then crimped onto a balloon. The structural design of the BVS consists of 19 W-shaped rings connected longitudinally by straight links (Figure 1). The BVS has delivered acceptable and durable clinical and angiographic results up to 2 years post-procedure when the scaffold has been completely resorbed.5,6 Unlike metallic stents,2,7–11 the translucency of the processed polylactide used in the Abbott Vascular BVS makes it particularly suitable for optical coherence tomography (OCT) imaging. The optical radiation can penetrate the translucent polymer, with significant backscattering occurring only at the borders of struts where the refractive index of the medium changes. Alternatively, the strut core has been characterized as a “black box”,3,5,6 signifying the absence of refractive index changes within the material (Figure 2). However, some OCT images show a focal hyperintense signal in the strut core without apparent contact with either the axial or transversal strut T
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