Objectives: To examine the ultrastructure of microvessels in normal and atherosclerotic coronary arteries and its association with plaque phenotype. Background: Microvessels in atherosclerotic plaques are an entry point for inflammatory and red blood cells. Yet there is limited data on the ultrastructural integrity of microvessels in human atherosclerosis. Methods: Microvessel density (MVD) and ultrastructural morphology were determined in the adventitia, intima-media border, and atherosclerotic plaque of 28 coronary arteries using immunohistochemistry for endothelial cells (Ulex europeaus, CD31/CD34), basement membrane (laminin, collagen IV), and mural cells (desmin, alpha-smooth muscle (SM) actin, smoothelin, SM1, SM2, Smemb). Ultrastructural characterization of microvessel morphology was performed by electron microscopy (EM). Results: MVD was increased in advanced plaques compared to early plaques, which correlated with lesion morphology. Adventitial MVD was higher than intraplaque MVD in normal arteries and early plaques, but adventitial and intraplaque MVD were similar in advanced plaques. Although microvessel basement membranes were intact, the percentage of thin-walled microvessels was similarly low in normal and atherosclerotic adventitia, in the adventitia and the plaque, and in all plaque types. Intraplaque microvascular endothelial cells (EC) were abnormal, with membrane blebs, intracytoplasmic vacuoles, open EC-EC junctions, and basement membrane detachment. Leukocyte infiltration was frequently observed by EM, and confirmed by CD45RO and CD68 immunohistochemistry. Conclusions: MVD was associated with coronary plaque progression and morphology. Microvessels were thin-walled in normal and atherosclerotic arteries, and the compromised structural integrity of microvascular endothelium may explain the microvascular leakage responsible for intraplaque hemorrhage in advanced human coronary atherosclerosis.

For peripheral endovascular intervention, self-expanding (SE) stents are commonly oversized in relation to target arteries to assure optimal wall apposition and prevent migration. However, the consequences of oversizing have not been well studied. The purpose of this study was to examine the effects of SE stent oversizing (OS) with respect to the kinetics of late stent expansion and the long-term histological effects of OS. Pairs of overlapped 8 x 28-mm Nitinol SE stents were implanted into the iliofemoral arteries of 14 Yucatan swine. Due to variations in target artery size, the stent-to-artery ratio ranged from 1.2:1 to 1.9:1. Lumen and stent diameters were assessed by quantitative angiography at the time of implantation. Following angiographic assessment at 6 months, stented arteries were perfusion-fixed, sectioned, and stained for histological analysis. Immediately following implantation, the stents were found to be expanded to a range of 4.7-7.1 mm, largely conforming to the diameter of the recipient target artery. The stents continued to expand over time, however, and all stents had enlarged to nearly their 8-mm nominal diameter by 6 months. The histological effects of OS were profound, with marked increases in injury and luminal area stenosis, including a statistically significant linear correlation between stent-to-artery ratio and area stenosis. In this experimental model of peripheral endovascular intervention, oversized Nitinol SE stents are constrained by their target artery diameter upon implantation but expand to their nominal diameter within 6 months. Severe OS (stent-to-artery ratio >1.4:1) results in a profound long-term histological response including exuberant neointimal proliferation and luminal stenosis.

Background-The Absorb everolimus-eluting bioresorbable vascular scaffold (Absorb) has shown promising clinical results; however, only limited preclinical data have been published. We sought to investigate detailed pathological responses to the Absorb versus XIENCE V (XV) in a porcine coronary model with duration of implant extending from 1 to 42 months. Methods and Results-A total of 335 devices (263 Absorb and 72 XV) were implanted in 2 or 3 main coronary arteries of 136 nonatherosclerotic swine and examined by light microscopy, scanning electron microscopy, pharmacokinetics, and gel permeation chromatography analyses at various time points. Vascular responses to Absorb and XV were largely comparable at all time points, with struts being sequestered within the neointima. Inflammation was mild to moderate (with absence of inflammation at 1 month) for both devices, although the scores were greater in Absorb at 6 to 36 months. Percent area stenosis was significantly greater in Absorb than XV at all time points except at 3 months. The extent of fibrin deposition was similar between Absorb and XV, which peaked at 1 month and decreased rapidly thereafter. Histomorphometry showed expansile remodeling of Absorb-implanted arteries starting after 12 months, and lumen area was significantly greater in Absorb than XV at 36 and 42 months. These changes correlated with dismantling of Absorb seen after 12 months. Gel permeation chromatography analysis confirmed that degradation of Absorb was complete by 36 months. Conclusions-Absorb demonstrates comparable long-term safety to XV in porcine coronary arteries with mild to moderate inflammation. Although Absorb was associated with greater percent stenosis relative to XV, expansile remodeling was observed after 12 months in Absorb with significantly greater lumen area at ≥36 months. Resorption is considered complete at 36 months. (Circ Cardiovasc Interv. 2014;7:330-342.)

The findings indicate desired pharmacologic levels with biologic effects at early and healing at late time points in the treated arteries, without evidence of significant downstream emboli or systemic toxicity, consistent with safety of the Lutonix DCB.

No abstract