Vulnerable and Disrupted Plaques Detected by Angioscopy as Yellow Plaque With or Without Thrombus

Coronary atherosclerotic lesions are generally detected as yellow plaques by angioscopy,¹ and their yellow color grade has been associated with their vulnerability.² Already disrupted plaques are detected as those with thrombus adhesion. Because angioscopy can sensitively detect yellow plaques and thrombus on the vessel wall, we can evaluate the changes in the vulnerability of the plaques and their disruption by the serial angioscopic observations.³ On the other hand, because the target lesions of percutaneous coronary intervention (PCI) often have already disrupted plaques (i.e., plaques with thrombus), their healing process can also be detected as the disappearance of thrombus. The healing of disrupted plaques and stabilization of vulnerable plaques are detected as the reduction in the yellow color grade. Furthermore, each stage of the vascular response against stent implantation elucidated by pathologic studies⁴ can be visualized by angioscopy. Angioscopy should play an important role in the macro-pathology of living humans.⁵

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Including the response against stent implantation, the vascular healing process of PCI target lesions can be visualized by angioscopy, and this response will differ according to the type of the stent used and various background characteristics of the patient.^6–12

In this issue of the Journal, Nishino et al.¹³ report on the healing process after PCI as evaluated by serial changes from 1 month to 12 months after PCI comparing 2 types of stents (BioFreedom and Xience). Because this was the subanalysis of the COLLABORATION study, optical coherence tomography (OCT) findings are also presented for each angioscopic evaluation.

This analysis presents some important findings. First, there was no new appearance of thrombus at 12 months, suggesting that the healing process presented as a reduction in the thrombogenicity of plaques or stents was consistently detected in all cases without exception, independent of the stent type or patients’ background characteristics, although residual thrombogenicity was still detected at 12 months in some cases. Second, diabetes mellitus had a negative impact on this healing process of losing thrombogenicity, whereas better neointimal stent coverage detected by OCT imaging had a beneficial impact. Third, regarding the analysis of the yellow color grade of the plaques, the use of Xience as compared with BioFreedom and less neointimal stent coverage by OCT imaging were predictors for the presence of yellow plaques at 12 months. The reduction in the yellow color grade is caused by neointimal coverage over the yellow plaque and reduction of lipid in the plaque. On the other hand, an increase in the yellow color grade is caused by the progression of atherosclerosis with increasing lipid content in the plaque and/or thinning of the fibrous cap. New appearance of yellow plaque at 12 months was detected in 2 of 5 white lesions at 1 month, and in both cases the Xience stent had been used. The authors of the report discuss whether the presence of polymer in the Xience stent might be a cause for the new appearance of yellow plaque (i.e., neoatherosclerosis), with delayed healing. In other words, better neointimal stent coverage with the BioFreedom stent as compared with the Xience stent would be beneficial for an enhanced healing process (i.e., the reduction in both thrombogenicity and yellow color grade of the plaques).

Clinically important messages from this study are that management of diabetes mellitus is important for vascular healing after stent implantation, and that polymer-free stents may be more beneficial for stabilizing plaque vulnerability. Further investigations are needed to confirm these findings and development of new polymer-free stents should be encouraged.

Disclosures

The author received research grant from Abbott, Daiichi-Sankyo, Teijin, Japan Lifeline, OrbusNeich, Janssen, Otsuka, Ono, Eli Lilly, Amgen, Novo Nordisk, and Novartis; and lecture fees from Abbott, Kowa, Bayer, Daiichi-Sankyo, Nipro, Takeda, AstraZeneca, Japan Lifeline, Novartis, Ono, Boehringer Ingelheim, PDR Pharma, Kaneka Medix, Mochida, Otsuka, and Amgen.

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