Fig. 6.1
Classification of coronary angioscopic findings. Plaque is classified into yellow and white according to the color and smooth or complex according to the shape. Thrombus is classified into red and white according to the color and mural or transluminal according to their shapes
Fig. 6.2
Angioscopic examples of normal coronary (normal intima), plaque, and thrombus. T thrombus, F flap, L lumen, YP yellow plaque, R red thrombus, M mixed thrombus, W white thrombus
Normal artery appears angioscopically smooth in contour and has a uniform glistering white.
6.2.1 Yellow Plaque and White Plaque
Many studies includingour previous study [14] showed that yellow plaque is more common in patients with acute coronary syndromes such as acute myocardial infarction or unstable angina; conversely, white plaque was seen in patients with stable coronary syndromes such as stable angina or old myocardial infarction. Yellow plaque is likely to be vulnerable, and white plaque seemed to be stable.
6.2.2 Comparison of Plaque Color and Pathological Findings
6.2.2.1 Autopsy Study
Lipid Pool (Lipid Core) Beneath Fibrous Cap
One hundred ninety-eight coronary segments were evaluated by angioscopy, and then 46 yellow plaque lesions and 61 white plaque lesions of atheroma (lipid pool beneath fibrous cap) were excised and prepared for pathological examination [15].
Yellow plaque has thin fibrous cap (Fig. 6.3). The thickness of fibrous cap was 58 ± 18 μm (35–90 μm) in yellow plaque group and 648 ± 356 μm (190–1,731 μm) in white plaque group. The thickness of fibrous cap was significantly thinner in the yellow plaque group than in the white plaque group (Fig. 6.4). White plaque has thick fibrous cap (Fig. 6.5).
Fig. 6.3
Comparison of yellow plaque and pathological finding. Angioscopy shows yellow plaque (right lower panel). Hematoxylin-eosin stain at the same segment of yellow plaque (right upper panel). Sudan III stain shows lipid pool (pink) with thin fibrous cap (left upper panel)
Fig. 6.4
Comparison of the thickness of the fibrous cap between yellow plaque group and white plaque group. The thickness of the fibrous cap is significantly thinner in the yellow plaque group than in the white plaque group (Isoda et al. [15])
Fig. 6.5
Comparison of white plaque and pathological findings. Angioscopy shows white plaque (right upper panel). Hematoxylin-eosin stain at the same segment of white plaque (left upper panel). Sudan III stain shows lipid pool with thick fibrous cap (lower panel)
Comparison of the stenosis and the plaque area between yellow and white plaque group showed both stenosis and plaque were significantly higher in the white plaque group than in the yellow plaque group. Comparison of the lipid core area and the lipid core (pool) size relative to overall plaque size between yellow plaque group and white plaque group is shown in Fig. 6.6. The lipid core (pool) area was not significant between two groups, but the lipid core (pool) size relative to plaque size was significantly higher in the yellow plaque group than in the white plaque group. Yellow plaque reflects thin fibrous cap rather than size of lipid pool [16].
Fig. 6.6
Comparison of the stenosis and the plaque area between yellow and white plaque group. The lipid core (pool) area was not significant between two groups, but the lipid core (pool) size relative to plaque size was significantly higher in the yellow plaque group than in the white plaque group (Isoda et al. [15])
Superficial or Diffuse Lipid Deposition with or Without Lipid Core
Superficial or diffuse lipiddeposition in intima is diagnosed as yellow plaque by angioscopy (Fig. 6.7). In this lipid deposition, tiny calcium particle, macrophage foam cells, or degenerated collagen fiber may glisten yellow plaque(glistening yellow plaque) [17, 18]. High yellow color intensity region may not necessarily represent thin-cap fibroatheroma.
Fig. 6.7
Diffuse lipid deposition with macrophage foam cell. Yellow plaque (Y) exists in the artery (left panel). Angioscopy revealed yellow plaque (right upper panel). A large amount of inflammation cells such as probably macrophage with diffuse lipid deposition is seen (right lower panel)
White plaque was histologically composed of dense collagen fiber (fibrous) or thick fibrous (Fig. 6.5) or calcified cap covered with lipid and macrophage foam cell-free endothelia with lipid pool below (Table 6.1).
Table 6.1
Classification of plaque according to color
Yellow plaque | Thin fibrous cap superficial or diffuse lipid deposition |
Glistening yellow plaque | Tiny calcium particle, macrophage foam cells, or degenerated collagen fiber |
White plaque | Dense collagen fiber (fibrous) or calcified cap covered with lipid-free and macrophage foam cell-free endothelia with lipid pool |
6.2.2.2 Directional Coronary Atherectomy Study
Yellow plaque color was closely related to degenerated plaque or atheroma. Gray white lesion represented fibrous plaque without degeneration in 64 % and with degeneration in 36 %. Fibrous cap could not be clarified by directional coronary atherectomy [19].
6.2.3 Quantitative Evaluation of Angioscopy
It is hypothesized that yellow color is due to visualization of reflected light from the lipid-rich yellow color through a thin fibrous cap. Thus, quantification of yellow color saturation (intensity) may estimate plaque cap thickness and identification vulnerable plaque [20] (Fig. 6.8). High yellow color saturation (intensity) is associated with lipid core underneath thin fibrous cap (Fig. 6.9) [21].
