Fig. 17.1
Representative optical coherence tomography (OCT) images of late stent thrombosis within incomplete stent struts coverage
Table 17.1
Proportions of uncovered stent struts observed by optical coherence tomography
Stent type | Stent position | Stent duration | |||
|---|---|---|---|---|---|
1 month | 3 months | 6–9 months | ≥12 months | ||
BMS | Single layered | 0.1% | 0.3–2.0% | 0.3–1.1% | |
Overlapped | 3.4% | ||||
SES | Single layered | 13–18% | 12.3% | 3.2–11.6% | |
Overlapped | 9.6% | ||||
PES | Single layered | 3.8% | 4.9% | 0.9% | |
Overlapped | 16.5% | ||||
ZES-P | Single layered | 0.1% | 0.02–1.2% | ||
Overlapped | 0.37% | ||||
EES | Single layered | 26.7% | 4.7% | 1.6–2.3% | 1.9–5.8% |
Overlapped | 51.6% | ||||
Side branch | 89.4% | 35.7% | |||
ZES-R | Single layered | 6.2% | 4.4% | ||
Side branch | 35.7% | ||||
BES | Single layered | 21.3% | 15.9–21.8% | 4.1% | |
Side branch | 35.7% | ||||
BP-EES | Single layered | 3% | 1.8% | ||
Table 17.2
Proportions of uncovered stent struts and malapposed struts according to initial clinical presentation
Clinical presentation | Authors | Stent type | Stent duration | Uncovered stent struts | Malapposed stent struts |
|---|---|---|---|---|---|
ACS | Takano et al. [22] | SES | 3 months | 18% | 8% |
Kim et al. [24] | ZES | 3 months | 0.1% | 0.4% | |
Guagliumi et al. [7] | BMS | 6 months | 1.98% | 0.15% | |
Guagliumi et al. [7] | ZES | 6 months | 0.00% | 0.00% | |
Davlouros et al. [25] | PES | 6 months | 8.6% | 2.2% | |
Kim et al. [26] | SES, PES, ZES | 9 months | 8.9% | 2.2% | |
Guagliumi et al. [9] | BMS | 13 months | 1.1% | 0.1% | |
Guagliumi et al. [9] | PES | 13 months | 5.7% | 0.9% | |
Räber et al. [27] | SES, PES | 5 years | 1.7% | 0.5% | |
Non-ACS | Takano et al. [22] | SES | 3 months | 13% | 5% |
Kim et al. [24] | ZES | 3 months | 0.1% | 0.02% | |
Kim et al. [26] | SES, PES, ZES | 9 months | 2.9% | 0.5% | |
Räber et al. [27] | SES, PES | 5 years | 0.7% | 0.13% |
The application of these findings to real clinical practice is the important task. A pathological study showed that uncovered stent strut after DES implantation was the best morphometric predictor of late stent thrombosis; the odds ratio for stent thrombosis in a stent with a ratio of uncovered to total stent struts per section >30% was 9.0 (95% confidence interval, 3.5–22) [28]. In a case-control study to evaluate uncovered stent strut on stent thrombosis with OCT, the length of an uncovered stent strut segment was one of the independent predictor of late stent thrombosis [29]. Another OCT study revealed that a greater percentage of uncovered struts (the cutoff value of ≥5.9% uncovered struts), as assessed by OCT at the 6–18-month follow-up, in asymptomatic DES-treated patients might predict increases in major adverse cardiac events which is very relevant to stent safety in the future [30]. Based on these studies, strut coverage assessed by OCT is an important marker for predicting serious adverse cardiovascular events in daily clinical practice. Typical representative examples of follow-up strut coverage by using cross-sectional OCT are shown in Fig. 17.2.
Fig. 17.2
Typical representative examples of follow-up strut coverage by using cross-sectional OCT. (a) OCT images of immediate after stent implantation revealed well-apposed stent struts, (b) OCT images of 6-month follow-up showed that uncovered stent strut at 6 o’clock (white arrow), (c) OCT images of 2-year follow-up showed well-covered strut
Serial analysis of the malapposed and uncovered struts at the strut level by current OCT analysis with conventional methods might be challenging during serial follow-up at different time points. Recent study suggested that a contour plot OCT analysis could be a possible method of assessing individual stent struts at the strut level practically; this comprehensive monitoring of stent strut status at different time points would then provide useful information regarding vascular healing status after DES implantation [31, 32]. Representative contour plot images at post-stenting and 12-month follow-up are shown in Fig. 17.3 [32].
Fig. 17.3
Representative contour plot images at post-stenting and 12-month follow-up. (a) Baseline plot of artery-strut spacing post-intervention. Malapposed and embedded struts are indicated with red and green circles, respectively. Grayscale indicates the artery-strut distance post-intervention (range 0.0–0.7 mm). (b) The neointimal coverage at follow-up as a function of circumferential arc length and stent length in a 3.0 × 18 mm biolimus-eluting stent; covered struts and struts crossing over the side branches are indicated with blue and orange circles, respectively. Grayscale indicates a stent strut coverage thickness range of −0.1 to 0.6 mm. (c) At a stent length of 13.6 mm from the distal stent margin, a malapposed strut at post-intervention turns into an uncovered strut at follow-up without malapposition (red arrows on contour plots and cross sections) in A and A’ . At a stent length of 6.0 mm from the distal stent margin, an embedded strut becomes a covered strut (green arrows) in B and B’. At a stent length of 4.6 mm from the distal stent margin, a malapposed strut post-intervention becomes a covered strut without malapposition at follow-up (blue arrows) in C and C’. Adapted with permission from Kim et al. [32]
17.2 Neointimal Characteristics
Pathological studies have demonstrated that neointima in stented coronary artery is consisted of various tissue components including proteoglycan, collagen, smooth muscle, fibrin, or thrombus [33, 34]. By using previous imaging modalities, such as conventional angiography or intravascular ultrasound, there are several limitations for detecting distinct neointimal characteristics due to their low resolution. However, intravascular OCT has higher resolution and is useful for both the qualitative as well as quantitative evaluation of neointimal tissue [35, 36]. The neointima within a stent could be assessed qualitatively to characterize the neointimal tissue as (1) homogeneous neointima, a uniform signal-rich band without focal variation or attenuation; (2) heterogeneous neointima, focally changing optical properties and various backscattering patterns; and (3) layered neointima, layers with different optical properties, namely, an adluminal high scattering layer and an abluminal low scattering layer [35–37]. Pathological studies have reported differential morphological characteristics of neointimal tissue, which was well correlated with histological findings [37, 38]. Representative OCT images of neointimal tissue are shown in Fig. 17.4. Comparing different OCT morphological characteristics with different in-stent neointimal tissue types analyzed by histology with swine in-stent restenosis models, the optical characteristics of neointimal formation seen in OCT were consistent with the histological studies on stent healing [37]. Fibrous connective tissue deposition was more frequently present in the homogeneous pattern (71.6%, P < 0.001), whereas significant fibrin deposits were more commonly seen in the heterogeneous pattern (56.9%, P = 0.007). Peri-strut inflammation was less frequently found in the homogeneous pattern (19.8%, P < 0.001) in comparison with the layered (73.9%) or heterogeneous patterns (43.1%). The presence of external elastic lamina (EEL) rupture was also more commonly seen in layered (73.9%) and heterogeneous (46.6%) patterns than in the homogeneous pattern (22.4%, P < 0.001) [37]. A recent histopathological OCT studies investigated 22 autopsy cases with a total of 36 lesions and 42 implanted stents (17 BMS, 11 first generation DES, and 14 second generation DES) [39] In this study, stented segments neointimal histologic characteristics revealed great variability of tissue components, which were not consistent with characteristics OCT features, except in the case of restenotic tissue (Fig. 17.5) [39]. This study suggested that it required more attention to interpret OCT imaging in non-restenotic tissues.
Fig. 17.4
Representative OCT images of neointimal tissue. (a) Homogeneous, (b) heterogeneous, (c) layered neointimal tissue
Fig. 17.5
Neointimal pattern and histologic findings. (a) Drug-eluting stent(s) (DES) (resolute) in the left anterior descending coronary artery, 238 days after implantation in the setting of stable coronary artery disease. (A1) Optical coherence tomographic (OCT) image shows heterogeneous backscattering. (A2) Corresponding histological cross section (hematoxylin and eosin [H&E]) shows an intense inflammatory reaction and focal fibrin deposits in the peri-strut regions. Higher magnification shows massive leukocyte infiltration and fibrin accumulation (scale bar = 1000 mm). (b) Bare metal stent(s) (BMS) (vision) 3 years after revascularization. (B1) Optical frequency domain image shows a homogeneous appearance. (B2) H&E-stained histopathological cross section showing smooth muscle cell-rich neointimal tissue coverage above all struts (scale bar = 1000 mm). (c) DES (endeavor) in the right coronary artery, 2 years after implantation in the setting of stable CAD. (C1) OCT image shows a layered pattern. (C2) Corresponding histological cross section, stained with hematoxylin and eosin, shows a layer of loose neointimal tissue with neovascularization and inflammation close to stent struts (small arrowhead; black bar represents strut) and a smooth muscle cell (SMC)-rich neointimal layer toward the lumen (large arrowhead) (scale bar = 1000 mm). Immunohistochemical staining (identification of SMCs by a-actin). Adapted with permission from Lutter et al. [39]
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