Extended follow-up by serial angioscopic observation for bare-metal stents in native coronary arteries: from healing response to atherosclerotic transformation of neointima

Angioscopic Comparison of Early- and Mid-Term Vascular Responses Following Treatment of ST-Elevation Acute Myocardial Infarction With Biodegradable vs. Durable Polymer Everolimus-Eluting Stents - A Prespecified Subanalysis of the MECHANISM AMI RCT

BACKGROUND

The vessel healing process after implantation of biodegradable polymer (BP) and durable polymer (DP) everolimus-eluting stent (EES) in ST-elevation myocardial infarction (STEMI) lesions remains unclear.

METHODS AND RESULTS

We conducted a multicenter prospective randomized controlled trial to compare early (2 weeks) and mid-term (12 months) vascular responses after implantation of BP-EES vs. DP-EES in STEMI patients. In this prespecified subanalysis, serial coronary angioscopy (CAS) analysis was performed in 15 stents in the BP-EES arm (n=10 patients) and 14 stents in the DP-EES arm (n=10 patients). At the 2-week follow-up, there was no significant difference in the estimated marginal means of the neointimal coverage grade (primary endpoint) between the 2 arms (mean [±SE] 0.00±0.00 in both arms; P>0.999). There were no significant differences between the BP-EES and DP-EES groups in the yellow color grade (1.046±0.106 vs. 0.844±0.114, respectively; P=0.201) or the presence of thrombus (77.8% vs. 88.8%, respectively; P=0.205). At 12 months, competent strut coverage, defined as yellow color grade ≤1, no thrombus, and a neointimal coverage grade ≥1 was achieved more frequently in the BP-EES than DP-EES arm (85.2% vs. 53.1%; adjusted odds ratio 2.11 [95% confidence interval 1.26-3.53]; P=0.023).

CONCLUSIONS

Neointimal coverage 2 weeks after implantation of BP-EES and DP-EES in STEMI lesions was comparable on CAS evaluation. However, at 1 year, BP-EES was independently associated with competent strut coverage.

Near-Infrared Spectroscopy-Guided Percutaneous Coronary Intervention: Practical Applications and Available Evidence

Intracoronary near-infrared spectroscopy (NIRS) has been extensively validated against the gold standard of histopathology to identify lipid-rich plaque. NIRS is currently in clinical use as a combined multimodality imaging catheter with intravascular ultrasonography. When used before PCI, NIRS has clinical utility in determining the mechanism underlying acute coronary syndromes and can be used to guide stent length selection and identify the risk of periprocedural myocardial infarction. When used after PCI, NIRS can identify vulnerable patients at increased risk of future patient-level cardiovascular events and can detect vulnerable plaques at increased risk of future site-specific coronary events.

Relationship Between Optical Coherence Tomography-Derived In-Stent Neoatherosclerosis and the Extent of Lipid-Rich Neointima by Near-Infrared Spectroscopy and Intravascular Ultrasound: A Multimodal Imaging Study

Background In-stent restenosis, especially for neoatherosclerosis, is a major concern following percutaneous coronary intervention. This study aimed to elucidate the association of features of in-stent restenosis lesions revealed by optical coherence tomography (OCT)/optical frequency domain imaging (OFDI) and the extent of lipid-rich neointima (LRN) assessed by near-infrared spectroscopy (NIRS) and intravascular ultrasound, especially for neoatherosclerosis. Methods and Results We analyzed patients undergoing percutaneous coronary intervention for in-stent restenosis lesions using both OCT/OFDI and NIRS-intravascular ultrasound. OCT/OFDI-derived neoatherosclerosis was defined as lipid neointima. The existence of large LRN (defined as a long segment with 4-mm maximum lipid core burden index ≥400) was evaluated by NIRS. In 59 patients with 64 lesions, neoatherosclerosis and large LRN were observed in 17 (26.6%) and 21 lesions (32.8%), respectively. Naturally, large LRN showed higher 4-mm maximum lipid core burden index (median [interquartile range], 623 [518-805] versus 176 [0-524]; P<0.001). In OCT/OFDI findings, large LRN displayed lower minimal lumen area (0.9±0.4 versus 1.3±0.6 mm²; P=0.02) and greater max lipid arc (median [interquartile range], 272° [220°-360°] versus 193° [132°-247°]; P=0.004). In the receiver operating characteristic curve analysis, 4-mm maximum lipid core burden index was the best predictor for neoatherosclerosis, with a cutoff value of 405 (area under curve, 0.92 [95% CI, 0.83-1.00]). In multivariable logistic analysis, only low-density lipoprotein cholesterol (odds ratio, 1.52 [95% CI, 1.11-2.08]) was an independent predictor for large LRNs. Conclusions NIRS-derived large LRN was significantly associated with neoatherosclerosis by OCT/OFDI. The neointimal characterization by NIRS-intravascular ultrasound has potential as an alternative method of OCT/OFDI for in-stent restenosis lesions.

Potential Mechanisms of In-stent Neointimal Atherosclerotic Plaque Formation

ABSTRACT

Percutaneous coronary intervention has become the main revascularization strategy for coronary artery disease. Compared with early percutaneous coronary angioplasty and the extensive clinical application of bare metal stents, drug-eluting stents can significantly reduce the stenosis caused by the elastic retraction of plaque and neoatherosclerosis (NA), but there is still a high incidence of in-stent restenosis (ISR), which restricts the clinical efficacy of stent implantation. In-stent neoatherosclerosis (ISNA), defined as atherosclerotic lesions in the neointima, is one of the main causes of late stent failure. ISNA plays an important role in stent thrombosis and ISR. The rate of target lesion revascularization and in-stent thrombosis is high when NA arises. Therefore, it is of great clinical significance to explore the occurrence of NA and its development mechanism after stent implantation to prevent ISR and improve stent implantation efficacy and associated clinical prognosis. In this article, we systematically reviewed the existing clinical research on ISNA and the role of optical coherence tomography in its evaluation.

In Vivo Illustration of Dendrite Formation on a Mobile Thrombus within a Wallstent in an Iliac Artery: A Fractal Phenomenon

The mechanism of stent thrombus formation following percutaneous transluminal stent implantation in an artery is unclear. This case report describes a 72-year-old man who had a mobile thrombus in a Wallstent in the right iliac artery despite daily oral administration of 100 mg of aspirin. This Wallstent was implanted 14 years ago. The unique in vivo angioscopic images show a solid mobile thrombus with some projections which rubbed yellow plaque on the stent struts.

Early vessel healing after implantation of biodegradable-polymer and durable-polymer drug-eluting stent: 3-month angioscopic evaluation of the RESTORE registry

The purpose of this study was to evaluate the vessel healing status 3 months after stent implantation of bioresorbable-polymer drug-eluting stents (BP-DESs) in comparison with durable-polymer DESs (DP-DESs) by angioscopy. Study design was a single-center all-comer prospective cohort study: the RESTORE registry (UMIN000033009). All patients who received successful angioscopic examination at planned 3-month follow-up after the DES implantation in the native coronary artery were enrolled. We evaluated main, maximum, minimum strut coverage grades and coverage heterogeneity score defined as a difference between maximum and minimum coverage grades. All lesions were divided into three segments: proximal, mid, and distal segments. A total of 108 patients (66.6 ± 10 years) with 124 lesions were analyzed (BP-DES 57 patients 61 lesions 226 segments vs. DP-DES 57 patients 63 lesions 203 segments; six patients had both BP-DES and DP-DES). Patient and lesion demographics, procedural characteristics were well balanced. Main coverage grade (mean ± standard error; 1.08 ± 0.02 vs. 1.05 ± 0.03, p = 0.354) and minimum coverage grade (1.00 ± 0.00 vs. 1.00 ± 0.00, p > 0.999) were not significantly different between BP-DES and DP-DES groups. Maximum coverage grade was significantly higher in the BP-DES than in the DP-DES (1.45 ± 0.04 vs. 1.35 ± 0.04, p = 0.049). Coverage heterogeneity score did not differ between BP-DES and DP-DES groups (1.05 ± 0.07 vs. 0.90 ± 0.07, p = 0.162). At 3-month follow-up, the current BP-DES had higher maximum stent coverage than the contemporary DP-DES, while main and minimum coverage grades and heterogeneity of the neointimal coverage were comparable. Further prospective randomized trials should be conducted to evaluate the clinical significance of the present imaging results.

The comparison of early healing 1-month after PCI among CoCr-everolimus-eluting stent (EES), biodegradable polymer (BP)-EES and BP-sirolimus-eluting stent: Insights from OFDI and coronary angioscopy

Background

Third-generation stents with abluminal biodegradable polymer (BP) might facilitate early healing. Therefore, we compared early healing between second-generation and third-generation stents using coronary angioscopy (CAS) and optical frequency domain imaging [OFDI].

Methods

We prospectively enrolled 30 consecutive patients with stent implantation for acute coronary syndrome (cobalt‑chromium [CoCr] everolimus-eluting stent [EES] [n = 10], BP-EES [n = 10], and BP-sirolimus eluting stent [SES] [n = 10]). All patients underwent CAS and OFDI 1 month after initial percutaneous coronary intervention. On OFDI, the stent coverage (SC), thrombus, and peri-strut low intensity area (PLIA) were assessed. CAS findings were recorded for the grade of SC, grade of yellow color (YC), and grade of the thrombus (TG).

Results

On OFDI, the incidences of any thrombus at the 1-month follow-up were 70%, 80%, and 80% in the CoCr-EES, BP-EES, and BP-SES groups, respectively. The percentage of coverage was comparable among the groups (CoCr-EES 79.8 vs. BP-EES 79.9 vs. BP-SES 80.1%, P = 0.96). However, the number of struts with PLIA was numerically higher in the BP-SES group than in the CoCr-EES and BP-EES groups (46.4 ± 25.1 vs. 21.6 ± 13.2 vs. 22.0 ± 7.2%, P = 0.08). In the CoCr-EES, BP-EES, and BP-SES groups, mean grades of SC were 1.25 ± 0.5, 1.25 ± 0.5, and 0.85 ± 0.70 (P = 0.60); mean grades of YC were 0.75 ± 0.5, 0.80 ± 0.45, and 0.88 ± 0.37 (P = 0.65), and mean grades of TG were 1.00 ± 1.00, 1.20 ± 0.83, and 0.88 ± 0.64 (P = 0.75), respectively.

Conclusion

Third-generation stents are not inferior to second-generation stents regarding stent coverage. However, PLIA on OFDI was often observed with BP-SESs, indicating involvement of the fibrin component.

Propylthiouracil-coated biodegradable polymer inhibited neointimal formation and enhanced re-endothelialization after vascular injury

Background

The drug-eluting stent is a standard approach for the treatment of coronary artery disease. Propylthiouracil (PTU), an antithyroid drug, has been proven to suppress neointimal formation after balloon injury.

Materials and methods

This study used a biodegradable polymer coating with PTU to test its effects on platelet function, re-endothelialization, and neointimal formation after vascular injury. Electrospinning was used to fabricate hybrid stents and generate PTU-loaded nanofibers.

Results

PTU-eluting stents maintained a stable release of PTU for 3 weeks. The PTU-coated stent markedly decreased the neointimal formation induced by vascular injury in the descending aorta of rabbits. Moreover, the PTU coating reduced platelet adhesion on the surface of the biodegradable membrane, which was reflected by the decreased expression of adhesion molecule in PTU-treated endothelial cells. The PTU coating enhanced re-endothelialization in injured aortas. In vitro, PTU exerted less suppressive effect on the proliferation and migration of endothelial cells than on those of vascular smooth muscle cells. Furthermore, treatment of endothelial cells with PTU induced phosphorylation (Ser1177) of endothelial nitric oxide synthase as well as its association with heat shock protein 90, supporting the protective role of PTU in endothelial function. The level of thyroid-stimulating hormone remained unchanged during the experimental period.

Conclusion

This study indicates that PTU can be released locally and steadily in injured aortas, with some local effects but without systemic effects. Furthermore, PTU-coated stents may have beneficial effects on neointimal formation, endothelial cell, and platelet functions.

Optical coherence tomography to evaluate coronary stent implantation and complications

Coronary optical coherence tomography (OCT) is now an established imaging technique in many catheterization laboratories worldwide. With its near-histological view of the vessel wall and lumen interface, it offers unprecedented imaging quality to improve our understanding of the pathophysiology of atherosclerosis, plaque vulnerability, and vascular biology. Not only is OCT used to accurately detect atherosclerotic plaque and optimize stent position, but it can further characterize plaque composition, quantify stent apposition, and assess stent tissue coverage. Given that its resolution of 15 μm is well above that of angiography and intravascular ultrasound, OCT has become the invasive imaging method of choice to examine the interaction between stents and the vessel wall. This review focuses on the application of OCT to examine coronary stents, the mechanisms of stent complications, and future directions of OCT-guided intervention.

Neoatherosclerosis: Coronary stents seal atherosclerotic lesions but result in making a new problem of atherosclerosis

Chronic inflammation of the native vessel wall with infiltration of lipid-laden foamy macrophages through impaired endothelium results in atherosclerosis. Percutaneous coronary intervention, including metallic stent implantation, is now widely utilized for the treatment of atherosclerotic lesions of the coronary artery. Bare-metal stents and the subsequently developed drug-eluting stents seal the atherosclerosis and resolve lumen stenosis or obstruction of the epicardial coronary artery and myocardial ischemia. After stent implantation, neointima proliferates within the stented segment. Chronic inflammation caused by a foreign body reaction to the implanted stent and subsequent neovascularization, which is characterized by the continuous recruitment of macrophages into the vessel, result in the transformation of the usual neointima into an atheromatous neointima. Neointima with an atherosclerotic appearance, such as that caused by thin-cap fibroatheromas, is now recognized as neoatherosclerosis, which can sometimes cause in-stent restenosis and acute thrombotic occlusion originating from the stent segment following disruption of the atheroma. Neoatherosclerosis is emerging as a new coronary stent-associated problem that has not yet been resolved. In this review article, we will discuss possible mechanisms, clinical challenges, and the future outlook of neoatherosclerosis.

OCT demonstrating neoatherosclerosis as part of the continuous process of coronary artery disease

Although the advent of drug-eluting stents has reduced the rates of target vessel revascularization, there are observations of ongoing stent failure occurring very late after stent implantation and presenting as very late restenosis or as very late stent thrombosis. The de novo development of atherosclerosis within the neointimal region, called neoatherosclerosis, has been identified as one of the pathomechanisms of these observed late stent failures. The mechanisms of neoatherosclerosis development and its association with stent failure are currently the subject of intensive research. Optical coherence tomography (OCT) is an invasive imaging modality that allows us to visualize the micromorphology of coronary arteries with near-histological resolution, thus providing detailed assessment of the morphological characteristics of the neointima after stent implantation, including neoatherosclerosis. Several OCT studies have tried to provide in vivo insights in the mechanisms of neoatherosclerosis development and its association with late stent failure. This review summarizes the current insights into neoatherosclerosis obtained with OCT and discusses the association of neoatherosclerosis with late stent failure.

Intra-stent tissue evaluation within bare metal and drug-eluting stents > 3 years since implantation in patients with mild to moderate neointimal proliferation using optical coherence tomography and virtual histology intravascular ultrasound

OBJECTIVE

We aimed to compare neointimal tissue characteristics between bare-metal stents (BMS) and drug-eluting stents (DES) at long-term follow-up using optical coherence tomography (OCT) and virtual histology intravascular ultrasound (VH-IVUS).

BACKGROUND

Neoatherosclerosis in neointima has been reported in BMS and in DES.

METHODS

Thirty patients with 36 stented lesions [BMS (n=17) or DES (n=19)] >3years after implantation were prospectively enrolled. OCT and VH-IVUS were performed and analyzed independently. Stents with ≥70% diameter stenosis were excluded.

RESULTS

The median duration from implantation was 126.0months in the BMS group and 60.0months in the DES group (p <0.001). Lipid-laden intima (58.8% vs. 42.1%, p=0.317), thrombus (17.6% vs. 5.3%, p=0.326), and calcification (35.3% vs. 26.3%, p=0.559) did not show significant differences between BMS and DES. When divided into 3 time periods, the cumulative incidence of lipid-laden neointima from >3years to <9years was similar between BMS and DES (42.9% vs. 42.1%, p=1.000). Furthermore, it continued to gradually increase over time in both groups. OCT-derived thin-cap fibroatheroma (TCFA) was observed in 17.6% of BMS- and 5.3% of DES-treated lesions (p=0.326). No stents had evidence of intimal disruption. The percentage volume of necrotic core (16.1% [9.7, 20.3] vs. 9.7% [7.0, 16.5], p=0.062) and dense calcium (9.5% [3.8, 13.6] vs. 2.7% [0.4, 4.9], p=0.080) in neointima tended to be greater in BMS-treated lesions. Intra-stent VH-TCFA (BMS vs. DES 45.5% vs. 18.2%, p=0.361) did not differ significantly.

CONCLUSION

At long-term follow-up beyond 3 years after implantation, the intra-stent neointimal tissue characteristics appeared similar for both BMS and DES.

Correlation between degree of neointimal hyperplasia and incidence and characteristics of neoatherosclerosis as assessed by optical coherence tomography

Emerging evidence suggests that neointimal degenerative changes with development of neoatherosclerosis (NA) may represent an important mechanism for late stent failure. The aim of the present study was to investigate the relation between degree of neointimal hyperplasia and incidence and characteristics of NA using optical coherence tomography. We identified a total of 252 stents with mean neointimal thickness (NIT) >100 μm in 212 patients: 100 bare metal stents (BMSs) and 152 drug-eluting stents (DESs). Based on the values of mean NIT, we divided stents into tertiles and compared neointimal characteristics among the 3 groups. NA was defined as the presence of lipid-laden intima and/or calcification inside the stent. In both BMS and DES, there was a difference in the prevalence of lipid-laden intima among the tertiles (18.2% vs 36.4% vs 47.1%, p = 0.042 [BMS]; 19.6% vs 56.9% vs 88.0%, p <0.001 [DES]). However, no difference in the prevalence of in-stent calcification was observed (21.2% vs 21.2% vs 2.9%, p = 0.053 [BMS]; 5.9% vs 9.8% vs 2.0%, p = 0.252 [DES]). In a multivariate model adjusting for stent type, follow-up duration, conventional coronary risk factors, statin, and angiotensin-converting enzyme inhibitor or angiotensin II receptor blockade use, mean NIT was independently associated with the presence of NA (odds ratio 2.53, 95% confidence interval 1.96 to 3.27, p <0.001). This study demonstrates the presence of a positive correlation between degree of neointimal hyperplasia after stent implantation and presence of lipid-laden intima. This association is independent from stent type and time from implantation and suggests a possible pathogenic link between the two processes.

A rare mechanism of very late bare metal stent thrombosis--role of optical coherence imaging in its evaluation and management

Very late stent thrombosis is an uncommon event following implantation with bare metal stents (BMS) in coronary arteries. Long term follow up studies have shown that a small number of BMS develop very late thrombosis following years of stability. Atherosclerotic transformation of neointimal tissue is increasingly being recognised as the cause of these adverse events. A 49 year-old male presented with acute inferior wall myocardial infarction resulting from thrombosis of the BMS implanted in his right coronary artery five years earlier. He was successfully thrombolysed and his coronary angiogram showed mild diffuse instent restenosis. The intravascular optical coherence tomography revealed instent neoatherosclerotic plaque rupture without any flow limiting stenosis as the likely culprit event.

A higher colour grade yellow plaque was detected at one year after implantation of an everolimus-eluting stent than after a zotarolimus-eluting stent

OBJECTIVE

Neoatherosclerosis or atherosclerosis progression is one of the mechanisms of long-term stent failure. Yellow plaque detected by angioscopy has been associated with advanced atherosclerosis and the future risk of a coronary event. We compared the yellow colour of the stented segment between zotarolimus-eluting stents (ZES) and everolimus-eluting stents (EES) at 1 year after implantation.

DESIGN

Cross-sectional study.

PATIENTS

Consecutive patients underwent angioscopic examination 1 year after the implantation of ZES (n=45) or EES (n=45) at a de novo native coronary lesion.

MAIN OUTCOME MEASURES

The maximum yellow colour grade (grade 0-3) of the stented segment, maximum and minimum neointima coverage grade (grade 0-2) and the presence of thrombus were examined. The neointima heterogeneity index was calculated as maximum - minimum coverage grade.

RESULTS

Maximum yellow colour grade was higher in EES than in ZES (1.3±0.9 vs 0.4±0.8, p<0.001) and maximum (2.0±0.2 vs 1.2±0.5, p<0.001) and minimum (1.5±0.6 vs 0.7±0.5, p<0.001) coverage grade was higher in ZES than in EES. The neointima heterogeneity index was not different between ZES and EES (0.4±0.5 vs 0.5±0.6, p=0.42). The incidence of thrombus was very low and was not different between ZES and EES (2% vs 4%, p=0.55).

CONCLUSIONS

Although both ZES and EES had good healing with homogeneous neointima coverage and a low incidence of thrombus, EES had more advanced atherosclerosis as shown by the presence of higher grade yellow plaque than ZES at 1 year after implantation.

Disruption of atherosclerotic neointima seven years after bare metal stent deployment

A 58-year-old male with a history of prior myocardial infarction, hypertension, and dyslipidemia was admitted due to deteriorating exertional angina. A bare metal stent (Multilink plus™, GUIDANT Corporation, Santa Clara, CA, USA) had been implanted into the proximal left anterior descending artery because of ST-elevation myocardial infarction 7 years earlier. Optical coherence tomography (OCT) showed a disruption of the atherosclerotic neointima overlying the stent. Intravascular imaging studies and pathological studies have shown that neointima within a bare-metal stent often transform into atherosclerotic tissue during an extended period of time. In the current report, OCT demonstrated that a disruption of the atherosclerotic neointima has the potential to cause the development of unstable clinical features. OCT examinations therefore help to understand the pathogenesis of acute coronary syndrome after stent implantation.

Effect of strut thickness on neointimal atherosclerotic change over an extended follow-up period (≥ 4 years) after bare-metal stent implantation: intracoronary optical coherence tomography examination

BACKGROUND

Neointima inside the bare-metal stents (BMSs) can transform into atherosclerotic tissue during an extended follow-up because of a persistent inflammatory reaction to the metal. We sought to investigate whether strut thickness may impact on the atherosclerotic change in neointima 4 years or more after BMS implantation using optical coherence tomography.

METHODS

Forty-six stented lesions of 41 patients with BMS ≥ 4 years after implantation who underwent optical coherence tomography were enrolled in the study. The strut was defined as thin when less than 100 μm and thick when ≥ 100 μm. According to these criteria, stents were divided into 2 groups (thin strut n = 19, thick strut n = 27). Neointimal tissue was categorized into normal neointima, characterized by a signal-rich band without signal attenuation, or lipid-laden intima, with marked signal attenuation and a diffuse border. Intimal disruption, thrombus, and neovascularization were also evaluated.

RESULTS

The mean period after implantation was 98.2 ± 25.8 months in the thin-strut group and 91.1 ± 22.8 months in the thick-strut group (P = .330). Lipid-laden intima (70% vs 32%, P = .016), thin-cap fibroatheroma-like intima (59% vs 16%, P = .0056), and intimal disruption (48% vs 16%, P = .031) were observed more frequently in the thick-strut group than in the thin-strut group, but no significant difference was observed in the frequency of thrombus. Although peristrut neovascularization was a common finding in both groups (thick vs thin 81% vs 79%, P = 1.000), the frequency of intraintima neovascularization tended to be higher in the thick-strut group (67% vs 42%, P = .135).

CONCLUSIONS

A thinner strut thickness may have favorable effects on neointimal atherosclerotic changes after BMS implantation.

Identification of vulnerable plaque in a stented coronary segment 17 years after implantation using optical coherence tomography

A patient presented with exertional chest pain two months prior to admission. Coronary angiography revealed a subocclusive stenosis within the boundaries of the stent. Optical coherence tomography showed remarkable intimal growth inside the stent, which demonstrated a heterogeneous appearance including low-intensity areas. These findings were congruent with the morphology of fibroatheroma in the native coronary artery and suggested that new atherosclerotic progression of the intima within the stent had occurred over 17 years following bare metal stent implantation. To the best of our knowledge, this is one of the most delayed instances of a bare metal stent restenosis described in the medical literature.

Evaluation of a newly designed endoscope for observing inner wall of large arteries for the use of endovascular intervention

A prototype endoscope for observing inner wall of large arteries was specially designed and evaluated through in vitro and in vivo tests. The purpose of this endoscope is to visualize the inner wall of large arteries, e.g., an aorta, without blocking off the blood stream aiming for the use of an assistive technique for endovascular interventions such as stent-graft placement for aortic aneurysm. The technique newly introduced for this purpose was the use of intermittent high-pressure saline jet synchronized to heart beat (diastolic phase). In the previous studies using commercially available bronchoscopes, we confirmed the validity of the system utilizing this technique [1, 2]. Based on these findings, in this study, we have specially designed a new endoscope with two channels, one for saline discharge and the other for forceps, and evaluated its performance through in vitro and in vivo tests. From the results of in vitro tests using a mock circulation system, it was confirmed that the newly designed endoscope was capable of visualizing a target installed on an inner surface of the mock system. Also confirmed through in vivo tests using swine was that we could observe bifurcation in descending aorta, e.g., left renal artery, without stopping off the blood stream.

Intravascular optical imaging technology for investigating the coronary artery

There is an ever-increasing demand for new imaging methods that can provide additional information about the coronary wall to better characterize and stratify high-risk plaques, and to guide interventional and pharmacologic management of patients with coronary artery disease. While there are a number of imaging modalities that facilitate the assessment of coronary artery pathology, this review paper focuses on intravascular optical imaging modalities that provide information on the microstructural, compositional, biochemical, biomechanical, and molecular features of coronary lesions and stents. The optical imaging modalities discussed include angioscopy, optical coherence tomography, polarization sensitive-optical coherence tomography, laser speckle imaging, near-infrared spectroscopy, time-resolved laser induced fluorescence spectroscopy, Raman spectroscopy, and near-infrared fluorescence molecular imaging. Given the wealth of information that these techniques can provide, optical imaging modalities are poised to play an increasingly significant role in the evaluation of the coronary artery in the future.

The possibility of delayed arterial healing 5 years after implantation of sirolimus-eluting stents: serial observations by coronary angioscopy

BACKGROUND

Although very late stent thrombosis occurs several years after implantation of sirolimus-eluting stent (SES), the morphologic changes of the stent beyond 2 years have not yet been systematically studied in living patients. The late vascular response to SES was therefore evaluated by serial angioscopic studies at 2 and 5 years after stent implantation.

METHODS

A total of 17 patients with 17 SES underwent a repeated angioscopy procedure at 2 and 5 years. Neointimal stent coverage (NSC) was classified as follows: grade 0, presence of uncovered struts; grade 1, visible struts through a thin neointima; or grade 2, complete neointimal coverage without visible struts. For each patient, the minimum and maximum NSC grade and the existence of in-stent thrombus were recorded.

RESULTS

The minimum and maximum NSC grade did not increase between the 2 and 5 years (0.59 ± 0.51 vs 0.88 ± 0.70, P = .17, and 1.82 ± 0.39 vs 1.94 ± 0.24, P = .30, respectively). The prevalence of patients with uncovered struts did not significantly decrease from 2 to 5 years (41% vs 29%, P = .49). During the follow-up period, 3 of 6 thrombi disappeared, whereas new thrombus formation was found in 3 patients without any clinical symptoms. In-stent thrombus did not decrease (35% vs 35%, P > .99).

CONCLUSIONS

The current serial angioscopic study suggests that incomplete NSC and the prevalence of latent thrombus within the SES segments did not decrease from 2 to 5 years. The risk of stent thrombosis related to incomplete healing of SES may continue for an extended period.

Coronary angioscopy: current topics and future direction

Disruption of vulnerable plaque and following thrombus formation are considered the main cause of acute coronary syndrome (ACS). Intracoronary angioscopy is an endoscopic technology that allows direct visualization of the coronary artery lumen and provides detailed information regarding plaque morphology in patients with coronary artery disease. The color and morphology of coronary plaque under angioscopy observation are proposed to be determinants for plaque stability. Angioscopically yellow plaque represents a thin-cap fibroatheroma, and is associated with a higher incidence of disruption and thrombus formation, and may be associated with future acute coronary syndromes. To circumvent the subjectivity of color interpretation, various quantitative methods have been proposed for identifying vulnerable plaques. Superior to other coronary imaging techniques such as VH IVUS and optical coherence tomography, angioscopy has impressively high sensitivity and specificity in detection of intraluminal thrombus. Angioscopy can also be used as an adjunctive technique during catheter intervention by directly visualizing the thrombus, stent struts and proliferating neointima. The time course and pattern of neointima coverage, as seen by angioscopy, various among different stent systems. Angioscopic assessment of serial changes after stent implantation may have potential benefits on patient's management after coronary stenting.

Coronary angioscopic evaluation for serial changes of luminal appearance after pharmacological and catheter interventions

Although preventive pharmacological therapies effectually reduce the risk of cardiovascular events, acute coronary syndrome (ACS) remains a leading cause of morbidity and mortality in our country, Japan. Disruption of atherosclerotic vulnerable plaques and flow-limiting thrombus formation in non-stent segments of native coronary arteries are considered a main mechanism of ACS. In addition, stent thrombosis originating from implanted metallic coronary stents, so-called vulnerable stents, occasionally appears as ACS in the clinical settings. Coronary angioscopy is a unique imaging modality permitting direct visualization of luminal structures, such as atherosclerotic plaque, thrombus, stent struts, and proliferating neointima. On the basis of accumulated angioscopic findings, intense yellow plaques and stents without neointimal coverage are considered vulnerable plaques and vulnerable stents, respectively. In contrast, morphological disappearance of vulnerable plaques or vulnerable stents by pharmacological and trans-catheter therapies imply stabilization of the plaques or stents. Hence, angioscopic assessment for vulnerability (or stability) of atherosclerotic plaques and implanted stents might be useful for risk classification in the future events of ACS. To evaluate serial changes of coronary lumen after pharmacological and catheter interventions using angioscopy might also provide important information on potential benefits and surrogate endpoints of the therapies and on patients' management.

Late loss in a disappearing frame of reference: is it still applicable to fully absorbable scaffolds?

Bioabsorbable stents are an important advancement in stent technology providing a temporary scaffold and may be augmented with drugs to suppress neointimal hyperplasia.Though changes are being made to the design of the stents, to ensure similar rates of acute recoil, residual stenosis postintervention remains higher when compared to contemporary durable stents. In order to achieve similar clinical restenosis outcomes, bioabsorbable stents must first show similar MLD or percent diameter stenosis at follow-up to drug-eluting stents.While variable different acute gain and post-procedure MLD for bioabsorbable stents make late lumen loss a poor marker for restenosis probability by itself, late loss can be an informative metric for neointimal hyperplasia over time in these stents.Metrics which are independent of acute gain such as minimal luminal diameter and percentage diameter stenosis may make better surrogates for restenosis (Table 1). Moreover, remodelling over time requires measurement of the vessel and lumen diameters in later follow-up. Since the natural history of the vascular response to bioabsorbable stents is in its infancy of investigation, follow-up of these stents at least beyond the duration of polymer is prudent. Finally, given a disappearing frame of reference, both careful angiographic and intravascular ultrasound assessments are helpful to delineate the varying contributions of recoil, remodelling, and neointima formation.