Optical coherence tomography endpoints in stent clinical investigations: strut coverage

Research progress of drug eluting balloon in arterial circulatory system

The arterial circulatory system diseases are common in clinical practice, and their treatment options have been of great interest due to their high morbidity and mortality. Drug-eluting balloons, as a new type of endovascular interventional treatment option, can avoid the long-term implantation of metal stents and is a new type of angioplasty without stents, so drug-eluting balloons have better therapeutic effects in some arterial circulatory diseases and have been initially used in clinical practice. In this review, we first describe the development, process, and mechanism of drug-eluting balloons. Then we summarize the current studies on the application of drug-eluting balloons in coronary artery lesions, in-stent restenosis, and peripheral vascular disease. As well as the technical difficulties and complications in the application of drug-eluting balloons and possible management options, in order to provide ideas and help for future in-depth studies and provide new strategies for the treatment of more arterial system diseases.

Effects of exenatide on coronary stent's endothelialization in subjects with type 2 diabetes: a randomized controlled trial. The Rebuild study

BACKGROUND

Subjects with type 2 diabetes (T2D) have a higher risk of in-stent restenosis and stent thrombosis. The activation of the glucagon-like peptide-1 receptor (GLP-1R) has been suggested to induce several effects on the vasculature that may reduce the risk of stent failure following an angioplasty. The aim of this study is to evaluate the effect of the GLP-1R agonist exenatide on endothelialization of a modern drug-eluting stent (DES) in subjects with T2D.

METHODS

38 subjects with T2D who were eligible for revascularization with implantation of DES were randomized to treatment with exenatide (once weekly) plus standard treatment, or to standard treatment alone. After 12 weeks, a new coronary angiography was performed to evaluate the percentage of strut coverage (primary endpoint) and the presence of neo-atherosclerosis by optical coherence tomography. This study was approved by the Stockholm's Ethical Review Board.

RESULTS

The two groups were well balanced regarding baseline clinical characteristics. Strut coverage was 95% (88.7-98.5%) in the exenatide group and 91.4% (88.8-98.5%) in the control group (p = 0.692). There were no significant differences between groups neither in the thickness of neo-intima (0.2 mm in both groups, p = 0.471), nor the maximal in-stent obstruction by neo-intima (15.5% in exenatide group vs 14.7% in control group, p = 0.801). No significant differences were detected in the rate of target lesion revascularization between groups (p = 0.224).

CONCLUSION

Twelve weeks treatment with exenatide did not lead to a significantly better stent coverage in people with T2D. No significant differences in the occurrence of neo-atherosclerosis were detected between groups.

TRIAL REGISTRATION

The study was registered at www.

CLINICALTRIALS

gov (Rebuild Study, NCT02621489).

Efficacy of Zotarolimus-Eluting Stents in Treating Diabetic Coronary Lesions: An Optical Coherence Tomography Study

BACKGROUND

Diabetes mellitus (DM) plays an important role in restenosis and late in-stent thrombosis (ST). The current study using optical coherence tomography (OCT) aims to compare target lesion neointima in patients with or without diabetes after zotarolimus-eluting stent (ZES) treatment.

METHODS

OCT images of 90,212 struts and quantitative coronary angiography (QCA) in 62 patients (32 with DM and 30 without DM) with 69 de novo coronary lesions (34 DM and 35 non-DM) both after ZES implantation and 12 ± 1 month angiographic follow-up were recorded. Patient characteristics, lesion characteristics, clinical outcomes, and OCT findings including neointimal thickness, coverage, malapposition, and intimal morphology were analyzed.

RESULTS

Baseline patient characteristics and lesion characteristics data were similar between the two groups. Higher neointimal thickness (0.14 ± 0.09 mm vs. 0.09 ± 0.04 mm, p = 0.021), more neovascularization (3.03 ± 6.24 vs. 0.52 ± 1.87, p = 0.017) and higher incidence of layered signal pattern (12.19 ± 19.91% vs. 4.28 ± 9.02%, p = 0.049) were observed in diabetic lesions comparing with non-diabetic lesions. No differences were found in malapposition, uncovered percentage, and thrombus between the two groups (all p > 0.05). Occurrence of clinical adverse events was also similar during the follow-up period (p > 0.05).

CONCLUSION

Although more neointimal proliferation and more neovascularization were found in diabetic coronary lesions when compared with non-diabetic lesions, treatment with ZES showed similar stent malapposition rate at 1-year follow-up. The data indicated that ZES treatment could possibly be effective in treating diabetic coronary lesions.

TRIAL REGISTRATION

ClinicalTrials.gov identifier, NCT01747356.

Application and Evaluation of Highly Automated Software for Comprehensive Stent Analysis in Intravascular Optical Coherence Tomography

Intravascular optical coherence tomography (IVOCT) is used to assess stent tissue coverage and malapposition in stent evaluation trials. We developed the OCT Image Visualization and Analysis Toolkit for Stent (OCTivat-Stent), for highly automated analysis of IVOCT pullbacks. Algorithms automatically detected the guidewire, lumen boundary, and stent struts; determined the presence of tissue coverage for each strut; and estimated the stent contour for comparison of stent and lumen area. Strut-level tissue thickness, tissue coverage area, and malapposition area were automatically quantified. The software was used to analyze 292 stent pullbacks. The concordance-correlation-coefficients of automatically measured stent and lumen areas and independent manual measurements were 0.97 and 0.99, respectively. Eleven percent of struts were missed by the software and some artifacts were miscalled as struts giving 1% false-positive strut detection. Eighty-two percent of uncovered struts and 99% of covered struts were labeled correctly, as compared to manual analysis. Using the highly automated software, analysis was harmonized, leading to a reduction of inter-observer variability by 30%. With software assistance, analysis time for a full stent analysis was reduced to less than 30 minutes. Application of this software to stent evaluation trials should enable faster, more reliable analysis with improved statistical power for comparing designs.

Three-month evaluation of strut healing using a novel optical coherence tomography analytical method following bioresorbable polymer everolimus-eluting stent implantation in humans: the TIMELESS study

AIMS

Bioresorbable polymer drug-eluting stent technologies have been considered to have the potential to enhance vascular healing by reducing polymer exposure to the vessel wall, potentially allowing the earlier discontinuation of dual antiplatelet therapy. At present, the early vascular healing response to this type of technologies is still unclear.

PATIENTS AND METHODS

The TIMELESS study is a multicenter, prospective, single-arm study that enrolled real-world patients undergoing percutaneous coronary intervention. All patients underwent Synergy stent implantation, which consists of a platinum-chromium platform coated with an ultra-thin abluminal bioabsorbable poly-D,L-lactide-co-glycolide polymer-eluting everolimus.

RESULTS

A total of 37 patients were included in the study. The majority of the patients underwent percutaneous coronary intervention because of acute coronary syndromes. At 3 months, angiographic follow-up showed a percentage diameter of stenosis of 8.1±7.5% and an angiographic late loss of 0.03±0.24 mm. In all analyzed struts, less than 1% of struts were definitely uncovered or covered with fibrin, 12.5% (5.0-18.5%) showed evidence of partial coverage, and the remaining (∼85%) were fully covered. No stent thrombosis was observed up to 12 months of clinical follow-up.

CONCLUSION

In a real-world population, the implantation of a bioresorbable polymer drug-eluting stent resulted in almost complete strut coverage throughout the entire stent length at 3 months. The clinical implications for antiplatelet therapy and outcomes should be investigated further.

Surrogate and clinical endpoints in interventional cardiology: are statistics the brakes?

BACKGROUND

Randomized controlled trials are the gold standard for demonstrating safety and efficacy of coronary devices with or without accompanying drug treatments in interventional cardiology. With the advent of last-generation drug-eluting stents having enhanced technical attributes and long-term clinical benefits, the proof of incremental angiographic or long-term clinical efficacy becomes more challenging. The purpose of this review is to provide an overview of the most common and alternative study endpoints in interventional cardiology and their potential reimbursement value. Moreover, we intend to describe the statistical limitations in order to demonstrate differences between potential treatment groups. Furthermore, careful endpoint recommendations for a given patient number are offered for future study designs.

METHODS

The number of patients per treatment group was estimated for various study designs such as noninferiority test hypotheses with hard clinical endpoints and various surrogate endpoints. To test for differences in various surrogate endpoint scenarios, the corresponding patient group sizes were explored. To evaluate these endpoints in terms of their reimbursement impact, preferred endpoints for technical appraisals in interventional cardiology at the National Institute of Health and Care Excellence (NICE) were used.

RESULTS

Even with the most stringent experimental control to reduce bias-introducing factors, studies with hard primary clinical endpoints such as the occurrence of major adverse cardiac events (MACE) or target-lesion revascularization (TLR) rates remain the gold standard, with numbers reaching into the 300-700 patient range per group. Study designs using loss in fractional-flow reserve (FFR) or stent-strut-coverage rates can be statistically formulated; however, the clinical ramifications for the patient remain to be discussed. Nonrandomized study designs with intrapatient angiographic controls in nontarget vessels may merit further thoughts and explorations.

CONCLUSIONS

From a reimbursement impact, the primary endpoints MACE and TLR are the best choices for a moderately sized study population of 500 patients per group. Angiographic endpoints, in particular minimal lumen diameter (MLD), are not useful in this context. The emerging endpoints such as loss in FFR or stent coverage require smaller patient populations. However, their impact on reimbursement-related decisions is limited.

Intravascular optical coherence tomography light scattering artifacts: merry-go-rounding, blooming, and ghost struts

We sought to elucidate the mechanisms underlying two common intravascular optical coherence tomography (IV-OCT) artifacts that occur when imaging metallic stents: “merry-go-rounding” (MGR), which is an increase in strut arc length (SAL), and “blooming,” which is an increase in the strut reflection thickness (blooming thickness). Due to uncontrollable variables that occur in vivo, we performed an in vitro assessment of MGR and blooming in stented vessel phantoms. Using Xience V and Driver stents, we examined the effects of catheter offset, intimal strut coverage, and residual blood on SAL and blooming thickness in IV-OCT images. Catheter offset and strut coverage both caused minor MGR, while the greatest MGR effect resulted from light scattering by residual blood in the vessel lumen, with 1% hematocrit (Hct) causing a more than fourfold increase in SAL compared with saline (p<0.001 ). Residual blood also resulted in blooming, with blooming thickness more than doubling when imaged in 0.5% Hct compared with saline (p<0.001 ). We demonstrate that a previously undescribed mechanism, light scattering by residual blood in the imaging field, is the predominant cause of MGR. Light scattering also results in blooming, and a newly described artifact, three-dimensional-MGR, which results in “ghost struts” in B-scans.

Drug-eluting metallic stents in urology

Drugeluting metal stents (DESs) have been extensively used in coronary and vascular disease. This type of stents has been proven to provide significantly lower restenosis rates due to the reduction of neo-intimal hyperplasia in comparison to the traditionally used bare metal stents (BMSs). The latter stents have been evaluated for more than a decade in urological practice in an attempt to provide permanent relief of urethral or ureteral obstruction. Although the initial results were promising, long-term experience revealed significant complications, which are mainly attributed to stent-related hyperplastic reaction compromising stent patency. The favorable experience of vascular DESs led to the application of DESs in both the urethra and ureter of animal models. These experimental results demonstrated a reduction of hyperplastic reaction of DESs in comparison to BMSs. Nevertheless, clinical data are currently not available. Considering the fact that DESs are under continuous development, the use of DESs in urology holds promise for the future and seems to be an intriguing field.

Optical coherence tomography provides images similar to histology and allows the performance of extensive measurements of drug-eluting metal stents in animal ureters

Optical coherence tomography (OCT) images and histology images of metal stents (MSs) inserted in animal ureters were compared, and the reliability of an OCT-based automated method for the performance of quantitative evaluation of ureteral MSs was evaluated. A zotarolimus-eluting metal stent (ZES) and a bare metal stent (BMS) were inserted in each ureter of ten pigs and six rabbits. OCT was performed in unobstructed stented ureters. Histopathologic examination of the stented ureters embedded in glycol-methacrylate took place. Quadrants of OCT images were compared to their respective histologic images by employing two independent observers who delineated different layers in the quadrants of OCT images and correlated them to the respective histologic quadrants. Manual (integrated OCT device software) and automated measurements of the OCT images using an automated strut detection method were compared. The observers highly agreed on the delineation of urothelium from the lamina propria and the lamina propria from the muscle layer of the ureteral wall. The algorithm measurements were similar to the manual measurements, and the algorithm proved to be reliable in the evaluation of ureteral MSs. Significantly higher endothelial hyperplasia of the BMSs in comparison to the ZESs was also quantitatively demonstrated by the strut detection method. OCT proved to be a reliable method for the evaluation of ureteral MSs. OCT provided images of the stented ureteral lumen similar to light microscopy quality. Measurements of the stented ureter are reliably performed by the automated strut detection method.

QCA, IVUS and OCT in interventional cardiology in 2011

Over the past 30 years, quantitative coronary arteriography (QCA) has been used extensively as an objective and reproducible tool in clinical research to assess changes in vessel dimensions as a result of interventions, but also as a tool to provide evidence to the interventionalist prior to and after an intervention and at follow-up when necessary. With the increasing complexities of bifurcation stenting, corresponding analytical tools for bifurcation analysis have been developed with extensive reporting schemes. Although intravascular ultrasound (IVUS) has been around for a long time as well, more recent radiofrequency analysis provides additional information about the vessel wall composition; likewise optical coherence tomography (OCT) provides detailed information about the positions of the stent struts and the quality of the stent placement. Combining the information from the X-ray lumenogram and the intravascular imaging devices is mentally a challenging task for the interventionalist. To support the registration of these intravascular images with the X-ray images, 3D QCA has been developed and registered with the IVUS or OCT images, so that at every position along the vessel of interest the luminal data and the vessel wall data by IVUS or the stent strut data by OCT can be combined. From the 3D QCA the selection of the optimal angiographic views can also be facilitated. It is the intention of this overview paper to provide an extensive description of the techniques that we have developed and validated over the past 30 years.

Serial three-dimensional optical coherence tomography assessment of strut coverage and intraluminal structures after drug-eluting stent implantation

Understanding of intraluminal structure and distribution of uncovered struts after drug-eluting stent implantation are limited by only 2-dimensional (2D) optical coherence tomography (OCT) images. We compared tissue coverage with 3-dimensional (3D) OCT and 2D quantitative analyses, and changes in intraluminal structure immediately after (baseline) everolimus-eluting stent (EES) implantation and at follow-up. The 2D analyses of uncovered struts ratio and tissue coverage thickness at a 0.5-mm interval were compared to 3D-OCT images and visually classified for the degree of tissue coverage. The difference in tissue coverage at baseline and follow-up after EES implantation was evaluated with tissue coverage scores (TCS) calculated by the 3D-OCT classification (Grade 0-3). 3D-OCT classifications were negatively correlated with uncovered-to-total struts (r = -0.864, P < 0.001) and positively correlated with tissue coverage thickness (r = 0.905, P < 0.001). Follow-up TCS was greater than baseline TCS (0.2 ± 0.4 vs. 1.4 ± 0.5, P < 0.001). Moreover, changes in intraluminal structures and longitudinal distribution of uncovered struts were assessed. Incomplete stent appositions, in-stent dissections, and thrombi were decreased at follow-up, indicating progressive arterial healing. The distribution of uncovered-to-total struts could be assessed by 3D-OCT, which was related to 2D analysis. Significant correlations between 3D-OCT classifications and quantitative analyses were shown. The classification and visual assessment of intraluminal structures by 3D-OCT were useful in evaluating arterial healing after EES implantation.

Early vascular healing with rapid breakdown biodegradable polymer sirolimus-eluting versus durable polymer everolimus-eluting stents assessed by optical coherence tomography

BACKGROUND

Differences in early arterial healing patterns after stent implantation between biodegradable and durable polymer based new generation drug-eluting stents are not well understood. The aim of this study was to compare the healing patterns of a novel rapid breakdown (≤8 weeks) biodegradable polymer sirolimus-eluting stent (BP-SES) with a durable polymer everolimus-eluting stent (EES) using intravascular optical coherence tomography (OCT) at 4 months.

METHODS

A total of 20 patients were randomly assigned to stenting with BP-SES (n=11) or EES (n=9). Overall intravascular imaging was available for 15 (75%) patients. The primary endpoint was the difference in rate of uncovered struts between BP-SES and EES. To account for strut-level clustering, the results in both treatment groups were compared using a generalized linear mixed model approach.

RESULTS

Regarding the primary endpoint, BP-SES as compared to EES showed similar rates of uncovered struts (37 [6.8%] versus 167 [17.5%], odds ratio (OR) 0.45 (95% CI 0.09-2.24), p=0.33). There were no malapposed struts in BP-SES group and 14 malapposed struts in EES group (p=0.97). No difference in percent neointimal volume (14.1±8.2% vs. 11.4±6.4%, p=0.56) was observed.

CONCLUSIONS

Although rapid-breakdown BP-SES as compared to EES showed signs of improved early tissue coverage, after adjustment for strut-level clustering these differences were not statistically significant. No differences in ability to suppress neointimal hyperplasia after stent implantation between 2 stents were observed.

Reproducibility of qualitative assessment of stent struts coverage by optical coherence tomography

Assessment of stent strut coverage by optical coherence tomography (OCT) is not standardized. The methodology most commonly used is based on a visual binary qualitative assessment (strut covered or not). However, the influence of magnification (zoom setting) to the inter- and intra-observer agreements has not yet been evaluated. Aim of our study was therefore to evaluate the agreements of this approach, taking into account various zoom settings. 126 struts from 10 selected frames were independently evaluated by four observers using a stepwise approach increasing the zoom setting as following: (1) full view of the lumen (FV), (2) half view of the lumen (HV) and (3) a quarter view of the lumen (QV). Intra- and inter-observer agreements (κ) were assessed. The rate of uncoverage was determined for each strut as the number of times it was defined as uncovered divided by the total number of observations (maximum 12 = 3 zoom settings × 4 analysts) and expressed as percentage. The inter-observer κ values (mean [range]) were 0.32 [0.07-0.63], 0.40 [0.18-0.69] and 0.33 [0.09-0.6], within FV, HV and QV respectively. The intra-observer κ values were 0.60 [0.50-0.70], 0.75 [0.75-0.76] and 0.60 [0.50-0.70], within FV, HV and QV respectively. By increasing zoom setting the κ value of intra-observer agreement was 0.74 [0.58-0.83] (from FV to HV), 0.70 [0.56-0.83] (from HV to QV) and 0.70 [0.37-0.86] (from FV to QV). Overall, the rate of uncoverage was 15.5% [8.3-100%]. The OCT qualitative evaluation of strut coverage has wide inter and intra-observer agreements and is dependent of the zoom setting used during the analysis. A more reproducible approach would be needed to eventually increase the probability to link uncovered struts with clinical events.

Automatic stent detection in intravascular OCT images using bagged decision trees

Intravascular optical coherence tomography (iOCT) is being used to assess viability of new coronary artery stent designs. We developed a highly automated method for detecting stent struts and measuring tissue coverage. We trained a bagged decision trees classifier to classify candidate struts using features extracted from the images. With 12 best features identified by forward selection, recall (precision) were 90%-94% (85%-90%). Including struts deemed insufficiently bright for manual analysis, precision improved to 94%. Strut detection statistics approached variability of manual analysis. Differences between manual and automatic area measurements were 0.12 ± 0.20 mm(2) and 0.11 ± 0.20 mm(2) for stent and tissue areas, respectively. With proposed algorithms, analyst time per stent should significantly reduce from the 6-16 hours now required.

Evaluation of zotarolimus-eluting metal stent in animal ureters

BACKGROUND AND PURPOSE

Drug-eluting stents proved to minimize neointimal hyperplasia in coronary vessels. Hyperplastic reaction is the most common unwelcome event related to the use of metal mesh stents in the ureter. We evaluated the effect of zotarolimus-eluting stent (ZES) Endeavor Resolute in the porcine and rabbit ureter.

MATERIALS AND METHODS

A ZES and a bare metal stent (BMS) were inserted in each ureter of 10 pigs and 6 rabbits. The insertion was performed by the retrograde approach. CT was used for the evaluation of porcine ureters while intraoperative intravenous urography (IVU) was used for rabbit ureters. The follow-up included CT or IVU every week for the following 4 weeks for pigs and 8 weeks for rabbits. Renal scintigraphies were performed before stent insertion and during the third week in all animals. Optical coherence tomography (OCT) has been used for the evaluation of the luminal and intraluminal condition of the ureters with stents. Histopathologic examination of the these ureters embedded in glycol-methacrylate was performed.

RESULTS

Hyperplastic reaction was present in both stent types. BMSs in seven porcine ureters were completely obstructed while porcine ureters with ZES stents had hyperplastic tissue that did not result in obstruction. Two rabbit ureters with BMS stents were occluded while no ZES was associated with ureteral obstruction. The function of the seven porcine renal units and the two rabbit units with obstructed ureters with stents was compromised. The OCT revealed increased hyperplastic reaction in the ureters with BMS stents in comparison with those with ZESs. Although, hyperplastic reaction was present in all cases, pathologic examination revealed significantly more hyperplastic reaction in BMSs.

CONCLUSION

ZESs in the pig and rabbit ureter were not related to hyperplastic reaction resulting in stent occlusion. These stents were related to significantly lower hyperplastic reaction in comparison with BMSs while inflammation rates were similar for both stent types.