IVUS radiofrequency analysis in the evaluation of the polymeric struts of the bioabsorbable everolimus-eluting device during the bioabsorption process

Fundamentals and role of intravascular ultrasound in percutaneous coronary intervention

Intravascular ultrasound (IVUS) is a catheter-based invasive imaging modality that has become an essential adjunctive tool to percutaneous coronary intervention (PCI) over the past 20 years. Clinical applications of IVUS in PCI include assessment of lesion severity, characterizing plaque morphology, optimization of acute stent results and clarification of mechanisms of stent failure. Numerous meta-analyses of large observational and randomized studies support the role of IVUS-guided PCI in reducing short and long-term adverse outcomes, including mortality and stent failure, particularly in patients receiving drug-eluting stents (DESs) and in complex lesion subsets. The current review provides a summary of the fundamental aspects and current clinical roles of IVUS in coronary intervention.

Methods to assess bioresorbable vascular scaffold devices behaviour after implantation

Bioresorbable vascular scaffolds (BRS) represent a novel approach for coronary revascularization offering several advantages as compared to current generation DES, potentially reducing rate of late adverse events and avoiding permanent vessel caging. Nevertheless, safety concerns have been raised for an increased risk of scaffold thrombosis (ScT) in both early and late phases, probably related to a suboptimal scaffold implantation. In this context, the use of different imaging methodologies has been strongly suggested in order to guarantee an optimal implantation. We herein analyze the different imaging methodologies available to assess BRS after implantation and at follow-up.

Echogenicity as a surrogate for bioresorbable everolimus-eluting scaffold degradation: analysis at 1-, 3-, 6-, 12- 18, 24-, 30-, 36- and 42-month follow-up in a porcine model

The objective of the study is to validate intravascular quantitative echogenicity as a surrogate for molecular weight assessment of poly-l-lactide-acid (PLLA) bioresorbable scaffold (Absorb BVS, Abbott Vascular, Santa Clara, California). We analyzed at 9 time points (from 1- to 42-month follow-up) a population of 40 pigs that received 97 Absorb scaffolds. The treated regions were analyzed by echogenicity using adventitia as reference, and were categorized as more (hyperechogenic or upperechogenic) or less bright (hypoechogenic) than the reference. The volumes of echogenicity categories were correlated with the measurements of molecular weight (Mw) by gel permeation chromatography. Scaffold struts appeared as high echogenic structures. The quantification of grey level intensity in the scaffold-vessel compartment had strong correlation with the scaffold Mw: hyperechogenicity (correlation coefficient = 0.75; P < 0.01), upperechogenicity (correlation coefficient = 0.63; P < 0.01) and hyper + upperechogenicity (correlation coefficient = 0.78; P < 0.01). In the linear regression, the R² for high echogenicity and Mw was 0.57 for the combination of hyper and upper echogenicity. IVUS high intensity grey level quantification is correlated to Absorb BVS residual molecular weight and can be used as a surrogate for the monitoring of the degradation of semi-crystalline polymers scaffolds.

Analysis of 1 year virtual histology changes in coronary plaque located behind the struts of the everolimus eluting bioresorbable vascular scaffold

Serial intravascular ultrasound virtual histology (IVUS-VH) after implantation of metallic stents has been unable to show any changes in the composition of the scaffolded plaque overtime. The everolimus-eluting ABSORB scaffold potentially allows for the formation of new fibrotic tissue on the scaffolded coronary plaque during bioresorption. We examined the 12 month IVUS-VH changes in composition of the plaque behind the struts (PBS) following the implantation of the ABSORB scaffold. Using IVUS-VH and dedicated software, the composition of the PBS was analyzed in all patients from the ABSORB Cohort B2 trial, who were imaged with a commercially available IVUS-VH console (s5i system, Volcano Corporation, Rancho Cordova, CA, USA), immediately post-ABSORB implantation and at 12 month follow-up. Paired IVUS-VH data, recorded with s5i system, were available in 17 patients (18 lesions). The analysis demonstrated an increase in mean PBS area (2.39 ± 1.85 mm² vs. 2.76 ± 1.79 mm², P = 0.078) and a reduction in the mean lumen area (6.37 ± 0.90 mm² vs. 5.98 ± 0.97 mm², P = 0.006). Conversely, a significant decrease of 16 and 30% in necrotic core (NC) and dense calcium (DC) content, respectively, were evident (median % NC from 43.24 to 36.06%, P = 0.016; median % DC from 20.28 to 11.36%, P = 0.002). Serial IVUS-VH analyses of plaque located behind the ABSORB struts at 12-month demonstrated an increase in plaque area with a decrease in its NC and DC content. Larger studies are required to investigate the clinical impact of these findings.

Novel drug-eluting stents in the treatment of de novo coronary lesions

Due to safety concerns in recent years, much effort has been devoted to improving the outcomes associated with drug-eluting stents (DESs). This review summarizes the current status of methodological and technical achievements reported in second-generation DES. Novel stents are described based on the component (the platform, the polymer, and the drug) that has undergone the most significant changes compared to earlier generation DES. An overview of the currently available evidence on the use of novel coronary devices in patients undergoing coronary revascularization is also reviewed.

Assessment of drug-eluting stents and bioresorbable stents by grayscale IVUS and IVUS-based imaging modalities

Grayscale IVUS and IVUS-based imaging modalities during the last years have become useful in the assessment not only of drug eluting stent, but also of new bioresorbable vascular scaffolds. Although IVUS resolution is not sufficient for determining stent coverage (optical coherence tomography is the gold standard), serial IVUS can measure intimal hyperplasia, assess acute and late incomplete stent apposition, detect the presence and persistence of edge dissections, study edge effects and look for causes of restenosis and thrombosis. In addition other IVUS-based imaging modalities, such as IVUS-VH, iMAP or palpography, can be used to study the serial compositional and mechanical changes of the plaque behind stent struts and also to follow the bioresorption of the new bioresorbable scaffolds, analyzing the backscattering signal coming from the polymeric struts. This review details and evaluates grayscale IVUS and IVUS-based techniques findings in clinical trials, highlighting the usefulness of these imaging modalities in the study of drug eluting stents and bioresorbable vascular scaffold.

Focus on the research utility of intravascular ultrasound - comparison with other invasive modalities

Intravascular ultrasound (IVUS) is an invasive modality which provides cross-sectional images of a coronary artery. In these images both the lumen and outer vessel wall can be identified and accurate estimations of their dimensions and of the plaque burden can be obtained. In addition, further processing of the IVUS backscatter signal helps in the characterization of the type of the plaque and thus it has been used to study the natural history of the atherosclerotic evolution. On the other hand its indigenous limitations do not allow IVUS to assess accurately stent struts coverage, existence of thrombus or exact site of plaque rupture and to identify some of the features associated with increased plaque vulnerability. In order this information to be obtained, other modalities such as optical coherence tomography, angioscopy, near infrared spectroscopy and intravascular magnetic resonance imaging have either been utilized or are under evaluation. The aim of this review article is to present the current utilities of IVUS in research and to discuss its advantages and disadvantages over the other imaging techniques.

Temporal changes of coronary artery plaque located behind the struts of the everolimus eluting bioresorbable vascular scaffold

Implantation of a coronary stent results in a mechanical enlargement of the coronary lumen with stretching of the surrounding atherosclerotic plaque. Using intravascular ultrasound virtual-histology (IVUS-VH) we examined the temporal changes in composition of the plaque behind the struts (PBS) following the implantation of the everolimus eluting bioresorbable vascular scaffold (BVS). Using IVUS-VH and dedicated software, the composition of plaque was analyzed in all patients from the ABSORB B trial who were imaged with a commercially available IVUS-VH console (s5i system, Volcano Corporation, Rancho Cordova, CA, USA) post-treatment and at 6-month follow-up. This dedicated software enabled analysis of the PBS after subtraction of the VH signal generated by the struts. The presence of necrotic core (NC) in contact with the lumen was also evaluated at baseline and follow-up. IVUS-VH data, recorded with s5i system, were available at baseline and 6-month follow-up in 15 patients and demonstrated an increase in both the area of PBS (2.45 ± 1.93 mm(2) vs. 3.19 ± 2.48 mm(2), P = 0.005) and the external elastic membrane area (13.76 ± 4.07 mm(2) vs. 14.76 ± 4.56 mm(2), P = 0.006). Compared to baseline there was a significant progression in the NC (0.85 ± 0.70 mm(2) vs. 1.21 ± 0.92 mm(2), P = 0.010) and fibrous tissue area (0.88 ± 0.79 mm(2) vs. 1.15 ± 1.05 mm(2), P = 0.027) of the PBS. The NC in contact with the lumen in the treated segment did not increase with follow-up (7.33 vs. 6.36%, P = 0.2). Serial IVUS-VH analysis of BVS-treated lesions at 6-month demonstrated a progression in the NC and fibrous tissue content of PBS.