Intracoronary Imaging for Assessment of Vascular Healing and Stent Follow-up in Bioresorbable Vascular Scaffolds

Bioresorbable Vascular Scaffolds (BVS) are polymer-based materials implanted in the coronary arteries in order to treat atherosclerotic lesions, based on the concept that once the lesion has been treated, the material of the implanted stent will undergo a process of gradual resorption that will leave, in several years, the vessel wall smooth, free of any foreign material and with its vasomotion restored. However, after the first enthusiastic reports on the efficacy of BVSs, the recently published trials demonstrated disappointing results regarding long-term patency following BVS implantation, which were mainly attributed to technical deficiencies during the stenting procedure. Intracoronary imaging could play a crucial role for helping the operator to correctly implant a BVS into the coronary artery, as well as providing relevant information in the follow-up period. This review aims to summarize the role of intracoronary imaging in the follow-up of coronary stents, with a particular emphasis on the role of intravascular ultrasound and optical coherence tomography for procedural guidance during stent implantation and also for follow-up of bioabsorbable scaffolds.

Two-year clinical outcomes of patients treated with overlapping absorb scaffolds: An analysis of the ABSORB EXTEND single-arm study

BACKGROUND

Preclinical data showed that overlapping (OVP) scaffolds might result in delayed healing and strut coverage compared to nonOVP scaffold segments. Furthermore, OVP in patients could result in increased periprocedure myocardial infarction (MI) rate secondary to side branch occlusion; however, little is known whether this may have an impact on long-term clinical outcomes.

METHODS

ABSORB EXTEND is a prospective, single-arm, open-label clinical study in which 812 patients were enrolled at 56 sites. In this study, we compared the immediate and 2-year clinical outcomes of patients with OVP scaffolds (n = 115) to those of patients with nonOVP scaffolds (n = 697). The primary objective was the comparison of major adverse cardiac event (MACE) (cardiac death, MI and ischemic-driven target lesion revascularization [TLR]) and scaffold thrombosis (ST) rates up to 2 years.

RESULTS

Baseline clinical and angiographic characteristics were comparable between cohorts except for longer lesions in the OVP patients as expected (16.7 ± 7.3 vs. 11.6 ± 4.4 mm, P < 0.0001), higher lesion complexity (B2) and numerically smaller vessel size. In-hospital, there was a marked increase in MACE in the OVP cohort (7.0 vs. 0.9%, P = 0.002), exclusively driven by a higher rate of periprocedure MI (7.0 vs. 0.9%, P = 0.002). Long-term MACE did not significantly differ between groups (10.4% in the OVP cohort vs. 6.6% in the no-OVP group, P = 0.1) with comparable rates of cardiac death (0.9 vs. 1.2%, P = 1.0) and ischemia-driven TLR (1.7 vs. 2.5%, P = 1.0). Cumulative incidence of MI was higher in the OVP cohort (7.8 vs. 3.0%, P = 0.02). Of note, the rate of MI between hospital discharge and 2-year follow-up was lower in the OVP cohort (0.8 vs. 2.1%, P = 0.04). Cumulative incidence of definite/probable ST was relatively low and comparable between groups (1.8 vs. 1.5%, P = 0.7).

CONCLUSIONS

In this low-to-moderate complex population treated with the ABSORB scaffold the OVP group showed a higher incidence of periprocedure MI with no immediate or long-term increase in cardiac death, TLR or ST.

The Safety and Efficacy of Absorb Bioresorbable Vascular Scaffold: A Systematic Review

Bioresorbable stents are novel devices designed to overcome the long-term limitations of permanent stent implantation. The Absorb bioresorbable vascular scaffold (BVS; Abbott Vascular, Santa Clara, CA) was the first bioresorbable stent with Conformité Européenne mark approval in coronary vessels and has been the subject of multiple clinical studies. Despite its potential advantages, the safety and efficacy of BVS remain unclear. To address this, we conducted a systematic review to examine the safety and efficacy of BVS. The MEDLINE, Embase, Current Index to Nursing & Allied Health Literature (CINAHL), Cochrane, and Science Citation Index Expanded (SCIE) databases were searched for studies examining BVS safety and efficacy. Our search was restricted to studies published in English or French. Outcomes of interest include cardiac death, myocardial infarction, target-lesion revascularization, restenosis, and composite endpoints. Eleven studies met our inclusion criteria (n = 2990), which included 1 randomized controlled trial and 10 cohort studies (2 controlled). These studies varied in size (11-1189) and follow-up duration (1-60 months). The incidence of major adverse cardiac events ranged from 2.6% to 15.5%, with no statistically significant difference between BVS and control in studies that included a comparison group. Although available data are limited, current evidence is promising and suggests that the use of BVS is not associated with a significant increase in major cardiac events in the short term. Numerous randomized controlled trials are currently in progress that will further improve our understanding of the safety and efficacy of this device.

Incidence and imaging outcomes of acute scaffold disruption and late structural discontinuity after implantation of the absorb Everolimus-Eluting fully bioresorbable vascular scaffold: optical coherence tomography assessment in the ABSORB cohort B Trial (A Clinical Evaluation of the Bioabsorbable Everolimus Eluting Coronary Stent System in the Treatment of Patients With De Novo Native Coronary Artery Lesions)

OBJECTIVES

This study sought to describe the frequency and clinical impact of acute scaffold disruption and late strut discontinuity of the second-generation Absorb bioresorbable polymeric vascular scaffolds (Absorb BVS, Abbott Vascular, Santa Clara, California) in the ABSORB (A Clinical Evaluation of the Bioabsorbable Everolimus Eluting Coronary Stent System in the Treatment of Patients With De Novo Native Coronary Artery Lesions) cohort B study by optical coherence tomography (OCT) post-procedure and at 6, 12, 24, and 36 months.

BACKGROUND

Fully bioresorbable scaffolds are a novel approach to treatment for coronary narrowing that provides transient vessel support with drug delivery capability without the long-term limitations of metallic drug-eluting stents. However, a potential drawback of the bioresorbable scaffold is the potential for disruption of the strut network when overexpanded. Conversely, the structural discontinuity of the polymeric struts at a late stage is a biologically programmed fate of the scaffold during the course of bioresorption.

METHODS

The ABSORB cohort B trial is a multicenter single-arm trial assessing the safety and performance of the Absorb BVS in the treatment of 101 patients with de novo native coronary artery lesions. The current analysis included 51 patients with 143 OCT pullbacks who underwent OCT at baseline and follow-up. The presence of acute disruption or late discontinuities was diagnosed by the presence on OCT of stacked, overhung struts or isolated intraluminal struts disconnected from the expected circularity of the device.

RESULTS

Of 51 patients with OCT imaging post-procedure, acute scaffold disruption was observed in 2 patients (3.9%), which could be related to overexpansion of the scaffold at the time of implantation. One patient had a target lesion revascularization that was presumably related to the disruption. Of 49 patients without acute disruption, late discontinuities were observed in 21 patients. There were no major adverse cardiac events associated with this finding except for 1 patient who had a non-ischemia-driven target lesion revascularization.

CONCLUSIONS

Acute scaffold disruption is a rare iatrogenic phenomenon that has been anecdotally associated with anginal symptoms, whereas late strut discontinuity is observed in approximately 40% of patients and could be viewed as a serendipitous OCT finding of a normal bioresorption process without clinical implications. (ABSORB Clinical Investigation, Cohort B [ABSORB B]; NCT00856856).

Lessons learned from acute and late scaffold failures in the ABSORB EXTEND trial

AIMS

Bioresorbable scaffolds are increasingly used in patients with coronary artery disease undergoing percutaneous coronary interventions. ABSORB EXTEND is an ongoing study that will recruit 800 patients. This report evaluates acute and late scaffold failure in the first 450 patients enrolled in ABSORB EXTEND who have completed 12 months follow-up.

METHODS AND RESULTS

Clinical event data from the first 450 patients enrolled in ABSORB EXTEND have demonstrated low rates of ischaemia-driven MACE (4.2%) and target vessel failure (4.7%) at 12 months. There have been seven cases of device failure in this study: three cases of scaffold dislodgement (0.67%) and four cases of subacute or late scaffold thrombosis (0.89%). All scaffold dislodgements occurred in the left circumflex (LCX), and in two cases dislodgement was observed after reinsertion of the same device. Two cases of subacute scaffold thrombosis and two late scaffold thromboses were observed. Two out of four cases of scaffold thrombosis seemed to be related to either premature discontinuation of dual antiplatelet therapy (DAPT) or resistance to clopidogrel.

CONCLUSIONS

This is the first report specifically describing the incidence and the potential mechanisms of scaffold dislodgement and scaffold thrombosis as seen in the ABSORB EXTEND trial.

Comparison of everolimus- and biolimus-eluting coronary stents with everolimus-eluting bioresorbable vascular scaffolds

BACKGROUND

The first CE-approved bioresorbable vascular scaffold (BVS) is effective at treating simple lesions and stable coronary artery disease, but it has yet to be assessed versus the best-in-class drug-eluting stents (DES).

OBJECTIVES

This study sought to compare the performance of a BVS with that of everolimus-eluting stents (EES) and biolimus-eluting stents (BES) in all-comer patients.

METHODS

The EVERBIO II (Comparison of Everolimus- and Biolimus-Eluting Stents With Everolimus-Eluting Bioresorbable Vascular Scaffold Stents II) trial was a single-center, assessor-blinded study of 240 patients randomly assigned in a 1:1:1 ratio to EES, BES, or BVS. The only exclusion criterion was a reference vessel diameter >4.0 mm, which precluded treatment with BVS. The primary endpoint was angiographic late lumen loss (LLL) at 9 months. Secondary endpoints included patient-oriented major acute coronary events (MACE) (death, myocardial infarction [MI], and any revascularization), device-oriented MACE (cardiac death, MI, and target lesion revascularization), and stent thrombosis at the 9-month clinical follow-up.

RESULTS

Follow-up angiography was performed in 216 patients (90.7%) at 9 months. In-stent LLL was similar between patients treated with BVS (0.28 ± 0.39 mm) and those treated with EES/BES (0.25 ± 0.36 mm; p = 0.30). Clinical outcomes were similar at 9 months: the patient-oriented MACE rate was 27% in BVS and 26% in the EES/BES group (p = 0.83) and the device-oriented MACE rate was 12% in BVS and 9% in the EES/BES group (p = 0.6).

CONCLUSIONS

New-generation metallic DES (EES/BES) were not superior to BVS in terms of angiographic LLL and clinical outcomes. (Comparison of Everolimus- and Biolimus-Eluting Stents With Everolimus-Eluting Bioresorbable Vascular Scaffold Stents [EVERBIO II]; NCT01711931).

Current status of bioresorbable scaffolds in the treatment of coronary artery disease

State-of-the-art drug-eluting metal stents are the gold standard for interventional treatment of coronary artery disease. Although they overcome some disadvantages and limitations of plain balloon angioplasty and bare-metal stents, some limitations apply, most notably a chronic local inflammatory reaction due to permanent implantation of a foreign body, restriction of vascular vasomotion due to a metal cage, and the risk of late and very late stent thrombosis. The development of biodegradable scaffolds is a new approach that attempts to circumvent these drawbacks. These devices provide short-term scaffolding of the vessel and then dissolve, which should theoretically circumvent the side effects of metal drug-eluting stents. Various types of these bioresorbable scaffolds are currently under clinical evaluation. This review discusses different concepts of bioresorbable scaffolds with respect to material, design, and drug elution and presents the most recent evidence.

Dynamics of vessel wall changes following the implantation of the absorb everolimus-eluting bioresorbable vascular scaffold: a multi-imaging modality study at 6, 12, 24 and 36 months

AIMS

To assess observations with multimodality imaging of the Absorb bioresorbable everolimus-eluting vascular scaffold performed in two consecutive cohorts of patients who were serially investigated either at 6 and 24 months or at 12 and 36 months.

METHODS AND RESULTS

In the ABSORB multicentre single-arm trial, 45 patients (cohort B1) and 56 patients (cohort B2) underwent serial invasive imaging, specifically quantitative coronary angiography (QCA), intravascular ultrasound (IVUS), radiofrequency backscattering (IVUS-VH) and optical coherence tomography (OCT). Between one and three years, late luminal loss remained unchanged (6 months: 0.19 mm, 1 year: 0.27 mm, 2 years: 0.27 mm, 3 years: 0.29 mm) and the in-segment angiographic restenosis rate for the entire cohort B (n=101) at three years was 6%. On IVUS, mean lumen, scaffold, plaque and vessel area showed enlargement up to two years. Mean lumen and scaffold area remained stable between two and three years whereas significant reduction in plaque behind the struts occurred with a trend toward adaptive restrictive remodelling of EEM. Hyperechogenicity of the vessel wall, a surrogate of the bioresorption process, decreased from 23.1% to 10.4% with a reduction of radiofrequency backscattering for dense calcium and necrotic core. At three years, the count of strut cores detected on OCT increased significantly, probably reflecting the dismantling of the scaffold; 98% of struts were covered. In the entire cohort B (n=101), the three-year major adverse cardiac event rate was 10.0% without any scaffold thrombosis.

CONCLUSIONS

The current investigation demonstrated the dynamics of vessel wall changes after implantation of a bioresorbable scaffold, resulting at three years in stable luminal dimensions, a low restenosis rate and a low clinical major adverse cardiac events rate.

CLINICAL TRIAL REGISTRATION INFORMATION

http://www.clinicaltrials.gov/ct2/show/NCT00856856.

Impact of stent strut design in metallic stents and biodegradable scaffolds

Advances in the understanding of healing mechanisms after stent implantation have led to the recognition of stent strut thickness as an essential factor affecting re-endothelialization and overall long term vessel healing response after Percutaneous Coronary Interventions (PCI). Emergence of Drug-eluting stents (DESs) with anti-proliferative coating has contributed to reducing the incidence of restenosis and Target Lesion Revascularization (TVR), while progress and innovations in stent materials have in the meantime facilitated the design of newer platforms with more conformability and thinner struts, producing lesser injury and improving integration into the vessel wall. Recent advances in biodegradable metal and polymer materials now also allow for the design of fully biodegradable platforms, which are aimed at scaffolding the vessel only temporarily to prevent recoil and constrictive remodeling of the vessel during the initial period required, and are then progressively resorbed thereby avoiding the drawback of leaving an unnecessary implant permanently in the vessel. The aim of this article is to review recent evolution in stent material and stent strut design while understanding their impact on PCI outcomes. The article describes the different metallic alloys and biodegradable material properties and how these have impacted the evolution of stent strut thickness and ultimately outcomes in patients.

Coronary artery stents: advances in technology

The introduction of percutaneous coronary intervention (PCI) in the late 1970s revolutionized the management of stable and unstable coronary artery disease, providing an effective, quick, safe, and increasingly widely available method for coronary revascularization for many patients. Rapid development in this field led to the introduction of a number of new technologies, including intracoronary stents that have resulted in improved efficacy and long-term safety. In this manuscript we review the experience with the 2 major available classes of stents (bare metal [BMS], drug-eluting [DES]) and describe the delivery systems for these stents. An evidence review of the large trial data comparing balloon angioplasty, BMS, and DES demonstrates the incremental advances over time, with the latest generation of DES achieving the lowest rates of restenosis, stent thrombosis, and recurrent myocardial infarction. In addition, we provide an overview of the latest developments in stent technology, including the introduction of bioresorbable stents and new stent delivery systems. These latest advances are hoped to further improve outcomes while reducing costs due to a reduction in the need for future procedures and hospitalizations due to recurrent coronary disease.

Current and future perspectives on drug-eluting bioresorbable coronary scaffolds

Despite improvements in stent platform, polymer and drug elution, the permanent metallic stents have significant limitations as they distort vessel physiology, predispose to late thrombosis and may preclude surgical revascularization. Bioresorbable scaffold (BRS) technology has evolved over the last few years to overcome these drawbacks. Actually, different BRS are either available or under clinical and preclinical investigation. However, the use of BRS has largely been restricted to patients recruited into clinical trials with a relatively small number of 'real world' patients treated with these devices. Here, we highlight the potentialities of these devices, describe the evidence from the recent clinical trials and discuss the potential advantages, as well as challenges, that this novel technology may face in routine clinical practice.

The Effect of Static and Dynamic Loading on Degradation of PLLA Stent Fibers

Understanding how polymers such as PLLA degrade in vivo will enhance biodegradable stent design. This study examined the effect of static and dynamic loads on PLLA stent fibers in vitro. The stent fibers (generously provided by TissueGen, Inc.) were loaded axially with 0 N, 0.5 N, 1 N, or 0.125–0.25 N (dynamic group, 1 Hz) and degraded in PBS at 45 °C for an equivalent degradation time of 15 months. Degradation was quantified through changes in tensile mechanical properties. The mechanical behavior was characterized using the Knowles strain energy function and a degradation model. A nonsignificant increase in fiber stiffness was observed between 0 and 6 months followed by fiber softening thereafter. A marker of fiber softening, β, increased between 9 and 15 months in all groups. At 15 months, the β values in the dynamic group were significantly higher compared to the other groups. In addition, the model indicated that the degradation rate constant was smaller in the 1-N (0.257) and dynamic (0.283) groups compared to the 0.5-N (0.516) and 0-N (0.406) groups. While the shear modulus fluctuated throughout degradation, no significant differences were observed. Our results indicate that an increase in static load increased the degradation of mechanical properties and that the application of dynamic load further accelerated this degradation.

[Coronary stents: 30 years of medical progress]

The history of interventional cardiology has been marked by several technologic revolutions since the late 1970s. The first key step was the use of inflatable balloon angioplasty as an alternative to CABG surgery for coronary revascularization, followed by intracoronary delivery of bare metal stent (BMS) and drug eluting stents (DES) to drastically reduce intracoronary restenosis observed with BMS. Improved stents platforms and polymers (absorbable or biocompatible) led to a dramatic reduction in the rate of late stent thrombosis. Self-expanding stents are now available to improve stent a position especially in acute myocardial infarction. The emergence of new fully bioabsorbable stents that can be combined with antiproliferative drugs is the ongoing revolution. A new generation of stents is continuously improving and likely to become the ideal stent for coronary revascularization in the near future.

[Position statement on bioresorbable vascular scaffolds in Portugal]

BACKGROUND

Bioresorbable vascular scaffolds (BVS) were recently approved for percutaneous coronary intervention in Europe. The aim of this position statement is to review the information and studies on available BVS, to stimulate discussion on their use and to propose guidelines for this treatment option in Portugal.

METHODS AND RESULTS

A working group was set up to reach a consensus based on current evidence, discussion of clinical case models and individual experience. The evidence suggests that currently available BVS can produce physiological and clinical improvements in selected patients. There are encouraging data on their durability and long-term safety. Initial indications were grouped into three categories: (a) consensual and appropriate - young patients, diabetic patients, left anterior descending artery, long lesions, diffuse disease, and hybrid strategy; (b) less consensual but possible - small collateral branches, stabilized acute coronary syndromes; and (c) inappropriate - left main disease, tortuosity, severe calcification.

CONCLUSION

BVS are a viable treatment option based on the encouraging evidence of their applicability and physiological and clinical results. They should be used in appropriate indications and will require technical adaptations. Outcome monitoring and evaluation is essential to avoid inappropriate use. It is recommended that medical societies produce clinical guidelines based on high-quality registries as soon as possible.

Short-term outcome of patients with ST-segment elevation myocardial infarction (STEMI) treated with an everolimus-eluting bioresorbable vascular scaffold

OBJECTIVES

To evaluate safety and efficacy of the everolimus-eluting bioresorbable scaffold (BVS) in patients with ST-segment elevation myocardial infarction (STEMI).

BACKGROUND

According to the current guidelines, drug-eluting stents are the treatment of choice in patients with STEMI. BVS represents a new technology capable to restore the native vessel vasomotion and potentially avoiding long-term limitations such as stent thrombosis.

METHODS

From October 2012 to May 2013, patients with evidence of STEMI eligible for BVS implantation were included in this study. Exclusion criteria were not defined.

RESULTS

A total of 25 patients, respectively 31 lesions, were treated. Procedural success was achieved in 97%. Two major adverse cardiac events occurred during hospitalization and follow-up: one patient with cardiogenic shock at the index procedure subsequently died. One patient suffered from instable angina with need for interventional revascularization of a previously untreated vessel. One target vessel failure as a consequence of an intra-procedural dissection was seen. However, no target lesion failure was noted. During 132.7 ± 68.7 days of follow-up none of the patients died.

CONCLUSION

Our findings suggest that implantation of BVS in STEMI patients is feasible in this small cohort of highly selected patients. Further evaluation in randomized-controlled trials is needed.

3D assessment of stent cell size and side branch access in intravascular optical coherence tomographic pullback runs

We present a semi-automatic approach to assess the maximum circular unsupported surface area (MCUSA) of selected stent cells and the side branch access through stent cells in intravascular optical coherence tomography (IVOCT) pullback runs. Such 3D information may influence coronary interventions, stent design, blood flow analysis or prognostic evaluation. First, the stent struts are detected automatically and stent cells are reconstructed with users' assistance. Using cylinder fitting, a 2D approximation of the stent cell is generated for MCUSA detection and measurement. Next, a stent surface is reconstructed and stent-covered side branches are detected. Both the stent cell contours and side branch lumen contours are projected onto the stent surface to indicate their areas, and the overlapping regions are measured as the side branch access through these stent cells. The method was evaluated on phantom data sets and the accuracy of the MCUSA and side branch access was found to be 95% and 91%, respectively. The usability of this approach for clinical research was proved on 12 in vivo IVOCT pullback runs.

Head to head comparison of optical coherence tomography, intravascular ultrasound echogenicity and virtual histology for the detection of changes in polymeric struts over time: insights from the ABSORB trial

AIMS

To analyse and to compare the changes in the various optical coherence tomography (OCT), echogenicity and intravascular ultrasound virtual histology (VH) of the everolimus-eluting bioresorbable scaffold (ABSORB) degradation parameters during the first 12 months after ABSORB implantation. In the ABSORB study, changes in the appearance of the ABSORB scaffold were monitored over time using various intracoronary imaging modalities. The scaffold struts exhibited a progressive change in their black core area by OCT, in their ultrasound derived grey level intensity quantified by echogenicity, and in their backscattering ultrasound signal, identified as "pseudo dense-calcium" (DC) by VH.

METHODS AND RESULTS

From the ABSORB Cohort B trial 35 patients had paired OCT, echogenicity and VH assessment at baseline and at six- (n=18) or 12-months follow-up (n=17). Changes in OCT strut core area, hyperechogenicity and VH-derived DC were analysed and compared at the various time points. At six months, the change (median[IQR]) in OCT strut core area was -7.2% (-14.0-+0.9) (p=0.053), in hyperechogenicity -12.7% (-33.7-+1.4) (p=0.048) and VH-DC 22.1% (-10.8-+48.8) (p=0.102). At 12 months, all the imaging modalities showed a decrease in the various parameters considered (OCT: -12.2% [-17.5--1.9], p=0.093; hyperechogenicity -24.64% [-36.6--16.5], p=0.001; VH-DC: -24.66% [-32.0--7.0], p=0.071). However, the correlation between the relative changes in these parameters was statistically poor (Spearman's rho <0.4).

CONCLUSIONS

OCT, echogenicity and VH were able to detect changes in the ABSORB scaffold struts, although the correlation between those changes was poor. This is likely due to the fact that each imaging modality interrogates different material properties on different length scales. Further studies are needed to explore these hypotheses.

First serial assessment at 6 months and 2 years of the second generation of absorb everolimus-eluting bioresorbable vascular scaffold: a multi-imaging modality study

BACKGROUND

Nonserial observations have shown this bioresorbable scaffold to have no signs of area reduction at 6 months and recovery of vasomotion at 1 year. Serial observations at 6 months and 2 years have to confirm the absence of late restenosis or unfavorable imaging outcomes.

METHODS AND RESULTS

The ABSORB trial is a multicenter single-arm trial assessing the safety and performance of an everolimus-eluting bioresorbable vascular scaffold. Forty-five patients underwent serial invasive imaging, such as quantitative coronary angiography, intravascular ultrasound, and optical coherence tomography at 6 and 24 months of follow-up. From 6 to 24 months, late luminal loss increased from 0.16±0.18 to 0.27±0.20 mm on quantitative coronary angiography, with an increase in neointima of 0.68±0.43 mm(2) on optical coherence tomography and 0.17±0.26 mm(2) on intravascular ultrasound. Struts still recognizable on optical coherence tomography at 2 years showed 99% of neointimal coverage with optical and ultrasonic signs of bioresorption accompanied by increase in mean scaffold area compared with baseline (0.54±1.09 mm(2) on intravascular ultrasound, P=0.003 and 0.77±1.33 m(2) on optical coherence tomography, P=0.016). Two-year major adverse cardiac event rate was 6.8% without any scaffold thrombosis.

CONCLUSIONS

This serial analysis of the second generation of the everolimus-eluting bioresorbable vascular scaffold confirmed, at medium term, the safety and efficacy of the new device.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT00856856.

Endothelial-dependent vasomotion in a coronary segment treated by ABSORB everolimus-eluting bioresorbable vascular scaffold system is related to plaque composition at the time of bioresorption of the polymer: indirect finding of vascular reparative therapy?

AIMS

To analyse the vasoreactivity of a coronary segment, previously scaffolded by the ABSORB bioresorbable vascular scaffold (BVS) device, in relationship to its intravascular ultrasound-virtual histology (IVUS-VH) composition and reduction in greyscale echogenicity of the struts. Coronary segments, transiently scaffolded by a polymeric device, may in the long-term recover a normal vasomotor tone. Recovery of a normal endothelial-dependent vasomotion may be enabled by scaffold bioresorption, composition of the underlying tissue, or a combination of both mechanisms.

METHODS AND RESULTS

All patients from the ABSORB Cohort A and B trials, who underwent a vasomotion test and IVUS-VH investigation at 12 and 24 months, were included. Acetylcholine (Ach) and nitroglycerin were used to test either the endothelial-dependent or -independent vasomotion of the treated segment. Changes in polymeric strut echogenicity-a surrogate for bioresorption-IVUS-VH composition of the tissue underneath the scaffold and their relationship with the pharmacologically induced vasomotion were all evaluated. Overall, 26 patients underwent the vasomotion test (18 at 12 and 8 at 24 months). Vasodilatory response to Ach was quantitatively associated with larger reductions over time in polymeric strut echogenicity (y= -0.159x- 6.85; r= -0.781, P< 0.001). Scaffolded segments with vasoconstriction to Ach had larger vessel areas (14.37 ± 2.50 vs. 11.85 ± 2.54 mm(2), P= 0.030), larger plaque burden (57.31 ± 5.96 vs. 49.09 ± 9.10%, P= 0.018), and larger necrotic core (NC) areas [1.39 (+1.14, +1.74) vs. 0.78 mm(2) (+0.20, +0.98), P= 0.006] compared with those with vasodilation.

CONCLUSION

Vasodilatory response to Ach, in coronary segments scaffolded by the ABSORB BVS device, is associated with a reduction in echogenicity of the scaffold over time, and a low amount of NC. In particular, the latter finding resembles the behaviour of a native coronary artery not caged by an intracoronary device.

Everolimus-eluting ABSORB bioresorbable vascular scaffold: present and future perspectives

Everolimus-eluting ABSORB bioresorbable vascular scaffolds represent a novel approach that provides transient vessel support with drug-delivery capability without the long-term limitations of the metallic drug-eluting stents (DESs). The technology has the potential to overcome many of the safety concerns associated with metallic DESs and possibly even convey further clinical benefit. In particular the scaffold is designed for providing a short-term lumen support (up to 6-12 months) and for thereafter being completely bioresorbed, eliminating the permanent caging typical of the metallic DES. The first clinical studies testing this device in a small number of patients have shown very promising results with good clinical outcome up to 5 years' follow-up, highlighting important morphological and functional modifications at the scaffolded segment level, such as late lumen enlargement and recuperation of a normal vasoreactivity. A randomized trial, comparing ABSORB with the Xience Prime stent, will evaluate the efficacy and safety of this device in a wide population.

Circumferential evaluation of the neointima by optical coherence tomography after ABSORB bioresorbable vascular scaffold implantation: can the scaffold cap the plaque?

OBJECTIVE

To quantify the circumferential healing process at 6 and 12 months following scaffold implantation.

BACKGROUND

The healing process following stent implantation consists of tissue growing on the top of and in the space between each strut. With the ABSORB bioresorbable vascular scaffold (BVS), the outer circumference of the scaffold is detectable by optical coherence tomography (OCT), allowing a more accurate and complete evaluation of the intra-scaffold neointima.

METHODS

A total of 58 patients (59 lesions), who received an ABSORB BVS 1.1 implantation and a subsequent OCT investigation at 6 (n=28 patients/lesions) or 12 (n=30 patients with 31 lesions) months follow-up were included in the analysis. The thickness of the neointima was calculated circumferentially in the area between the abluminal side of the scaffold and the lumen by means of an automated detection algorithm. The symmetry of the neointima thickness in each cross section was evaluated as the ratio between minimum and maximum thickness.

RESULTS

The neointima area was not different between 6 and 12 months follow-up (1.57±0.42 mm(2) vs. 1.64±0.77 mm(2); p=0.691). No difference was also found in the mean thickness of the neointima (median [IQR]) between the two follow-up time points (210 μm [180-260]) vs. 220 μm [150-260]; p=0.904). However, the symmetry of the neointima thickness was higher at 12 than at 6 months follow-up (0.23 [0.13-0.28] vs. 0.16 [0.08-0.21], p=0.019).

CONCLUSIONS

A circumferential evaluation of the healing process following ABSORB implantation is feasible, showing the formation of a neointima layer, that resembles a thick fibrous cap, known for its contribution to plaque stability.

Evaluation of the second generation of a bioresorbable everolimus-eluting vascular scaffold for the treatment of de novo coronary artery stenosis: 12-month clinical and imaging outcomes

OBJECTIVES

The aim of this study was to demonstrate that the prevention of early scaffold area shrinkage of the ABSORB BVS (Rev.1.1, Abbott Vascular, Santa Clara, California) was sustained and not simply delayed by a few months.

BACKGROUND

With improved scaffold design and modified manufacturing process of its polymer, the second iteration of ABSORB (BVS 1.1) has improved performance to prevent a scaffold area reduction at 6 months.

METHODS

Fifty-six patients were enrolled and received 57 ABSORB scaffolds. Quantitative coronary angiography, intravascular ultrasound (IVUS), analysis of radiofrequency backscattering, echogenicity and optical coherence tomography (OCT) were performed at baseline and at 12-month follow-up.

RESULTS

Overall the scaffold area remained unchanged with IVUS as well as with OCT, whereas the radiofrequency backscattering and the echogenicity of the struts decreased by 16.8% (p < 0.001) and 20% (p < 0.001), respectively; more specifically, the strut core area on OCT decreased by 11.4% (p = 0.003). Despite the absence of scaffold area loss, pharmacological vasomotion was restored. On an intention-to-treat basis, the angiographic late lumen loss amounted to 0.27 ± 0.32 mm with an IVUS relative decrease in minimal lumen area of 1.94% (p = 0.12), without significant changes in mean lumen area. The OCT at follow-up showed that 96.69% of the struts were covered and that malapposition, initially observed in 18 scaffolds was only detected at follow-up in 4 scaffolds. Two patients experienced peri-procedural and iatrogenic myocardial infarction, respectively, whereas 2 underwent repeat intervention, resulting in the major adverse cardiac event rate of 7.1% (4 of 56).

CONCLUSIONS

The 12-month performance of the second-generation ABSORB bioresorbable everolimus-eluting scaffold justifies the conduct of a randomized trial against current best standards. (A Clinical Evaluation of the Bioabsorbable Everolimus Eluting Coronary Stent System [BVS EECSS] in the Treatment of Patients With de Novo Native Coronary Artery Lesions; NCT00856856).

Comparison between the first and second generation bioresorbable vascular scaffolds: a six month virtual histology study

AIMS

To compare the intravascular ultrasound virtual histology (IVUS-VH) appearance of the polymeric struts of the first (Revision 1.0) and the second (Revision 1.1) generation bioresorbable vascular scaffold (BVS).

METHODS AND RESULTS

IVUS-VH misrepresents polymeric struts as dense calcium (DC) and necrotic core (NC) so that their presence and disappearance could be used as potential artifactual surrogate of bioresorption. DC and NC were assessed in both revisions of the BVS by analysing IVUS-VH from all patients in the ABSORB cohort A (Revision 1.0) and cohort B (Revision 1.1) study who had an IVUS-VH post-treatment and at 6-month follow-up. Post-treatment and 6-month follow-up IVUS-VH results, available in 60 patients (BVS 1.0 n=28; BVS 1.1 n=32), indicated an insignificant rise in DC+NC area compared to baseline with Revision 1.1 (0.10 ± 0.46 mm2, p=0.2), whilst a significant reduction was seen with Revision 1.0 (-0.57 ± 1.3 mm2, p=0.02). A significant correlation has been found between the change in the DC+NC area and the change in external elastic membrane area (y=0.68x-0.1; r=0.58, p=0.03).

CONCLUSIONS

Based on 6-months IVUS-VH analysis, the BVS 1.1 appears to have a different backscattering signal compared to the BVS 1.0, which may reflect differences in the speed of chemical and structural alteration.

Comparison of in vivo eccentricity and symmetry indices between metallic stents and bioresorbable vascular scaffolds: insights from the ABSORB and SPIRIT trials

OBJECTIVE

To compare the geometrical parameters of a bioresorbable vascular scaffold (BVS) with a standard metallic stent.

BACKGROUND

The introduction of polymeric bioresorbable materials in the design of novel coronary scaffolds may affect some geometrical parameters, such as eccentricity and symmetry indices, previously introduced as IVUS criteria for optimal metallic stent deployment.

METHODS

From ABSORB Cohort A, ABSORB Cohort B, SPIRIT I, and SPIRIT II, all patients implanted with BVS 1.0, BVS 1.1, or XIENCE V, respectively and intravascular ultrasound analyses post-implantation were selected. The eccentricity index was calculated frame by frame and expressed as an average per device (minimum diameter/maximum diameter). The symmetry index of the device was reported as ([maximum diameter - minimum diameter]/maximum diameter). Six months major adverse cardiac events (MACE) were analyzed.

RESULTS

A total of 242 patients were selected (BVS 1.0: n = 28, BVS 1.1: n = 94, XIENCE V: n = 120). The BVS exhibited a significantly lower eccentricity index (BVS 1.0: 0.83 ± 0.09; BVS 1.1: 0.85 ± 0.08; XIENCE V: 0.90 ± 0.06; P < 0.01) and a significantly higher symmetry index (BVS 1.0: 0.30 ± 0.07; BVS 1.1: 0.31 ± 0.06, XIENCE V 0.26 ± 0.07; P < 0.01) as compared to the XIENCE V. An inverse correlation was found between the symmetry and eccentricity indices for both (BVS r = -0.69, P < 0.01; XIENCE V r = -0.61, P < 0.01). No differences in MACE were detected between the groups according to their geometrical parameters.

CONCLUSIONS

The introduction of a new polymeric material in the design of BVS resulted in a lower eccentricity index and a higher symmetry index as compared to metallic stents, without detectable impact in MACE, at 6 months.

Quantitative multi-modality imaging analysis of a fully bioresorbable stent: a head-to-head comparison between QCA, IVUS and OCT

The bioresorbable vascular stent (BVS) is totally translucent and radiolucent, leading to challenges when using conventional invasive imaging modalities. Agreement between quantitative coronary angiography (QCA), intravascular ultrasound (IVUS) and optical coherence tomography (OCT) in the BVS is unknown. Forty five patients enrolled in the ABSORB cohort B1 study underwent coronary angiography, IVUS and OCT immediately post BVS implantation, and at 6 months. OCT estimated stent length accurately compared to nominal length (95% CI of the difference: -0.19; 0.37 and -0.15; 0.47 mm(2) for baseline and 6 months, respectively), whereas QCA incurred consistent underestimation of the same magnitude at both time points (Pearson correlation = 0.806). IVUS yielded low accuracy (95% CI of the difference: 0.77; 3.74 and -1.15; 3.27 mm(2) for baseline and 6 months, respectively), with several outliers and random variability test-retest. Minimal lumen area (MLA) decreased substantially between baseline and 6 months on QCA and OCT and only minimally on IVUS (95% CI: 0.11; 0.42). Agreement between the different imaging modalities is poor: worst agreement Videodensitometry-IVUS post-implantation (ICCa 0.289); best agreement IVUS-OCT at baseline (ICCa 0.767). All pairs deviated significantly from linearity (P < 0.01). Passing-Bablok non-parametric orthogonal regression showed constant and proportional bias between IVUS and OCT. OCT is the most accurate technique for measuring stent length, whilst QCA incurs systematic underestimation (foreshortening) and solid state IVUS incurs random error. Volumetric calculations using solid state IVUS are therefore not reliable. There is poor agreement for MLA estimation between all the imaging modalities studied, including IVUS-OCT, hence their values are not interchangeable.