Bioresorbable Scaffolds: Contemporary Status and Future Directions

Percutaneous coronary intervention, which is safe, effective, and timely, has become an important treatment for coronary artery diseases and has been widely used in clinical practice. However, there are still some problems that urgently need to be solved. Permanent vessel caging through metallic implants not only prevents the process of positive vessel remodeling and the restoration of vascular physiology but also makes the future revascularization of target vessels more difficult. Bioresorbable scaffolds (BRSs) have been developed as a potential solution to avoid the above adverse reactions caused by permanent metallic devices. BRSs provide temporary support to the vessel wall in the short term and then gradually degrade over time to restore the natural state of coronary arteries. Nonetheless, long-term follow-up of large-scale trials has drawn considerable attention to the safety of BRSs, and the significantly increased risk of late scaffold thrombosis (ScT) limits its clinical application. In this review, we summarize the current status and clinical experiences of BRSs to understand the application prospects and limitations of these devices. In addition, we focus on ScT after implantation, as it is currently the primary drawback of BRS. We also analyze the causes of ScT and discuss improvements required to overcome this serious drawback and to move the field forward.

Different behaviors of bioresorbable vascular scaffold in different types of calcified lesion: Insights from intravascular imaging

A 55-year-old male underwent percutaneous coronary intervention (PCI) for left anterior descending artery chronic total occlusion. After lesion preparation with non-compliant (NC) balloon, two bioresorbable vascular scaffolds (2.5/28 mm, 3.0/28 mm, Absorb BVS, Abbott Vascular, Santa Clara, CA, USA) were implanted followed by 1:1 sized NC balloon post-dilatation at 20 atm. Final intravascular ultrasound (IVUS) showed acceptable BVS expansion in diffusely calcified lesions. Twenty-one months' follow-up coronary angiography revealed severe restenosis with reocclusion at the distal edge of the distal BVS. After recanalization with a 1.0 mm balloon, optical coherence tomography (OCT) was performed. Quantitative analysis comparing OCT and IVUS at the index procedure demonstrated that minimum scaffold area at follow-up became significantly smaller and with higher eccentricity, suggesting severe recoil at the lesions with thick calcium spot, whereas these changes were not observed at the lesion with relatively thin calcification. The lesions were successfully revascularized with drug-eluting stents and final OCT showed symmetric expansion of metallic stents. Our case demonstrates that different types of calcification can have an impact on BVS expansion and recoil. In calcified lesions, an optimal implantation technique is mandatory to achieve the best possible results, and characterization of calcified lesions with intravascular imaging may be helpful to decide PCI strategy with BVS. <Learning objective: Calcified lesions represent a challenging lesion subset for bioresorbable vascular scaffold (BVS) because of less radial strength of the latter. Quantitative analysis with intravascular imaging demonstrated that different types of calcification can have an impact on BVS expansion and recoil. In calcified lesions, an optimal implantation technique is mandatory to achieve the best possible results, and characterization of calcified lesions with intravascular imaging may be helpful to decide percutaneous coronary intervention strategy with BVS.>.

Bioresorbable vascular scaffold implantation for severely calcified lesions after excimer laser lesion preparation

Bioresorbable vascular scaffolds (Absorb BVS, Abbott Vascular, Santa Clara, CA) temporarily elute antiproliferative drugs and provide vessel support, which then subsequently resorb to allow restoration of normal vessel function and architecture. To attain the best possible results with BVS, a dedicated implantation technique (PSP: adequate lesion preparation, proper sizing, postdilatation) is considered mandatory, and calcified lesions are one of the most challenging lesion subsets for BVS implantation. In five cases with severe calcifications refractory to balloon predilatation, we performed excimer laser catheter ablation (ELCA: Turbo Elite catheter; Spectranetics Corporation, Colorado Springs, CO, USA), which facilitated adequate lesion expansion with high-pressure noncompliant balloon inflation and BVS implantation. During the follow-up period (481 days [interquartile range: 445-579]), all patients continued dual antiplatelet therapy (DAPT) and there were no cases of cardiac death, myocardial infarction, or scaffold thrombosis. For treatment of severely calcified lesions with bioresorbable scaffolds, ELCA could be considered an effective potential strategy. After the procedure, prolonged DAPT was prescribed.

The State of the Absorb Bioresorbable Scaffold: Consensus From an Expert Panel

Significant progress has been made in the percutaneous coronary intervention technique from the days of balloon angioplasty to modern-day metallic drug-eluting stents (DES). Although metallic stents solve a temporary problem of acute recoil following balloon angioplasty, they leave behind a permanent problem implicated in very late events (in addition to neoatherosclerosis). BRS were developed as a potential solution to this permanent problem, but the promise of these devices has been tempered by clinical trials showing increased risk of safety outcomes, both early and late. This is not too dissimilar to the challenges seen with first-generation DES in which refinement of deployment technique, prolongation of dual antiplatelet therapy, and technical iteration mitigated excess risk of very late stent thrombosis, making DES the treatment of choice for coronary artery disease. This white paper discusses the factors potentially implicated in the excess risks, including the scaffold consideration and deployment technique, and outlines patient and lesion selection, implantation technique, and dual antiplatelet therapy considerations to potentially mitigate this excess risk with the first-generation thick strut Absorb scaffold (Abbott Vascular, Abbott Park, Illinois). It remains to be seen whether these considerations together with technical iterations will ultimately close the gap between scaffolds and metal stents for short-term events while at the same time preserving options for future revascularization once the scaffold bioresorbs.

Impact of calcium on procedural and clinical outcomes in lesions treated with bioresorbable vascular scaffolds - A prospective BRS registry study

BACKGROUND

There is limited data on the impact of calcium (Ca) on acute procedural and clinical outcomes in patients with lesions treated with bioresorbable vascular scaffolds (BRS). We sought to evaluate the effect of calcium on procedural and clinical outcomes in a 'real world' population.

METHODS

Clinical outcomes were compared between patients with at least 1 moderately or heavily calcified lesion (Ca) and patients with no/mild calcified lesions (non-Ca) enrolled in our institutional BRS registry.

RESULTS

455 patients (N) with 548 lesions (L) treated with 735 BRS were studied. Patients in the Ca group (N=160, L=200) had more complex (AHA B2/C lesion: 69.0% in Ca vs 14.9% in non-Ca, p<0.001) and significantly longer lesions (27.80±15.27 vs 19.48±9.92mm, p<0.001). Overall device success rate was 99.1% with no significant differences between the groups. Despite more aggressive lesion preparation and postdilation compared to non Ca, acute lumen gain was significantly less in Ca lesions (1.50±0.66 vs 1.62±0.69mm, p=0.040) with lower final MLD (2.28±0.41 vs 2.36±0.43, p=0.046). There were no significant differences in all-cause mortality, total definite scaffold thrombosis (ST), target lesion revascularization and myocardial infarction between the 2 groups. Late ST was more frequent in the Ca group compared to non Ca group (late ST: 2.1 vs 0%, p=0.02).

CONCLUSIONS

Clinical outcomes after BRS implantation in calcified and non-calcified lesions were similar. A remarkable difference in timing of thrombosis was observed, with an increased rate of late thrombosis in calcified lesions.

Comparative Characterization of Biomechanical Behavior and Healing Profile of a Novel Ultra-High-Molecular-Weight Amorphous Poly-l-Lactic Acid Sirolimus-Eluting Bioresorbable Coronary Scaffold

BACKGROUND

Clinically available bioresorbable scaffolds (BRS) rely on polymer crystallinity to achieve mechanical strength resulting in limited overexpansion capabilities and structural integrity when exposed to high-loading conditions. We aimed to evaluate the biomechanical behavior and vascular healing profile of a novel, sirolimus-eluting, high-molecular-weight, amorphous poly-l-lactic acid-based BRS (Amaranth BRS).

METHODS AND RESULTS

In vitro biomechanical testing was performed under static and cyclic conditions. A total of 99 devices (65 Amaranth BRS versus 34 Absorb bioresorbable vascular scaffold [BVS]) were implanted in 99 coronary arteries of 37 swine for pharmacokinetics and healing evaluation at various time points. In the Absorb BVS, the number of fractures per scaffold seen on light microscopy was 6.0 (5.0-10.5) when overexpanded 1.0 mm above nominal values (≈34%). No fractures were observed in the Amaranth BRS group at 1.3 mm above nominal values (≈48% overexpansion). The number of fractures was higher in the Absorb BVS on accelerated cycle testing over time (at 24K cycles=5.0 [5.0-9.0] Absorb BVS versus 0.0 [0.0-0.5] Amaranth BRS). Approximately 90% of sirolimus was found to be eluted by 90 days. Optical coherence tomography analysis demonstrated lower percentages of late scaffold recoil in the Amaranth BRS at 3 months (Amaranth BRS=-10±16.1% versus Absorb BVS=10.7±13.2%; P=0.004). Histopathology analysis revealed comparable levels of vascular healing and inflammatory responses between both BRSs up to 6 months.

CONCLUSIONS

New-generation high-molecular-weight amorphous poly-l-lactic acid scaffolds have the potential to improve the clinical performance of BRS and provide the ideal platform for the future miniaturization of the technology.

Three-Year Outcomes With the Absorb Bioresorbable Scaffold: Individual-Patient-Data Meta-Analysis From the ABSORB Randomized Trials

BACKGROUND

The Absorb bioresorbable vascular scaffold (BVS) completely resorbs within 3 years after coronary artery implantation. The safety and effectiveness of BVS through this critical 3-year period have not been characterized.

METHODS

We performed an individual-patient-data pooled meta-analysis of the 4 randomized ABSORB trials in which 3389 patients with coronary artery disease were randomly assigned to everolimus-eluting Absorb BVS (n=2164) or cobalt-chromium everolimus-eluting stents (n=1225). The primary efficacy outcome measure was target lesion failure (cardiac mortality, target vessel myocardial infarction, or ischemia-driven target lesion revascularization), and the primary safety outcome measure was device thrombosis.

RESULTS

BVS compared with cobalt-chromium everolimus-eluting stents resulted in higher 3-year rates of target lesion failure (11.7% versus 8.1%; risk ratio [RR], 1.38; 95% confidence interval [CI], 1.10-1.73; P=0.006), driven by greater target vessel myocardial infarction (7.8% versus 4.2%; RR, 1.72; 95% CI, 1.26-2.35; P=0.0006) and ischemia-driven target lesion revascularization (6.6% versus 4.4%; RR, 1.44; 95% CI, 1.05-1.98; P=0.02), with comparable cardiac mortality (1.1% versus 1.1%; RR, 0.93; 95% CI, 0.47-1.88; P=0.85). Device thrombosis rates through 3 years were also higher with BVS (2.4% versus 0.6%; RR, 3.71; 95% CI, 1.70-8.11; P=0.001). Between 1 and 3 years, target lesion failure rates (6.1% versus 3.9%; P=0.02) and device thrombosis rates (1.1% versus 0.0%; P<0.0001) were higher with BVS than cobalt-chromium everolimus-eluting stents.

CONCLUSIONS

In the present individual-patient-data pooled meta-analysis of the ABSORB trials, BVS was associated with increased rates of target lesion failure and device thrombosis between 1 and 3 years and cumulatively through 3 years of follow-up compared with everolimus-eluting stents.

CLINICAL TRIAL REGISTRATION

URL: https://clinicaltrials.gov. Unique identifiers: NCT01751906, NCT01844284, NCT01923740, and NCT01425281.

Correlates and Impact of Coronary Artery Calcifications in Women Undergoing Percutaneous Coronary Intervention With Drug-Eluting Stents: From the Women in Innovation and Drug-Eluting Stents (WIN-DES) Collaboration

OBJECTIVES

The aim of this study was to investigate the clinical correlates and prognostic impact of coronary artery calcification (CAC) in women undergoing percutaneous coronary intervention with drug-eluting stents (DES).

BACKGROUND

The clinical correlates and the prognostic significance of CAC in women undergoing percutaneous coronary intervention with DES remain unclear.

METHODS

Patient-level data from female participants in 26 randomized trials of DES were pooled. Study population was categorized according to the presence of moderate or severe versus mild or no target lesion CAC, assessed through coronary angiography. Co-primary endpoints of interest were the composite of death, myocardial infarction (MI), or target lesion revascularization and death, MI, or stent thrombosis at 3-year follow-up.

RESULTS

Among 11,557 women included in the pooled dataset, CAC status was available in 6,371 women. Of these, 1,622 (25.5%) had moderate or severe CAC. In fully adjusted models, independent correlates of CAC were age, hypertension, hypercholesterolemia, smoking, previous coronary artery bypass graft surgery, and worse left ventricular and renal function. At 3 years, women with CAC were at higher risk for death, MI, or target lesion revascularization (18.2% vs. 13.1%; adjusted hazard ratio: 1.56; 95% confidence interval: 1.33 to 1.84; p < 0.0001) and death, MI, or stent thrombosis (12.7% vs. 8.6%; adjusted hazard ratio: 1.48; 95% confidence interval: 1.21 to 1.80; p = 0.0001). The adverse effect of CAC on ischemic outcomes appeared to be consistent across clinical and angiographic subsets of women, including new-generation DES.

CONCLUSIONS

Women undergoing PCI of calcified lesions tend to have worse clinical profile and remain at increased ischemic risk, irrespective of new-generation DES.

Mechanical behavior of polymer-based vs. metallic-based bioresorbable stents

Bioresorbable scaffolds (BRS) were developed to overcome the drawbacks of current metallic drug-eluting stents (DES), such as late in-stent restenosis and caging of the vessel permanently. The concept of the BRS is to provide transient support to the vessel during healing before being degraded and resorbed by the body, freeing the vessel and restoring vasomotion. The mechanical properties of the BRS are influenced by the choice of the material and processing methods. Due to insufficient radial strength of the bioresorbable material, BRS often required large strut profile as compared to conventional metallic DES. Having thick struts will in turn affect the deliverability of the device and may cause flow disturbance, thereby increasing the incidence of acute thrombotic events. Currently, the bioresorbable poly-l-lactic acid (PLLA) polymer and magnesium (Mg) alloys are being investigated as materials in BRS technologies. The bioresorption process, mechanical properties, in vitro observations and clinical outcomes of PLLA-based and Mg-based BRS will be examined in this review.

Complex bifurcation lesions: Randomized comparison of a fully bioresorbable modified t stenting strategy versus bifurcation reconstruction with a dedicated self-expanding stent in combination with bioresorbable scaffolds, an OCT study: Rationale and design of the COBRA II trial

OBJECTIVE

There is an ongoing controversy regarding the efficacy and safety of different percutaneous stenting techniques for coronary bifurcation lesions needing >1 stent. The promise of safe vessel restoration with bioresorbable scaffolds (BRS) may not be transferable to complex double BRS bifurcation techniques, and permanent metallic scaffolding of the bifurcation core may be needed. We identified modified-T stenting as the most promising fully bioresorbable 2-stent strategy in a preclinical setting. The objective of this study is to assess acute performance and compare long-term vessel healing with this strategy, versus an approach combining BRS with a dedicated metallic drug-eluting bifurcation stent.

STUDY DESIGN

In a single center, 60 consecutive patients with true and complex coronary bifurcation lesions will be randomly assigned to treatment with the dedicated self-expanding Axxess^™ biolimus-eluting bifurcation stent in the proximal main vessel and additional Absorb^™ everolimus-eluting BRS in the branches versus a modified T technique using Absorb^™ only. Angiography and optical coherence tomography (OCT) will be performed immediately after implantation and at 30 months, and clinical follow-up is foreseen up to 5 years after implantation. The primary endpoint is the change in minimal luminal area assessed with OCT from baseline to 30 months in pre-specified bifurcation segments.

CONCLUSION

To date the use of Absorb^™ BRS in complex coronary bifurcations has not been evaluated in a randomized clinical trial setting. The COBRA II study will examine the role and safety of a double BRS strategy in coronary bifurcations, alone or in combination with a metallic dedicated bifurcation device. © 2016 Wiley Periodicals, Inc.

Expansion in calcific lesions and overall clinical outcomes following bioresorbable scaffold implantation optimized with intravascular ultrasound

OBJECTIVES

This study aimed to investigate clinical outcomes following bioresorbable scaffold (BRS) optimized with intravascular ultrasound (IVUS), and furthermore expansion of BRS in calcific lesions.

BACKGROUND

Although IVUS use has contributed to improved clinical outcomes with metallic stent implantation, it is unclear if this is also true with regards to BRS, especially in calcified lesions.

METHODS

Between May 2012 and April 2015, 291 lesions in 198 patients were treated with BRS with IVUS use. We evaluated overall clinical outcomes at 1-year and investigated the expansion and eccentricity index of BRS amongst quadrants categorized by calcium arc (CA) every 90-degrees.

RESULTS

The rates of major adverse cardiac events were 5.4% (at 6 months) and 10.7% (at 12 months). TLR was observed in 3.1% at 6-month and 7.5% at 12-month follow up. Although there was a significant difference among quadrants regarding to eccentricity of calcium (0°≦CA < 90°: 0.82 ± 0.09, 90°≦CA < 180°: 0.75 ± 0.12, 180°≦CA < 270°: 0.78 ± 0.11, and 270°≦CA≦360°: 0.79 ± 0.09, ANOVA P = 0.002), the BRS expansion index [minimal scaffold area (MSA) divided by BRS area expanded at a nominal pressure] was comparable between quadrants.

CONCLUSIONS

The use of IVUS to optimize BRS implantation results in favorable clinical outcomes even for complex lesions. Although eccentric calcium distribution resulted in asymmetric expansion of BRS, the final MSA was comparable irrespective of calcium distribution. © 2016 Wiley Periodicals, Inc.

Absorb Bioresorbable Vascular Scaffold in Complex Coronary Bifurcation Interventions: Insights From an In Vivo Multimodality Imaging Study

BACKGROUND

Although bioresorbable scaffolds offer potential advantages compared with metallic drug-eluting stents in the treatment of complex coronary bifurcation lesions, there are concerns that the polymeric scaffold integrity may be compromised. This in vivo study sought to provide insights about the feasibility of performing complex bifurcation stenting with Absorb bioresorbable vascular scaffolds (Abbott Vascular, Santa Clara, CA).

METHODS AND RESULTS

Twenty New Zealand white rabbits underwent stenting of the nondiseased aortoiliac bifurcation with bioresorbable vascular scaffolds using provisional (PS, n=5), culotte (n=5), modified-T (n=5), or T-and protrusion (n=5) stenting techniques. Angiography, optical coherence tomography, and microcomputed tomography were performed. Angiographic results were excellent without evidence of dissection or side branch (SB) compromise. PS optimally opened the SB ostium without deforming the main vessel (MV) bioresorbable vascular scaffolds, avoiding malapposition, and revealing a single connector fracture in 1 of 5 cases on microcomputed tomography. Culotte stenting resulted in complete bifurcation coverage with extensive segments of double-layered struts and inappropriately apposed struts at the bifurcation level in 3 of 5 cases. On microcomputed tomography, there was MV and SB scaffold distortion at the bifurcation with single strut fractures in 4 of 5 and double fractures in 1 of 5. Modified-T and T-and protrusion resulted in complete bifurcation coverage and in minimal double-strut layers at the neocarina. On microcomputed tomography, no strut fractures were present after modified-T, whereas in 3 of 5 T-and protrusion procedures single strut fractures were noted.

CONCLUSIONS

Bifurcation stenting using bioresorbable vascular scaffolds is feasible with excellent angiographic results. PS with additional T-and protrusion whenever needed seems a reasonable approach. Whenever a 2-stent technique is planned, modified T-stenting appears the most promising.

Everolimus-eluting stent platforms in percutaneous coronary intervention: comparative effectiveness and outcomes

Despite the remarkable benefits obtained following the introduction of the first-generation drug-eluting stent (DES), concerns were raised over its long-term safety, particularly with regard to very late (beyond 1 year) stent thrombosis. Newer-generation DESs have been developed to overcome this limitation using novel stent platforms, new drugs, more biocompatible durable polymers, and bioabsorbable polymers or backbones. To date, new-generation DESs have virtually replaced the use of first-generation DESs worldwide. In this review article, we discuss in detail the design, pharmacology, and mechanism of action of the newer-generation permanent and bioresorbable everolimus-eluting platforms. Furthermore, we present and evaluate the current evidence on the performance and safety of these devices compared to those of other available stent platforms.