The aim of bioresorbable scaffold (BRS) therapy is to provide short-term mechanical support and local drug application at a previously stenosed vessel segment and then to degrade completely in order to avoid the need for a permanent implant that remains in the vessel wall long term.¹ A number of BRS devices was approved for use worldwide, and one of them—the poly-L-lactic acid-based, everolimus-eluting BRS—has several published randomized trials comparing the device against metallic drug-eluting stents in patients with predominately stable coronary artery disease. Due to disappointing results and especially an increased rate of device thrombosis,^2,3 the BRS investigated in these trials is no longer available for clinical use.

There is a lack of data regarding BRS use in the setting of an acute myocardial infarction (MI), a niche potentially well-suited to treatment with BRS. Patients with MI are younger, often with lower atherosclerotic burden and often presenting focal lesions located in vessel areas with a larger diameter.⁴ Thus, ISAR-Absorb MI (A Prospective, Randomized Trial of BVS Versus EES in Patients Undergoing Coronary Stenting for Myocardial Infarction) investigated patients with acute MI undergoing BRS implantation.

ISAR-Absorb MI is a prospective, multicenter, randomized-controlled clinical trial of patients with acute MI. Enrolled patients were treated either with a poly-L-lactic acid-based, everolimus-eluting BRS or a durable polymer metallic everolimus-eluting stent (EES) in a 2:1 ratio. The key inclusion criteria were ST-segment elevation MI (STEMI) or non-ST-segment elevation MI (NSTEMI) with visual evidence of thrombus during coronary angiography, de novo lesion located in a native coronary vessel or bypass graft, and a reference vessel diameter ≥2.5 mm and ≤3.9 mm. Patients with lesions located in the left main trunk, lesions including a bifurcation with a side branch >2 mm, and severe calcification were excluded. The primary endpoint was the in-segment percentage diameter stenosis at coronary angiographic follow-up 6-8 months after the index procedure, evaluated by off-line quantitative coronary angiographic analysis at a central core laboratory (ISAResearch Center, Munich, Germany). Clinical secondary endpoints were assessed 12 months after randomization and included the composite of cardiac death/target vessel MI/target lesion revascularization (device-oriented composite endpoint), the composite of death/any MI/all revascularization (patient-oriented composite endpoint), and the individual components of the combined endpoints as well as the incidence of scaffold or stent thrombosis.

A total of 262 patients was enrolled, of which 173 were treated with BRS and 89 with EES. There were no statistically significant differences found regarding the baseline characteristics of both groups. The mean age was 61.7 ± 11.0 years in the BRS group and 63.3 ± 9.9 in the EES group; the minority of patients was female (20.2% vs. 27.0%; p = 0.28). Overall, 75.2% presented a STEMI at hospital submission, whereas 24.8% presented an NSTEMI with angiographically visible thrombus. Lesion characteristics were also comparable in both groups. Regarding the procedural parameters, pre-dilation (95.3% vs. 81.8%; p < 0.001) and post-dilation (56.6% vs. 34.8%; p = 0.001) were performed more often in patients treated with BRS. Angiographic follow-up data 6-8 months after the index procedure were available in 81.3% of the patients. Quantitative coronary angiographic analysis demonstrated that the primary endpoint of in-segment percentage diameter stenosis was 24.6 ± 12.2% with BRS and 27.3 ± 11.7% with EES (mean difference -2.7%, upper limit of one-sided 97.5% confidence limit 0.7%, prespecified margin of non-inferiority 5%, p_{non-inferiority} < 0.001). Clinical follow-up data at 12 months were available in nearly all patients. The device-oriented composite endpoint occurred in 7.0% in the BRS group versus 6.7% in the EES group (hazard ratio [HR] 1.04; 95% confidence interval [CI], 0.39-2.78), and the patient-oriented composite endpoint was noted 15.1% versus 14.6% (HR 1.02; 95% CI, 0.53-1.99). The incidence of definite/probable stent thrombosis at 12 months was 1.7% with BRS and 2.3% with EES (HR 0.76; 95% CI, 0.13-4.56). Subgroup analysis regarding the primary endpoint revealed evidence of interaction in relation to type of MI at presentation:

• STEMI: BRS 23.7 ± 11.4 versus EES 29.3 ± 12.1, p = 0.002
• NSTEMI: BRS 27.8 ± 14.5 versus EES 22.2 ± 8.8, p = 0.35; p_interaction = 0.004)

When interpreting the data, it must be noted that this trial was not powered to detect differences of the clinical endpoints and that long-term follow-up beyond 12 months will be required.

In summary, in the ISAR-Absorb MI trial, BRS were non-inferior to EES in patients presenting with acute MI in terms of a surrogate endpoint assessed at angiographic follow-up at 6-8 months. Furthermore, clinical event rates at 1 year were comparable between both groups. These findings are in line with the only other randomized trial comparing clinical results of BRS and EES in patients with acute MI.⁵ It is hypothesized that acute MI and especially STEMI may represent a clinical setting in which further assessment of BRS is warranted.

References

1. Wiebe J, Nef HM, Hamm CW. Current status of bioresorbable scaffolds in the treatment of coronary artery disease. J Am Coll Cardiol 2014;64:2541-51.
2. Ali ZA, Gao R, Kimura T, et al. Three-Year Outcomes With the Absorb Bioresorbable Scaffold: Individual-Patient-Data Meta-Analysis From the ABSORB Randomized Trials. Circulation 2018;137:464-79.
3. Cassese S, Byrne RA, Ndrepepa G, et al. Everolimus-eluting bioresorbable vascular scaffolds versus everolimus-eluting metallic stents: a meta-analysis of randomised controlled trials. Lancet 2016;387:537-44.
4. Loh JP, Pendyala LK, Kitabata H, et al. Comparison of outcomes after percutaneous coronary intervention among different coronary subsets (stable and unstable angina pectoris and ST-segment and non-ST-segment myocardial infarction). Am J Cardiol 2014;113:1794-801.
5. Sabaté M, Windecker S, Iñiguez A, et al. Everolimus-eluting bioresorbable stent vs. durable polymer everolimus-eluting metallic stent in patients with ST-segment elevation myocardial infarction: results of the randomized ABSORB ST-segment elevation myocardial infarction-TROFI II trial. Eur Heart J 2016;37:229-40.

Clinical Topics: Acute Coronary Syndromes, Cardiac Surgery, Cardiovascular Care Team, Invasive Cardiovascular Angiography and Intervention, Noninvasive Imaging, Atherosclerotic Disease (CAD/PAD), ACS and Cardiac Biomarkers, Interventions and ACS, Interventions and Coronary Artery Disease, Interventions and Imaging, Angiography, Nuclear Imaging

Keywords: Acute Coronary Syndrome, Coronary Artery Disease, Drug-Eluting Stents, Coronary Angiography, Myocardial Infarction, Constriction, Pathologic, Polymers, Dilatation, Absorbable Implants, Prospective Studies, Follow-Up Studies, Random Allocation, Myocardial Revascularization, Thrombosis, Stents, Biomarkers

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