The ABSORB A study enrolled 30 stable patients with single de novo native short lesions of 3.0 mm calibre and tested the first generation of Absorb stent version 1.0.5 In-stent angiographic late lumen loss was 0.44 ± 0.35 mm at 6 months. Intravascular ultrasound (IVUS) analysis revealed a small neointimal area but also a significant reduction in stent area, probably due to recoil of the Absorb stent version 1.0. Four-year clinical results with complete follow-up are excellent with only one cardiac event (non-ST elevation acute coronary syndrome) and no stent thrombosis.6
The ABSORB B study enrolled 101 stable patients, again with single de novo lesions, suitable for the implantation of the Absorb stent version 1.1 sized 3.0/18 mm. Excellent clinical results were reported up to four years and, again, there was no stent thrombosis. Planned 6 month invasive assessment of cohort B1 (45 patients) revealed late lumen loss 0.19 ± 1.18 mm and optical coherence tomography (OCT) subanalysis(25 patients) demonstrated 96.8 % strut coverage.7 Similar invasive results were documented at 12, 24, and 36 months.8,9
The BIOSOLVE-I study enrolled 46 patients with stable or unstable angina with one or two de novo short (12 mm or less) and simple lesions with a reference vessel diameter between 3.0 and 3.5 mm for implantation of Dreams stents (3.25/16 mm or 3.5/16 mm).
Late lumen loss at 6 months was 0.65 ± 0.50 mm. OCT subanalysis (seven patients) demonstrated 97.2 % of struts to be well apposed at 6 months follow-up. The 12-month rate of clinically driven target lesion revascularization was 4.6 %.4 No further events were reported at the 3-year follow-up, no stent thrombosis occurred. The DESolve Nx study enrolled 126 patients with mostly stable coronary artery disease with a single de novo short lesion (12 mm or less) and reference vessel diameter between 3.0 and 3.5 mm. Angiographic late lumen loss was 0.21 ± 0.34 mm at 6 months. OCT subanalysis (38 patients) demonstrated 98.9 % of struts to be covered. The major adverse cardiac event rate at 12 months was 5.7 % and there was one case of stent thrombosis.
In summary, the first-in-man studies of selected three bioresorbable stents have included a total of 303 patients with mostly stable coronary artery disease. Patients with de novo, short, and ‘simple’ lesions were selected. Acute procedural results were excellent and the angiographic outcomes at 6 months were acceptable. Most importantly, the safety profile seems to be outstanding.
No results from randomized studies are available. ABSORB II started enrollment in 2011 and compares Absorb stent version 1.1 with the Xience Prime (Abbott Vascular, Santa Clara, California, US) stent in a 2:1 randomized fashion in patients with stable or unstable angina (myocardial infarction is an exclusion criterion). The larger ABSORB III study started enrollment in 2012 in the same fashion and should be sufficiently powered to prove clinical noninferiority. The estimated date of the primary outcome measure completion is August 2015.
Further Reported Data
Quantitative coronary angiography analysis demonstrated that the Absorb stent version 1.1 acute recoil is not different, and has better conformability, from metallic stents (Multi-Link or Xience V, Abbott Vascular, Santa Clara, California, US).10,11 Description of strut resorption and surrounding plaque composition by IVUS after Absorb 1.0 and Absorb 1.1 implantation has been reported.12–14 OCT provides excellent resolution but analysis of polymeric structures is different in comparison from metallic stents. The optically translucent polymeric struts appear as a black central core framed by light-scattering borders that do not shadow the vessel wall thus allowing excellent visualization of the vessel wall behind the struts and evaluation of stent apposition. Stent strut apposition was 95 % at baseline and 98 % at 6 months. A lack of tissue coverage was present in only 1.6 % of struts at 6 months.15 Normalization of local vascular compliance was demonstrated at 6 months.16 The use of online quantitative coronary angiography and especially measurement of maximal diameter of reference segment as a guide to stent size results in more favorable post implantation OCT findings.17,18 Absorb stent version 1.1 implantation was associated with a higher incidence of postprocedural side branch occlusion compared with the everolimus-eluting metallic stent Xience V. This effect was more pronounced with small side branches with a calibre of ≤0.5 mm.19
As far as expanding the use of bioresorbable stents into more challenging clinical scenarios, first case reports or small cohort studies have been reported, generally with encouraging results including: ST segment elevation myocardial infarction (STEMI),20–22 retrograde approach to chronic total occlusion,23 stenting of left main bifurcation,24 vein graft,25 or cardiac allograft vasculopathy intervention.26 The metal-free struts of Absorb stent version 1.1 (and likely all other polymer-based stents) allow unrestricted coronary computed tomography angiography. 27