study that enrolled 131 patients from Australia, Belgium, Denmark, France,
the Netherlands, New Zealand, Poland and Switzerland. Key endpoints of the study include assessments of safety – major adverse cardiac events (MACE, defined as nonfatal myocardial infarction, cardiac death and/or target vessel revascularization) and treated-site thrombosis rates – at 30 days and at 6, 9, 12 and 24 months, with additional annual clinical follow-up for up to five years, as well as an assessment of the acute performance of the device. Other key endpoints of the study include imaging assessments by
angiography, intravascular ultrasound (IVUS), optical coherence tomography (OCT), and other imaging modalities at 6, 12, 18, 24, 36 and 60 months. At two years, the device was safe with no cardiac deaths, ischemia- driven target lesion revascularisations, or stent thromboses recorded, and only one myocardial infarction (non-Q wave). 18-month multi-slice CT (assessed in 25 patients) showed a mean diameter stenosis of 19%. At 2-year angiography, the in-stent late loss of 0.48mm and the diameter stenosis of 27% did not differ from the findings at six months. The luminal area enlargement on OCT and intravascular ultrasound between six months and two years was due to a decrease in plaque size without change in vessel size. At two years, 34.5% of strut locations presented no discernible features by OCT, confirming decreases in echogenicity and in radiofrequency backscattering; the remaining apparent struts were fully apposed. Additionally, vasomotion occurred at the stented site and adjacent coronary artery in response to vasoactive agents. A multicenter single-arm evaluation, the ABSORB EXTEND study is currently enrolling patients in preparation for a pivotal non-inferiority trial compared to metallic stents, but further investigation should determine whether bioabsorbable stents are suitable for patients with more complex coronary artery disease than those treated in the early-phase studies.
Figure 1: The Abbott ABSORB Bioresorbable Vascular Scaffold (BVS)
REMAINING CHALLENGES (LIMITATIONS) Before bioabsorbable stents become widely accepted, they must meet several requirements. Ease of use is a desirable feature, but the insertion of bioabsorbable stents is more difficult and requires more attention to detail than the insertion of metallic stents. The BVS has 37-µm platinum markers at each end for angiographic visualization, but the scaffold itself is radiolucent. The rigid crystalline backbone of the BVS will be less tolerant of plastic deformation than metallic stents and will require more accurate vessel sizing to avoid overexpansion, scaffold fracture, and an increased risk of thrombosis. Correct sizing will require quantitative coronary angiography in every case, and optimal stent deployment will likely require either intravascular ultrasound or optical coherence tomography as well. Due to possible limitations in radial support, bioabsorbable stents may be unsuitable for calcified vessels, ostial stenoses, complex bifurcation stenoses, or resistant lesions.
CONCLUSION The concept of a stent that does its job and disappears has appeal. The outcome of studies suggest that a temporary scaffold like ABSORB provides durable results over the long term and a permanent implant may not be necessary to effectively treat patients with coronary artery disease. At two years after implantation the stent was bioabsorbed, had vasomotion restored and restenosis prevented, and was clinically safe, suggesting freedom from late thrombosis. The clinical results suggest that this innovative therapy could provide long-term benefits for patients with coronary artery disease. While current evidence suggests that no single stent design or polymer type is optimal for all lesions or patients, the availability for selected patients of a bioabsorbable stent with negligible restenosis and no risk of stent thrombosis would be ideal.
018 ARAB HEALTH MAGAZINE ISSUE 2 2012
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