By Lorenzo Azzalini, MD MSc, and Philippe L. L’Allier, MD
Interventional Cardiology, Department of Medicine
Montreal Heart Institute, Montreal, QC, Canada
Bioresorbable vascular scaffolds (BVSs) are considered by some as the third great revolutionary advance in the field of interventional cardiology, after balloon angioplasty and metallic stents. They provide temporary scaffolding and then
disappear within two to four years after implantation, once plaque healing has occurred. This property has theoretically several beneficial consequences: (1) the restoration of epicardial vasomotion at the treatment site (hence normal coronary physiologic response to external stimuli); (2) late luminal gain through positive remodeling (with lower incidence of restenosis); (3) the possibility of anastomosing a coronary artery bypass in case it is needed in the future; and (4) decreased risk of intrastent neo-atherosclerosis formation and very late scaffold thrombosis. Early results from the ABSORB trials are encouraging, but data from real-world use are needed before BVS can be considered as a workhorse device in clinical practice. In particular, there have been some isolated reports of BVS thrombosis, which have raised concern on this important complication.
We interrogated our database to identify all cases of BVS thrombosis during the first 12 months after Absorb BVS (Abbott Vascular) became available. We identified 4 cases of BVS thrombosis among 339 patients treated with 504 scaffolds (1.2%). All were early definite thrombosis. All patients were on aspirin and generic clopidogrel. All patients presented several risk factors for stent/scaffold thrombosis. Optical coherence tomography was performed in two cases and ruled a mechanical cause. In one case, BVS thrombosis was due to scaffold underexpansion plus uncovered plaque across the proximal edge of the device.
We further explored the theoretical mechanisms of device thrombosis that are specific to BVS. There is evidence that hints at an unfavorable peristrut rheology for BVS, as compared with metallic stents. Computational fluid dynamic data showed low shear stress regions and altered flow patterns in-between BVS struts (Figure). It is known that a positive correlation between strut thickness and flow disturbances exists and that this relation carries negative clinical consequences (higher restenosis and target vessel revascularization rates). Even though a direct comparison between BVS and metallic stents is not currently available, these flow disturbances could be more pronounced with BVS (struts thickness 150-200 μm versus 75-124 μm).
Due to their reabsorption, BVS were believed to be almost immune from late and very late scaffold thrombosis. However, this and other recent reports suggest that they are not immune from subacute thrombosis and that risk factors similar to those for metallic stents should be considered. It seems prudent to obtain long-term safety data prior to BVS widespread clinical utilization. It will be very interesting to assess late thrombosis, and very late BVS thrombosis in particular.
Figure. Rheology disturbances in proximity to BVS struts.
To read the entire article in this month’s Journal of Invasive Cardiology, please visit Bioresorbable Vascular Scaffold Thrombosis in an All-Comer Patient Population: Single-Center Experience