ABSTRACT & COMMENTARY
Bioabsorbable Coronary Scaffolds: Promise and Peril
By Jeffrey Zimmet, MD, PhD
Associate Professor of Medicine, University of California, San Francisco, Director, Cardiac Catheterization Laboratory, San Francisco VA Medical Center
Capodanno D, et al. Percutaneous coronary intervention with everolimus-eluting bioresorbable vascular scaffolds in routine clinical practice: Early and midterm outcomes from the European multicentre GHOST-EU registry. EuroIntervention 2014; Jul 18.
doi: 10.4244/EIJY14M07_11. [Epub ahead of print].
Clinical outcomes from percutaneous coronary intervention (PCI) have steadily improved over time, with transitions from balloon angioplasty to bare-metal stenting, and more recently from first-generation drug-eluting stents (DES) to second- and third-generation designs. The latest-generation DES are considered to be more efficacious in preventing repeat revascularization compared with earlier models, but are also thought to be safer in terms of failure events such as stent thrombosis. The permanent lining of the vessel with metallic stents is, however, widely considered to be a major drawback of this approach. The long-term presence of a foreign body may lead to effects on vascular remodeling, and is considered to be a nidus for very late events, including stent thrombosis. Thus, the excitement is centered on the concept of fully resorbable stents, commonly referred to as bioresorbable vascular scaffolds (BVS). Abbott Vascular has been early out of the BVS gate with its Absorb device, which is a semi-crystalline poly-L-lactide (PLLA) framework that elutes everolimus, similar to its Xience stent platform. Current data suggest that these BVS are fully resorbed in a time frame between 2 and 4 years after implantation. Although FDA approval will hinge on the results of the not-yet-complete ABSORB III and IV trials, the Absorb BVS received the European CE Mark of approval back in 2011 and was launched internationally in 2013. The trials released to date have been small, and have focused on specific patient populations with relatively restrictive exclusion criteria.
The GHOST-EU (Gauging coronary Healing with biOresorbable Scaffolding plaTforms in EUrope) registry is a retrospective study conducted at 10 high-volume European hospitals. The study includes data from 1189 patients enrolled between late 2011 and early 2014. This is truly an all-comers registry, including all patients with coronary artery lesions for whom implantation of an Absorb BVS was intended. Included in the study were patients with acute myocardial infarction (MI), renal and left ventricular dysfunction, ostial and bifurcation disease, and left main disease. Notably, more than 18% of patients received both a BVS and a conventional metallic stent.
Target lesion failure (TLF), defined as the combination of cardiac death, target vessel MI, or clinically driven target lesion revascularization, occurred in 67 of the 1189 patients during the follow-up period, at a median of 109 days after scaffold implantation. By applying the Kaplan-Meier method, the authors calculated a cumulative incidence of TLF of 2.2% at 30 days and 4.4% at 6 months, with a predicted annualized TLF rate of more than 10%. Patients receiving a combination of BVS and conventional stents had an even higher TLF rate, at 5.6% at 6 months. Although this was not a randomized trial and included no comparison group (as the anticipated US ABSORB trials will do), these TLF rates are higher than those reported in similar all-comers trials with second-generation metallic DES (the RESOLUTE All-Comers and TWENTE trials reported 1-year TLF of just over 8%). Of particular interest is the data on stent thrombosis (ST), which is always a concern with coronary stents. Definite ST was seen in 20 patients at a median of 6.5 days from implantation, while probable ST was seen in an additional three patients. The cumulative incidence of ST was 1.5% at 30 days and 2.1% at 6 months, which is significantly higher than would be expected for conventional DES. The authors concluded that BVS hold considerable promise, but current models are not outperforming conventional DES.
COMMENTARY
BVS is one of the most highly anticipated technologies in coronary intervention, with the potential to change the way coronary disease is treated. As with many such technologies, however, the full story of promise and peril will only come with more data, and this paper represents the largest numbers reported to date. Much remains to be learned about the optimal use of these devices, including appropriate patient and lesion selection. Because the devices are significantly different from conventional stents, the authors sought to investigate the influence of the learning curve on clinical outcomes. To do this, they compared outcomes of patients who were among the first 50 treated with BVS at any particular center with those who were treated after. In a surprising turn, the TLF rates at 6 months were significantly higher with greater BVS experience. As might be expected, more complex patients and lesions were treated in the latter group, including more ACS patients and more lesions with thrombus and ostial locations.
Scaffold thrombosis rates were clearly higher than anticipated, and this may be cause for tempered enthusiasm. The greater strut thickness (compared with current-generation metallic stents) certainly could play a role in an increased propensity for thrombosis. It may also be that certain types of lesions are not appropriate for BVS, or that these devices may give less margin for error when it comes to lesion preparation and vessel sizing when compared with conventional stents. Ultimately, answering these questions will require a rigorous randomized, controlled trial comparing BVS with current-generation DES.
