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In certain patients with ST-segment elevation myocardial infarction (STEMI), implantation of a fully bioresorbable vascular scaffold (BVS) appears feasible and safe, according to early results of a small prospective study published online January 12, 2014, ahead of print in the European Heart Journal. However, broader use of the device in this population is currently hampered by the device’s thick profile and limited range of sizes as well as a paucity of data on clinical outcomes, the authors say.

Initial results from the ‘Prague 19’ study were presented in May 2013 at EuroPCR in Paris, France.

In the multicenter trial, investigators led by Petr Widimský, MD, DSc, of Charles University (Prague, Czech Republic), analyzed data from 142 consecutive STEMI patients who underwent primary PCI at their center between December 2012 and August 2013, when use of BVS was the default strategy.

Forty-one patients (28.9%) received 49 BVS (Absorb; Abbott Vascular, Santa Clara, CA), while 57 patients who did not meet the prespecified inclusion/exclusion criteria received BMS or conventional DES and served as a control group. The remaining 45 patients either presented with severe acute heart failure (n = 24) or did not receive stents (n = 21) and thus were not included in the comparison, although their baseline characteristics were recorded “to put BVS use into proper perspective within a real-life STEMI scenario,” the authors write.

The Absorb BVS is a balloon-expandable device consisting of a polylactic acid polymer backbone processed for increased radial strength with a thin amorphous everolimus/polylactic coating for controlled drug release. In preclinical studies, the polymer backbone was fully absorbed in 2 to 3 years, although the polymer coating was absorbed sooner.

Good Procedural Results

BVS implantation was successful in 40 of 41 patients (98%); in 1 patient, implantation was blocked in an angulated left circumflex artery take-off and a BMS was substituted. QCA showed that TIMI 3 flow was restored in 95% of patients, with a 9.7% rate of acute recoil.

Following PCI, OCT in 21 BVS patients showed that although 1.1% of scaffold struts were malapposed in 47.6% of patients, there were no cases of significant malapposition (> 5% of struts per patient). Edge dissections were seen in 38% of patients, but all were small and clinically silent.

Comparison of QCA and OCT measurements showed important differences. The proximal reference diameter measured by OCT was larger by 0.29 ± 0.56 mm than the maximal proximal diameter measured by QCA (P = 0.028). The scaffold-to-artery ratio based on QCA/OCT was 1.26/1.14, indicating a significant oversizing. OCT-derived scaffold oversize was a negative predictor of strut malapposition (P = 0.035). Scaffold oversize, measured by either OCT or QCA, did not predict the occurrence of edge dissection.

Kaplan-Meier estimates at 6 months showed similar rates of event-free survival (cardiac death, MI, or TVR) between the BVS and control groups (95% vs. 93%; P = 0.674). There were 2 events in the BVS group:

• One patient with 2 BVS in the LAD experienced scaffold thrombosis on day 13, 3 days after stopping all prescribed medication including ticagrelor and aspirin

• The second patient with 3 BVS in the LAD underwent planned staged PCI of the left circumflex with DES and had a small MI due to side branch occlusion

The study results show that “BVS implantation in acute STEMI is feasible and safe and could be potentially used in a larger proportion of patients,” the authors write. Moreover, “[t]he strategy of significant scaffold oversizing in the setting of primary PCI results in excellent acute procedural results.” However, they add, although the short-term clinical outcomes are encouraging, longer-term follow-up is necessary.

Parity with DES in Question

“In all the major [BVS] trials, what we are hoping for is parity with [current-generation DES] with regard to early events and superiority later,” Stephen G. Ellis, MD, of the Cleveland Clinic (Cleveland, OH), told TCTMD in a telephone interview. “The concern that we might not achieve [early] parity is largely based on the scaffold size. The strut thickness is about 150 microns, whereas that of current second-generation DES is in the range of 80 to 90 microns. Because of that, the BVS may be more predisposed to thrombus formation.”

This experience with 40 patients is “better than an anecdote, but I wouldn’t give it too much credence with regard to safety,” Dr. Ellis commented.

In an e-mail communication with TCTMD, Robert Jan van Geuns, MD, of Erasmus Medical Center (Rotterdam, The Netherlands), agreed. Although the procedural results of this study and another recent trial at his own center are “very good,” he said, both series are small, and “the QCA and OCT surrogate endpoints do not predict longer-term outcomes such as stent thrombosis, where DES rates are extremely low.”

In addition, “there are some issues of deliverability” with the current BVS, Dr. Ellis noted. “And there are a lot of questions about [scaffold] overlap—because the stent strut is so thick, overlapping them presents a fair obstruction.”

However, Dr. van Geuns said he considers “deliverability in young ACS patients very good, and with a strategy of thrombus aspiration and achieving sufficient flow for adequate vessel diameter assessment, embolization and malapposition can be [comparable to those] with current metallic balloon-expandable stents.”

However, both Drs. van Geuns and Ellis stressed that the key concern with BVS remains acute and subacute stent thrombosis potentially related to strut thickness. The recent reduction in stent thrombosis rates is due to a mix of factors including new drugs and different drug doses, novel polymers, and thinner struts, Dr. van Geuns observed, so “returning to thicker struts [carries] a risk.”

Nonetheless, he concluded, the current data “support designing large studies to prove noninferiority [of BVS] at 1 year, with superiority on secondary endpoints like vessel restoration and late TLR, especially in younger patients.”

Meanwhile, the technology is evolving, Dr. Ellis said, adding, “There will be potential changes in the dimensions of this scaffold, and a number of other scaffolds are under development.”

Kočka V, Malý M, Toušek P, et al. Bioresorbable vascular scaffolds in acute ST-segment elevation myocardial infarction: A prospective multicenter study ‘Prague 19’. Eur Heart J 2014;Epub ahead of print.

Disclosures:

• Dr. Widimský reports receiving speaker’s honoraria from Abbott Vascular.
• Dr. Ellis reports serving as the co-principal investigator for the ABSORB III and IV trials and as a consultant to Abbott Vascular, Boston Scientific, and Medtronic.
• Dr. van Geuns reports receiving speaker’s fees from Abbott Vascular.

Related Stories:

• PRAGUE-19 Registry: Bioresorbable Scaffolds an Option for Certain STEMI Patients
• Bioresorbable Scaffolds Show Promise in Select STEMI Patients
• ABSORB III and IV Trials Aim to Prove Superiority of BVS