Increased Risk of Device Thrombosis With Bioresorbable Scaffold, but Some Say Risks Can Be Mitigated

Another published report is highlighting an increased risk of device-related thrombosis among patients treated with the bioresorbable vascular scaffold, with investigators reporting the incidence to be as high as 3% at 12 months.

Importantly, more than half of patients with scaffold thrombosis in the multicenter European study presented with STEMI, including 1 patient who died during immediate follow-up. An additional 6 cases presented as sudden cardiac death, prompting operators to take a good hard look at what could be done to mitigate the problem.

“When we started, we were really keen on this technology, on this concept of vascular regeneration, and then we saw a few scaffold thrombosis [cases],” said senior investigator Tommaso Gori, MD, of University Medical Center Mainz in Germany. “This is a very ominous complication. There is a mortality rate, and it usually comes up as a myocardial infarction. It’s something one does not want to have, so our interest was triggered to figure out if this was a problem with the scaffold and whether it was more frequent with the scaffold than with stents.

The new report, published online ahead of print in the March 1, 2016, issue of the Journal of the American College of Cardiology, supports previous analyses showing a signal of increased risk of stent thrombosis with the Absorb everolimus-eluting bioresorbable vascular scaffold (Abbott Vascular).

In 1 meta-analysis, for example, the rate of definite or probable scaffold thrombosis after a median of 12 months was approximately two-fold higher among patients who received the Absorb bioresorbable scaffold compared with those who received an everolimus-eluting metallic stent. Another report, one that included 8,351 patients treated with the Absorb scaffold, also showed the risk of definite/probable stent thrombosis was two-fold higher when compared with 2,159 patients who received a drug-eluting stent.

To TCTMD, Gori said these reports prompted the researchers to examine data from consecutive patients treated with the bioresorbable vascular scaffold from 2 German and 2 Swiss hospitals. As part of their analysis, Gori said they wanted to identify possible predictors and/or underlying mechanisms of scaffold thrombosis with the technology.

Among 1,305 patients who received the Absorb stent, scaffold thrombosis occurred in 42 patients. The incidence of probable/definite scaffold thrombosis was 1.8% at 30 days and 3.0% at 12 months, with rates similar across all hospitals. Of these cases, scaffold thrombosis occurred within 1 day in 10 patients and within 1 month in 11 patients. For the remaining cases, scaffold thrombosis occurred late in 11 patients (30 to 365 days) and beyond 1 year in 10 patients.

Regarding clinical events, 6 presented with sudden cardiac death, 22 patients presented with STEMI, 9 patients with NSTEMI, and 3 patients with unstable angina. Nine of the patients who developed scaffold thrombosis were not taking dual antiplatelet therapy, including 3 who had already stopped after 12 months of treatment.  

Predictors of Scaffold Thrombosis

In the analysis, the researchers examined various clinical and procedural characteristics to identify possible predictors of scaffold thrombosis. Left ventricular ejection fraction and the treatment of ostial lesions were significant predictors of scaffold thrombosis, both of which have been identified as predictors of stent thrombosis with drug-eluting stents.  

The researchers also analyzed quantitative coronary angiography data from the 42 patients with scaffold thrombosis and compared the data with 84 matched control subjects who were treated with the Absorb device but did not have an adverse event. To TCTMD, Gori said the risk of scaffold thrombosis increased when implanted in small vessels and when the stent was incompletely deployed. For example, the risk of scaffold thrombosis increased for post-procedural minimum lumen diameters less than 2.4 mm (for the 2.5- to 3.0-mm devices) and less than 2.8 mm (for the 3.5-mm device).

In 2014, the hospitals adopted a strategy for implanting the bioresorbable scaffold that included predilatation, using the device only in vessels where it could be fully deployed, implanting the device only in reference vessels of the same size, and post-dilatation. In doing this, the group significantly lowered the incidence of scaffold thrombosis to 1.0% at 1 and 12 months.

“What’s important is that we showed that the reason for the failure was not really the scaffold itself but really the way one would implant it,” said Gori. The technology, at least in its current iteration, does appear to be less “forgiving” than current metallic stents. “But if you do things right, then the complications really are as frequent as with drug-eluting stents,” he noted.

Going Forward

Gori said the rationale behind a stent that degrades over time once the drug is eluted, eliminating the need for a metallic stent that remains in the coronary vasculature, is still sound and that he hopes other centers learn from their early experience. While the incidence of scaffold thrombosis at 1 year is significantly higher than rates observed with the latest-generation drug-eluting stents, he thinks operators can reduce the risk if they adopt a similar strategy they adopted when implanting.

In an editorial, Salvatore Cassese, MD, and Adnan Kastrati, MD, both of the Deutsches Herzzentrum (Munich, Germany), highlight the previous reports showing an excess risk of device thrombosis with the Abbott Absorb stent and state that the initial enthusiasm regarding the bioresorbable vascular scaffold has given way to a heightened skepticism. Early studies that uncovered the risk tested the bioresorbable stent in lower-risk patients with only moderately complex disease, a worrisome finding given that future studies will include higher-risk populations, such as STEMI patients or those with in-stent restenosis.

“The body of evidence regarding the performance of [bioresorbable vascular scaffold] technology confers a certain sense of déjà vu,” state Cassese and Kastrati. As with earlier drug-eluting stents, “the concerns regarding a higher risk of adverse events became apparent with the availability of larger sample sizes and a broader clinical use.”     

The editorialists agree that bioresorbable scaffolds for the treatment of coronary disease will likely follow the same path as drug-eluting stents, with advances leading to improved safety and efficacy. In the meantime, the use of the technology—which gained CE Mark in Europe in 2011 but is not yet approved in the United States (in March, a Food and Drug Administration advisory committee will debate a potential approval)—should follow device-specific protocols and be guided by evidence. As they point out, the long-term advantages of the “disappearing” stent are not yet proven and will take time before such data is available.

“Until then, cases of scaffold thrombosis will remain a matter of concern,” conclude Cassese and Kastrati. “The combination of optimism with healthy skepticism will certainly push forward the progress in BVS technology and revolutionize the field of percutaneous coronary interventions.”

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Sources: 
1. Puricel S, Cuculi F, Weissner M, et al. Bioresorbable coronary scaffold thrombosis. J Am Coll Cardiol. 2016;67:921-931.
2. Cassese S, Kastrati A. Bioresorbable vascular scaffold technology benefits from healthy skepticism [editorial]. J Am Coll Cardiol. 2016;67:932-934.  

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