Very Late Thrombosis in Bioresorbable Scaffolds

The presence of a metallic device interrupts normal laminar flow and creates an artery environment that favors thrombosis, leaving the vessel vulnerable to very late thrombosis. Dual antiplatelet therapy, a better implantation technique, and several improvements in new drug-eluting stents (DES) (thinner struts, and higher polymer stability and biocompatibility) have lowered significantly the incidence of this event, which is now less than 1% at 1 year. While these outcomes are much better than what they were for first-generation DES, they are still far from being perfect.

Bioresorbable scaffolds were developed while focusing on long-term safety and efficacy. Immediate scaffolding to prevent elastic recoil, sealing dissections, carrying anti-proliferating agents such as everolimus, and subsequent bioresorption so that the artery can go back to its normal anatomy and physiology would theoretically translate in clinical benefit during a long-term follow-up.

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Everolimus-eluting bioresorbable scaffold “Absorb” was found non-inferior to everolimus-eluting stent “Xience” after a 1-year follow-up. However, it also presented higher rates of target-vessel infarction and thrombosis. The promises of “Absorb” should have started to come true after 1 year, which explains the high expectations surrounding this much awaited scientific evidence.

This meta-analysis included 5 randomized studies and a total of 1730 patients. It compared Absorb and Xience after a follow-up of at least 24 months. The primary safety endpoint was definite/probable thrombosis.

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Patients treated with Absorb had a higher risk of definite/probable thrombosis compared with patients treated with Xience (odds ratio [OR]: 2.93; 95% confidence interval [CI]: 1.37-6.26; p = 0.01). Very late thrombosis occurred in 13/996 patients in the Absorb group (1.4%) vs. 1/701 patients in the Xience group (0.5%). In general, 92% of all cases of very late thrombosis in the Absorb group occurred once dual antiplatelet therapy had been interrupted.

Conclusion

Compared with Xience, bioresorbable scaffold Absorb was associated with a higher rate of very late thrombosis, which occurred in 1.4% of all patients.

Editorial

Expectations as regards the long-term benefit of bioresorbable scaffolds are completely shot down by the emergence of this evidence.

Scaffold thrombosis seems to present a bimodal distribution, with an early peak (<30 days) and a late peak after 1 year. The incidence of thrombosis with Absorb (1.4%) is similar to that presented by first-generation DES such as Taxus, and it is three times the incidence presented by new-generation DES such as Xience. These outcomes prove the falsehood of promises of higher safety, as well as of higher efficacy, since the rates of target-vessel revascularization are significantly higher than for Xience.

In that sense, we still do not know if prolonged dual antiplatelet therapy might protect these patients from a risk for very late thrombosis.

Original title: Late Thrombotic Events After Bioresorbable Scaffold Implantation: A Systematic Review and Meta-Analysis of Randomized Clinical Trials.

Reference: Carlos Collet et al. European Heart Journal (2017) 0, 1-8. Epub ahead of print.

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