Clinical Pearls & Morning Reports

Published June 14, 2017

Why might there be higher rates of device thrombosis with bioresorbable scaffolds than with metallic stents?

The Amsterdam Investigator-Initiated Absorb Strategy All-Comers Trial (AIDA) was designed to compare the bioresorbable vascular scaffold with the metallic stent in a patient population that reflects that seen in routine clinical practice. Wykrzykowska et al. published an early report of the data, which the data and safety monitoring board recommended to be released owing to safety concerns.

Clinical Pearls

Q. How might bioresorbable vascular scaffolds improve upon metallic stents for percutaneous coronary intervention (PCI)?

A. Drug-eluting stents are the standard of care in PCI. Nevertheless, their rigid metallic cages hamper vasomotion, and they are associated with the development of neoatherosclerosis, which results in an ongoing risk of stent thrombosis (rate of 0.1 to 0.2% per year) and repeat revascularization (rate of 2 to 3% per year). Bioresorbable vascular scaffolds theoretically leave no permanent implant and allow for restoration of vessel function.

Q. How did the bioresorbable scaffold compare to the metallic stent with respect to target vessel-failure in the AIDA trial?

A. In the study by Wykrzykowska et al., the primary end point of target-vessel failure was a composite of cardiac death, target-vessel myocardial infarction, or target-vessel revascularization. The primary end point of target-vessel failure occurred in 105 patients in the scaffold group and in 94 patients in the stent group (hazard ratio with bioresorbable scaffolds, 1.12; 95% confidence interval [CI], 0.85 to 1.48; P=0.43). Kaplan–Meier estimates of target-vessel failure rates at 2 years were 11.7% in the scaffold group and 10.7% in the stent group (difference in rates, 1.0 percentage point; 95% CI, −2.1 to 4.2).

Q: Are bioresorbable scaffolds associated with an increased risk of device thrombosis?

A: Concern about an increased rate of scaffold thrombosis was first raised by investigators who examined data from the GHOST-EU (Gauging Coronary Healing with Bioresorbable Scaffolding Platforms in Europe) registry and reported a 2.1% rate of scaffold thrombosis at 6 months. A recent meta-analysis of 16,830 patients showed an overall rate of scaffold thrombosis of 1.8% at a median follow-up of 1 year. Furthermore, in the ABSORB Japan trial, four cases of definite scaffold thromboses (in 1.6% of the patients) occurred between the first and second year after implantation. In the study by Wykrzykowska et al., the authors found that the rate of definite or probable device thrombosis in the scaffold group was approximately 3.5 times as high as that in the stent group over the course of 2 years.

Morning Report Questions

Q:Why might there be higher rates of device thrombosis with bioresorbable scaffolds than with metallic stents?

A: The causes of the higher rate of device thrombosis with scaffolds than with stents are only partly understood. Incomplete lesion coverage, underdeployment, and malapposition have been observed with the use of optical coherence tomography in acute and subacute cases of scaffold thrombosis. Thick stent struts are associated with blood-flow alterations and thrombogenicity, especially when they are left malapposed. Late events might be related to a combination of nonembedded and nonabsorbed scaffold struts in complex lesions and late structural discontinuity or device dismantling. Newer generations of bioresorbable scaffolds, with thinner struts, increased radial strength, different composition, and faster resorption, may overcome these issues.

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