By Jeffrey Zimmet, MD, PhD
Associate Professor of Medicine, University of California, San Francisco; Director, Cardiac Catheterization Laboratory, San Francisco VA Medical Center
SYNOPSIS: In this long-term follow up of the ABSORB IV trial, the five-year rate of target lesion failure was significantly higher with the everolimus-eluting bioabsorbable scaffold compared with its metallic counterpart, despite strict adherence to recommended implantation techniques.
SOURCE: Stone GW, Kereiakes DJ, Gori T, et al. Five-year clinical outcomes after coronary bioresorbable scaffolds and drug-eluting stents: The ABSORB IV randomized trial. J Am Coll Cardiol 2023; May 13: S0735-1097(23)05527-4. doi: 10.1016/j.jacc.2023.05.003.
[Online ahead of print].
Modern percutaneous coronary intervention (PCI) relies heavily on permanent metallic stents to scaffold the artery at the time of the procedure. Bioresorbable vascular scaffolds (BVS) have been proposed as a means to gain the benefits of a scaffold for immediate lumen gain and treatment of intervention-induced vessel injury, but without the long-term detriment of a permanent implant. Long-term disadvantages of the current generation of stents include loss of vessel vasomotion, an ongoing year-over-year rate of very late restenosis and thrombosis, jailing of side-branches, and making stented portions of the vessel unavailable as downstream surgical targets.
The Absorb stent, composed of poly(L-lactide) and using everolimus as an anti-restenotic agent, is the BVS with the most worldwide experience to date. Early trials of Absorb showed higher rates of early events compared with the metallic Xience stent. Much of the narrative around this device at the time proposed that inadequate technique underlay much of the difference in outcomes. Specifically, the thick struts of the BVS and lower radial strength meant small vessels (less than 2.25 mm in diameter) were not well-suited for this device. Aggressive lesion preparation and high-pressure post-dilatation were necessary to achieve better outcomes. The ABSORB IV trial was designed to test whether the Absorb BVS, implanted with careful vessel selection and oversight of technique, could produce similar long-term outcomes to metallic drug-eluting stents.
To this end, Stone et al randomized 2,604 patients undergoing PCI to receive either the Absorb BVS or the Xience cobalt-chromium everolimus-eluting stent. Pre- and post-dilatation was strongly encouraged, and was performed in 99.9% and 84.3% of BVS lesions, respectively. Implanted BVS devices were larger in relation to vessel diameters compared with the metallic stents, and dilatation pressures were higher. Despite this, acute luminal gain was lower with BVS, and residual stenosis was higher. Procedural and device success were similarly lower in the BVS group.
At five years, target lesion failure occurred in 17.5% of the BVS group and in 14.5% of the metal stent group (HR, 1.24; 95% CI, 1.02-1.52; P = 0.03). This was driven primarily by higher rates of target vessel myocardial infarction and ischemia-driven revascularization after BVS. Five-year rates of cardiac and all-cause mortality were similar between the groups. When examined over the course of the study, rates of target vessel failure and device thrombosis were higher in the BVS group during the first three years of the study, but were similar in years 4 and 5.
The authors concluded that despite improved implantation techniques, patients treated with BVS recorded a higher five-year rate of target lesion failure compared with those treated with metallic drug-eluting stents. They noted this increased hazard was confined to the first three years after deployment, which corresponds to the time of complete scaffold resorption, with similar subsequent event rates.
COMMENTARY
Improper implantation technique is not the only factor contributing to worse short-term outcomes for the Absorb BVS. Compared with metallic stents, the struts of this scaffold are considerably thicker, the radial strength is weaker, and vessel recoil is stronger. Even with strict adherence to trial protocols concerning vessel size, lesion preparation, and post-dilatation, device and procedural success rates were lower for these devices. Note that many higher-complexity lesions were excluded from this trial, including heavily calcified lesions, bifurcation lesions, and chronic total occlusions. Despite these restrictions, short- and intermediate-term outcomes were poorer in this study compared with metallic drug-eluting stents.
The impetus behind the development of BVS relies on the idea that ultimately there will be nothing left behind in the vessel, potentially allowing for better long-term outcomes. In this study, after five years of follow-up, no evidence of longer-term gains were seen. The best we can say is the modest penalty for implanting BVS in terms of target lesion failure and scaffold thrombosis essentially stops at three years, at which time the scaffold should have been resorbed. In this trial, outcomes subsequent to that point are the same as for metal stents — not better, but the same. This conclusion raises questions about the concepts behind the development of BVS in the first place: the idea of a long-term and ongoing rate of metallic stent-related adverse events.
Does this study rule out the possibility of a longer-term benefit to a resorbable stent? No, it does not. Stone et al posited even larger studies with follow-up out to 10 years might be needed to prove whether BVS can reduce late event rates beyond device resorption at three years. The Absorb device itself is no longer available outside clinical trials and registries, both in the United States and abroad. It remains to be seen whether improved BVS in development, perhaps with different characteristics and composition, would perform differently.
In this long-term follow up of the ABSORB IV trial, the five-year rate of target lesion failure was significantly higher with the everolimus-eluting bioabsorbable scaffold compared with its metallic counterpart, despite strict adherence to recommended implantation techniques.
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