The Absorb bioresorbable vascular scaffold (BVS) (Abbott Vascular; Abbott Park, Illinois) received Conformité Européenne (CE) mark approval in 2011 and has been implanted in over 100,000 patients globally, according to prominent advertisements at the May EuroPCR meeting in Paris, France. It is anticipated that BVS will come before the US Food and Drug Administration in 2016. So, what do US interventional cardiologists have to look forward to?

A Stent Doesn't Have to Be for Life

Placing a metallic stent at the time of percutaneous coronary intervention (PCI) helps reduce acute vessel occlusion[1] and restenosis.[2] However, having a metal frame embedded in the artery has long-term disadvantages; notably, incomplete healing can induce a chronic inflammatory state, increasing the risk for thrombosis.[3] Permanent stents can also impair endothelial function,[4] prevent late favorable remodeling,[5] and hamper future imaging and reintervention.

"All other things being equal, most of us would prefer a stent that after 5 years has disappeared," commented Dr Robert Byrne (Deutsches Herzzentrum Munich, Germany) in a telephone interview with Medscape. He added that the polymer-coated drug-eluting stents (DES) are a potential nidus for adverse events, such as late stent thrombosis, in-stent restenosis, and neoatherosclerosis.

But as the coauthor of an editorial[6] on these devices that was subtitled "An Immature Technology in Need of Mature Application," Byrne is not ready to abandon DES anytime soon. "Of our daily PCI practice, about 10%-20% of patients are suitable for BVS. I wouldn't say it's any higher than that."

Robert A. Byrne, MB BCh

The Abbott product comprises a poly-L lactide (PLLA) everolimus-eluting stent. Over time, the PLLA is broken down by hydrolysis to yield water and CO2. "The space that was occupied by the stent struts tends to be filled by a proteoglycan matrix that after 5 years or so is not discernably different from the surrounding tissue," explained Byrne. All that remains, according to Abbott, is two pairs of tiny metallic markers, which help guide placement and enable a physician to see where the device was placed.

The DESolve® myolimus-eluting bioresorbable coronary scaffold system (Elixir Medical Corporation; Sunnyvale, California) is another PLLA-based device with a CE mark, but it's further behind in the US pipeline.

DAPT Ain't Disappearing

In 2006, when the DES thrombosis issue erupted, disappearing stents were proposed as a solution with the promise of abbreviated dual-antiplatelet therapy[7] (DAPT)—a promise that is unlikely to be realized.

"The stent thrombosis rate is about 1.5%-2% at 6-12 months, which is higher than our experience with current-generation metallic stents," noted Byrne. This is based on the published data so far from ABSORB II[8] and the largest registries, ABSORB-EXTEND[9] and GHOST-EU.[10]

Dr Azeem Latib (San Raffaele Hospital, Milan, Italy) agrees. "The incidence of subacute and late scaffold thrombosis appears to be at least the same, if not higher in, some real-world registries, such as GHOST-EU. The jury is still out on very late (after 1 year) scaffold thrombosis," he wrote in an email exchange with Medscape. "I don't believe that BVS will result in a shorter duration of DAPT, especially with the current generation of thick-strut BVS," he added.

To inform a European expert review on BVS implantation, Latib and colleagues[11] surveyed 14 high-volume BVS implanters and found that 80%-90% use at least 12 months of DAPT.

Azeem Latib, MB BCh

"As a general rule, we're recommending 12 months for BVS," concurred Byrne, who is involved in the ongoing ISAR-Absorb MI study.[12]

Dr Dean Kereiakes (Christ Hospital Heart and Vascular Center/Lindner Research Center, Cincinnati, Ohio), who is co-principal investigator of the US premarketing approval ABSORB III trial,[13] confirmed by phone that the protocol specifies a DAPT duration of 12 months. He believes that BVS should be associated with a low rate of late events because these are usually due to stent fracture or neoatherosclerosis; however, he acknowledges that this will be difficult to prove. To investigate late-term outcomes for BVS, ABSORB III will morph into the ABSORB IV study, and another 3000 patients will be added and followed for 5 years.

Vasomotion Restoration

There is more optimism about demonstrating the other perceived benefits of bioresorbable stents. Restoration of vasomotion is potentially the most important advantage, according to Latib. "We are already seeing clinical evidence of this from our own experience, and I can't wait to see the data from the ABSORB studies," he expanded. Vasomotion is possibly restored as early as 12 months according to Byrne, but the stent struts themselves take considerably longer to break down—"I would say 3-4 years," he said, referring to the Absorb BVS device.

Kereiakes also cites vasomotion as the most attractive feature of BVS. "Arteries are meant to be dynamic," he said, adding that this allows them to enlarge to accommodate atherosclerosis or in response to increased demand (eg, when you are running), whereas a caged metallic structure confers rigidity on the artery.

Dean J. Kereiakes, MD

Latib is also excited about the imaging options that BVS allow. "We have been routinely using multislice CT for follow-up on these patients, and I can only say that the imaging results are amazing. Not only are you able to truly evaluate the scaffolded segment as well as with conventional angiography, but there is also evidence of plaque regression."

Piggybacking on the Global Learning Curve

One benefit for US practitioners coming late to the BVS party is that they can take advantage of the lessons learned across the globe. At a session on the use of BVS in real-world settings at EuroPCR, Dr Piera Capranzano (Ferrarotto Hospital, Catania, Italy) presented an update on the GHOST-EU registry[14] showing that thrombotic events were clustered mostly in the first 30 days after PCI, suggesting the need for more accurate lesion selection and optimal implantation technique.

In an editorial on bioresorbable stents, Dr Alexandre Abizaid (Instituto Dante Pazzanese de Cardiologia, São Paulo, Brazil) noted that "Metallic stents and the current BVS devices are deployed differently... careful vessel sizing, aggressive pre-dilation, and particular attention to the balloon used for post-dilation help minimize risk of scaffold damage."[15] Byrne and Latib concurred that the critical step is lesion preparation. "Post-dilation is a big topic, but in our clinical experience, if you don't get the predilation right, then the post-dilation doesn't help you very much," observed Byrne. Latib added that lesion preparation is more important for ensuring BVS expansion and symmetry than for deliverability.

Kereiakes confirmed that predilation is mandatory per protocol in the ABSORB III trial, and post-dilation is strongly encouraged. Operators in the trial received training, and the study includes a lead-in patient phase before randomization (two patients per center maximum), he explained.

In addition to pre- and post-dilatation, the liberal use of intracoronary imaging with optical coherence tomography (OCT) or intravascular ultrasound (IVUS) is recommended for BVS implantation.[11,15]

All-Comers or the Select Few?

Complex lesions, such as left main or bifurcation lesions or heavily calcified ones, are excluded from ABSORB III. Meanwhile, on the other side of the pond, over 20% of the more than 1700 lesions treated with BVS in the GHOST-EU registry were bifurcation lesions, and EuroPCR included challenging case presentations on the use of these devices in left main lesions and others. Are the Europeans running amok, or is there a role for PLLA stents in all-comers?

Latib, who has published a paper[16] analyzing BVS in bifurcation lesions, uses these devices in younger patients (<70 years) and "CTOs [chronic total occlusions], vessel reconstruction of diffuse disease, multivessel intervention, long lesions, and bifurcation lesions." He added that "we have also treated calcified lesions, restenosis, and STEMI[ ST-segment elevation myocardial infarction], but the data are still limited as to whether these will be ideal lesions."

Byrne is more cautious. "The main exclusion criteria for us are heavily calcified vessels, even if you do substantial plaque modification (rotoblation, cutting balloon, etc)," he said, explaining that the mechanical strength of the lactic acid-based stents is not as good as that of metallic stents. He also avoids major bifurcations and large vessels (diameter ≥ 4 mm), "which obviously includes the left main stem." The size limitation is because the largest BVS available is 3.5 mm and the maximal postexpansion recommended is 0.5 mm over the nominal diameter.

In Byrne's opinion, "Patients treated with these stents should be entered in randomized controlled trials or postimplantation surveillance studies."

Note his use of the word "stent" rather than "scaffold." The European Society of Cardiology/European Association of Percutaneous Coronary Interventions task force on the evaluation of coronary stents in Europe[17] came to the consensus that these should be called "bioresorbable stents" because "stent is an internationally acceptable word and is the default word in most languages," said Byrne. The other side of that argument is that "scaffold" may be a more appropriate term, because it implies a temporary arterial support.[18] "It looks like a stent, it works like a stent—just call it a stent," opined Byrne.

Whatever you call them, there will be more data to look forward to this year. The upcoming European Society of Cardiology meeting in London will see the results of the ABSORB STEMI-TROFI II study[19] comparing BVS vs EES in patients with STEMI, and ABSORB Japan[20] which compares the two devices in stable patients. ABSORB III will be presented at the Transcatheter Cardiovascular Therapeutics (TCT) meeting in October, probably with simultaneous publication.

Disclosures: Drs Byrne and Latib report having no relevant disclosures. Dr Kereiakes reports having served as an advisor or consultant for: Abbott Laboratories; Boston Scientific; Svelte Medical Systems, Inc.; and REVA Medical, Inc.

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