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WASHINGTON -- Rather than gaining ground on conventional permanent scaffold stents as hoped, longer-term data with the Absorb bioabsorbable scaffold stent continued to fall flat.

Two-year follow-up from the ABSORB China trial and 3-year follow-up in the ABSORB II trial again showed noninferiority to Xience but numerical advantage favoring the conventional stents and worrying signals on scaffold thrombosis.

In ABSORB China, , of Fuwai Hospital in China, reported the following findings for the bioabsorbable stent against the Xience V everolimus-eluting stent:

• Composite endpoint of all-cause death, MI, and revascularization (10.1% vs 11.4%, P=0.66)
• Device-related events of cardiac death, target vessel MI, or ischemia-driven target lesion revascularization (4.2% vs 4.6%, P=0.82)
• Major adverse cardiac events (5.1% vs 5.1%, P=1.00)
• Target vessel failure (5.5% vs 6.8%, P=0.57)

Event rates were "generally low" among the patients, Gao told the audience at the Transcatheter Cardiovascular Therapeutics (TCT) annual meeting. There were two scaffold thrombosis cases, one early and one occurring very late.

While infrequent in the Absorb arm, such late events were "absolutely zero" among drug-eluting stent recipients in the Absorb series of studies, noted , of The Christ Hospital in Cincinnati. At a TCT press conference, he nonetheless conceded that Gao's data were "in some ways reassuring."

ABSORB China was a prospective analysis that included patients randomized to the bioresorbable vascular scaffold (n=236) or the Xience V stent (n=231). The trial first reported a benefit with in-segment late loss with Absorb after 1 year.

Another randomized study presented at TCT, ABSORB II, reported "disappointing" 3-year outcomes of the bioresorbable vascular scaffold, including worse vasomotion and late lumen loss compared with Xience.

Absorb not only failed to meet the co-primary endpoint of superior in-device vasomotion, but did not match the drug-eluting stent for vasomotor reactivity (0.047 mm for Absorb vs 0.056 mm for Xience, P=0.49 for superiority).

"The trial did not meet its mechanistic co-primary endpoints of superior vasomotor reactivity because Xience showed unexpected vasomotion which had been hypothesized to be zero," said , of Imperial College London.

Moreover, the co-primary endpoint of late lumen loss on angiography was more pronounced among Absorb recipients (0.371 mm vs 0.250 mm, P=0.78 for non-inferiority, P=0.0003 for difference).

Of the 335 patients that received the bioresorbable scaffold, Serruys reported one case of acute scaffold thrombosis and listed others that occurred during the subacute (n=1), late (n=1), and very late phases (n=6). None of their 166 peers in the Xience cohort had stent thrombosis.

"The incidence of very late scaffold thrombosis is a signal that warrants further careful monitoring of the patient having a clinical follow-up of longer than 2 years," he said.

The scaffold takes at least 3 to 4 years to be fully absorbed. Some have speculated that it could be even 8 years before the theoretical advantages of "uncaging" the vessel are realized in clinical outcome advantage.

The device-oriented composite endpoint -- accounting for cardiac death, target vessel MI, and clinically-indicated target lesion revascularization -- was more common in the bioresorbable vascular scaffold arm (10.4% vs 4.9%, P=0.043).

Exercise testing and answers on the Seattle Angina Questionnaire yielded similar results between groups over follow-up. Combined rates of all-cause death, MI, and revascularization were also no different (20.8% for Absorb vs 24.0% for Xience, HR 0.86, 95% CI 0.58-1.27).

Serruys expressed disappointment at the results. "It's not what we were expecting," he said, though he acknowledged that Absorb is still a first-generation device with room for improvement.

The same could not be said for drug-eluting stents, suggested panelist , of Houston Methodist Hospital. Absorb II showed that "with current-generation stents and stenting techniques, we are all of a sudden looking at event rates that are beyond our wildest dreams," he said.

Prolonged dual antiplatelet therapy appears to be the course for Absorb patients, Serruys suggested. That is, "until we have a device that is strong, small, and bioresorbs fast, which may be something difficult to achieve."

Damage control by device maker Abbott pointed to implantation techniques for Absorb, "which has a slightly larger profile than commonly-used metallic stents," as being a factor.

"In a post-hoc analysis in a subset of patients where proper implant techniques were followed, there were no cases of stent thrombosis at three years for patients receiving Absorb in the trial," a statement from the company said.

Because poor outcomes have been observed after scaffold placement in vessels under 2.5 mm, the label for the device "strongly" recommends quantitative coronary angiography or intravascular imaging to confirm appropriate vessel sizing. Abbott noted its "revamped" training program to emphasize pre- and post-dilation and proper sizing.