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WASHINGTON -- The Absorb bioresorbable vascular scaffold failed to beat a current-generation stent for many late patient outcomes -- and still exhibited worrying signals of scaffold thrombosis, two randomized studies reported.

Two-year outcomes of the Absorb China trial were similar between patients who got Absorb and those that received the Xience V everolimus-eluting stent, according to , of Fuwai Hospital in China:

• Composite endpoint of all-cause death, myocardial infarction (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.

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).

However, 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).

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."