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PARIS -- The sirolimus-eluting Orsiro stent with a biodegradable polymer coating performed comparably to the everolimus-eluting Xience Prime stent with a durable coating in patients with de novo coronary lesions, a randomized trial showed.

At 9 months, in-stent late lumen loss was 0.10 mm with Orsiro and 0.11 mm with Xience Prime, satisfying criteria for noninferiority (P<0.0001), according to Stephan Windecker, MD, of Bern University Hospital in Switzerland.

Clinical event rates were low and similar in the two groups, although the trial was not powered for those outcomes, he reported at the EuroPCR meeting here.

"These results certainly will need to be extended to larger randomized trials powered for clinical endpoints including more complex patients," he said, noting that an all-comers trial powered for clinical endpoints -- called BIOSCIENCE -- has recently completed enrollment of more than 2,000 patients.

Windecker reported results from the BIOFLOW-II trial, which included 452 patients with de novo coronary lesions in up to two native coronary arteries who were randomized 2:1 to Orsiro or Xience Prime. It took place at 24 centers in eight European countries.

The patients were well matched according to baseline characteristics, lesion location, and lesion type. The average lesion length was 13.36 mm in the Orsiro group and 13.65 mm in the Xience Prime group.

Device success was 100% in each group and procedure success was 97.5% in each group.

At the 9-month follow-up, there were no differences between the two groups on angiographic characteristics, including late loss, minimum lumen diameter, percent diameter stenosis, and binary restenosis. The in-segment restenosis rate was 3.96% with Orsiro and 4.7% with Xience Prime (P=0.72).

Rates of various clinical outcomes did not differ between the two groups either, including cardiac death (0.7% with Orsiro versus 0% with Xience Prime, P=0.40), target-vessel MI (2.4% versus 2.6%, P=0.95), clinically driven target lesion revascularization (2.1% versus 2.7%, P=0.66), and target lesion failure (4.8% versus 5.3%, P=0.47). No definite or probable stent thrombosis occurred in either group.

Imaging with optical coherence tomography (OCT) and intravascular ultrasound in a subset of patients revealed that the neointimal area was significantly smaller in the Orsiro group (0.74 versus 1.00 mm², P=0.024) but the change in neointimal hyperplasia was greater in the Xience Prime group (0.43 versus 0.16 mm², P=0.043).

"Whether this difference does translate into any clinical difference I think it's premature to say," Windecker said.

There was no difference between the groups in the percentage of well-apposed struts, incomplete strut apposition, and non-apposed side branch, but the percentage of covered struts was slightly higher in the Orsiro group (98.3% versus 97.5%, P=0.042).

Commenting on the results, Alexandre Abizaid, MD, PhD, of the Instituto Dante Pazzanese de Cardiologia in São Paolo, said three features were notable about the Orsiro stent -- a 25% thinner strut compared with Xience Prime, which might reduce injury to the vessel wall, the use of a limus drug, and the biodegradable polymer.

"I think those three factors can contribute to a safer device," he said in an interview, adding that the findings might increase use of the stent, which has been approved in Europe.

"It's always good to go against the best in class," Abizaid said. "Xience became really the gold standard, so I think that whoever is brave enough to go against Xience will have a good market share."

But, he said, "I think a more definitive benefit is yet to be proven in a clinical study with the right sample size."

Andreas Baumbach, MD, of the University of Bristol in England, agreed, saying after Windecker's presentation, "I think these early studies with proxy endpoints like late lumen loss and OCT assessment of new endothelium [are] reassuring, at best. But we need to see whether that translates into clinical benefit or indeed a late catch-up in the long run."

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