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A novel biodegradable polymer stent appears at least as good as one of its conventional, permanent polymer competitors over the longer term, researchers found.

The biolimus-eluting BioMatrix Flex stent cut composite cardiac death, myocardial infarction, and target vessel revascularization rates by a relative 19% compared with the sirolimus-eluting Cypher stent, Stephan Windecker, MD, of Bern University Hospital in Bern, Switzerland, and colleagues reported online in The Lancet.

These four-year results from the LEADERS trial met noninferiority criteria at P<0.0001 with borderline significance for superiority at P=0.050.

The results were simultaneously reported at the Transcatheter Cardiovascular Therapeutics (TCT) meeting in San Francisco.

A strong trend for fewer revascularizations largely stemmed from fewer very late definite stent thrombosis events from years one to four, with 80% lower risk than seen with the durable polymer stent (P=0.004).

That is what researchers hoped to see by getting rid of the durable polymer, which has been suspected to be a nidus for inflammation and thrombosis after it elutes off the protective drug it carries.

A meta-analysis of the LEADERS three year data pooled with that of other novel biodegradable polymer stent trials also supported a reduction in definite stent thrombosis with fewer major cardiac adverse events as well.

While promising, it's too soon to declare superiority over even first-generation durable polymer drug-eluting stents, Ron Waksman, MD, and Gabriel Maluenda, MD, both of Washington Hospital Center in Washington, D.C., cautioned in an accompanying editorial.

Because LEADERS was not designed as a superiority trial, the difference in event rates, "should be carefully interpreted when translating to clinical practice," they warned.

The study included 1,707 patients with a total of 2,472 coronary artery disease lesions randomized to receive the novel biodegradable polymer stent or the durable polymer Cypher Select stent.

At four years, the rate of the primary composite endpoint encompassing cardiac death, myocardial infarction, and clinically-indicated target vessel revascularization was 19.7% with the biodegradable polymer stent compared with 22.6% with the conventional stent (rate ratio 0.81, 95% confidence interval 0.66 to 1.00).

These rates started to diverge in the first month with more pronounced separation of the curves between years one and four, though this was not a statistically significant difference compared with the first year of follow-up.

The biggest driver of the late advantage was a reduction in MI (RR 0.60 after the first year, P=0.031 for interaction with duration of follow-up).

Definite stent thrombosis also showed a strong trend for reduction with the novel stent (RR 0.62, P=0.09).

Very late definite stent thrombosis, with an overall rate 0f 0.12% per year with the novel stent and 0.6% per year with the durable polymer stent, showed no difference in the first year between stent types but thereafter occurred less often with the biodegradable polymer stent (P=0.017 for interaction).

The only subgroup for which the results differed was the group that entered the study with an ST-segment elevation MI at baseline. Those patients saw significantly fewer major cardiac adverse events with the biodegradable polymer stent (RR 0.45, 95% CI 0.70 to 0.83), though the small numbers made this a hypothesis-generating result only.

Another limitation was that outcomes might not generalize from the selected high-volume, experienced European sites where the study was conducted.

The researchers pointed to the overall long-term results and the treatment effect interaction with time as proof of the concept of biodegradable polymer coatings, "which in turn might have implications for the recommended duration of dual antiplatelet therapy."

However, in the trial, duration of dual antiplatelet therapy was similar between stent groups at 12 months and up to four years, Waksman and Maluenda noted.

"With polymer degradation that lasts nearly a year, to claim shorter duration of dual antiplatelet therapy with this biodegradable polymer over durable polymers would be difficult," they argued in the editorial.

Both they and the researchers cautioned about extrapolating the results to compare with second-generation drug eluting stents, though tempting since the Cypher line of stents are due to be discontinued at the end of 2011.

The editorialists noted that preclinical results suggested less inflammation with the newer durable polymer drug-eluting stents than with the first generation.

"Although biodegradable polymer technology is scientifically appealing and the long-term results of LEADERS are encouraging, we are not yet in a position to confirm whether biodegradable polymers will replace durable polymer for drug-eluting stent technology," they concluded.