Less stent thrombosis with biodegradable vs permanent polymers: Meta-analysis

Rates of stent thrombosis were 50% lower with the bioerodable polymer stents, said Dr Robert Byrne (Deutsches Herzzentrum, Munich, Germany), who presented the study results during a late-breaking science session here Friday at EuroPCR 2011.

Byrne pointed out that the whole rationale behind using a biodegradable polymer is that it can help control drug release but won't be left behind on the stent, which may aggravate the healing process.

" The issue to date has been that because late adverse events are very rare, we need large numbers of patients so we can detect any differences," he said. " I think this is probably the first time that we've detected a clear signal toward reduced clinical events. It may be that these differences only start to emerge or we can only tease them out after three years, and earlier time points aren't really showing the benefit of these platforms."

Byrne and colleagues combined data from three randomized trials of stents with bioerodable polymers: ISAR-TEST-3 and ISAR-TEST-4, both of which studied the Yukon Choice PC stent (Translumina Therapeutics), and the LEADERS study of biolimus-eluting Biomatrix Flex stent (Biosensors International). All three studies used the Cypher sirolimus-eluting stent for comparison. In all, 2358 patients received a biodegradable-polymer stent and 1704 received a Cypher stent.

At three years, rates of definite stent thrombosis were significantly lower in the biodegradable-stent group, at 1.2%, than in the permanent-polymer group, at 2.1% (hazard ratio 0.50, p=0.013). Despite the fact that the trials used different polymers and different drugs, tests showed little heterogeneity between study results, Byrne said.

Clinical outcomes at three years also tilted in favor of the biodegradable polymer stents, with the composite primary end point, made up of cardiac death, MI, and target lesion revascularization, reaching 18.2% for the patients treated with the biodegradable-polymer stents and 20.1% in the permanent-polymer group (hazard ratio 0.85, p=0.04).

" With a biodegradable polymer DES, when we analyze large numbers of patients, we can see a clear signal toward reduced late adverse events, and we see overall improved cardiovascular outcomes," Byrne said. " We have two different biodegradable polymers in this study, [yet] the results seem consistent."

Newer-generation DES produced by the " big three" stent manufacturers have not moved to biodegradable polymers, although polymer technology is an arena of fast-paced change. Asked if he thought improvements in permanent polymers could ultimately match the promise of a polymer that disappears altogether, Byrne was skeptical.

" I think you can try many different modifications to improve biocompatibility, but with durable polymers, you will still have polyfragments persisting long term in the vessel wall, and these can induce inflammatory reactions," he told heartwire. " I'm not sure that simply enhancing the biocompatibility of durable polymers will necessarily result in improved longer-term outcomes."

Whether bioerodable stents retain this edge when compared against newer stent designs remains to be seen. A similar analysis, comparing pooled results against the Xience stent, is to be presented at this year's upcoming European Society of Cardiology meeting.

Byrne acknowledged that the absolute difference in the rate of the primary end point between the two groups was small, in the range of 2%. " But what was interesting was really some of the differences in stent-thrombosis rates—it's the first time we've seen a signal that's been statistically significant."