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PARIS -- Longer follow-up hasn't yielded any differences in clinical outcomes among biodegradable-polymer drug-eluting stents (DES) nor given them an edge over the current durable-polymer DES products that have been the gold standard, according to trial updates reported here.

Several issues may be contributing to the missing evidence that removing the potentially inflammatory effect of polymers long term, by having them degrade over the course of months, results in clear improvements for patients, discussants said during a late-breaking trial session here at the annual .

For one, the variety of devices being compared make it hard to know the mechanism behind how they may make a difference in clinical outcomes, said Ron Waksman, MD, of MedStar Washington Hospital Center in Washington, D.C.

Having every biodegradable DES differ by some combination of strut thickness, polymer type, and drug makes it difficult to pin down optimal DES design and patient selection, he said.

"I think permanent polymers keep their drug for a longer time," added panelist Renu Virmani, MD, of CVPath Institute in Gaithersburg, Maryland, who noted that researchers are unable to measure exactly how much drug is left in a person and must instead rely on data from animal studies.

"Have we come as far as we are going to go with metallic stents as far as the device itself?" asked Nick West, MD, of Royal Papworth Hospital in Papworth Everard, England.

Perhaps the real impact will be felt only with different implantation technique and dual antiplatelet therapy, he suggested.

DESSOLVE III

The first biodegradable DES in the spotlight during the session was the MiStent, which stood toe-to-toe with the Xience everolimus-eluting durable-polymer stent in terms of cardiac death, target vessel MI, and clinically-indicated target lesion revascularization 24 months (8.7% vs 8.6%, log-rank P=0.958).

There were no differences in the individual components of the combined endpoint, nor in others such as stent thrombosis, all-cause death, and MI, according to William Wijns, MD, PhD, of National University of Ireland Galway.

Wijns and co-investigators randomized patients to the MiStent (n=703) or Xience (n=695) at sites in the Netherlands, Germany, France, and Poland. Of the all-comers population, 59% had an acute coronary syndrome (ACS).

The MiStent was designed to sustain sirolimus elution to 9 months, while the polymer disappears after 3 months. With its 64-µm struts, the device had already shown non-inferiority to Xience in terms of the device-oriented composite endpoint in the earlier 1-year analysis.

BIO-RESORT

Two different bioresorbing-polymer DES were then shown to hold up against the durable-polymer Resolute Integrity DES at the 2-year mark.

At 2 years, the target vessel failure rate reached 8.3% with Resolute Integrity, 6.8% with Synergy, and 6.6% for Orsiro, with no statistical difference between groups, reported Marlies Kok, MD, of Thoraxcentrum Twente in the Netherlands. Odds of cardiac death, target vessel MI, and target vessel revascularization rates were all similar between groups, as was stent thrombosis (1.0% Synergy versus 0.8% Resolute Integrity versus 0.6% Orsiro).

BIO-RESORT enrolled all-comers, with ACS in 70% of patients. The group was randomized 1:1:1 to Synergy (n=1,172), Resolute Integrity (n=1,173), and Orsiro (n=1,169) stents.

The biodegradable-polymer Orsiro and Synergy stents have thinner struts than the Resolute Integrity -- at 60 µm and 74 µm versus 91 µm. Orsiro elutes sirolimus from a polymer that resorbs at over 12 months, whereas Synergy releases everolimus from a polymer that reabsorb in 4 months due to differences in the polymer coating used.

Virmani took issue with calling Orsiro a "biodegradable-polymer" DES given the long time it takes to resorb. She preferred to say its polymer is "somewhere in between" durable and biodegradable.

At the end of the day, however, the polymer and drug only factor in for so long before they disappear, leaving strut thickness as the only relevant issue in the long-term, commented another discussant, Henning Kelbaek, MD, DMSc, of Roskilde Hospital in Denmark.

CENTURY II

The next trial compared stents with essentially the same strut thickness: The Ultimaster biodegradable-polymer DES was similar in performance against Xience in 5-year data presented by Shigeru Saito, of Japan's Shonan Kamakura General Hospital.

In long-term follow-up, freedom from target lesion failure was 90.0% for Ultimaster recipients and 91.1% for those who got Xience (log-rank P=0.56). Investigators also observed no differences in angina status, dual antiplatelet therapy, bleeding rate, or stent thrombosis between groups.

CENTURY II trialists randomized their study population to the biodegradable-polymer DES with 80-µm thick struts (n=551) or the durable polymer DES with 81-µm struts (n=550). A total of 58 sites located in Europe, Japan, and Korea participated.

Abiding by Japanese regulations, the investigators had to exclude individuals with a recent acute MI, which Kelbaek said limits the generalizability of the trial's findings.