In coronary artery stents, the coverage of the internal structures with neo-intimal formation has been regarded as a negative development leading to restenosis and loss of luminal space in the blood vessel. However, some coverage of the stent can be beneficial, providing coverage of protrusions in the internal stent structure that may otherwise constitute a thrombotic risk. Recent studies have compared different types of coronary artery stents pre-coated with drug compounds to assess their performance in terms of luminal loss and long-term outcome.

One study comparing the drug-eluting stents (DES) CYPHER (Cordis) and TAXUS (Boston Scientific) and the polymer-free rapamycin-coated YUKON DES (Translumina GmbH) showed that the permanent polymer used on the two most well-known DES is likely to be responsible for the often seen late luminal loss (LLL).¹ In-stent LLL after approximately six to eight months and at two years following surgery was compared and showed that both the CYPHER and TAXUS stents appeared to undergo a process described as ongoing erosion of the luminal space, whereas the polymer-free stent showed negligible increases in late loss over the same period. The authors concluded that the findings support the hypothesis of a possible late ‘catch-up’ restenosis. This is a phenomenon that has been seen both anecdotally and in early animal models of DES.

The polymer-free stent was produced using a technology that was clinically tested in the Individualised Drug-Eluting Stent System to Abrogate Restenosis (ISAR) project by the Munich Research Group. This is a two-part system comprising a mobile stent-coating machine for the sterile spraying process and a single-use cartridge containing the premounted microporous DES (Translumina, YUKON) (see Figure 1). The stent can be coated on-site directly in the cath lab with various drugs, e.g. with rapamycin (sirolimus). Previous studies have shown this inhouse prepared ISAR DES to be safe and effective when coated with a 2% rapamycin-coating solution.^2,3 A commercially available stent-coating machine (Translumina) is pictured in Figure 2.

The present study had a prospective, observational design and was a three-arm comparison of the CYPHER permanent-polymer rapamycineluting stent (RES), the TAXUS permanent-polymer paclitaxel-eluting stent (PES) and the YUKON polymer-free rapamycin-eluting stent (ISAR). The study included a total of 2,030 patients who underwent angiography at six to eight months post-stent implantation.¹ Of these, 259 subsequently underwent target lesion revascularisation (TLR) and were therefore not included in the follow-up study. The remaining 1,771 patients underwent a second angiogram after two years, allowing investigators to compare LLL changes between six to eight months and two years. Patient disposition throughout the trial is shown in Figure 3. In-stent LLL was lowest for the CYPHER stent at six to eight months compared with both the TAXUS and the polymer-free YUKON stent. Between six to eight months and two years, however, late loss – late luminal creep – continued to progress for the CYPHER and TAXUS stents but not for the ISAR stent (see Table 1). Multivariate analyses indicated that stent type was the only predictor of LLL, and results favoured the polymer-free YUKON stent. A plot of LLL for percutaneous coronary intervention (PCI) at six to eight months and two years for the three different stents is given in Figure 4.