News:Absorbable drug eluting stents are safe up to one year in single de novo coronary artery lesions

March 14, 2008 By Vijayalakshmi Kunadian MBBS MD MRCP [mailto:vkunadian@perfuse.org]

Although associated with a small incidence of late stent thrombosis, over the last five years, the drug eluting stents have played a major role in the reduction of restenosis. Metals such as stainless steal and cobalt chromium have been used which act as a back bone for the coronary stents providing the scaffold thereby preventing recoil. More recently in the absorbable stents, Poly-L-lactic Acid (PLA) is used as a back bone. In contrast to the metal stents, the PLA gets absorbed over a period of time.

In a study published in the latest issue of the Lancet, researchers determined the safety and efficacy of the bioabsorbable everolimus-eluting stents (BVS, Abbott Vascular, Santa Clara, CA). These stents consist of PLA as the back bone which contains and controls the release of everolimus (Novartis, Switzerland), the anti-proliferative drug.

In the study, 30 patients from Poland, New Zealand, Denmark and Holland with single de novo coronary artery lesions were included. Two different stent sizes were used (3x18mm and 3x12mm). Patients with acute myocardial infarction, lesions containing thrombus, left main stem lesions, restenotic lesions and lesions involving large side branches were excluded from the study. Although patients are being followed up for five years, this study provides outcome results up to one year. In total, 26 patients underwent angiography and 24 patients underwent intravascular ultrasound studies at six months. The primary endpoint of this study consists of cardiac death, myocardial infarction and ischemic target vessel revascularization.

The procedure was successful in 100% of the cases. The device was successfully implanted in 94% of the cases. Major adverse cardiac event was 3.3% at one year. There was no late stent thrombosis. Incomplete stent strut apposition at baseline was observed in 24% of cases. At six months, the angiographic in-stent late loss was 0.44±0.35 [this is more than that observed with previous metallic everolimus eluting stent studies (0.15 mm)] and the binary restenosis occurred in 12%.

On intravascular ultrasound, there was 11.8% reduction in the stent area and 16.8% reduction in mean lumen area at 6 month follow-up compared to baseline (p<0.00001). On the other hand the neointimal area was small (0.30±0.44 mm2) indicating the anti-proliferative action of everolimus. The echogenicity of the polymeric stent struts appeared as dense white on virtual histology. At 6 months, the initial dense white areas reduced by 8% and there was an increase in the fibro-fatty and fibrous areas by 8% on IVUS analysis. This according to the investigators indicated the first signs of expected bioabsorption of the struts.

Although there is reduction in the late loss with the absorbable stents and minimal intra-stent neointimal hyperplasia, one of the main problems with the PLA stents as depicted in this study is that the PLA stents do not have radial strength comparable to the metal stents which lead to the occurrence of acute and chronic recoil. Stent malapposition lead to the reduction in stent area at follow-up and is an important consideration given the association of stent malapposition with stent thrombosis. The impact of reduction in the stent area has not significantly impacted the clinical outcome in the present study. This might be due to the small numbers in the present study. Further long-term results of this study are awaited. In addition, this study included patients with single de novo lesions. Its wider applicability is yet to be examined.

Reference

 * 1) Ormiston, JA et al. A bioabsorbable everolimus-eluting coronary stent system for patients with single de-novo coronary artery lesions (ABSORB): A prospective open- label trial. The Lancet 2008;371:873-874