Drug-eluting stents (DES) became available for the treatment of atherosclerotic coronary heart disease about five years ago. The polymer coatings used in the first-generation DES (Cypher™ and Taxus™) were non-biodegradable. Virmani et al. studied autopsy patients and suggested that late stent thrombosis post-DES implantation might be caused by the polymer.1 Recently, using a hierarchical classification of stent thrombosis, Mauri et al. reported a significantly higher incidence of definite or probable stent thrombosis events in the DES group than in the bare-metal stent (BMS) group during a four-year follow-up.2 Nowadays, the consensus is to extend clopidogrel usage for a minimum of 12 months (perhaps longer in patients post-DES implantation) to prevent stent thrombosis. However, the 2005 updated American College of Cardiologists (ACC)/American Heart Association (AHA) Percutaneous Coronary Intervention (PCI) Guidelines recommend that clopidogrel 75mg/day should be given for at least one month after BMS implantation, for three months after sirolimus-eluting stent placement and for six months after paclitaxel-eluting stent implantation.
Besides biocompatibility, there are now concerns about polymer layer integrity. Otsuk et al. assessed discontinuities and other irregularities in the polymer layer by scanning electron microscopy.3 Several types of defect in the polymer layer have been found after balloon expansion on several commercially available first-generation DES (Cypher, Taxus and BiodivYsio™), and these defects may be responsible for thrombosis, coronary microembolism and late inflammatory or neointimal reactions post-DES placement.
There are two ways to resolve the problems associated with the biocompatibility of polymers. One method uses a permanent but completely biocompatible polymer such as phosphocholine. Another method is to use a bioabsorbable polymer. A DES with a bioabsorbable polymer is defined as a second-generation DES. This may have potential advantages regarding the long-term result, as the new stent has no sustained stimulation to the local tissue. This article will focus on the newly available DES with bioabsorbable polymers.
Many biodegradable materials have been investigated in pre-clinical studies. Polyglycolic acid/polylactic acid, polycaprolactone, polyhydroxybutyrate valerate, polyorthoester and polyethyleneoxide/ polybutylene terephthalate were tested in a porcine model, and all induced significant inflammation reactions.4 Minimal inflammation reactions were seen after poly-L-lactic acid (PLA) stent implantation in a dog model.5
- Virmani R, Guagliumi G, Farb A, et al., Localised hypersensitivity and late coronary thrombosis secondary to a sirolimus-eluting stent: should we be cautious?, Circulation, 2004;109:701–5.
- Mauri L, et al., Stent thrombosis in randomised clinical trials of drug-eluting stents, N Engl J Med, 2007;356:1020–29.
- Otsuka Y, Chronos NA, Apkarian RP, Robinson KA, Scanning electron microscopic analysis of defects in polymer coatings of three commercially available stents: comparison of BiodivYsio, Taxus and Cypher stents, J Invasive Cardiol, 2007;19:71–6.
- van der Giessen WJ, et al., Marked inflammatory sequelae to implantation of biodegradable and non-biodegradable polymers in porcine coronary arteries, Circulation, 1996;94:1690–97.
- Zidar J, et al., Biodegradable stents, In: Topol EJ (ed), Textbook of Interventional Cardiology 2nd edn, 1994;787–802.
- Tsuchiya Y, Lansky AJ, Costa RA, et al., Effect of everolimus-eluting stents in different vessel sizes (from the pooled FUTURE-I and -II trials), Am J Cardiol, 2006;98:464–9.
- Ge J, et al., Effectiveness and safety of the sirolimus-eluting stents coated with bioabsorbable polymer coating in human coronary arteries, Catheter Cardiovasc Interv, 2007;69:198–202.
- Liu HB, Xu B, Qiao SB, et al., A comparison of clinical and angiographic outcomes after Excel bioabsorbable polymer versus Firebird durable polymer rapamycin-eluting stent for the treatment of coronary artery disease in a ‘real world’ setting: six-month follow-up results, Chin Med J, 2007;120:574–7.
- Zhang YX, Lu CY, Xue Q, et al., Safety and efficacy comparison between rapamycin-eluting stent with biodegradable polymer or permanent polymer in patients with coronary artery disease, 2006;34:971–4.
- Chevalier B, Serruys PW, Silber S, et al., Randomised comparison of Nobori™, biolimus A9-eluting coronary stent woth a Taxus®, pacletaxel-eluting coronary stent in patients with stenosis in native coronary arteries: the Nobori 1 trial, Euro Interv, 2007;2:426–34.
- Grube E, Buellesfeld L, BioMatrix Biolimus A9-eluting coronary stent: a next-generation drug-eluting stent for coronary artery disease, Expert Rev Med Devices, 2006;3:731–41.
- Tamai H, Igaki K, Kyo E, et al., Initial and six-month results of biodegradable poly-l-lactic acid coronary stents in humans, Circulation, 2000;102:399–404.
- Yamawaki T, Shimokawa H, Kozai T, et al., Intramural delivery of a specific tyrosine kinase inhibitor with biodegradable stent suppresses the restenotic changes of the coronary artery in pigs in vivo, J Am Coll Cardiol, 1998;32:780–86.
- Vogt F, Stein A, Rettemeier G, et al., Long-term assessment of a novel biodegradable paclitaxel-eluting coronary polylactide stent, Eur Heart J, 2004;25:1330–40.