Drug-eluting stents have been used in the past as stents. These stents release a drug that stops cell proliferation. This prevents fibrosis (scar tissue) that, together with clots (thrombi), could otherwise block the stented artery, a process called restenosis. The use of metal drug-eluting stents presents some potential drawbacks. These include:
- A predisposition to late stent thrombosis
- Restenosis occurance in DES
- Prevention of late vessel adaptive or expansive remodeling
- Hindrance of surgical revascularization
- Impairment of imaging with multislice CT.
To overcome some of these potential drawbacks, several companies are pursuing the development of bioresorbable or bioabsorbable stents. Like metal stents, placement of a bioresorbable stent will restore blood flow and support the vessel through the healing process. However, in the case of a bioresorbable stent, the stent will gradually resorb and be benignly cleared from the body, leaving no permanent implant.
Studies have shown that the most critical period of vessel healing is largely complete by approximately three months. Therefore, the goal of a bioresorbable stent is to fully support the vessel during this critical period, and then resorb from the body when it is no longer needed.
Meta-analyses — The efficacy of bioresorbable polymer stents in terms of a similar or lower risk of target lesion revascularization compared to older DES seen in the above trials was affirmed in a 2012 meta-analysis of pooled individual patient data from the ISAR-TEST 3, ISAR-TEST 4, and LEADERS trials. This study found that the risks of target lesion revascularization and stent thrombosis at four years were lower in patients treated with bioresorbable polymer DES compared to first generation, durable polymer SES (hazard ratios 0.82, 95% CI 0.68-0.98 and 0.56, 95% CI 0.35-0.90). The lower rate of stent thrombosis was driven by a lower risk of very late stent thrombosis.
Two subsequent large, pooled analyses of randomized trials (network meta-analyses), which compared all intracoronary stents, including bare metal stents, first, and second generation DES, and bioresorbable polymer stents, came to similar conclusions.
SUMMARY — Newer stent types are being developed to overcome some of the limitations of current stents, such as the development of stent thrombosis after placement of any intracoronary stent and the residual rate of restenosis after drug-eluting stent (DES). These newer stent types fall into three broad categories: stents with bioresorbable polymer; drug-eluting stents that are polymer free; or stents with a bioresorbable scaffold.
lactic acid-based biodegradable stent (left) and zinc-bases stent. Zinc is showing a great deal of promise.
References: Up-To-Date and Wikipedia