Are we soon going to see stents that vanish?
Going by the buzz among cardiologists, the eagerly-awaited fourth-generation stents, which are bioabsorbable, are not too far away.
Balbir Singh, interventional cardiologist, Indraprastha Apollo Hospitals, Delhi, is looking forward to preliminary results on biodegradable stents that he says will be presented at the annual TCT (Transcatheter Cardiovascular Therapeutics) meet of cardiologists in October in Washington. Cardiologists in India are hopeful that by 2010, the path-breaking stent would have cleared all trials and gained regulatory approvals.
The excitement is understandable. As Madhukar Shahi, interventional cardiologist at Artemis Healthcare, Gurgaon, puts it, “Stents that can simply dissolve and disappear—that is the holy grail of angioplasty.”
Gone when the work is done
Dr Shahi likens a stent to the scaffolding of a building. Once the construction is done, the scaffolding comes off. Unfortunately, till now, stents (which performed the function of a scaffold inside the artery, holding the arterial vessel open and preventing closure while the procedure was done) had to stay put in the human body. “Whereas, ideally, you want a stent that stays only a finite time in your body,” says Dr Shahi.
Riding on fears of stent thrombosis and other complications (clots, interference with future surgeries, immune reactions), scientists and researchers have been pushing the envelope in developing this fourth-generation technology. As Dr Singh points out, it is not desirable for a foreign body to remain inside our body when its usefulness is over.
Soluble solution: Like this candle, the new generation of stents will simply melt away once their job is done.
The coronary stent: a history
It was way back in 1986 that the first coronary stent was used—these were bare metal stents. Unfortunately, bare metal stents were associated with a high degree of restonosis (artery narrowing again). In 2001, this led to the introduction of drug-eluting stents (DES)—a coronary stent system composed of a drug-eluting polymer layer and an antiproliferative drug, which would prevent restonosis. However, stent thrombosis (blood clot formation), though a rare occurrence, continues to be an issue plaguing angioplasty.
Race for a better stent
As Dr Shahi explains, the ideal stent would be one which would have enough force to prevent the elastic recoil of the vessel during the procedure, contain drugs that can prevent restenosis from happening and disappear six months later when medication is no longer needed.
Today, a lot of companies are in the race for the biodegradable stent, which is in various phases of trials. Abbot, Igaki Tamai and Biotronik have had human trials of their biodegradable stents. Both polymer-based and magnesium-based bioabsorbable stents are in the development pipeline. Opinion, however, is tilted towards the polymer-based bioabsorbable stent.
Still second best in India
In India, manufacturers of medical devices estimate that at least 150,000 stents are placed in blocked arteries during the ballooning angioplasty procedure every year. Unlike the US, where angioplasty is the preferred option over bypass surgeries, in India, more patients opt for surgery. If the technology of stents improves, the ratio could change in India, though there are other reasons for surgery being the preferred route here: economic reasons (a single stent is cheaper than a bypass, but if multiple stents are used, the cost is higher; some insurance policies do not cover stents though they cover bypass surgery) and also because of the diffused pattern of cardiac disease in India (that is, there is often diabetes and other complications as well to contend with). Also, surgery is perceived by patients as a more permanent and long-term solution. But that’s another story.
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