SPENT ON A STENT?

Not for the first time, two powerful enemies have got together to face a common threat.
In the world of cardiology, Boston Scientific Corporation, a giant company worth around $25 billion is working with its arch-enemy Cordis Corporation, part of the $200 billion behemoth called Johnson and Johnson. The agenda: studying a phenomenon called stent thrombosis.

Trouble suddenly blew out in September this year at the World Cardiology Congress in Barcelona when Donald Baim, the chief scientific and medical officer of Boston Scientific let it out to a reporter that there were disturbing reports of late thrombosis after use of their Taxus stent. There was a huge buzz in medical circles that is still ongoing today.

So what is the fuss all about? What, one may be forgiven for asking, is a stent?

The stent, a $5.6 billion product, is a thin metal tube that is used to open up a blocked coronary artery (one that causes a heart attack). Years of fat deposition resulting from unhealthy eating habits, stress, lazy lifestyle, drinking and smoking cause the coronary arteries to get blocked by cholesterol deposits in the disease called atherosclerosis. The heart muscle gets less blood and oxygen from the narrowed arteries and dies, resulting in a heart attack. The stent is deployed by the cardiologist through a wire passed through a groin artery and keeps the blocked artery open, allowing blood supply to the heart.
However, the steel stent irritates the artery’s inner lining and its muscle cells, creating a scar that clogs it, a so-called re-stenosis. Since 2001, drugs that prevent this scar from forming were added to the metal stent. These are the drug eluting stents (DES). In the Taxus stent made by Boston Scientific, the agent is an anti-cancer drug called paclitaxel, while in the CYPHER stent made by Cordis the drug is sirolimus. Many trials confirmed that the incidence of restenosis reduced from 30 percent in six months to around 3 percent. This was the main reason that led to the mass usage of these costly (each one costs over a lakh of rupees) devices all over the world.
The advent of DES threatened to make bypass surgery superfluous in most cases, and led to a boom in invasive cardiology. 6 million stents have been used in three short years. Now, after billions of dollars have been expended and countless lives saved and lost, comes a series of trials, some showcased in the prestigious New England Journal of Medicine, showing that the drug eluting stents are, in fact, not much better than simple, cheap, bare metal stents. In fact, after the initial six to twelve months, the results are that patients with DES have higher rates of heart attacks and deaths, compared to bare metal stents. This is because of late thrombosis (blood clotting) in the stent itself. To prevent this fatal event, stented patients are prescribed blood-thinning drugs like clopidogrel and aspirin for one or two years. Though some experts recommend lifetime consumption of these, the cost and the side effects like bleeding are undesirable.
As the stent makers start poring over fine print to really make sense of the trial statistics, the next generation of stents is already in place.
Says Rabin Chakraborty, Head of the Department of Cardiology, Apollo Gleneagles Hospitals, Kolkata, “Second generation stents have a cobalt frame and are thinner and more flexible, allowing us to use them on smaller vessels, which we cannot access with stainless steel stents. One of these is XIENCE, and the other is Endeavor, which are showing thrombosis rates of only 0.5%.”
Scientists in New Zealand are conducting human trials of the world’s first dissolvable third generation stent: the ‘bioabsorbable’ stent that releases a drug called everolimus. The material used is like the ones used in absorbable stitches. After two years of implantation, the material disintegrates completely, having deployed the drug into the lining of the artery. This way, there is no ‘full metal jacket’ in the artery that could act as a clot magnet.

How are the companies reacting to the adverse results of worldwide trials?
A. Vaidheesh, Executive Vice President of Johnson and Johnson, India, downplays the impact of the studies: “The trials have included complicated cases of multiple vessel disease as well as patients with diabetes, well known as bad prognostic factors”. Vaidheesh and his company assert that their stent is an excellent product and “the complication rates are negligible”.
Medtronics Inc. is now conducting a huge trial, (called the PROTECT Trial) for the first time in India, among other countries, comparing the results of their Endeavor stent versus the Cypher by Cordis, specifically comparing the incidence of stent thrombosis between the two.
The latest treatment of stent blockage or restenosis is an angioplasty using a paclitaxel-coated balloon, just reported in the NEJM.
As things stand, the jury is still out on whether DES is an overrated and overused product. Till such time, try not to get a heart attack!

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