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 Post subject: A dissolving heart stent
 Post Posted: Tue Dec 12, 2006 1:20 am 

Joined: Sun Apr 24, 2005 5:38 pm
Posts: 58
A dissolving heart stent

The stent is flexible, and should produce fewer side effects
A new type of heart "stent" or tubular mesh has been developed to unblock diseased arteries and then dissolve without a trace.

It may improve on permanent metal stents by reducing the risk of side effects, such as secondary blood clots at the stent site.

Stents are used in angina or heart attack patients to hold open a narrowed artery.

The new type is being perfected by Auckland City Hospital in New Zealand.

I think we'll look back in 10 years' time and laugh at the idea of putting bits of metal into coronary arteries that stay there for ever
Dr John Ormiston

At present, only metal stents are in clinical use. These remain in a patient's artery for the rest of their lives.

The new BVS stent is made of a polymer that dissolves into lactic acid over two to three years.

Lactic acid is a naturally-occurring substance in the body, produced after exercise.

It breaks down into carbon dioxide and water, and is absorbed by the body.

This is what happens to the tiny traces of lactic acid produced by the stent.

Lead researcher Dr John Ormiston said: "You wouldn't want to keep a cast on a broken arm after its mended. In the same way, there is no point keeping a stent in place after the artery has healed.

"I think we'll look back in 10 years' time and laugh at the idea of putting bits of metal into coronary arteries that stay there for ever."

Possible advantages

The use of dissolving stents is likely to make it much easier to perform further surgery on the artery if necessary.

They should also help to reduce the number of cases of late stent thrombosis - when a clot forms on the uneven surface of a stent months or years after its been put in.

John Lamb: Now I can do everything I did before

Such events are rare, but can be life threatening, as they may lead to a heart attack.

Their use should also allow clearer imaging of the heart. Metal stents interfere with scanning techniques, such as CT and MRI, which are becoming increasingly important in diagnosing cardiac problems.

And because they are made of a more flexible material, it should conform to the shape of the artery more precisely.

Clinical trials

So far, the BVS stent has been put into 30 patients in Europe and New Zealand.

Dr Ormiston carried out eight of these procedures and is impressed by the early results.

He said: "In the 30 patients, we had perfect 30-day study data, there were no adverse reactions."

That included no further heart attacks, or restenosis, the re-narrowing of a blocked artery once it has been treated.

The BVS stent works in two ways, as with the more recent metal stents.

It mechanically holds the artery open, and releases a drug called "everolimus", which helps to prevent re-narrowing.

John Lamb, from New Zealand, was the first patient in the world to receive this stent.

At the age of 65 he suffered from angina, which meant he had severe chest pains during exercise.

He had the BVS stent put in nine months ago, and has not experienced any treatment-related adverse effects.

"Now I can do everything I did before, and my six-month angiogram (heart test) was as good as gold.

"The idea of a dissolving stent made sense to me. I liked the idea of not having the metal permanently there".

Next steps

A dissolving stent has been the goal of research for years.

Bioabsorbable polymers have been used in many other medical applications, such as capsules for drug delivery, dissolvable sutures and screws for securing bone.

But their use in stent manufacture posed a greater challenge: the polymer had to be strong enough to hold the artery open without being too bulky.

Now a small number of companies have such devices in early development, but trials in patients have been limited.

The BVS stent is the first drug-releasing absorbable stent to reach this stage of clinical development.

In March 2007, six-month data from the first 30 patients will be released. If the results are promising, larger randomised trials are expected.

Professor Martin Cowie, a leading cardiologist at the National Heart and Lung Institute in London, said that the prospect of dissolving stents was exciting, but that more trials are needed to see if they really improve care.

The British Heart Foundation also believes the possible advantages are significant.

Associate Medical Director Professor Jeremy Pearson said: "In principle a stent should only be needed temporarily to encourage the blood vessel to repair itself correctly.

"However, it is not yet clear that their medium- or long-term benefit is better than permanent stents.

"Further carefully monitored animal and human studies will be needed."

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