About Bioresorbable polymeric stents

by Margo White / 03 November, 2012
Stents that dissolve in the body could be of big benefit to heart patients.
About Bioresorbable polymeric stents


It was only a matter of time before it would come to this: a stent made of bioresorbable polymer that dissolves in the body. According to the press release from the pharmaceutical company that developed it, this innovation “represents a true paradigm shift in how we treat coronary artery disease”. This assessment is probably premature. The dissolving stent has been available in New Zealand only since October, and although it will undoubtedly be popular in the private health sector, it will be available only to a few in the public system. Still, it does highlight how far and how fast stenting, now a mainstay in the treatment of blocked coronary arteries, has evolved.

It was only in 1981 that cardiologists in New Zealand began using angioplasty, a procedure that involved widening blocked arteries by inserting a balloon at the end of a catheter, which was blown up to squeeze the build-up of plaque back against the arterial walls. The problem was that many of those who received treatment were back in hospital after six months with re-narrowed arteries, and it was some time before researchers figured out that this wasn’t a reappearance of the original problem but the arterial wall responding to the trauma of being stretched and pushed by the balloon.

This process, known as restenosis, is now recognised as a response to the trauma of the operation, which can result in a shrinking of the artery, but also in an excess production of healing tissue; both result in narrowed arteries. Minuscule mesh-metal tubes called stents were developed to prop open arteries and stop them from shrinking in response to the trauma. The first plain-metal stents were used in New Zealand in the 1990s. But although they stopped the artery shrinking, they didn’t stop it producing excessive healing tissue. And so came what has been dubbed the third revolution in stent technology: so-called drug-eluting stents coated with a pharmacological agent to dampen down the excessive healing response. The only problem was that people were left with small bits of stainless steel (or some other metal) in their arteries. Well, if they can make dissolvable sutures, screws and plates, surely they could develop a dissolvable stent?

It took some time, but they now have a stent that props open the wall in those crucial post-surgery months, then dissolves back into carbon dioxide and water. Think of it as getting rid of the cast after the bone has healed. It’s not yet clear whether this will make any significant difference to people’s cardiovascular health. John Ormiston, interventional cardiologist and medical director of Mercy Angiography, who first inserted a biodegradable stent at Auckland Hospital in 2006, is confident they will. The metal stent is inflexible; a polymer stent reabsorbs, so the artery can expand and contract according to the physiological needs of the person.

It’s also possible that atheroma (a build-up of fatty tissue in the artery some years after stenting) is less likely to occur in an artery that doesn’t have foreign material in it. These potential benefits have yet to be scientifically proven, but a biodegradable stent has appeal at an intuitive level. “If you ask a patient, ‘Do you want something permanent or, if all else is equal, do you want something that did its job and went away’, they’d always choose the latter,” says Ormiston. “The same with cardiologists; we want to return the artery to a more natural state, which we think will be better in the long term.” So far, the dissolvable stent is being used mainly for those with angina rather than those who’ve had a heart attack. “Usually when something new is introduced, you use it in simple lesions first and then increasingly more difficult situations,” says Ormiston. “So there haven’t been many put in with people with heart attacks, but that will come. My guess is that in 10 or 15 years’ time, most stents will be dissolvable.”

Is the bioresorbable stent really, as some (including the company that developed it) claim, a “fourth revolution”? Ormiston thinks so. “A lot of people might disagree with that, and it needs to be proven. These are early stages, and it will take a long time and use in more complicated diseases over many years before we can say that it is. But it’s looking very promising.”

Health briefs


JUST JUICE

Contrary to popular belief – and a subtle marketing campaign – cranberry juice is unlikely to stop urinary tract infections, according to a systematic review published in the Cochrane Library. Gathering evidence from 24 studies, the research found that although cranberry juice offered small benefits for women suffering from recurring infections, they’d have to consume two glasses of the juice daily for long periods to prevent one infection.

BIPOLAR AND THE ARTS


A study in the Journal of Psychiatric Research has confirmed previous studies that suggest bipolar disorder is more prevalent in people with artistic or scientific professions, such as dancers, researchers, photographers and authors. The researchers also found authors are more commonly diagnosed with depression, anxiety syndrome and substance abuse.

STROKING HELPS


Scientists think stress in pregnancy can affect an infant in later life by reducing the activity of genes that play a role in stress response, yet studies of rats have suggested those effects can be reversed if a mother grooms her pups soon after birth. A similar effect from stroking may be true of people, according to researchers from the universities of Liverpool, Manchester and London. After following first-time mothers from pregnancy through to the first years of their children’s lives, the researchers found links between prenatal stress and the emotions of fear and anger in the infants, and the babies’ response to stress changed according to how often a mother stroked her baby in the early weeks.
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