Kinky bypass grafts last longer

William Wagner · medicine forum Guru Joined: 29 Apr 2005 Posts: 809

Kinky bypass grafts last longer

http://www.newscientist.com/article.ns?id=dn7496&feedId=online-news_rss20

€ 11:46 10 June 2005
€ NewScientist.com news service

Twisty implant
Get kinky. Go with the flow. This is not a lifestyle recommendation,
it's the latest advice to vascular surgeons. Evidence is mounting that
bypass grafts work much better, and last much longer, if they have
helical twists.
When surgeons make a graft to bypass a blockage in a blood vessel they
often have to use prosthetic tubes because suitable arteries and veins
are hard to come by. Similarly, when patients with renal disease have
dialysis, a loop of tubing may be fitted between a vein and an artery,
usually in the arm. This loop, made from polytetrafluoroethylene (PTFE),
is called a shunt.
The problem with this is that blood flow in these prosthetic tubes is
different from in natural blood vessels. Arteries naturally twist like a
corkscrew and this 3D structure makes the blood swirl as it flows, which
stops it stagnating. In contrast, blood flows through an artificial tube
like water in a river, leading to areas of faster and slower flow, and
stagnant zones, resembling the inside of river bends where sand builds
up (New Scientist, 6 February 1999, p 32).
"Stagnation is bad news for blood vessels," says Colin Caro, a
bioengineer at Imperial College London. It increases cell death in the
blood vessel wall, and more platelets are formed. This leads to
coagulation and causes a disease called intimal hyperplasia (IH), a
thickening of the blood vessels, which is the most common reason for the
failure of shunts and bypass grafts.
And many shunts and grafts do fail. More than 300,000 people have renal
shunts fitted per year, and about two-thirds fail and have to be
replaced within the first 12 months. Of the more than half a million
bypass grafts fitted annually, about half fail in the first year.
Helical twists
The solution is to make blood flow in grafts and shunts mimic natural
arteries. To do this, Caro makes PTFE tubes with helical twists, dubbed
SwirlGrafts. Fluids flow through the twisty tubes and beyond in swirls.
Now Caro, working with Nick Cheshire, a vascular surgeon at St Mary's
Hospital, London, has fitted lab pigs with SwirlGrafts to test their
effectiveness in live animals. Each test animal had both a SwirlGraft
and a conventional, non-twisting shunt fitted. When the grafts were
examined eight weeks later, the results were clear cut: the conventional
shunts were thickened and clogged with coagulated blood while the
SwirlGrafts looked almost brand new (Journal of the Royal Society
Interface, DOI: 10.1098/rsif.2005.0044).
European regulatory authorities have given their approval for
SwirlGrafts to be used in people and clinical trials have begun in seven
renal patients in the University Medical Centre, Utrecht, and nearby
hospitals in the Netherlands. "Two patients have had a SwirlGraft fitted
for about six months, and are going well," says Caro. If SwirlGrafts
live up to their promise, the improvement in patient welfare, not to
mention the financial savings, will be dramatic. "We're talking millions
of dollars," says Caro.
Journal reference: Journal of the Royal Society Interface (DOI:
10.1098/rsif.2005.0044)

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