WASHINGTON (AP)
_ Scientists are developing a novel way to prop open clogged
heart arteries: using a stent designed to dissolve once
it finishes the job.
Heart
stents are tiny metal-mesh tubes that have been implanted
in millions of people worldwide to hold arteries open
after doctors push back fatty deposits that clog them.
Stents
are credited with preventing heart attacks while avoiding
open-heart surgery. But they are at the center of a heated
controversy because doctors recently discovered that the
most popular type, drug-coated ones, sometimes cause potentially
fatal blood clots months or years after they are inserted.
So
a stent that could help an artery heal and then dissolve
would be ``a major milestone,'' said Dr. John Ormiston
of Auckland, New Zealand. He announced Tuesday that the
first human experiment with just such a device is under
way in his hospital and a few others in Europe.
Only
26 patients have been implanted in a study designed to
test whether the new type of stent, made by Abbott Laboratories,
is safe enough to be tried in larger experiments. Thirty
days after receiving the device, all patients are faring
well so far, Ormiston told a meeting of cardiologists.
It's
called a bioabsorbable stent, made of the same kind of
material as certain dissolvable stitches but designed
to last longer.
Animal
studies suggest the body completes its breakdown of the
device in about two years.
Here's
the issue: When a heart artery is clogged enough to risk
a heart attack, doctors frequently use a balloon to push
back the plaque so blood can flow freely again. Stents
then are inserted to keep the newly widened artery from
collapsing, and drug-coated ones prevent scar tissue from
reclogging it.
But
stents do not need to be permanent, Ormiston contended.
If an artery stays open for six months after being unclogged,
it essentially is healed, he said.
``There's
not much sense in a permanent implant for a temporary
problem,'' he said. ``I think patients like the concept
of a device that goes away.''
The
new absorbable stent is coated with a drug, as today's
most-used versions are, to prevent reclogging. After the
drug has permeated the artery walls, the stent should
start dissolving.
In
the spring, Ormiston is scheduled to announce how the
first patients fared at that critical six-month period,
the first hint of whether the approach might really work.
His
announcement came as cardiologists vehemently debated
just how big a problem the blood-clot risk is for today's
devices. Apparently it occurs because the drug coating
allows the stent's metal parts to remain exposed and act
as a clot magnet, instead of gradually being overgrown
with a thin layer of cells.
The
risk seems very rare, occurring in about one of every
500 or so patients, Harvard Medical School's Dr. Donald
Cutlip said at Tuesday's meeting of cardiologists who
specialize in stenting.
But
given that about 6 million people worldwide have the drug-coated
devices, critics say that could translate into thousands
of heart attacks or deaths. The Food and Drug Administration
will assess the risk, and how it compares to older bare-metal
stents that have their own side effects, at a meeting
in early December.
