Most
Heart Stents
Are Placed Imperfectly, Increasing Risk of Heart Attack or
Reclosure
S.T.L.L.R. Study Calls for Better
Understanding and
Better Technique for Stent Placement
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May 30, 2007 -- Could it be that
two-thirds of the stents implanted in patients' coronary arteries are
not properly placed? Dr. Marco A. Costa of the University
of Florida College of Medicine in Jacksonville told Angioplasty.Org:
"It's unbelievable,
but it's
the reality. Those are the data. Those are the facts.... Based
on the criteria that were defined in the S.T.L.L.R. trial, two-thirds
of the
stents that
are placed nowadays are not properly deployed."
Dr. Costa is lead investigator
for the S.T.L.L.R. clinical trial, the complete name of which is "The
Impact of Stent Deployment Techniques on
Clinical Outcomes of Patients Treated
With the CYPHER® Stent". In this prospective double-blinded study
of almost 1,500 patients, treated with the Johnson & Johnson / Cordis
drug-eluting CYPHER stent, the
correct
placement of the stent was measured and the patients followed up for one
year. What were the results for those stents imperfectly placed? States
Dr. Costa:
"Three times the increased chance of heart attack. And twice the chance
of repeat procedures."
The results of this study, which
was funded by stent manufacturer Cordis, are striking. The study is currently
undergoing peer review by a major cardiology journal, but the findings
were first
discussed at
last fall's TCT 2006 meeting and were also reported by
Avery Johnson and Ron Winslow in yesterday's Wall Street
Journal ("Scrutiny
of Stent Problems Turns to Doctors"). The article, and accompanying
"Health
Blog" entry, state that, while the focus has been on
the stent devices as a possible cause of late stent thrombosis (blood clots
occurring
many months or years after implantation) attention may now be shifting
to "overconfidence" on the part of interventional cardiologists
that has led
to "sloppy" and
"poor technique".
Dr. Costa disagrees with this characterization and told
Angioplasty.Org:
"I didn't say that. That was not my opinion at all.
What I said was that we need to learn from S.T.L.L.R. and need to learn
more
judicious technique. We, as operators, need to pay attention to the
S.T.L.L.R. results, understand those results...because
we can avoid many of the mistakes. However we need improvement in
the device side, we need better devices so we can do our job easier.
We need better
definition on who is at risk, so we need to learn about the anatomical
factors of the patients. And I think we need improvement in our imaging
aspect. I think IVUS (intravascular ultrasound) is a great technology
that can help us to get it better."
He continued that there had never been a study
like S.T.L.L.R. before, showing that this suboptimal placement (or "geographic
miss")
was so widespread, so this information was not really known.
Stents are tiny metal mesh sleeves that are inserted
into blocked areas of the artery and expanded against the
artery wall by inflating a balloon. The balloon is then withdrawn, leaving
the expanded stent to keep the artery open and the blood flowing. Over
a couple of months, cells cover the metallic stent, incorporating it into
the arterial wall. The study identified two ways in which stents were not
optimally placed. In some cases
the
stent did not completely
cover
the diseased
surface of the artery -- allowing those areas to build up tissue and "reclose"
more often.
However, in an equal number of cases, the problem was
that the stent was not fully expanded, leaving
a small "pocket" or space between the stent and the wall of the artery.
This is a complex issue, because cardiologists don't want to overexpand
the
stent, for fear of tearing the arterial wall, which is a serious complication.
Another difficulty for the cardiologist is that angiography,
the imaging method used in all angioplasties, does not tell the physician
the
entire
story. Many doctors, including Dr. Costa, feel that the addition of
intravascular ultrasound (IVUS) imaging can fill that need. One of the
pioneers of stenting,
Dr. Antonio Colombo of Milan, told Angioplasty.Org, that he now uses intravascular
ultrasound in all of his stent cases:
"Because I can verify an optimal implantation with
good expansion of the stent which matches the appropriate size of
the vessel
and the presence of disease in the wall of the vessel. Angiography
is not the best tool to evaluate appropriate stent dilatation. Angiography
gives
incomplete information because we only know the lumen size, but
we don’t
know exactly the vessel size. And we can’t assess
if the stent is adequately dilated and well-apposed to the media;
we only
know if the stent is apposed to the plaque."
The media is the true arterial wall, and defines the
boundary of the vessel. But angiography, which uses X-rays and dye to
get a shadow profile image of the artery, only reveals the actual opening,
or lumen, which in a diseased or blocked artery may be significantly smaller
than the true vessel. By being cautious and only expanding the stent to
what can be seen under angiography, the cardiologist may unwittingly be
making a "geographic miss" and under-deploying the stent. The implications
of an underdeployed stent can be serious, as Dr. Colombo explains:
"Then you have a stent which is in a less optimal
contact with the vessel wall. You have more turbulence. You have struts
that are
not perfectly attached or embedded in the plaque, and you may have
more foreign body protruding into the lumen, increasing the risk of
restenosis
and thrombosis."
Dr. Colombo continued that using IVUS is critical, because
after you expand the stent, you can very quickly check how well the stent
is placed in relation to the artery wall and, if it is underexpanded, you
can go back in with a larger balloon and expand the stent to a more perfect
fit. Without this additional imaging tool, it would be difficult to judge.
While IVUS has been around for more than a decade, its
use has suddenly increased in the past year -- most likely in reaction
to the concerns about stent placement and its association with thrombosis.
The two IVUS manufacturers, Volcano
Corporation and Boston Scientific,
report increased sales and, as Dr. William O'Neill of the University
of Miami's Miller School of Medicine told the Wall Street Journal:
...patients who are candidates for stent procedures
might ask their doctors how often they use the [IVUS] imaging technology.
"If they say 'never,' shy away from them," he says. "Ultrasound
is a surrogate for quality."
Read more about IVUS in Angioplasty.Org's
special Intravascular Ultrasound
Center, including our exclusive
interview with Dr. Antonio Colombo.
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