TCT 2011 brought it to our attention, now experts discuss what you need to know about the rare but problematic phenomenon known as longitudinal stent deformation.
With more than 20 late-breaking trials and first report sessions and
nearly 800 abstracts, the program of last year’s Transcatheter
Cardiovascular Therapeutics Scientific Symposium in San Francisco delved into
some of the most talked about topics in the field of intervention. Yet,
surprisingly, one of the hottest topics presented at the conference was not on
the initial program and involved what had up until that point been a
little-known phenomenon called longitudinal stent deformation.
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Paul D.
Williams |
This late addition to the program coincided with publications from
EuroIntervention that illustrated several cases where this
complication had been observed. In one paper, Paul D. Williams, MD,
fellow with the Manchester Heart Center, United Kingdom, who presented on this
topic at TCT 2011 in November, and colleagues reported nine cases of
longitudinal stent deformation — often referred to as longitudinal stent
compression (see Sidebar) — with adverse events as serious as stent
thrombosis.
“What we found was that among all the stents that were implanted in
our study, stent deformation occurred in about 0.2% of the population over a
4-year time period,” Williams told Cardiology Today
Intervention. “A majority of these patients had quite significant
stent deformation to the extent that it proved difficult to pass further
equipment through afterward and they needed additional treatment.”
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Simon J.
Walsh |
One month earlier, in October, Colm G. Hanratty, MD, and Simon
J. Walsh, MD, consultant cardiologists at Belfast Health & Social Care
Trust, Belfast, Northern Ireland, United Kingdom, also published a study in EuroIntervention highlighting three cases of stent
deformation and remarked on the potential for stent thrombosis, as well as a
latent risk of restenosis as a potential adverse event.
Walsh was one of the first to observe this phenomenon and said that it
initially came to his attention in 2009 while performing a complex PCI case.
What he found was that a stent, which had been deployed at the ostium of the
left anterior descending coronary artery, was significantly compressed over its
length by a post-dilation balloon.
“This first case caught me by surprise and it took a few minutes to
figure out the exact mechanism behind what had happened,” Walsh said.
Breaking Down the Phenomenon
As was later realized, longitudinal stent deformation, or the distortion
or shortening of a stent in the longitudinal axis following successful stent
deployment, is the result of modifications to the stent design that have
reduced the number of connectors, making the devices thinner and more flexible.
“But the cost is to reduce the longitudinal stability of the stent
itself,” Walsh said.
Longitudinal stent deformation becomes particularly problematic in cases
of complex disease. “If you treat complex disease, you may well get this
complication, and it can be very difficult to predict when it will
happen,” Williams said.
In a study published in March of this year in
EuroIntervention, Williams and co-author Mamas A. Mamas, MD,
used the FDA’s Manufacturer and User Facility Device Experience
Database to perform a systematic search of patients who had longitudinal stent
deformation. They found that the cases were very complex, with a lot of ostial
disease, bifurcation disease, and calcification and tortuosity.
“We also saw that this complication has been reported in very small
numbers as far back as 2004, so it’s not a new complication,”
Williams said. “However, over the last 2 years, there has been an
absolutely dramatic increase in incidence.”
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Currently, a consensus has not yet been reached in the
precise terminology for this phenomenon, with papers referring to it as either
longitudinal stent deformation or longitudinal stent compression.
“The first paper published on this by Colm G.
Hanratty, MD, and Simon J. Walsh, MD, used the term compression and
the talk titles we were given by the TCT organizers called it stent compression
to keep it standard among all the physicians,” Paul D. Williams,
MD, said. “However, in the literature, there seems to be more of a
shift now toward deformation.”
In his research, Williams prefers to use the term
longitudinal stent deformation, “because you can have cases where the
stent is not actually compressed, but you have widespread disruption of the
stent struts within the stent known as pseudo-fracture rather than compression
from the sides,” he said. “So I think deformation is a bit more
encompassing and includes all the different types.”
John A. Ormiston, MD, also prefers the term
deformation, “because while it is most commonly compression, elongation
can also occur,” he said.
However, for Walsh, either term is acceptable. “There
is a spectrum of disruption that can occur. Longitudinal stent deformation can
be minor and occur as a very subtle phenomenon at the most proximal ring of the
stent. As increasing force is applied to the stent, there will be progressive
compression over the stent length. After the stent shortens by a significant
percentage, the term concertina is also used,” he said. – B.E.
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Some Stents More Susceptible than Others
In December, John A. Ormiston, MD, medical director for Mercy
Angiography, Auckland, New Zealand, and colleagues presented bench test data on
the longitudinal integrity of several contemporary stents in a paper published
in the Journal of American Cardiology: Cardiovascular
Interventions. The findings suggested that certain models were more
likely to have less longitudinal strength than others. Specifically, stents
with two connectors between hoops, in this case the Element (Boston Scientific)
and the Driver (Medtronic), were more likely to distort under longitudinal
pressure than those with three or more connectors.
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John A.
Ormiston |
Ormiston said in an interview that contemporary stents are, on a whole,
a major advance and deformation is a rare event that must be kept in
proportion. “Longitudinal strength is but one desirable characteristic of
stents with others being flexibility, recoil, radial strength, radio-opacity
and side-branch access,” he said.
The 2011 study published by Williams and colleagues in
EuroIntervention suggested a clinical correlation with the bench data.
“The majority of the stent deformation cases did
involve the Promus Element platform and a couple with the Driver platform. In
fact, about 1% of Element stents implanted had stent deformation, whereas we
didn’t have any cases with the Cypher (Cordis) or Xience V (Abbott)
stents,” Williams said. “It seems that for the Element stent, the
longitudinal strength is clinically relevant. Paradoxically, the vessels in
which you would be more likely to use the Element stent, because it is so
deliverable and gets down calcified, tortuous vessels more so than other
stents, are more likely to result in longitudinal stent deformation.”
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Figure 1.
An elderly patient with ACS was treated with PCI for critical calcific proximal
left anterior descending artery disease. Following high-speed rotational
atherectomy, a drug-eluting stent was deployed at the ostium of this
vessel.
Images: Simon J Walsh, MD; reprinted
with permission.
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Figure 2.
Following stent deployment, a postdilation balloon was advanced into the
vessel. This secondary device caught the most proximal segment of the stent and
compressed the deployed stent along its longitudinal axis. Significant
shortening of the stent is demonstrated and a compressed segment of the stent
is clearly visible.
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However, it is important to note the limitations of the
EuroIntervention paper, as it was retrospective and a lot of cases relied
on operators remembering cases, according to Williams.
When reached for comment, representatives from both device manufacturers
implicated in these findings provided a statement to Cardiology Today
Intervention.
“Longitudinal compression of coronary stents stems largely from
device design. It’s not a class effect that applies to all stents,”
said Joe McGrath, spokesman for Medtronic. “Medtronic’s Integrity
stent platform, which employs an engineering advance called continuous sinusoid
technology, enables superior deliverability, without compromise. Due to the
device’s unique manufacturing process and aligned-crown design, the
Integrity platform exhibits both excellent longitudinal and radial
strength.”
According to Boston Scientific’s spokeswoman Denise Kaigler:
“Longitudinal stent compression is a rare event that may occur with all
coronary stents, regardless of manufacturer, strut thickness or alloy
composition. While longitudinal stent compression has been previously observed
in coronary stents, it went largely undetected and therefore unreported.
Platinum Chromium (PtCr) provides a significant improvement in visibility over
previous stent generations, aiding in accurate stent placement and allowing
physicians to have greater confidence in acute procedural results. With the
improved visibility of the PtCr stent series, physicians can more easily
identify it and address this issue, which may occur with any stent.”
Progress Has Its Price
For some, longitudinal stent deformation is an inevitability of
technological progress in the treatment of occluded arteries.
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Emmanouil S.
Brilakis |
“I look at this complication as a compromise because the question
is whether you are willing to accept a small risk of longitudinal compression
in exchange for enhanced deliverability,” Emmanouil S. Brilakis, MD,
PhD, director of the cardiac catheterization laboratory at the VA North
Texas Health Care System, Dallas, said in an interview. “Most
interventionalists would happily make the compromise in cases where they cannot
deliver a stent in spite of multiple attempts.”
In his practice, Brilakis, who is also a member of the Cardiology
Today Intervention Editorial Board, has yet to witness a single case of
stent deformation; although he noted that he does not use the Element stent.
While this is a rare phenomenon and does not represent a major adverse
issue for interventional cardiology, according to Walsh, he also said it is
likely being underreported for several reasons.
“In less visible stent platforms, it may not be apparent
angiographically. In more visible platforms, there is a spectrum of stent
compression and the more minor cases that are dealt with routinely during the
procedure probably do not prompt the cardiologist to report an adverse
incident,” Walsh said. “We should remember that minor stent
deformations occur normally as a routine part of many two-stent bifurcation
procedures and patients do very well when a technically good result
occurs.”
Modifications to Patient Care
Despite the overall rarity of the complication, experts suggested
interventionalists still be mindful of stent deformation while performing
coronary interventions.
“It is important that cardiologists are aware that it can happen
and recognize longitudinal stent deformation when it does occur,” Walsh
said. “Fixing the issue at the time it occurs confers a good long-term
outcome for the patient. However, not realizing it and leaving significantly
deformed devices in the coronary over the long term will likely lead to an
adverse risk for the patient.”
Williams and Ormiston recommended a more judicious selection of stents
among patients with calcified, tortuous vessels, while Ormiston added that in
some situations, including ostial or left main interventions, a stent with
known higher longitudinal strength may be selected to resist the compressive
forces of guide catheter engagement into the coronary artery.
“The other thing is, once you’ve deployed the stent, if you
are concerned about the vessel and there is a chance that the proximal stent
struts might be malapposed and still need post-dilatation, you need to be very
careful when passing the post-dilatation balloon,” Williams said.
“This is something we are now more cautious with, especially regarding the
Element stent. If there is any resistance, we go back and get a smaller balloon
and take it up more gradually because it doesn’t take a lot of force to
cause a stent deformation.”
Once recognized, Walsh said deploying the distorted stent with further
post-dilation and/or deploying a second stent to treat the previously covered
area may be necessary. “I would always use adjunctive imaging (IVUS or
optical coherence tomography) if I suspect a longitudinal compression and make
sure that a technically optimal result is the final outcome,” he said.
“Under these circumstances, my experience is that patients do well.”
In the future, Walsh foresees longitudinal stent stability being
reported as a standard parameter for devices, and stent manufacturers will
begin to consider this variable when designing their stent platforms.
“I suspect that the next generation of stent platforms will be less
prone to this complication,” he said. “We are also likely to see
stents being designed for specific lesions, such as the left main ostium, as
well as the left main bifurcation. This will make the phenomenon of
longitudinal compression less likely to occur.” – by Brian Ellis
References:
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Hanratty CG. EuroIntervention.
2011;7:872-877.
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Mamas MA. EuroIntervention. 2012;
[published online ahead of print March 3].
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Ormiston JA. J Am Coll Cardiol Intv.
2011;4:1310-1317.
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Williams PD. EuroIntervention. 2011;
[published online ahead of print Nov. 4].
Disclosure: Dr. Brilakis receives speaker
honoraria from St. Jude Medical and Terumo, research support from Abbott
Vascular and InfraReDx, and his spouse is an employee of Medtronic; Dr.
Ormiston is an advisory board member for and has received minor honoraria from
Abbott Vascular and Boston Scientific; Drs. Walsh and Williams report no
relevant financial disclosures.