Issue: March/April 2012

April 10, 2012

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Deconstructing Longitudinal Stent Deformation

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.

Issue: March/April 2012

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.


	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.”


	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.”

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.

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.


	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.”

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.

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.

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.


	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:

Hanratty CG. EuroIntervention. 2011;7:872-877.

Mamas MA. EuroIntervention. 2012; [published online ahead of print March 3].

Ormiston JA. J Am Coll Cardiol Intv. 2011;4:1310-1317.

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.