Shelley Wood

November 09, 2011

November 8, 2011 (San Francisco, California) — Interventional cardiologists here at TCT 2011 are hashing over the emerging issue of longitudinal stent compression, with the bulk of experts concluding that this phenomenon is rare, grabbing undue attention, and in many cases avoidable with meticulous technique. Most agreed, however, that stent design may play a factor in making some stents more vulnerable than others.

Two last-minute presentations dealing with this issue were added to the TCT program Monday, along with a third already in the print program. Several online-before-print papers on the same topic were also published over the past few days in EuroIntervention.

Ten Anecdotal Cases

One of the last-minute additions to the program was a 10-case report by Dr Paul Williams (Manchester Heart Centre, UK); nine of the 10 cases were also published in a paper in EuroIntervention online November 4, 2011 [1]. All cases were identified retrospectively, after asking operators if they remembered any procedures in which signature stent-compression problems may have arisen.

The 10 stent cases presented by Williams involved one Endeavor, one Biomatrix, one Taxus, and seven Promus Elements. The mechanism of stent deformation involved the guide catheter (two cases), the guide extension (two cases), the balloon catheter (four cases), the thrombectomy catheter (one case), and distal crush (one case). In nine cases, stent deformation was recognized and treated, typically through reexpansion, although in one of the cases, deformation of the stent inlet was recognized after a previously treated patient returned to hospital with anterior STEMI due to stent thrombosis.

Williams emphasized that this complication was rare--seen 10 times in over 9411 stents (in 4526 cases), yielding a deformation rate of 0.11% (or 0.22% of cases).

"Longitudinal stent deformation is rare, with a rate of about one in 500 in our small series," he told the audience. "There were differences in the rate between different [drug-eluting stents] DES; in our series this complication was most often seen in the Promus Element.

"It's important to recognize and treat, as it may be associated with late stent thrombosis."

Irish Advice

Dr Simon Walsh (Belfast Health and Social Care Trust, Northern Ireland), one of the first investigators to publicly report three cases of longitudinal stent compression with newer-generation DES, previously covered by heartwire , also reviewed a number of cases during the Monday session. He was more reluctant to single out a specific stent type, instead advising cardiologists to do everything to avoid the problem in the first place. His recommendations: recross all deployed stents with care, always optimize the proximal segment, beware of long stents in tapered vessels, and watch out for wire bias/tortuosity.

Walsh also recommended using intravenous ultrasound (IVUS) or optical coherence tomography (OCT) imaging when a case of stent compression is suspected. "When recognized and treated, patients do well," he said. But problems arise if the physician doesn't look for it, doesn't see it, and doesn't fix it, he added. "A stent thrombosis is far from a surprise."

Still, he continued, "This is a rare complication, we've seen a very small number of cases, and since we realize how it happens we avoid it, and we do not see this as a recurring phenomenon."

This is not another ESC 2006.

This is not, he reminded the audience, something that was seen in the large randomized clinical trials of next-generation drug-eluting stents, and the attention this issue is garnering now is "anecdotal or marketing in these circumstances. . . . We should pay attention to this issue but not get too excited about it." Referring to the stent-thrombosis "firestorm that gripped the DES field five years ago, Walsh quipped, "This is not another ESC 2006."

Analysis Raises Eyebrows

The second paper published in EuroIntervention raised some eyebrows at TCT, since it was conducted and authored by Abbott Vascular [2]. Its analysis, using a specially designed bench test, found Abbott's MultiLink 8 (same design as Xience Prime) and MultiLink Vision (same as Xience V) stents to be associated with the greatest "compression resistance," while those of competitor Boston Scientific (Omega--"same stent design as the Promus Element, Taxus Element, and Ion) have the lowest.

Those conclusions, however, drew fire from an accompanying editorial by Drs Gérard Finet and Gilles Rioufol (Cardiovascular Hospital, Hospices Civils de Lyon, France), noting that the Williams paper, plus the three cases previously reported by Walsh, still constitute "exceptional" complications that were not seen in large clinical trials.

"To go beyond the precise analytic description of the 12 cases reported, specifically implicating a stent design with respect to its mechanical behavior, remains, in the present state of our knowledge, entirely hypothetical and deductive, as it is difficult to isolate a mechanical parameter without influencing the global mechanical behavior of the stent," Finet et al concluded.

Trade-Off Decisions

Another early observer of the stent-compression phenomenon, Dr John Ormiston (Mercy Angiography, Auckland, New Zealand), also presented a compression analysis Monday afternoon, comparing eight drug-eluting stents. In testing, the Omega/Element and Driver stents were least able to withstand compression, and the now-defunct Cypher select was the most able to withstand the force. Separately, in an "elongation test," whereby the same stents were pulled using a little hook, the Cypher stent required the most force to distort its structure, longitudinally, while the Omega and Driver required the least.

But Ormiston, too, emphasized operator technique as the key factor.

To avoid longitudinal distortion, said Ormiston, operators could select a stent with "higher structural integrity" but also avoid accidentally entangling catheters with the stents during deployment. This potential complication is only one of many, often more important, factors to consider when selecting a stent. For example, stents with lower longitudinal strength may, as in the case of the Element, have high radial strength.

Without question, Ormiston concluded, "reducing the number of connectors between hoops and thinning struts improves a number of performance characteristics but at the cost of reduced longitudinal strength."

He continued by saying that interventional cardiologists need to be aware of the limitations and strengths of different stents, but manufacturers need to understand the trade-offs being made for future-iteration design. "I think the longitudinal-integrity issues were not anticipated," he said. Going forward, he added, echoing a point also made by Williams et al, companies should adopt standardized longitudinal-strength–testing protocols that can be provided to cardiologists.

Lots of Talk, Few Cases

Speaking with heartwire after the session, Walsh reiterated his call for calm.

"I think there's been a lot of hype around this issue, and it's not even a clinical problem. What we're looking at is a large number of people who are talking about a tiny number of cases of this problem in an anecdotal fashion, and if you go back and look at the large randomized clinical-trial data and look across thousands and thousands of patients, we're not seeing a signal of this coming up. I think where we should focus is on clinical results, and we should be using meticulous technique during PCI to avoid this."

Experts Weigh In

The TCT audience heard from a wide range of panel members after the session wrapped up, with most saying they would be unlikely to change their practice in any way. Dr Tullio Palmerini (Istituto di Cardiologia, Bologna, Italy) acknowledged, "We are a little bit more careful with the Promus than we were before, and there are certain circumstances where we might use a different stent. The final thing is, we're just more aware when we deliver secondary equipment now, particularly with Promus Element stents, and if we feel any resistance at all, we stop straight away."

Dr Peter C Smits (Maasstad Ziekenhuis, Rotterdam, the Netherlands) agreed. "No, this won't affect my practice. However, knowing this, we should be more aware in our practice, and second, I think I will use more of these adjunctive stent imaging techniques to recognize what we are doing."

Dr Gregg Stone (Columbia University, New York, NY), who presented an update on the everolimus-eluting stent program during the same session, pointed out that Promus Element has the highest radiopacity, making it the easiest stent in which to see compression issues, which may account at least in part for the higher reports of this problem with this device, he said.

"I think this an important tool in the toolbox, and I'm sure I wouldn't be willing to give it up," Dr Louis Cannon (Northern Michigan Hospital Heart and Vascular Institute, Petoskey, MI) observed. "It can be a little bit of a Ferrari around a wet curve, and you need to be careful and judicious and use finesse."

Finally, Dr David Kandzari (Piedmont Heart Institute, Atlanta, GA) told heartwire , "I think in general there's a large opportunity for misleading information, both on behalf of the reported studies and also on behalf of the competitive rhetoric between companies. . . . This is not a new issue, nor is it an issue that is necessarily specific to the Promus Element design."

He continued, "We need to be aware of this issue, and it's best avoided with awareness and common sense and good technique, and when it happens, it can be fixed."

Finally, Kandzari added, "I do think that the competitive messaging about this is something that the industry needs to be very cautious of right now. Physicians don't want to hear more negative messaging about PCI in general, and second, if we overexaggerate the impact of this phenomenon, what ultimately is going to happen is we're going to impose greater restrictions on the development of new stent designs."

From the Manufacturers

heartwire also asked the major companies for statements, who emailed the following:

Abbott Vascular: "Longitudinal compression is not a class effect of next-generation stents but is a function of stent design. Based on their designs, stents have differing degrees of longitudinal strength and stability. Abbott's stents Xience V and Xience Prime are designed to have substantial longitudinal stability. They have a peak-to-valley design that promotes longitudinal stability--the connecting links are aligned to withstand pressure. The 300-million implant months of data for Xience and the bare-metal version Vision stent do not indicate an issue with longitudinal compression."

Boston Scientific: "Axial length change (ALC) is a rare event that may occur with all coronary stents, regardless of manufacturer, strut thickness, or alloy composition. ALC is not a new issue, but as a result of improved visibility with the Platinum Chromium stent series, in comparison with older stent platforms, physicians can now more easily and quickly identify and address ALC when it occurs."

Medtronic: "Longitudinal stent compression stems largely from device design. It's not a class effect that applies to all stents. Medtronic's Integrity stent platform, which employs an engineering advance called continuous sinusoid technology that enables each device to be formed from a single wire, exhibits excellent longitudinal strength, because the design features aligned crowns."

Cannon disclosed receiving grant support/research contracts from Boston Scientific and consulting, honoraria, and speaker's bureau fees from Abbott Vascular and Medtronic. Finet and Rioufol declared having no conflicts of interest. Kandzari disclosed having minor consulting and educational honoraria from Boston Scientific and Abbott and significant consulting and educational honoraria from Medtronic and Micell Technologies. Ormiston disclosed receiving consulting, honoraria, and speaker's bureau fees from Abbott Vascular and Boston Scientific. Stone disclosed receiving consultant fees/honoraria/speaker's bureau fees from all the major stent manufacturers. Walsh, Williams, Palmerini, and Smits disclosed having no conflicts of interest.