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Avoiding and Repairing Coronary Stent Distortion
Editor's Commentary on Stent Longitudinal Compression or "Crumpling"
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December 1, 2011 -- The first time that I heard about the issue of second and third generation drug-eluting stents becoming compressed or distorted was during a small interventional meeting this past summer. A cardiologist from Brazil showed slides of a few cases in which a PROMUS Element stent had been deformed due to catheter manipulation through the deployed stent. He thought it was important to point this out in case other physicians in the audience encountered this problem -- a problem which he easily solved by redilating the stent with a high pressure balloon. He did, however, note that, as a result of these occurrences, his cath lab was no longer using this particular stent.

Since then similar cases have been published in EuroIntervention and the Journal of Interventional Cardiology; this phenomenon also was the subject of hastily-called seminars during the TCT 2011 meeting in November. It seems that this issue occurred predominantly with Boston Scientific's Element platform, but a case here and there involved an Endeavor, a Biomatrix or a Taxus stent.

Dr. John A. Ormiston
Dr. John A. Ormiston

Yesterday, Dr. John Ormiston, considered to be New Zealand's most experienced interventional cardiologist and co-principal investigator for Abbott's ABSORB first-in-man bioabsorbable stent trial, and his co-authors, Dr. Bruce Webber and Dr. Mark W. I. Webster, published their findings on this subject in JACC Cardiovascular Interventions, after extensive bench-testing of seven of the leading stent platforms. The result? Longitudinal compression had very much to do with the design of the stent -- and, of the new iteration of stents, Boston Scientific's Element/Omega design was the most susceptible (although it should be noted that the Element does score high in terms of flexibility and radial strength). Abbott's XIENCE V and XIENCE Prime platforms were the least susceptible with Medtronic's new Integrity platform very close behind. But Boston Scientific's Element showed 3-5 times the distortion. For more details, read our report about this study.

Of course, for many of the interventional cardiologists I have informally polled about this issue, stent distortion is not that big a deal. It doesn't occur that frequently, especially when proper technique is employed, although Dr. Ormiston told me he thinks stent distortion is under-recognized and occurs more frequently than say, late stent thrombosis (although it is far less severe a complication since late stent thrombosis can be fatal). Additionally, stent distortion, if recognized, can be corrected.

Speaking of "proper technique", as I learned waaaaaay back in the beginnings of balloon angioplasty, good technique means being very careful when crossing a treated area of the artery with a wire, a balloon, with anything. It's why interventionalists learn to treat the distal part of the artery first and work one's way back. It's kind of like not painting yourself into a corner: you don't want to walk over wet paint -- and you don't want to jiggle a catheter or guide wire through a recently placed stent.

But sometimes you have to; sometimes you are in a situation, like an ostial lesion (one near the origin of the artery) where deep catheter engagement or manipulation is required. In such cases it is important to understand the issues involved. To whit, I hereby reprint Dr. Ormiston's thoughts, which he sent to me, about avoiding and repairing coronary stent distortion:

There are clinical situations that predispose to longitudinal distortion, especially with stents with lower longitudinal integrity. The risk is increased if the struts, especially proximal struts, are not fully apposed to the arterial wall such as in a tapered vessel. Risk may increase with stents deployed on bends where wire bias directs the post-dilation balloon to the edge of the stent. Non-compliant balloons are stiffer than compliant balloons and more likely to "catch" on struts. If there is resistance to advancing a post-dilating balloon, a change to a compliant balloon may be advisable.

For proximal stents, alteration of the wire alignment by, for instance, altering guide catheter orientation may alter wire bias. Sometimes the use of a Guideliner (Vascular Solutions, Minneapolis, MN) may overcome resistance to passage of a post-dilating balloon possibly by changing the orientation of the wire and/or crossing device. However it may itself cause damage.

Care needs to be taken passing devices such as an IVUS catheter, another stent delivery system or an aspiration catheter through a deployed stent because of risk of disruption. While distortion is more likely at the proximal end of a stent it can occur in the body or distal end of a stent and the distortion may separate struts and be misinterpreted as strut fracture. If there are tandem lesions, it remains best to treat the distal first. If there is judged to be a high risk of stent longitudinal distortion, then selection of a stent with high longitudinal stability and low risk of distortion may be wise.

Guide catheter management can reduce distortion risk. With ostial or proximal stenting such as left main coronary stenting or proximal right coronary stenting, care needs to be taken to limit contact of the guide catheter and stent because deep intubation may deform the proximal end of a deployed stent. Guide catheter control is essential. Care should be taken to deflate balloons fully before withdrawal to limit the deep guide engagement that sometimes occurs with withdrawal of partially deflated balloons. In addition, disengagement of the guide and forward pressure on the guide-wire before balloon withdrawal may limit deep guide intubation. Another situation that predisposes to deep uncontrolled guide engagement is the forceful removal of a guide-wire that has been deliberately trapped outside a stent to protect the side-branch during bifurcation stenting. For an ostial or proximal location selection of a stent with known high longitudinal integrity may be advisable.

-- Dr. John A. Ormiston

It should also be noted that Section 6.3 of the FDA-mandated Directions for Use (DFU) packaged with the PROMUS Element Plus Stent System is titled "Longitudinal Stent Deformation" and contains additional cautions regarding this issue.

Reported by Burt Cohen, December 1, 2011