Editorial Comment

Opportunities forImprovement—TheDisappearing Stent

David R. Holmes, Jr., MD

Consultant in Cardiovascular MedicineMayo Clinic, Rochester, MN

The field of interventional cardiology continues toevolve having followed the path of balloon angioplastyalone to a variety of ablative devices to bare metalstent-based procedures and now drug-eluting stent pro-cedures which dominate the landscape. At each turn,new technology was developed to meet both the real aswell as the perceived problems present at that time.Techniques that were found to be both safe and effi-cacious in randomized trials and registry experiencesbecame dominant; those that were not were marginalizedand sometime disappeared. Drug-eluting stents haveundergone intense scrutiny and have become predicatedevices. They have dramatically decreased both angiogra-phic and clinical restenosis rates compared to either baremetal stents or to angioplasty alone. Problems (orbetter-stated opportunities) for improvement remain.Drug-eluting stents have not completely eliminated

restenosis. While in selected patients restenosis rates aresingle digit, in other patients with higher risk lesions,for example, bifurcation disease and diffuse small vesseldisease, restenosis rates remain increased. The etiologyof the restenosis varies from strut fracture to inadequatedrug concentration, to excess drug concentration, and toinflammation from the polymer.The potential for delayed subacute thrombosis has

been well documented. While this occurs with both baremetal and drug-eluting stents, its timing may be differ-ent. With drug-eluting stents, it may be delayed. Theetiology of this event varies from inflammation to de-layed endothelialization, to side branch involvement,and to penetration of the necrotic arthrosclerotic core.The most important hazard for this catastrophic event ispremature discontinuation of dual antiplatelet therapy.This has important implications for performance of noncardiac surgery after stent placement.There are other potential issues. There is increasing

use of non invasive screening in patients with coronaryartery disease. The presence of the stent makes thisproblematic because of artifact. In addition, the pres-

ence of the stent may change the possibility of havingsubsequent cardiac surgery because it may exclude agraft touchdown site.For these as well as other reasons, there continues to

be interest in stents that may not be permanent. Thearticle by Waksman et al is an early foray into the fieldwith a bioabsorbable magnesium alloy stent. Althoughthis stent is currently being implanted in Europeanpatients with coronary artery disease, animal data is stillrequired to learn more about basic issues.The current paper addresses some of these issues par-

ticularly safety and efficacy in an animal model. Whatcan we learn from this experience?

1. The magnesium alloy stents can be safely deployedand can achieve a good initial angiographic resultthat is comparable to bare metal stents.

2. At 28 days, there is already initial bioabsorption ofthese stents, so the concept of metal bioabsorption isreal and can be documented.

3. At three months, the percent area of stenosis andpercent diameter stenosis are improved when mea-sured by angiographic analysis in the magnesiumalloy stent group, and in addition, neointimal is lessthan with bare metal stents.

4. There was no excess of inflammation in the histo-logic segments compared with the bare metal stent.

5. The authors do point out an at least interesting andperhaps concerning finding although there was areduction in neointimal formation when assessing theresults with histologic morphometry, this did nottranslate into ‘‘a larger vessel lumen and the overallstented segment was significantly smaller when com-pared to the stainless steel stent’’. That finding is diffi-cult to explain in that the quantitative coronaryangiography at three months documents that the diam-eter stenosis was actually less and minimal lumendiameter was greater in the animals treated with themagnesium alloy stent. While there are a number of

Correspondence to: David R. Holmes, Jr.

E-mail: holmes.david@mayo.edu

Received 14 March 2006; Revision accepted 14 March 2006

DOI 10.1002/ccd.20923

Published online 12 September 2006 in Wiley InterScience (www.

interscience.wiley.com).

' 2006 Wiley-Liss, Inc.

Catheterization and Cardiovascular Interventions 68:618–619 (2006)

potential reasons for this, as the authors point out, thismight just be related to processing artifact.

This study does not answer all of the questions,including, will a longer-term follow up be required,information on eventual restenosis rates, will a drug berequired along with the bioabsorbable metal, and the

potential late effects of the process of bioabsorption.Additional areas of investigation will be the effect oneventual remodeling, and the relative merits of bioab-sorbable metals versus bioabsorbable polymers.Will this become a predicate group of devices or will

this type of stent go away like the metal itself goes away?Only time will tell, but this concept and the problems thatit potentially solves is an important venture.

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