In patients undergoing primary percutaneous coronary intervention (PCI), use of a self-expanding stent is less likely to result in early stent malapposition than a conventional balloon-expandable device, according to a study published in the December 2012 issue of JACC: Cardiovascular Interventions. Malapposition has previously been linked to increased risk of stent thrombosis.

Data from the APPOSITION (Randomized Comparison Between the Stentys Self-expanding Coronary Stent and a Balloon-expandable Stent in Acute Myocardial Infarction) II trial were originally presented at the annual Transcatheter Cardiovascular Therapeutics (TCT) scientific symposium in September 2010.

Investigators led by Stefan Verheye, MD, PhD, of the Antwerp Cardiovascular Center (Antwerp, Belgium), randomized 80 STEMI patients to treatment with the nitinol self-expanding Stentys device (Stentys SA, Paris, France; n = 43) or a bare-metal balloon-expandable Vision or Driver stent (Abbott Vascular, Clara, CA; Medtronic, Minneapolis, MN; n = 37) at 9 European centers between December 2009 and June 2010.

OCT Zeroes in on Malapposition

Shortly after the procedure, optical coherence tomography (OCT) showed that the self-expanding group had both a lower percentage of malapposed stent struts and fewer patients with significant stent malapposition, defined as at least 5% of struts poorly positioned. After 3 days, differences in strut positioning became more pronounced, with 10 times fewer malapposed struts and no stent malapposition, the primary endpoint, in the self-expandable group (table 1).

Table 1. OCT Outcomes

^a Per patient, defined as ≥ 5% of struts malapposed.

In addition, quantitative coronary angiography showed a difference in late lumen loss between the 2 groups at 3 days. Minimal lumen diameter decreased slightly from baseline with balloon-expandable stents while it increased with self-expandable stents (-0.12 ± 0.29 mm vs. 0.04 ± 0.21 mm; P = 0.011).

At 30-day follow-up, no episodes of MACE (composite of cardiac death, MI, emergent CABG, or clinically driven TLR) or stent thrombosis had occurred. At 6 months, 1 TLR was reported in the self-expanding group, but MACE rates remained similar between the self-expanding and balloon-expandable groups (2.3% and 0, respectively; P = NS).

Solving the Sizing Problem

In a telephone interview with TCTMD, Stephen G. Ellis, MD, of the Cleveland Clinic (Cleveland, OH), observed that STEMI patients are good candidates for self-expandable stents because they are at the highest risk for stent thrombosis. That is due in part to the difficulty of stent sizing in a setting of gradual resolution of vessel spasm and dissolution of abundant thrombus.

“There’s a pretty good literature suggesting that we often undersize stents, and that’s what this study is trying to address,” he said.

According to the authors, the Stentys device helps overcome the dilemma by providing constant, gentle expansion in the days after deployment.

In a telephone interview with TCTMD, Maurice Buchbinder, MD, of the Foundation for Cardiovascular Medicine (La Jolla, CA), said another important finding is that as the self-apposing stent expands, so does the lumen diameter. This increases blood flow, facilitating thrombus resolution in both the vessel and myocardial tissue, he explained, noting that inadequate final minimal lumen diameter is the main driver of subsequent adverse events.

In an accompanying editorial, William Wijns, MD, PhD, and Stylianos A. Pyxaras, MD, both of the Cardiovascular Center Aalst (Aalst, Belgium), add that by reducing mechanical trauma, a gently self-expanding stent also lowers the risks of distal embolization and no reflow from disrupted plaque or thrombus debris.

Clinical Significance of OCT Malapposition Unproven

However, a lingering question, Drs. Wijns and Pyxaras write, is “whether spontaneous [stent] expansion is preferable to additional in-stent post-dilation using balloons.” Confounding the issue, they note, is the fact that in the study nearly two-thirds of the self-expanding group underwent balloon expansion immediately after stenting and 40.5% underwent predilation.

“Conceptually, it may seem that balloon expansion, either pre- or post-stent placement, may jeopardize some of the benefits related to softer self-expansion,” they comment.

Echoing the editorial, Dr. Ellis observed that although “OCT is the most sensitive tool we have for assessing malapposition, we really don’t know the clinically relevant definition of malapposition as it relates to stent thrombosis risk in a particular patient population. So APPOSITION II is an interesting conceptual study, but it needs to be fleshed out with more patients.”

Beyond APPOSITION II

In fact, “the world has moved on from APPOSITION II,” Dr. Buchbinder said. A 1-year interim analysis of the first 600 patients from APPOSITION III, a real-world European registry of STEMI patients who received the Stentys device, was presented at TCT 2012 in Miami, FL. The rate of MACE (9.0%) was reduced compared with historical controls, while clinically driven TLR (5.8%) was comparable to results with standard BMS, he reported.

Moreover, Dr. Buchbinder pointed out that hypothetical concern about the adverse impact of postdilation is countered by data from APPOSITION III, showing no loss of TIMI flow or blush grade in conjunction with mandatory postdilation

The Stentys device, which received CE mark approval in Europe in 2010, is not approved in the United States. However, APPOSITION V, a pivotal clinical trial slated to enroll up to 880 STEMI patients at 64 international sites, is just getting under way, said Dr. Buchbinder, who is a co-principal investigator.

The editorial suggests that the main limitation of the self-expanding stent concept is the current bare-metal device, which yields restenosis rates that are “high, at best.” However, Dr. Buchbinder noted that a sirolimus-eluting version of Stentys with a bioresorbable polymer is currently being evaluated in STEMI patients.

If the drug-eluting model performs as expected, it will become “the stent of choice for STEMI as well as a good contender in ACS patients,” he predicted.

 

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Sources:
1. van Geuns R-J, Tamburino C, Fajadet J, et al. Self-expanding versus balloon-expandable stents in acute myocardial infarction: Results from the APPOSITION II study. Self-expanding stents in ST-segment elevation myocardial infarction. J Am Coll Cardiol Intv. 2012;5:1209-1219.

2. Wijns W, Pyxaras SA. Self-expanding stents for primary percutaneous coronary intervention during acute myocardial infarction: Did we find the right indication . . . at last! J Am Coll Cardiol Intv. 2012;5:1220-1222.

 

 

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