Deferred Stenting After Infarct-Artery Opening May Limit MI Size, Says Study

Deborah Brauser

October 23, 2015

SAN FRANCISCO, CA — Holding off stent implantation for several days after patients have undergone thrombectomy, balloon angioplasty, or both to open STEMI-related arteries may be safe and beneficial, especially in those with anterior-wall MI, suggests new research.

The INNOVATION trial of 104 Korean patients showed that those who were randomly assigned to stenting 3 to 7 days after their initial procedure for STEMI "had a strong tendency" toward reduction in infarct size (the primary end point) a month later, as well as reduced microvascular obstruction (MVO) vs those who had received immediate stenting. They also had significantly reduced MVO-to-infarct ratio (P=0.02).

In addition, the subgroup of deferred-stenting patients with anterior-wall MI showed significant reductions in infarct size, MVO size, and MVO/infarct ratio (P=0.02, 0.01, and 0.03, respectively).

Dr Cheol Woong Yu (Korea University Anam Hospital, Lisbon, South Korea) told attendees at TCT 2015 that the important point is that deferred patients need to be monitored closely.

Session moderator Dr David O Williams (Brigham and Women's Hospital, Boston, MA) later told heartwire from Medscape that INNOVATION showcased a "very clever" concept.

During primary stenting in a PCI patient, "it's not uncommon to get the artery open, get decent flow, put a stent in at relatively high pressure, and then the flow goes down. That should go backward," said Williams, who is also associate editor at Circulation and senior associate editor at Circulation: Interventions.

"I think the idea is not bad: that if you can open up an artery, let some of that thrombus clear out over time, and then put the stent in, you might avoid some of the problems," he said. However, he added that he's not sure all of this actually happened in this study.

"It did suggest superiority, but the strength of the study is modest. I don't think it's the final answer, but I congratulate them on the concept."

Addressing Infarct Size

Yu noted that although PCI with immediate stenting is the current standard of care for STEMI patients, this could cause additional injury to myocardium "by increasing distal embolization of clot."

The "proof-of-concept" DEFER-STEMI study, published last year in the Journal of the American College of Cardiology by UK researchers[1], showed that deferred vs immediate stenting reduced no reflow and increased "myocardial salvage" in high-risk STEMI patients.

For the current study, Yu and his investigative team wanted to especially focus on whether the two strategies would reduce infarct size, which was defined as "percentage of left ventricular volume."

Within 12 hours of symptom onset, the INNOVATION participants (mean age 60 years) were screened at one of two centers in South Korea and achieved TIMI 3 flow after their initial STEMI procedure: thrombectomy alone in 15% of the deferred group vs 8% of the immediate group; balloon angioplasty in 22% and 26%, respectively; and both thrombectomy with balloon angioplasty in 63% and 65%, respectively. All were then randomly assigned to either immediate (n=52) or deferred stenting (n=52).

Infarct size was measured by cardiac magnetic resonance imaging 30 to 35 days after primary reperfusion and was smaller in the deferred-stenting group, albeit not significantly, than in the immediate group (14.9 g vs 18.9 g, respectively; P=0.07). Reduced MVO size also just missed significance in the deferred group (0.3 g vs 0.6 g, respectively; P=0.051).

In the anterior-wall-MI subgroup (n=62), those who received deferred stenting had significantly smaller infarct size vs those receiving immediate stenting (15.6 vs 22.5, respectively), as well as reduced MVO size (0.3 g vs 0.7 g) and reduced MVO incidence (39.3 vs 67.7).

Secondary End Points

When researchers examined other secondary end points in all of the participants, mean peak CK-MB after stenting was significantly lower in the deferred vs the immediate groups(199 IU/L vs 260 IU/L, P=0.04).Although more members of the deferred-stenting group reached myocardial blush grade 3 (39 vs 28, respectively) and TIMI myocardial perfusion grade 3 (28 vs 18, respectively), neither of these two end points were statistically significant (P=0.06 and P=0.09, respectively).

There were also no between-group differences in incidence of slow or no reflow or in corrected TIMI frame count.

As for safety measures, the deferred-stenting group showed no significant differences between the end of the first procedure and start of the second procedure in residual stenosis or coronary dissection over time. However, Yu noted that some of these findings could have been affected by the small sample size and because six members of the deferred-stenting group crossed over to the immediate-stenting group.

Still, "we showed that deferred stenting could be performed without additional risk of adverse events with meticulous monitoring during the initial procedure compared with immediate stenting," he summarized.

"Food for Thought"

After the presentation at a TCT featured clinical research session, moderator Williams noted that the study "provided food for thought that could potentially provide data for further, larger investigations."

"This was an excellent presentation and an interesting trial concept," added discussant Dr Harold L Dauerman (University of Vermont Medical Center, Burlington). "But I'm curious about next steps, given the borderline P values and the small sample size."

He noted that "the history of reperfusion-injury interventions in STEMI is absolutely dismal" and the secondary findings from this study were thought-provoking, especially in the subgroup analysis.

"But every time we get to a large-scale trial, it's negative. So I'm curious, based on these results, what's the next step in studying this strategy? I'm just not sure," said Dauerman.

Yu reported receiving grant/research support from the Korean Society of Interventional Cardiology, Sejong Medical Research Institute, Terumo, and Isu Abxis.

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