Next Steps With NIRS: Lipid-Rich Plaque Study Shows Promise Identifying High-Risk Patients, Plaques

SAN DIEGO, CA—The identification of non-flow-limiting, untreated, lipid-rich plaques by intravascular near-infrared spectroscopy (NIRS) imaging is associated with adverse events over 24 months following PCI for de novo culprit lesions, according to results of the Lipid Rich Plaque (LRP) study.

“The goal is to use this as a discriminator for who is at high risk and who is at low risk,” said Ron Waksman, MD (MedStar Washington Hospital Center, Washington, DC), who presented the results today in a late-breaking trial session at TCT 2018. “The nice thing about this technology is it's ‘plug and play’—you don't have to calculate anything, you don’t have to measure anything. The operator can get the chemogram as you do the pullback, and in seconds you get a number.”

For the LRP study, Waksman and colleagues looked at a total of 1,563 patients with suspected CAD (46.3% stable angina) who underwent cardiac catheterization with PCI for an index event at 44 US and European sites between February 2014 and March 2016. NIRS-IVUS imaging was performed in two or more nonculprit arteries, and the team followed patient- and plaque-level events for 2 years among those with at least one maxLCBI4mm segment ≥ 250 and a randomly selected 50% of patients with all maxLCBI4mm segments < 250.

The adjusted patient-level analysis (n = 1,271) found an 18% higher risk of experiencing a nonculprit MACE event within 24 months for each 100-unit increase in maxLCBI4mm, with MACE rates of 12.6% and 6.3% in patients with maxLCBI4mm ≥ 400 and < 400, respectively. Also, the plaque-level analysis (n = 5,744) demonstrated a 45% higher risk of events within 24 months with each 100-unit increase in maxLCBI4mm in a coronary segment, with MACE rates of 3.7% versus 0.8% for plaques with maxLCBI4mm ≥ 400 and < 400, respectively.

Ready for a Randomized Trial

In a panel discussion following the presentation, James Muller, MD (Brigham and Women’s Hospital, Boston, MA), said he has had patients in the past say things to him like, “‘Doctor, that 40% lesion in the proximal LAD that they didn't stent, is that going to kill me?’ What I've been saying is wait until September 24, and I'll be able to have a better answer,” he said, adding that this study is a “triumph of what I would call collective science.”

In the future, panel member David Erlinge, MD, PhD (Skane University Hospital, Lund, Sweden), said it “will be very useful not only to find yellow plaques but also to exclude plaques that are not dangerous [given that] we are doing CT angio on more and more people and we're seeing a lot of vulnerable plaques. The patients will ask us, ‘What can we do with this?’ If we have a red plaque we can say this is safe, we don’t have to do anything. If it’s very yellow, we probably will treat in the future.”

Of course, how best to treat remains an open question, Erlinge noted. “We will get some information in the prospective ABSORB studies that we are conducting,” he said.

Panelist Gary Mintz, MD (Cardiovascular Research Foundation, New York), said with these data he is now ready for a large-scale, randomized trial in this field using either stents or pharmacotherapies. “It’s always nice to have a second confirmatory registry, but I think we have evidence that we have a class action effect of imaging,” he said. “We’re at the point where we have to stop talking about trying to identify and predict vulnerable plaques and decide whether or not it makes sense to treat them and if so how, whether pharmacologically or mechanically.”

What to Do Differently?

Speaking with TCTMD, Anthony N. DeMaria, MD (Sulpizio Cardiovascular Center at the University of California, San Diego), who was not involved in the study, said it is difficult to pinpoint where the field should move based on these data. “It's clearly a positive study,” he said. “This technique is able to identify lipid pretty accurately and the identification of a big lipid core seems to convey risk. Now, an increase in risk is a funny thing, isn't it, because . . . you have to look at it in terms of what's the absolute risk and so that's something that needs to be explored a little bit more.”

Specifically, DeMaria expressed interest in seeing how many patients had events and what the absolute risk of having one would be based on the presence of vulnerable plaque. Also, “it wasn't 100% clear to me that this risk was independent of, let’s say, the LDL,” he said. “People have huge LDL levels, they're at risk, and does this convey more?”

The last remaining question, he said, echoing a point also made by the panelists, is what to do once a plaque has been identified as high risk. “I suppose you could say further lipid-lowering if there was evidence that anti-inflammatory therapy works, which there isn't at the moment,” DeMaria said. “You're certainly not going to put a stent in a nonculprit lesion that's not significant just because of this, I don't think.”

DeMaria said a future randomized trial of NIRS imaging should not be out of the question, but that the treatment options for patients with these vulnerable plaques, pharmacologic or interventional, are “not very attractive.” He said he’d be “shocked” if funding was secured for a trial like this at this time, unless a PCSK9 inhibitor manufacturer took an interest in this type of lesion or patient.

“For this technology to be incorporated into the mainstream as a usual or more routine procedure, it would require demonstration of some intervention that could be undertaken that would change the outcome,” he concluded.