NIRS-IVUS Imaging Spots Vulnerable Plaques, At-Risk Patients

Marlene Busko

October 05, 2018

SAN DIEGO — Intravascular near-infrared spectroscopy (NIRS) imaging identified non-flow-limiting, untreated lipid-rich plaque in patients with suspected coronary artery disease (CAD) undergoing coronary angiography, in the large Lipid-Rich Plaque (LRP) study.

Moreover, patients with greater amounts of this vulnerable plaque were more likely to have a major adverse cardiac event (MACE) within 2 years of percutaneous coronary intervention (PCI) for de novo culprit lesions.

"Intravascular NIRS imaging in mildly or nonobstructive coronary arteries can be used as a tool to identify both patients and nonculprit arteries at high risk for future events and should be considered for use in patients undergoing cardiac catheterization with possible PCI," Ron Waksman, MD, MedStar Washington Hospital Center, Washington, DC, told the press during a briefing before a late-breaking clinical trial session at Transcatheter Cardiovascular Therapeutics 2018.

The nice thing about NIRS is that "it's a plug-and-play technology" where the operator instantly receives a lipid core burden index (LCBI) number for the scanned coronary artery segment, he said.

"Of course, the million-dollar question is, What do you do differently with that information?" Deepak L. Bhatt, MD, from Brigham and Women's Hospital, Boston, who was a discussant at the late-breaking session, told theheart.org | Medscape Cardiology.

Should a patient be treated more aggressively with "a systemic cholesterol-lowering drug or an anti-inflammatory drug," he asked, "or is it something that should be treated focally with a stent, for example, a bioabsorbable stent?"

"It is always a bit disconcerting seeing, for example, a 50% narrowing in someone's left anterior descending artery that supplies blood to the front of the heart," Bhatt said, "which you shouldn't be stenting, based on current guidelines and evidence."

Similarly, Morton J. Kern, MD, University of California, Irvine, said that the LRP study "tells us, if you've got a lot of plaque, you're at risk," which we already know.

However, NIRS — which was coupled with intravascular ultrasound (IVUS) in this study and could be coupled with optical coherence tomography — "could be an advance" in identifying risk in patients with acute coronary syndrome (ACS) as well as stable angina, he told theheart.org | Medscape Cardiology.

But like Bhatt, Kern stressed that "currently, we lack knowledge about how patient outcomes are impacted by this incremental knowledge about lipid-rich plaques."

Building on Previous Evidence

The feasibility of using intravascular NIRS to identify patients with lipid core plaque who had a higher risk for future MACE was previously demonstrated in a few small trials.

In 2010, the US Food and Drug Agency approved the first coronary catheter with dual NIRS–IVUS technology for the detection and characterization of coronary plaques with a lipid core.

The LRP study used the current version of this intravascular imaging system (Makoto, InfraReDx), which will likely be launched in the United States early next year.

The system displays the results in a "chemogram," or colored image, in which clear coronary arteries appear red and any lipid-rich plaque appears yellow. It also displays numbers for the maximum lipid core burden in a 4-mm segment (maxLCBI4mm).

To investigate this technology in a larger population, investigators enrolled 1563 patients with suspected CAD who underwent cardiac catheterization with PCI at 44 sites in the United States and Europe between February 2014 and March 2016. Of these, 1552 patients had analyzable coronary arteries.

About half of the patients had stable angina (46.0%); the rest had unstable angina (37.0%), non-ST-segment MI (14.0%), or stabilized STEMI (2.5%).

The mean age of the patients was 64 years, and 70% were male, 37% had diabetes, 23% were current smokers, 80% had hypertension, and 80% had hyperlipidemia.

The researchers imaged a mean of 2.1 vessels per patient with NIRS–IVUS and analyzed patient- and plaque-level outcomes for 2 years in all patients with at least one maxLCBI4mm segment of at least 250 and in half of all patients with maxLCBI4mm segments below 250 randomly assigned to follow-up. In all, there were 1271 patients and 5744 coronary artery segments.

At 2 years, nonculprit MACE events were cardiac death in 2.2% of patients, cardiac arrest in 0.4%, ACS in 2.9%, non-fatal MI in 1.3%, rehospitalization in 0.7%, PCI in 5.3%, and coronary artery bypass grafting in 1.2%.

After adjustment, the risk of experiencing a nonculprit MACE event within 24 months was 18% higher for each 100-unit increase in maxLCBI4mm. Nonculprit MACE rates among patients with maxLCBI4mm of at least 400 and among those with maxLCBI4mm below 400 were 12.6% and 6.3%, respectively.

In the plaque-level analysis, patients had a 45% increased risk of experiencing a nonculprit MACE within 24 months for each 100-unit increase in maxLCBI4mm. Nonculprit MACE rates were 3.7% and 0.8%, respectively, for patients with maxLCBI4mm of at least 400 and for those with maxLCBI4mm below 400.

"Multivessel NIRS can be easily and safely performed to assess and identify vulnerable patients and vulnerable plaques," Waksman concluded.

C. Michael Gibson, MD, Harvard Medical School, Boston, pointed out that these patients have "vulnerable plaque," but they also have "vulnerable blood" — that is, abnormal levels of risk markers, such as cholesterol and C-reactive protein (CRP).

NIRS imaging "could be a valuable technique," he speculated, but these are early days. Hospitals might not have the technology and "it's a little tougher to do" this assessment than to measure CRP or LDL-cholesterol, he told theheart.org | Medscape Cardiology.

"If further studies validate an actual way to reduce the risk associated with this imaging finding, that would change the way we practice medicine," Bhatt said when interviewed. "I think this opens up a lot of potential areas of investigation."

The LRP study was funded by Infraredx Nipro Company. Waksman reports serving on advisory boards for Abbott Vascular, Amgen, Boston Scientific, Medtronic, Philips Volcano, Pi-Cardia LTD, and Cardioset; consulting for Abbott Vascular, Amgen, Biosensors, Biotronik, Boston Scientific, Medtronic, and Philips Volcano; receiving grant support from Abbott Vascular, AstraZeneca, Biosensors, Biotronik, Boston Scientific, and Chiesi; serving on the speaker's bureau for AstraZeneca and Chiesi; and being an equity holder in MedAlliance, DOMed, Pi-Cardia, and Cardioset. Bhatt reports serving on multiple advisory boards and receiving research funding and royalties from several drug and device manufacturers. Gibson reports grant support/research contracts with Angel Medical, Bayer AG, CSL Behring, Janssen, Johnson & Johnson, and Portola Pharmaceuticals; and consultant fees/honoraria/speaker's bureau participation with several drug and device manufacturers.

Transcatheter Cardiovascular Therapeutics (TCT) 2018. Presented September 22, 2018.

Circulation. Published online September 22, 2018. Abstract

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