Spectroscopy Catheter Finds Lipid-Rich Coronary Lesions Safe for PCI in COLOR Trial

Neil Osterweil

November 02, 2016

WASHINGTON — Seeing is believing: near-infrared spectroscopy (NIRS) studies with or without intravascular ultrasound (IVUS) indicate that PCI performed on lipid-rich plaque (LRP) is not associated with a higher risk of major adverse cardiac events (MACE) than PCI performed on non-LRPs[1].

In the prospective COLOR registry trial, the rate of MACE—a composite end point of cardiac death, MI, stent thrombosis, revascularization, and hospitalization—was 14.1% among all patients, with 6.0% of events related to the culprit lesions, 8.3% related to the nonculprit, nontreated lesions, and 2.4% of indeterminate origin, reported Dr Giora Weisz (Shaare Zedek Medical Center, Jerusalem, Israel).

"PCI of NIRS-defined LRPs was safe and was not associated with increased periprocedural or late adverse outcomes compared with PCI of non-LRPs," he said here at TCT 2016.

LRPs have been associated with increased PCI risk in autopsy studies, and prior small studies or case reports have suggested that LRP as seen on NIRS is associated with PCI periprocedural outcomes, he said.

COLOR-ful Results

To clarify the potential association of coronary LRPs on NIRS with periprocedural and long-term events after PCI, researchers studied outcomes for 1899 patients with indications for coronary angiography and possible revascularization. Of this group, 705 patients underwent NIRS alone, and 1194 received NIRS with IVUS delivered over a single catheter.

Dr Giora Weisz

As Weisz described, the imaging modality produces images with high contrast showing LRPs in vivid yellow and adjacent, non-LRP lesions in bright red. Outcomes of interest for investigators and clinicians include lipid core burden index (LCBI), calculated as the fraction of yellow pixels within a scanned region multiplied by 1000, and maximum LCBI in any 4-mm segment (maxLCBI­4mm).

Culprit-related events were defined as MACE related to the culprit PCI segment as imaged by NIRS. Nonculprit-related events were defined as clinical symptoms plus any of the following: >20% diameter stenosis progression from baseline to event or rupture/thrombus, objective evidence of ischemia such as a positive stress test, 50% or greater diameter stenosis at follow-up with or without revascularization, or <50% diameter stenosis at follow-up with revascularization.

Of the 1899 patients enrolled, 192 were excluded from analysis because of missing or poor NIRS data or planned CABG, leaving 1168 patients with 1265 identified pre-PCI culprit lesions on NIRS and 927 patients with 1072 nonculprit lesions.

At 2 years, 2.4% of patients experienced cardiac death (0.3% culprit-lesion–related, 0% nonculprit-lesion–related, and 2.1% of indeterminate origin). In all, 2.4% of patients experienced an MI (1.6%, 0.6%, and 0.3%, respectively). Stent thrombosis occurred in 0.8% of all patients (0.5%, 0.3%, and 0), revascularization occurred in 8.3% of all patients (4.5%, 5.4%, and 0%), and 11.5% required hospitalization (4.9%, 8.2%, and 0.3%).

Overall composite MACE rates among all patients were as noted above. Among the 1168 patients who underwent PCI, the composite MACE rate was 15.4%, with 7.0% attributed to culprit lesions, 9.4% to nonculprit lesions, and 2.3% of indeterminate origin.

An analysis of culprit-lesion–related MACE by maxLCBI4mm showed no differences between a maximum index level of less than 304 and 304 or greater.

In a multivariable model looking at factors associated with culprit-lesion–related MACE, lesion length (per mm) was weakly associated with greater risk (hazard ratio [HR] 1.02, P=0.02), and the use of a second-generation drug-eluting stent was associated with significantly lower risk (HR 0.58, P =0.046).

Weisz noted that the study was limited by virtue of the use of voluntary registry data, meaning that selection bias can't be ruled out, nonblinding of operators to NIRS/IVUS imaging, which may have influenced the treatment strategy, lack of routine post-PCI imaging or angiographic follow-up, and the fact that only a few lesions responsible for nonculprit-lesion–related events were imaged at baseline, precluding in-depth analysis.

Clinical Research Tool

Asked by heartwire from Medscape how he uses the technology, Weisz said that "for the flow-limiting lesion where you're going to put in a stent, for that short segment it doesn't matter if you do near-infrared spectroscopy.

"But it might be that you find information more distal to this lesion or more proximal to this lesion that can help you change or maybe not change your decision about what to do with this patient, whether it's medical therapy to push down the LDL even further or to find other lesions that need treatment," he added.

"I'm actually very excited about this technology after hearing about it, because I think of what it can actually do to prevent later events in those nonculprit lesions," commented Dr Jeffrey J. Popma (Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA), an invited discussant in a media briefing where Weisz presented the data.

More important, he said, the technology promises to be an important clinical research tool. "With the [proprotein convertase subtilisin/kexin type 9] PCSK9 inhibitors right now, it seems like a huge opportunity to be able to study lipid-rich plaque and be able to see whether, if we drive the cholesterol down to 30, there is a reduction in lipid-rich plaque," he said.

Codiscussant Dr David R Holmes Jr (Mayo Clinic College of Medicine, Rochester, MN), asked whether the NIRS/IVUS findings might lead to more lesions being treated without an adequate evidence base.

"How are we going to be guided by this? Because when we do IVUS of culprit lesions, I'm always amazed that the rest of the artery looks like it's got lots of stuff in it, so how often do you see that the whole segment has lots of stuff in it, and how do you know what to treat?" he asked Weisz.

The finding that there was no difference in outcomes between culprit and nonculprit lesions suggests that "it doesn't matter: you don't have to be afraid of it," Weisz replied.

He noted that the clinical significance of NIRS-defined nonculprit LRPs will be determined by two ongoing prospective outcome trials: theLRP study and the PROSPECT-II trial.

The COLOR trial was supported by InfraReDx. Weisz discloses being on a medical advisory board for AngioSlide, AstraZeneca, Bayer, Calore, Corindus, Medtronic, Medivisor, MI Medical Incentives, TriSol, and Vectorius; receiving grant/research support from AngioSlide, Boehringer Ingelheim, Corindus, and Matrizyme; and having ownership in Filterlex. Popma disclosed grant support, consulting fees, and equity in various companies, but not InfraReDx. Holmes reported having no relevant financial relationships.

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