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Vessel lumens were bigger and clinical outcomes possibly better after percutaneous coronary intervention (PCI) on non-obstructive vulnerable plaques, researchers showed in a pilot trial.

People randomized to Absorb bioresorbable vascular scaffold (BVS) treatment of vulnerable plaques had a mean minimum lumen area (MLA) of 6.9 mm² at 25 months, whereas peers getting guideline-directed medical therapy (GDMT) alone had MLA averaging just 3.0 mm² (P<0.0001), according to Gregg Stone, MD, of Icahn School of Medicine at Mount Sinai and the Cardiovascular Research Foundation in New York City.

Safety was comparable between groups given similar rates of 24-month target lesion failure, counting cardiac death, target vessel-related MI or clinically-driven target lesion revascularization (4.3% vs 4.5%, P=0.96), Stone told the audience at this year's meeting, hosted virtually by the Cardiovascular Research Foundation.

A full manuscript of the 182-person PROSPECT ABSORB trial was simultaneously published online in the Journal of the American College of Cardiology.

How to Treat Vulnerable Plaque with High Plaque Burden?

"The present study is the first randomized trial to examine whether PCI of plaques with high-risk 'vulnerable' characteristics is safe and effective in enlarging luminal dimensions while generating a 'neocap' of intimal hyperplasia over the original lesion, potentially leaving the atheroma more resistant to rupture and thrombosis," according to the authors.

"Currently there is no accepted indication to revascularize vulnerable plaques as most are angiographically mild and sufficiently non-stenotic to fall below the ischemic threshold. Nonetheless, progressive atherosclerosis and thrombosis of these lesions may result in an increasing frequency of progressive and unstable angina, MI and cardiac death over time," they noted.

Major adverse cardiac events (MACE) numerically favored the Absorb BVS group (4.3% vs 10.7%; OR 0.38, 95% CI 0.11-1.28) over a median follow-up of 4.1 years, which "warrants the performance of an adequately powered randomized trial to determine whether PCI treatment of focal vulnerable plaques improves patient outcomes," Stone said.

However, the difference in MACE was driven by progressive angina episodes alone (1.1% vs 9.0%), as there were few cases of randomized lesion-related MIs and no cardiac deaths in either group during follow-up.

This was a "dubious" result to Renu Virmani, MD, of CVPath Institute in Gaithersburg, Maryland, who suggested during a press conference that the patients may not have been totally blinded during the course of the study.

Stone's defense was that the trial was not powered to detect a clinical difference between the BVS and GDMT groups.

"As yet there isn't enough data to say 'go invasively'" when it comes to treating vulnerable plaque, Virmani concluded. "I think stents have their own problems," she cautioned, emphasizing the role of high-dose medical therapy for now.

Stone and colleagues had 898 people who received successful PCI for an MI subsequently undergo three-vessel imaging using a combination intravascular ultrasound (IVUS) and near-infrared spectroscopy (NIRS) catheter as part of the .

The 182 patients who turned out to have vulnerable plaque (according to the sole criterion of IVUS plaque burden ≥65%) were randomized to GDMT with or without additional BVS treatment as part of the PROSPECT ABSORB analysis.

Median angiographic diameter stenosis of lesions with vulnerable plaques was a mild 41.6%. Fractional flow reserve (FFR) or instantaneous wave-free ratio was negative in 95.9% of affected lesions.

By NIRS-IVUS, however, median plaque burden was large at 73.7%, MLA was a small 2.9 mm², and maximum lipid plaque content was high at 33.4%.

One BVS-related thrombosis occurred and was attributed to plaque shift and not the scaffold itself. There was one borderline aneurysm that resulted in late strut malapposition and scaffold discontinuities, Stone said.

There were no true aneurysms on follow-up angiography, he emphasized during the press conference.

PROSPECT ABSORB was limited by a small sample and the use of the troubled first-generation Absorb BVS that is no longer sold.

"If you decide to do a preventive PCI, you need to make sure that the risks of the procedure per se and the ones associated with the implanted device are close to zero. BVS is most likely not the most suitable device to achieve this considering that in flow-limiting lesions it is inferior to metallic DES [drug-eluting stents]," commented Marco Valgimigli, MD, PhD, of Cardiocentro Ticino in Lugano, Switzerland.

However, non-flow-limiting lesions have never been treated with any device, so there are no comparative effectiveness data between DES and BVS in this setting, he said.

The investigators acknowledged that the mechanism of reduced lesion lipid content after BVS treatment remains unknown.

Stone noted that the ongoing seeks to determine if PCI stops lesion growth over time and improves outcomes in a study population of 1,600 people with at least two high-risk plaque characteristics.

"The concept is potentially revolutionary but we need to be cautious at this stage, because there is no evidence here that this strategy impacts patient outcomes and [yet it] requires complex and costly procedures to be accomplished," Valgimigli said.

High Lipid Burden, Thin-Cap Fibroatheroma Also Signal Risk

Two such characteristics -- high lipid burden and plaque burden -- were found to put patients at especially high risk of future MACE, according to a separate report from the PROSPECT II group.

MACE reached 13.2% of patients overall, with non-culprit lesion-related MACE in particular affecting 8.0% by 3.7 years post-PCI, reported David Erlinge, MD, PhD, of Lund University and Skane University Hospital in Sweden.

That subset of MACE was significantly much more common in lesions with maxLCBI_4mm ≥324.7 and plaque burden ≥70% on NIRS-IVUS (7.0% vs 0.2% in lesions not meeting either condition; OR 36.73, 95% CI 13.59-99.28).

Additionally, another group reported that thin-cap fibroatheroma was a high-risk lesion characteristic associated with increased MACE risk in people with diabetes.

Among nearly 400 people with FFR-negative lesions who stayed on optimal medical therapy, more than 25% turned out to hold thin-cap fibroatheromas on optical coherence tomography (OCT), according to Elvin Kedhi, MD, PhD, of Isala Hartcentrum in Zwolle, The Netherlands.

Those with thin-cap fibroatheromas suffered more target lesion-related MACE by 18 months (13.3% vs 3.1% without these fibroatheromas, HR 4.7, 95% CI 2.0-10.9), Kedhi reported on behalf of the study group.

Ultimately, deciding which is the best parameter of vulnerable plaque is important because it is "very impractical" to perform all three assessments (i.e., plaque burden from IVUS, lipid burden from NIRS, and thin-cap fibroatheroma presence on OCT), commented Adnan Kastrati, MD, of Deutsches Herzzentrum in Munich, during the press conference.

Researchers should also go to the next step of finding identifiers of vulnerable plaque on non-invasive imaging modalities such as CT angiography, he suggested.

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