Repeat CT: Unraveling Plaque Changes in CAD With Elevated Lp(a)

Patrice Wendling

January 19, 2022

New research suggests serial coronary CT angiography (CCTA) can provide novel insights into the association between lipoprotein(a) and plaque progression over time in patients with advanced coronary artery disease.

Researchers examined data from 191 individuals with multivessel coronary disease receiving preventive statin (95%) and antiplatelet (100%) therapy in the single-center Scottish DIAMOND trial, and compared CCTA at baseline and 12 months available for 160 patients.

As reported in the Journal of the American College of Cardiology, patients with high Lp(a), defined as at least 70 mg/dL, had higher baseline high-density lipoprotein cholesterol and ASSIGN scores than those with low Lp(a) but had comparable coronary artery calcium (CAC) scores and total, calcific, noncalcific, and low-attenuation plaque (LAP) volumes.

At 1 year, however, LAP volume — a marker for necrotic core — increased by 26.2 mm3 in the high-Lp(a) group and decreased by -0.7 mm3 in the low-Lp(a) group (P = .020).

There was no significant difference in change in total, calcific, and noncalcific plaque volumes between groups.

In multivariate linear regression analysis adjusting for body mass index, ASSIGN score, and segment involvement score, LAP volume increased by 10.5% for each 50 mg/dL increment in Lp(a) (P = .034).

"It's an exciting observation because we've done previous studies where we've demonstrated the association of that particular plaque type with future myocardial infarction," senior author Marc R. Dweck, MD, PhD, University of Amsterdam, the Netherlands, told | Medscape Cardiology. "So, you've potentially got an explanation for the adverse prognosis associated with high lipoprotein(a) and its link to cardiovascular events and, in particular, myocardial infarction."

The team's recent SCOT-HEART analysis found that LAP burden was a stronger predictor of myocardial infarction (MI) than cardiovascular risk scores, stenosis severity, and CAC scoring, with MI risk nearly five-fold higher if LAP was above 4%.

As to why total, calcific, and noncalcific plaque volumes didn't change significantly on repeat CCTA in the present study, Dweck said it's possible that the sample was too small and follow-up too short, but also that "total plaque volume is really dominated by the fibrous plaque, which doesn't appear affected by Lp(a)." Nevertheless, Lp(a)'s effect on low-attenuation plaque was clearly present and supported by the change in fibro-fatty plaque, the next-most unstable plaque type.

At 1 year, fibro-fatty plaque volume was 55.0 mm3 in the high-Lp(a) group vs -25.0 mm3 in the low-Lp(a) group (P = .020).

Lp(a) was associated with fibro-fatty plaque progression in univariate analysis (β = 6.7%; P = .034) and showed a trend in multivariable analysis (β = 6.0%; P = .062).

"This study shows you can track changes in plaque over time and highlight important disease mechanisms and use them to understand the pathology of the disease," Dweck said. "I'm very encouraged by this."

What's novel in the present study is that "it represents the beginning of our understanding of the role of Lp(a) in plaque progression," Sotirios Tsimikas, MD, University of California San Diego, and Jagat Narula, MD, PhD, Icahn School of Medicine at Mount Sinai, New York, say in an accompanying commentary.

They note that prior studies, including the Dallas Heart Study, have struggled to find a strong association between Lp(a) with the extent or progression of CAC, despite elevated Lp(a) and CAC identifying higher-risk patients.

Similarly, a meta-analysis of intravascular ultrasound trials turned up only a 1.2% absolute difference in atheroma volume in patients with elevated Lp(a), and a recent optical coherence tomography study found an association of Lp(a) with thin-cap fibroatheromas but not lipid core.

With just 36 patients with elevated Lp(a), however, the current findings need validation in a larger data set, Tsimikas and Narula say.

Although Lp(a) is genetically elevated in about one in five individuals and measurement is recommended in European dyslipidemia guidelines, testing rates are low, in part because the argument has been that there are no Lp(a)-lowering therapies available, Dweck observed. That may change with the phase 3 cardiovascular outcomes Lp(a)HORIZON trial, which follows strong phase 2 results with the antisense agent AKCEA-APO(a)-LRx and is enrolling patients similar to the current cohort.

"Ultimately it comes down to that fundamental thing, that you need an action once you've done the test and then insurers will be happy to pay for it and clinicians will ask for it. That's why that trial is so important," Dweck said.

Tsimikas and Narula also point to the eagerly awaited results of that trial, expected in 2025. "A positive trial is likely to lead to additional trials and new drugs that may reinvigorate the use of imaging modalities that could go beyond plaque volume and atherosclerosis to also predict clinically relevant inflammation and atherothrombosis," they conclude.

Dweck is supported by the British Heart Foundation and is the recipient of the Sir Jules Thorn Award for Biomedical Research 2015; has received speaker fees from Pfizer and Novartis; and has received consultancy fees from Novartis, Jupiter Bioventures, and Silence Therapeutics. Coauthor disclosures are listed in the paper. Tsimikas has a dual appointment at the University of California San Diego (UCSD) and Ionis Pharmaceuticals; is a coinventor and receives royalties from patents owned by UCSD; and is a cofounder and has an equity interest in Oxitope and its affiliates, Kleanthi Diagnostics and Covicept Therapeutics. Narula reports having no relevant financial relationships.

J Am Coll Cardiol. 2022;79:223-233, 234-237. Full text, Editorial

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