Amount of Calcium, Not Calcium Progression, May Be Best for Gauging CV Risk

It may not be necessary to take into account progression of coronary artery calcium (CAC) when trying to estimate a patient’s risk of cardiovascular disease (CVD) events, according to a new analysis. The most recent CAC scan is in fact just as good of a predictor as the calculations based on changes that occur over time.

Previous studies have investigated the predictive ability of calculating absolute change and percentage change as well as the usefulness of baseline scores, but this study is the first to show a single, recent score could be the best indicator of CVD event risk, researchers say.

“You don’t have to calculate it,” senior author Benjamin Levine, MD (Institute for Exercise and Environmental Medicine at Texas Health Presbyterian Hospital and UT Southwestern Medical Center, Dallas, TX), told TCTMD. “You don’t have to figure out how fast it’s progressing. What matters is how much atherosclerosis you have. What's that last value? That’s the one that matters.”

Levine, who said the idea to analyze the most recent calcium score came from coauthor Andre Paixao, MD, also pointed out that this is the first study the predictive value of CAC scans for CV events as a whole.

One Scan Is Enough

The researchers used information from the Cooper Center Longitudinal Study (CCLS), which started testing for CAC in 1998, on patients who were scanned twice using electron beam computed tomography (EBT) between 1998 and 2007. The mean time between scans was 3.5 years.

The total number of patients came to 5,933 after excluding certain patients who underwent revascularization between EBT scans or within 90 days of their follow-up, had a prior CVD event, or CAC regression of 50 Agatston units or greater.

CAC was detected in the initial scans of 2,870 patients (48% of the cohort). Over a mean follow-up time of 7.3 years, 161 individuals experienced a CVD event (including CVD death, nonfatal MI, nonfatal atherosclerotic stroke, CABG, or PCI).

CAC progression was associated with the likelihood of CVD events when adjusted for the baseline scan, but progression contributed less than did the initial CAC. If only the follow-up scan was included in the model, progression no longer mattered. Importantly, a model based only on the follow-up scan was just as predictive as the one involving both baseline CAC and progression.

“These findings imply that if serial CAC scanning is performed, the latest scan should be used for risk assessment, and in this context, CAC progression provides no additional prognostic information,” the paper concludes.

Deciding When to Scan and Rescan

According to an accompanying editorial by Prediman K. Shah, MD (Cedars Sinai Heart Institute, Los Angeles, CA), current “guidelines recommend judicious adjunctive use of CAC score to refine risk estimates especially in low-to-intermediate-risk populations.

“Because of the dynamic nature of atherosclerosis, it has also been suggested that serial changes in CAC score might reflect changes in atherosclerosis progression and thus have additional prognostic value,” he explains. “Furthermore, it has also been suggested a serial change in CAC score might provide an objective measure of the effectiveness of therapeutic interventions such as statins known to reduce CHD risk.”

Yet “the real significance of change in CAC score, especially as compared with the baseline or follow-up CAC score—bad, good, or indifferent—remains uncertain or at least more nuanced,” Shah writes, suggesting that, while more research is needed, the “addition of other variables that incorporate regions of change, change in regional density and other volumetric aspects of CAC change, extracoronary calcification, and epicardial fat volume may improve the value and relevance of a change in CAC score.”

Nathan Wong, MD (University of California, Irvine), who was not involved in the study, told TCTMD that “progression is still important, but the value that the data that a single scan provides is more important. And we know from numerous studies that a single calcium scan is far more important predictor of risk than just about anything else.”

Calcium scores are most often used to tip the balance on the decision to start a patient on preventive measures such as statins, according Wong, who published a study on the predictive power of CAC baseline scores last year. If a patient has other high risk factors but his or her physician is not sure it is necessary to start treatment, then a calcium scan will be employed.

“There is currently no guideline that has recommended remeasuring it to check whether someone’s disease has progressed or to check the effects of therapy,” Wong said.

Now, the findings of the current study are presenting enough evidence to prompt reconsideration for using CAC scans more than once, according to Wong’s colleague Robert Detrano, MD (University of California, Irvine).

“Perhaps, if someone had a scan 5 years ago that showed no CAC and then led a very bad, risk-prone life style, I might be more inclined now to recommend a second scan than before the study,” Detrano wrote to TCTMD via email.

Use of CAC scanning has been convoluted in many ways, he said, including being done in patients who don’t meet the guideline recommendations. “In fact, CAC scanning is the most overused and underused diagnostic test I know of,” Detrano commented. “The CAC scanning industry is driven too much by economics and not enough by science.”

Levine said that the perception of CAC scanning is changing as more studies are providing evidence of the assessment’s value. In fact, it is only a matter of time before it will become one of the main ways to predict CV events, he predicted.

“There’s increasing evidence that coronary calcium is one of the very best tools to enhance risk prediction,” Levine said. “And I think the next version of many of the recommendations and equations that are used to assess cardiovascular risk will include coronary calcium.”

Michael H. Wilson is the 2016 recipient of the Jason Kahn Fellowship in Medical Journalism.

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