Researchers from several institutions reviewed the medical records of asymptomatic individuals who had CT coronary calcium scans at Centennial Medical Center in Nashville, TN, between 1996 and 1999. During an almost 15-year mean follow-up period, the 936 study participants who died succumbed at rates that increased in a linear fashion, from 3% to 28%, corresponding with their coronary artery calcium (CAC) scores.
"I think there's a greater and greater evidence base with calcium scoring," lead author Leslee Shaw, PhD, from Emory University, said in an interview with AuntMinnie.com. "So in addition to lung cancer screening and breast cancer screening, we have a wealth of evidence that coronary calcium is quite helpful in identifying risk in patients."
Taming a big problem
Heart disease remains the single largest cause of death in the U.S., killing 40% more people than all cancers combined. However, unlike some cancer screening tests, screening for heart attack risk has not been universally adopted for asymptomatic individuals.
The CT CAC screening test, which takes five minutes and examines all of the calcium in the coronary arteries for less than $100, has the potential to fill that screening void.
Clinicians rely on CAC scores to predict the risk of myocardial infarction, and CAC can also predict all-cause mortality for several years. The current study sought to determine the long-term predictive power of CAC scoring, which has been unknown (Ann Intern Med, July 7, 2015, Vol. 163:1, pp. 14-21).
The researchers examined the records of 9,715 individuals who were referred by their primary care physicians for calcium scoring. The subjects underwent either electron-beam tomography (EBT) or MDCT; as in previous studies, the correlation between the two tests was high.
Shaw and colleagues also collected risk factor and demographic information, including patient history of diabetes, hyperlipidemia, hypertension, and heart disease, as well as family history of coronary artery disease. All subjects underwent a coronary artery calcium test, and they were sorted by CAC score into six groups: 0, 1-10, 11-100, 101-399, 400-999, and 1,000 or greater.
The researchers tracked the status of all participants using the National Death Index, a central computerized index managed by the U.S. National Center for Health Statistics. Based on when the patients entered the study, the mean follow-up period was 14.6 years after the scan. Finally, the group calculated the risk of death from any cause.
Calcium and all-cause death
In models that adjusted for coronary artery disease risk factors, CAC score strongly predicted all-cause mortality (p < 0.001), the researchers found. Over the 15-year study period, 936 patients died at rates that correlated with increasing calcium scores.
|Unadjusted all-cause mortality vs. calcium score
||Relative hazard for all-cause death (p-value)
||1.68 (p < 0.001)
||2.91 (p < 0.001)
||4.52 (p < 0.001)
||5.53 (p < 0.001)
||6.26 (p < 0.001)
Other significant factors that contributed to the risk of all-cause mortality included age decile, hypertension, dyslipidemia, diabetes, being a current smoker, and a family history of coronary heart disease (all p < 0.0001).
Age itself is strongly related to CAC burden, of course, with the incidence rising in older patients. But the study results showed more than 20% risk-category reclassification for individuals with CAC in addition to risk factors beyond age and other cardiac factors. As for relative risks, age was No. 1, followed by calcium score, Shaw said.
"Age and coronary calcium are the top predictors of mortality, they always are, and in this case calcium would be the No. 1 predictor because of the variability you get with age," she said.
On the plus side, an asymptomatic individual with a calcium score of 0 has a minimal risk of death from any cause over the next 15 years.
"It's a very long-term warranty period," said co-author Dr. James Min from Weill Cornell Medical College (formerly from Cedars-Sinai Medical Center) in a statement.
CAC score as patient aid
Conversely, the presence of any calcium in the arteries means that there is risk. Knowing their scores can help individuals with high scores adopt healthier lifestyles and begin medical therapy such as statin drugs, if warranted, to improve their odds of long-term survival.
"The help with having longer-term follow-up is that you really start to approach life expectancy with patients," Shaw told AuntMinnie.com. "If a patient is 55 and you have a 15-year follow-up, then you're really starting to get more and more of an idea of how a given test impacts their life expectancy. So that's kind of the big impetus for this study -- that the very long-term follow-up provides a lot of data on how well the calcium scores themselves predict over time."
One potential complication learned from other forms of screening is that patients at lower risk as a result of screening tend to become less compliant over time. They stop taking their medications and adhering to new lifestyle regimens, eventually reaching higher risk levels, Shaw said. Fortunately, that phenomenon wasn't reflected in these results.
For those at the top of the CAC chart, however, mortality "is quite high and can approach 30%, 40%, and 50% over 15 years," she said.
Calcified vs. noncalcified plaque
Should we also be looking at noncalcified plaque with coronary CT angiography?
"For years people have been saying that calcified plaque is a surrogate for noncalcified plaque, and I think that's what we're seeing here," Shaw said.
But in the context of what the study and the U.S. Preventive Services Task Force (USPSTF) are looking for, the coronary calcium scan is probably a good enough test -- and probably the only practical one.
"I don't believe we're going to be able to convince the public to do a full-blown CT angiogram," Shaw said.
Cost is an issue and radiation doses are still not uniformly low, she noted, despite the ultralow-dose achievements of some researchers.
And finally, "right now, we don't have good ways of easily quantifying the amount of plaque," Shaw said. "So looking at other markers like low-attenuation plaque, noncalcified plaque, the volume and burden of plaque -- it takes a lot of quantification, and it's time-consuming. So even though the data is intriguing, it's not nearly what it is for calcium."
Coronary calcium scanning is a rare example of an easy-to-do test that may not be perfect, but serves its purpose by providing essential information at a low cost, Shaw said. And hopefully it does so in time to alter the patient's trajectory with lifestyle changes or medication.
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