Identifying At-Risk Patients Using Coronary Artery Calcium Scores
Ordering CT scans on young patients may result in unnecessary exposure to radiation.
In a recently published article in JAMA Cardiology, Dr John Carr from Vanderbilt University Medical Center and coauthors evaluated data from the Coronary Artery Risk Development in Young Adults study also known as CARDIA1.
The study examined whether the presence of coronary artery calcium (CAC) in younger individuals, as evaluated by a non-contrast computed tomography scan (CT), was associated with an increased risk for developing clinically significant coronary heart disease.
For the study, 5115 participants — ages 18 through 30 — were recruited between March 1985 and June 1986, and baseline demographics and cardiovascular risk factors were collected. Their CAC scores were measured using standard non-contrast CT scan at years 15 and 20 of the study, when the participants were age 32 to 46.2
The researchers found that those who had any measurable CAC — any score above zero — had a 5 times greater risk for having a fatal or nonfatal coronary event than those with no coronary calcium. Further, after breaking CAC scores into groups, they found that risk of a coronary event for participants with a CAC score between 1 and 19 was 2.6 times higher than for those with CAC scores of zero. Participants with CAC scores of 100 or more had a 3.7-fold increase in all-cause mortality.2
These results are very different from prior studies, which have found that elevated risk for adverse cardiovascular events is associated only with CAC scores greater than 100. Individuals with scores less than 100 have traditionally been considered to be at low cardiovascular risk.
However, Carr, et al. argue that exponential increases in CAC burden occurs at a younger age than previously thought — as early as age 32 and 56 — and that those individuals with high CAC are at higher risk for poor outcomes, despite the fact that their CAC scores are reasonably low and irrespective of their Framingham risk.2
What does this mean for future practice?
For starters, we already know that we need to do a better job of identifying younger patients who are at high risk for developing coronary artery disease. Unfortunately, for patients younger than age 40, few tools are available. Framingham risk and other more modern risk scores are based on traditional risk factors that are not as good at predicting future morbidity or mortality in younger patient populations. CAC may be a better way of assessing that risk for these younger patients.
However, ordering CTs on younger, seemingly healthy individuals solely to get a CAC score would increase the economic burden on our already financially strained health-care system and expose more patients to harmful radiation.
Recognizing this, the research team used their findings to build a prediction model to determine the likelihood of having CAC before the age of 56 based on traditional risk factors such as age, race, gender, education, smoking history, cholesterol, body mass index and blood pressure.
Using the model, the researchers were able to group patients into low or high risk. Applying their model to the data from CARDIA, and proposing that CTs be used only for those with a risk at or above the median value, they found that they would be able to reduce the number of individuals screened by 50%, while still capturing 77% of all participants with CAC scores higher than 1 and 95.5% of participants who had had a coronary event.2
Should we start using their prediction model to determine who should get a screening CT? Not yet. More research is needed to determine the downstream effects of applying such a prediction model to the general population. We also need to determine whether widespread testing would curb outcomes without increasing other risks, such as the risk for cancer from the additional radiation exposure.
In the meantime, an alternative strategy suggested by the authors would be to standardize CAC reporting on conventional chest CTs ordered for other reasons. This approach may have some merit.
One study, published in December 2000 by Dr Mettler at the University of New Mexico, found that 19% of all patients seen in his department had had at least one CT scan, and 36% of all patients had had a prior CT scan. Further, he found that the highest percentage of scans was done in patients age 36 to 50.3 While only 9% of those CTs were chest CT scans, the finding supports that it may be reasonable to obtain CAC scores from existing data for precisely the age group that we are interested in risk-stratifying.
This approach, coupled with a more traditional evaluation of modifiable risk factors, could help identify younger individuals who are at risk for adverse atherosclerotic events and prompt earlier prevention. It may trigger earlier lifestyle modifications and possibly even drug therapy — all without exposing individuals to additional radiation exposure.
- Friedman GD, Cutter GR, Donahue RP, et al. CARDIA: study design, recruitment, and some characteristics of the examined subjects. J Clin Epidemiol. 1988;41(11):1105-1116. doi: 10.1016/0895-4356(88)90080-7
- Carr JJ, Jacobs DR Jr., Terry JG. Association of coronary artery calcium in adults aged 32 to 46 years with incident coronary heart disease and death [published online February 8, 2017]. JAMA Cardiol. doi: 10.1001/jamacardio.2016.5493
- Mettler FA Jr., Wiest PW, Locken JA, Kelsey CA. CT scanning: patterns of use and dose. J Radiol Prot. 2000;20(4):353-359