CAC Screening Might Help Stratify Low-Risk Womem

Lisa Nainggolan
December 17, 2007 — A new analysis of the Multi-Ethnic Study of Atherosclerosis (MESA) shows that a third of women considered to be low risk based on the Framingham Risk Score (FRS) had detectable coronary artery calcium (CAC) on computed tomography (CT) scan and were at increased risk for coronary heart disease (CHD) compared with those without detectable CAC.
In addition, almost 5% of the women classified as low-risk based on FRS had advanced CAC (Agatston score of 300 of greater), and these women were at even higher risk of cardiovascular events, say Dr Susan G Lakoski (Wake Forest School of Medicine, Winston-Salem, NC) and colleagues in the Archives of Internal Medicine [1].
In an accompanying editorial [2], Drs Sarah Rosner Preis and Christopher J O'Donnell (Framingham Heart Study, Framingham, MA) say the results of Lakoski et al, "raise the important question of whether CAC screening is warranted among at least some women who are currently classified as 'low risk.' " But they conclude that, for a number of reasons, it is still too early to recommend this.
Lakoski agrees. She told heartwire: "I think this is a promising study in a population that is not normally studied. In the women with very high CAC scores we found that CAC changed their absolute risks pretty impressively despite their known risk factors." But she stressed that her group is far from advocating CT scans of CAC for low-risk women. "There's still much work to be done — the question, for novel risk factors, is can they improve upon standard risk stratification? There has to be a lot of scrutiny. There are risk/benefits to every test."
First known study to focus on predictive value of CAC in low-risk women
Lakoski et al studied 3601 women aged 45 to 84 participating in MESA and measured their CAC by CT scan. Excluding those with diabetes and those aged over 70 years, 90% of women in MESA were classified as 'low-risk' based on FRS.
The prevalence of CAC (Agatston CAC score > 0) was 32% (n = 870). Compared with women with no detectable CAC, low-risk women with a CAC score > 0 were at increased risk for CHD (hazard ratio [HR] 6.5) and cardiovascular disease (HR 5.2). Their absolute risk of events remained low, however — 2.1% for CHD and 2.8% for CVD.
In the 5% of women who had advanced rates of CAC (score 300 or greater), this was highly predictive of future events — the HR for CHD was 8.3 and that for CVD 6.0 compared with those without detectable CAC. This subset of women had absolute event rates of 6.7% for CHD and 8.6% for CVD over a 3.75-year period.
"These results are of importance," say Lakoski et al, "because, to our knowledge, this is the first known study to focus on the predictive value of CAC in a low-risk population of women." They add that the study "provides novel data in support of the 2007 guidelines on CVD prevention in women, suggesting that women with CAC are at potentially higher risk than an FRS-classification would suggest."
The women with advanced CAC in particular could potentially be candidates for more intensive treatment, they say. However, they note that "a longer duration of follow-up will be required to understand the implications of CAC scoring and whether both screening and more aggressive pharmacologic therapy in lower-risk populations of women . . . will reduce overall CHD and CVD burden."
Evidence base for CAC screening currently insufficient
In their editorial, Preis and O'Donnell say there are several reasons that the evidence base is currently insufficient to recommend CAC screening in low-risk women, including the fact that "the potential risks and costs of screening need to be considered in the overall benefit-risk equation."
In the meantime, there may be a case for risk algorithms to be updated to include further factors that have already been shown to be strong, consistent and independent predictors in addition to traditional risk factors, they note. Examples of these include parental history of myocardial infarction, or level of C-reactive protein (CRP), they say.
Lakoski agrees. "When we think about risk in women, we look traditionally at the FRS and think about smoking, hypertension etc, but there are other very strong predictors of coronary disease such as obesity and premature family history."
For instance, women with a family history of premature CHD "should be aware of this, see a doctor and discuss this," she says. "At that point, the physician might want to measure cholesterol and take blood pressure a little more carefully. Maybe people don't know they have other risk factors because they never go to the doctors."
But she also notes that "Traditional risk factors do a great job already, and it's going to be difficult to do much better. Another take-home message to women is that even if they have only one risk factor, they can offset their risk by lifestyle changes and that's really important."
The authors have disclosed no relevant financial relationships.
Sources
Lakoski SG, Greenland P, Wong ND et al. Coronary artery calcium scores and risk for cardiovascular events in women classified as 'low risk' based on Framingham Risk Score. Arch Intern Med 2007;167(22):2437-2442
Preis SR and O'Donnell CJ. Coronary heart disease risk assement by traditional risk factors and newer subclinical disease imaging. Is a "one-size fits-all" approach the best option? Arch Intern Med 2007; 167(22):2399-2401