The absence of coronary artery calcium (CAC) at CT strongly excludes patients from obstructive disease, while coronary atherosclerotic plaque burden is correlated with CAC scores in all ages, according to a study published in the February issue of Academic Radiology.

Despite the correlation with plaque burden, the absence of CAC does not exclude the presence of coronary atherosclerotic plaque, especially in patients younger than 55 years, according to Tae-Young Choi, MD, of Kwandong University College of Medicine, Goyang-Si, South Korea, and colleagues.

“Plaque composition shifted from noncalcified to calcified plaque with increasing age, which may affect the vulnerability of these lesions over time,” wrote the authors.

Choi and colleagues aimed to assess the relationship of CAC score with total plaque burden, as well as the differences in underlying plaque composition across differing age groups, as limited data are available on the association of plaque type with age.

Results of the study were based on 64-slice multidetector CT images of 781 consecutive patients evaluated using a 15-coronary segment model. Segment involvement, stenosis and plaque characteristics were measured, with total CAC scores stratified by age tertiles—lowest, younger than 55 years; middle, 55-65 years; highest, older than 65 years.

“With increasing age, higher segment involvement scores, segment stenosis scores, and total plaque scores were noted,” reported Choi and colleagues. Plaque burden was significantly correlated with total CAC scores in all age tertiles.

In the oldest age group, 87 percent of plaque contained calcium, compared with 63 percent in younger patients. Patients older than 65 years were unlikely to have isolated noncalcified plaque at a rate of less than 3 percent, whereas more than 20 percent of younger patients had isolated soft plaque.

“Although CAC is present in atherosclerotic arteries and regarded as a process of the atherosclerosis, CAC may not be a sufficient tool to determine overall plaque burden and plaque composition,” wrote the authors. “Our study showed that older patients had more plaque burden and that older age was more strongly associated with a higher burden of calcified plaque among all plaque subtypes with higher propensity for heterogeneous plaque burden.”

The authors noted that reliance on CAC in younger symptomatic populations may be “problematic,” and that CT angiography may be reasonable for these patients. However, previous studies have found that CT angiography does not add prognostic information in asymptomatic cohorts, thus the results of the current study should not be applied to asymptomatic populations, they added.