High prevalence of ultrasound detected carotid atherosclerosis in subjects with low Framingham risk score: potential implications for screening for subclinical atherosclerosis

Abstract

Background: The cardiovascular (CV) risk assigned by the Framingham risk score (FRS) misses many subjects destined for CV events. Coronary artery calcification (CAC) as measured by computed tomography and carotid intima-media thickness (CIMT) and plaque assessment using B-mode ultrasound can identify subclinical atherosclerosis. The comparative relation of CAC and CIMT and carotid plaque after integration into the FRS is not established. The aim of this study was to develop a CV screening approach incorporating FRS, CAC, and CIMT.

Methods: The prevalence of subclinical atherosclerosis, defined as CAC score > 0, CIMT > or = 75th percentile, or plaque > or = 1.5 mm, was determined in the groups with low, intermediate, and high FRS among 136 asymptomatic subjects. The CIMT and CAC values were used to determine "vascular age" and "coronary calcium" age, respectively, with established nomograms.

Results: In the 103 low-risk (FRS < 10%) subjects, 41%, 50%, 59%, and 66% had CAC scores > 0, CIMT > or = 75th percentile, plaque > or = 1.5 mm, and CIMT > or = 75th percentile or plaque > or = 1.5 mm, respectively. In the 33 subjects with intermediate (n = 14) or high (n = 19) FRS, 70%, 81%, 87%, and 87% had CAC scores > 0, CIMT > or = 75th percentile, plaque > or = 1.5 mm, and CIMT > or = 75th percentile or plaque > or = 1.5 mm, respectively. Fifty-two percent of subjects with coronary calcium scores of zero had carotid plaque. Adjusted for FRS, body mass index was an independent predictor of abnormal CIMT in the low-FRS group, but not of abnormal CAC. Mean vascular CIMT age was significantly higher than coronary calcium age (61.6 + or - 11.4 vs 58.3 + or - 11.1 years, P = .001), and both were significantly higher than chronologic age (56.9 + or - 10.1 years) (P < .0001 and P < .04, respectively). CIMT upgraded or downgraded FRS by >5% in more cases than CAC (42% vs 17%).

Conclusion: In asymptomatic patients without CV disease, CIMT and plaque assessment are more likely to revise FRS than CAC. Body mass index predicts increased CIMT in low-FRS subjects. These findings may have broad implications for screening in low-FRS subjects.