Screening young to middle-aged patients with ultrasound for carotid plaque or carotid intima-media thickness (CIMT) is likely to uncover cardiovascular risk in patients with a low Framingham risk score (FRS). In addition, carotid ultrasound proved better than a coronary artery calcium (CAC) score via CT to predict risk, according to two studies in the August issue of the Journal of the American Society of Echocardiography.
In one study, Mackram Eleid, MD, and colleagues from the department of internal medicine at the Mayo Clinic College of Medicine in Scottsdale, Ariz., retrospectively reviewed records of 441 subjects younger than 65 years old (mean age 49), with no history of coronary artery disease or diabetes. They found 42 percent had high-risk carotid ultrasound findings (either CIMT greater than the 75th percentile or findings of plaque greater than 1.5 mm).
Of the 336 patients with the lowest FRS (less than 5 percent), 38 percent had high-risk carotid ultrasound findings (17 percent plaque, 21 percent CIMT). Of this 38 percent, 61 percent were recommended for lipid-lowering therapy, primarily in an internal medicine and family medicine practice.
"The lack of radiation exposure, relatively low cost and ability to detect early-stage atherosclerosis suggest that carotid ultrasound for CIMT and plaque detection should continue to be explored as a primary tool for cardiovascular risk stratification in young to middle-aged adults with low FRS," the researchers concluded.
Eleid and colleagues noted that atherosclerosis begins early in life and can progress silently over decades and that the FRS does not incorporate variables such as family history of premature coronary artery disease, remote smoking history, waist circumference, impaired fasting glucose and triglyceride levels.
While the FRS is useful in the "epidemiology of large populations, it has limitations in predicting cardiovascular risk in individuals," they wrote.
They also found that women had similar prevalence of high-risk carotid ultrasound findings, plaque and abnormally thickened CIMT as men despite having lower body mass indexes, significantly higher HDL and much lower FRS. "This finding suggests a role for carotid ultrasound in identifying women at higher risk for adverse cardiovascular events with minimal traditional cardiovascular risk factors," they said.
In an interview, Eleid said that he anticipates more insurers paying for a CIMT screening in the future. "Once the internal medicine organizations, such as the American College of Physicians, embrace it, which has not happened yet, then we will see more widespread use and reimbursement."
In the second study, Tasneem Z. Naqvi, MD, from the University of Southern California, Los Angeles, and colleagues from Cedars Sinai Heart Institute in Los Angeles, evaluated 136 asymptomatic subjects with no history of cardiovascular events.
Of the 103 subjects with low-risk FRS (less than 10 percent):
- 41 percent had CAC scores greater than zero;
- 50 percent had CIMT greater than the 75th percentile;
- 59 percent had plaque; and
- 66 percent had CIMT or plaque.
Of the 33 subjects with intermediate (14) or high (19) FRS:
- 70 percent had CAC scores greater than zero;
- 81 percent had CIMT greater than the 75th percentile;
- 87 percent had plaque; and
- 87 percent had CIMT or plaque.
Overall, 52 percent of subjects with CAC scores of zero had carotid plaque. Body mass index was an independent predictor of abnormal CIMT in the low-FRS group, but not of an abnormal CAC score. Also, CIMT upgraded more patients to intermediate and high risk than CAC.
While CAC measurement is less operator dependent and more reproducible than CIMT or carotid plaque assessment, it is associated with ionizing radiation. Also, CAC scans may produce false negatives in younger subjects whose soft plaque has not fully calcified, according to researchers.
Naqvi and colleagues noted that CIMT measurement is more standardized than plaque assessment, but CIMT measurement is more labor intensive.
Another finding was that the mean vascular CIMT age was significantly higher than coronary calcium age (61.6 vs. 58.3 years), and both were significantly higher than chronologic age (56.9 years).
"In low-risk subjects, initial screening by CIMT and plaque assessment is likely to provide the highest yield to detect subclinical atherosclerosis," they concluded.