JACC: Repeat scanning unnecessary for those with zero CAC score
For patients with a coronary artery calcium (CAC) score of zero, repeat scanning is unnecessary, and for those with positive scores, CAC scoring becomes a “robust predictor" of its progression," according to a study published March 16 in the Journal of the American College of Cardiology (JACC).

“CAC scoring has been proposed as a useful atherosclerosis imaging method for stratification and reclassification of risk of coronary heart disease (CHD),” the authors wrote.

James K. Min, MD, of New York Presbyterian Hospital in New York City, and colleagues evaluated 422 patients with normal CAC scan (CAC score equal to zero) who were undergoing annual CAC scanning for five years to assess proportional increases of CAC and to also assess conversions of a normal to an abnormal CAC scan.

The researchers compared the aforementioned group of patients to a separate cohort of 621 patients who had a baseline CAC scan of greater than zero.

According to the authors, “increasing degrees of CAC predict adverse CHD events and all-cause mortality, whereas a normal CAC scan is a reliable predictor for low risk and is used clinically to signify the absence of any major atherosclerosis.”

The patient cohort was taken from data from the Tennessee Heart and Vascular Institute. The 422 patients with a CAC score of zero underwent yearly CAC scanning until researchers detected a positive CAC score. The remaining 621 patients underwent two CAC tests.

During the study, a nurse or research coordinator collected patient data regarding cardiac conditions such as arterial hypertension, diabetes mellitus, dyslipidemia, smoking history, history of coronary artery disease (CAD) and Framingham risk score.

Researchers used electron beam CT (Imatron C-150; Imatron) to acquire 30 to 40 contiguous axial slices with a 3-mm thickness. CAC was defined as a minimum of three contiguous pixels with a peak Hounsfield unit density greater than or equal to 130.

CAC conversion was defined by the development of any CAC during any of the subsequent serial scans performed.

According to the researchers, of those patients who had a CAC score of zero, one-half had hypertension, two-thirds dyslipidemia and 92.2 percent had a CAD risk factor greater or equal to one. The average number of CAD risk factors was reported to be 2.1, compared to the average risk factor of 2.4 in the patient group who had CAC scores greater than zero.

Patients who had a CAC score greater than one were more likely to be older, male and exhibited greater rates of hypertension (194 vs. 351), diabetes (40 vs. 101) and dyslipidemia (280 vs. 476) compared to the other group.

After follow-up, 25.1 percent (n=101) of patients who first exhibited CAC scores of zero converted to having a positive CAC score. After a one-, two-, three-, four- and five-year follow-up, conversion from a CAC score of zero to a positive CAC score occurred in two, five, 24, 26 and 49 patients, respectively.

Of patients who exhibited an abnormal CAC score after follow-up, the researchers found that age, smoking, diabetes and hypertension correlated to the increase after a five-year follow-up.

Eighty percent of the 621 patients with a starting CAC score of zero experienced progression of CAC during the study.

“Our study provides unique insights into the 'warranty period' relative to a CAC scan remaining normal over time,” the authors wrote. “We observed that there was a substantial four-year lag period before coronary calcium development in asymptomatic individuals with baseline CHD risk factors but a score of CAC equal to zero.”

According to the researchers, during the first two years of follow-up, the conversion to CAC in patients was “extremely low,” while that number progressed significantly during the fourth and fifth years of follow-up.

“Given the magnitude of data supporting the use of CAC score to identify individuals at risk for CHD events, the results from this study suggest that individuals with baseline score of CAC equal to zero do not require frequent repeat scanning and that later repeat CAC scanning of individuals with a score of CAC greater than zero may permit more accurate updating of CHD risk,” the authors concluded.

In an accompanying editorial, Harvey S. Hecht, MD, of the Lenox Hill Heart and Vascular Institute in New York City, wrote that “the report by Min et al paves the way for a fresh approach to a large segment of the primary prevention population.”

Additionally, he said that annual CAC scans and conversion rates would unlikely be factored into future protocol, but offered that “the cost of over-treatment in this lowest-risk asymptomatic population is quite high; CAC=0 is priceless,” he concluded.