SNOWMASS, COLO. — The most intriguing potential application for coronary artery calcium imaging is as a tool to track atherosclerosis progression over time in response to treatment, Dr. Matthew J. Budoff said at a conference sponsored by the Society for Cardiovascular Angiography and Interventions.
“I'm not suggesting that this is a current application, but the data now emerging are pretty interesting,” according to Dr. Budoff, director of cardiac CT at Harbor-UCLA Medical Center, Torrance, Calif.
He cited an observational study in which investigators tracked the change in coronary artery calcium (CAC) on serial electron-beam CT scans in 495 statin-treated asymptomatic patients. Forty-one subjects had an acute MI during up to 7 years of follow-up. The relative risk of an MI was increased 17-fold in those with at least a 15% per year rise in CAC score (Arterioscler. Thromb. Vasc. Biol.2004;24:1272–7).
“This might be a way, in the future, of monitoring therapy. You're on a statin, your LDL is pretty good, but your CAC is increasing—maybe we should do something more,” Dr. Budoff said at the conference cosponsored by the ACC.
He also described several current uses for CAC imaging:
▸ Screening asymptomatic patients with an intermediate Framingham risk score. Forty percent of asymptomatic adults fall into the Framingham intermediate-risk category, meaning they have an estimated 10%–20% risk of a coronary event within the next 10 years. Most acute MIs occur in this mid-risk group. Dr. Budoff was coauthor of a 2007 ACC/AHA Clinical Expert Consensus Statement that endorsed CAC measurement as a means of further stratifying Framingham intermediate-risk patients in order to identify a higher-risk subgroup in whom aggressive primary preventive measures are warranted (J. Am. Coll. Cardiol. 2007;49:378–402).
The Multi-Ethnic Study of Atherosclerosis (MESA), a National Institutes of Health-sponsored prospective study of 6,814 patients followed for 3.5 years now in press, was merely the most recent of several large studies showing that a CAC score of 100 or more was associated with a 10-fold increased risk of incident coronary heart disease.
And a prospective study sponsored by the NIH of more than 10,700 asymptomatic persons free of known coronary heart disease when they underwent CAC measurement showed that a baseline CAC of 97–409 was linked with an adjusted 9.7-fold greater risk of nonfatal MI or CHD death in the next 3.5 years, compared with subjects with a CAC of 0 (Am. J. Epidemiol. 2005;162:421–9).
“A CAC greater than 100 is more robust as a predictor of future events than Framingham risk factors … and more robust than C-reactive protein or carotid intimal-medial thickness,” observed Dr. Budoff, who is on the speakers bureau for General Electric.
▸ Identification of very-low-risk patients needing no further evaluation for coronary artery disease. Four studies totalling nearly 6,000 patients indicate a CAC of 0 has a 95%–99% negative predictive value for obstructive coronary disease. A fifth study, by Dr. Budoff and coinvestigators, concluded that a CAC score of 0 on an initial scan has at least a 5-year warranty before a repeat scan is appropriate because the likelihood of CAC progression during that first half-decade is so low (Int. J. Cardiol. 2007;117:227–31).
▸ A tool to improve compliance. In a study by Dr. Budoff's group, showing patients their CAC image was tied with 91% adherence to statin therapy over 3 years among those who scored in the top CAC quartile (Atherosclerosis 2006;185:394–9).