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,” said Dr. Budoff, director of cardiac CT at Harbor-UCLA Medical Center, Torrance, Calif.
He cited an observational study by Dr. Paolo Raggi of Tulane University, New Orleans, and coinvestigators, who measured the change in coronary artery calcium (CAC) on serial electron-beam tomography scans in 495 statin-treated asymptomatic patients.
During up to 7 years of follow-up, 41 subjects had an acute MI. The relative risk of an MI was increased 17-fold in those with at least a 15% per year rise in CAC score. CAC progression provided incremental prognostic value beyond that associated with LDL cholesterol level, which was a mean of 118 mg/dL in patients who had an MI and a similar 122 mg/dL in those with no MI (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 commented at the conference cosponsored by the American College of Cardiology.
He also described several current uses for CAC imaging:
▸ Screening asymptomatic patients with an intermediate Framingham risk score. Of asymptomatic adults, 40% 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/American Heart Association Clinical Expert Consensus Statement that endorsed CAC measurement as a means of identifing 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, 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 (CHD).
Prior to MESA, Dr. Budoff conducted an observational study of 25,253 consecutive asymptomatic patients referred by their primary care physicians for CAC scanning. After adjustment for traditional cardiovascular risk factors, a baseline CAC of 100 or greater was associated with a 10.4-fold increased rate of all-cause mortality over the next 10 years, compared with a CAC of 0 (J. Am. Coll. Cardiol. 2007;49:1860–70).
And an NIH-sponsored prospective study of more than 10,700 asymptomatic individuals free of known CHD showed that a baseline CAC of 97–409 was associated 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, which are traditionally in the realm of two- to threefold increased risk, and more robust than C-reactive protein or carotid intimal-medial thickness, where relative risks are in the 1.5–3 range,” said 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 has at least a 5-year warranty before a repeat scan is appropriate because the likelihood of CAC progression during that period is so low (Int. J. Cardiol. 2007;117:227–31).