Coronary artery calcium scoring by CT can be a useful tool in the evaluation of asymptomatic patients with an intermediate risk of coronary heart disease but not those with low or high risk, according to expert consensus.
On Jan. 23, the American College of Cardiology Foundation and the American Heart Association jointly released an expert consensus document that updates information and opinion on coronary artery calcium (CAC) scoring by CT, particularly with regard to global cardiovascular risk assessment and evaluation of patients with chest pain (J. Am. Coll. Cardiol. 2007;49:378–402). The last consensus document on the use of electron-beam CT for the diagnosis and prognosis of coronary artery disease (CAD) was published in 2000.
On the basis of data available since that time, the committee concluded that CAC measurement using CT scanning is a reasonable tool for evaluating asymptomatic patients with a 10-year risk of estimated CHD events between 10% and 20%.
“The test does what it does very well—it detects calcium. It's a marker of atherosclerosis and ergo a marker of higher risk,” said Dr. Robert O. Bonow, a member of the writing committee and chief of the division of cardiology at Northwestern Memorial Hospital in Chicago in an interview. With the intermediate group, CAC measurement could help cardiologists decide how aggressive to be with treatment.
However, the authors advised against the use of CAC measurement in patients with low CHD risk (below 10% 10-year risk of estimated CHD events). They noted that CAC measurements in this patient group would be similar to using the technique for population screening, which the committee also counseled against.
Likewise, the authors advised against the use of CAC measurements in asymptomatic patients with high CHD risk (greater than 20% 10-year risk of estimated CHD events or established coronary disease, or other high-risk diagnoses). Patients in this category “should be treated aggressively consistent with secondary prevention goals based upon the current National Cholesterol Education Program III guidelines and thus should not require additional testing, including CAC scoring, to establish this risk evaluation,” they wrote.
“If you have someone at low risk and a positive calcium scan doubles your risk from 1% to 2%, it's still low risk,” said Dr. Bonow. “If you're very high risk, it's high risk no matter what.”
While the recommendations give the thumbs up to the use of CAC to evaluate patients with intermediate risk, the authors noted that there have been no head-to-head comparisons of CAC with other assessment tools. Some, such as ankle/brachial index or carotid ultrasound, may be less expensive.
There have also been no randomized trials that demonstrate that CAC measurement improves outcomes. “This created a lot of discussion in the committee,” said Dr. Bonow. “The problem is that it's not clear that the trial will ever be done. Meanwhile, we have data that [CAC] might be a useful test in certain subsets of patients,” said Dr. Bonow.
The committee also noted that the strongest CAC data are for white men. Until additional data in other groups are available, the authors recommended caution in extrapolating CAC data derived from these studies in women and ethnic minorities.
The committee also reviewed the use of CAC measurement in patients with diabetes. It has been noted in several cross-sectional studies that patients with diabetes have a higher prevalence and degree of coronary calcium than nondiabetic patients.
The authors noted that there is some evidence to suggest “that coronary calcium might be useful to further stratify short-term risk in diabetic patients.” However, they cautioned that additional studies from nonreferral populations with longer follow-up are needed.
'If you have someone at low risk and a positive calcium scan doubles your risk from 1% to 2%, it's still low risk.' DR. BONOW