The utility of screening for calcium in coronary arteries has been a controversial topic in the cardiology community over the past decade, with some questioning whether it adds sufficient clinical information to justify its use. Its predictive value among the spectrum of patients at risk and its effect on the subsequent use of further diagnostic testing, particularly among those who obtain the scans privately, has also been at issue.

In June 2000, the American College of Cardiology/American Heart Association released a consensus document2,3 on this type of testing, concluding that while it may be useful in certain situations and, with more data, may hold promise in a variety of other settings, there was insufficient compelling evidence for it to be used widely, particularly in screening asymptomatic populations. More specifically, they suggested it might hold promise in determining which of those patients at intermediate risk by the FRS are actually at high risk.

Their cautious conclusion met with emotional debate, not only in the community, led in particular by the Society of Atherosclerosis Imaging, but within the writing committee for the statement itself, as previously reported by heartwire.

Dr Robert C Detrano (Harbor-UCLA Research and Education Institute, Torrance, CA), senior author on the current paper, whose previous data were heavily considered for the ACC/AHA document, told heartwire that the writing committee had pointed out that one of their reservations about the correlations in his previous work was that they had been based on risk factors reported by subjects, not on measured risk factors.

"Basically, that group was extremely cautious in recommending that the test could be used or might be helpful in people who are at intermediate risk of having heart attacks," Detrano said. With this paper, he added, "we confirmed that this is indeed the case, and we did it with a very careful and scientific method, where we measured all the risk factors. We found that even when you do this, the coronary calcium test adds important prognostic information. It does assist a physician in determining who's at higher risk among the intermediate groupand that's a lot of peopleand can therefore help guide therapy in terms of lowering risk."

However, he added, "I don't think any of the coauthors are endorsing the practice of direct marketing of the test to the public."

In the current report, the researchers used data from the South Bay Heart Watch, a prospective observational population-based study of 1461 asymptomatic adults with coronary risk factors. Subjects with at least one coronary risk factor underwent CT examination between 1990 and 1992. They were then followed yearly for up to 8.5 years after the scan for the incidence of nonfatal MI or CHD death.

Of 1312 subjects with scans, the researchers excluded 269 patients with diabetes, considered to be at high risk, and another 14 participants were either missing data or had a coronary event before the baseline scan, leaving 1029 subjects for this analysis.

During a median of seven years of follow-up, 84 patients had an MI or CHD death, and 70 died of any cause. The FRS was more than 20% in 291 (28%) subjects, and 221 (21%) had a CACS of more than 300.

As expected, both the FRS alone and the CACS were able to rank participants according to CHD risk in a graded fashion, the researchers report. Compared with an FRS of less than 10%, a Framingham score of more than 20% significantly predicted the risk of MI or CHD, with a hazard ratio of 14.3 (95% CI 2.0-104, p=0.009). Compared with a CACS of zero, a calcium score of 300 or more was also predictive, with a hazard ratio of 3.9 (95% CI 2.1-7.3, p<0.001).

However, across categories of FRS, the calcium score significantly modified risk prediction in all categories among patients with an FRS of higher than 10% (p<0.001) but not in patients with an FRS of less than 10%. "The increment in predicted risk was equal to a 3% to 9% increase in 10-year event risk compared with FRS alone for every category of FRS estimate when the CACS was more than 300," they write. "Additionally, among the 316 participants with a CACS of zero, 14 coronary events were observed (4.4%); thus, absence of CACS did not preclude risk of a CHD event, as has been reported in some other studies."