Coronary artery calcium and cardiac events: is electron-beam tomography ready for prime time?

Cardiovascular diseases in general and coronary artery disease in particular remain the number one cause of death and disability in all industrialized and many emerging countries all over the world. There has been considerable interest in developing better methods to predict future events so that preventive therapy can be targeted toward those at increased risk. Although in excess of 300 risk factors have been identified, most are highly collinear with each other, such that they are not independent. The number of independent risk factors is relatively small. Perhaps the best prediction algorithm for people who are at risk but who have not had a previous event is the Framingham risk score.1 The Framingham score, which measures age, sex, total cholesterol, high-density lipoprotein cholesterol, cigarette smoking, and systolic blood pressure, has been incorporated into the National Cholesterol Education Program Adult Treatment Panel III guidelines, and thus has been recommended to help guide therapy.2 There is recognition that the Framingham risk score is limited. It has been evaluated with a c index. The c index is equivalent to the area under a receiver-operator characteristic curve, and measures for any pair of patients, one who has an event and one who has not, the fraction of pairs correctly identified. A c index of 0.5 is equivalent to chance and a c index of 1.0 is perfect discrimination. The Framingham score has a c index of 0.68 to 0.77, depending on the exact specifications of the model.2 Clearly, there has been interest in improving the ability to predict future events. Recently, C-reactive protein (CRP), a measure of inflammation, has been shown to predict future events, to be independent of other risk factors in the Framingham score, and to be a more powerful predictor of events than low-density lipoprotein cholesterol.3 There is also interest in determining whether measures of oxidative stress, such as myeloperoxidase or nitrotyrosine, can also predict events, although the data for measures of oxidative stress remain less certain than measures of inflammation.4,5