The role of atherosclerosis imaging in redefining normal and abnormal cholesterol values, and risk reduction in primary prevention statin trials

The emergence of atherosclerosis imaging, using coronary calcium scanning (CAC) and carotid intima media thickness (CIMT) and plaque as stronger predictors of cardiovascular events than risk factors of atherosclerosis, has created a paradigm shift in the primary prevention of cardiovascular disease. Rather than population-derived indices to define normal or abnormal low-density lipoprotein (or other lipid values) in the untreated individual patient, it is more appropriate to define "normal" as "cholesterol values at which level there is no subclinical atherosclerosis" and "abnormal" as "cholesterol values at which level there is subclinical atherosclerosis," with the severity of "abnormal" depending on the degree of subclinical atherosclerosis. Similarly, the low-density lipoprotein treatment goal is the level at which atherosclerosis progression is halted. Extension of the subclinical atherosclerosis risk-based paradigms to primary prevention trials dramatically changes the manner in which trials should be conducted in the future, as well as the results of trials already performed. For example, asymptomatic patients with a CAC score of 0 have an extraordinarily low event rate but have been included in primary prevention statin trials even though their risk without treatment is very small. Reanalysis of the statin primary prevention trials after excluding the percentage (40%) of patients who would be expected to have a CAC score of 0 yields an absolute risk increase of 60% in both the placebo group (from 5.4% to 8.5%), and the statin group (from 3.0% to 4.8%). Absolute risk reduction increased by 58% (from 2.4% to 3.8%). Relative risk reduction of 44% was unchanged. In conclusion, 1) the presence or absence of atherosclerosis as measured by CAC redefines normal or abnormal lipid levels in an individual patient; 2) statin absolute risk reduction is significantly greater than previously appreciated; and 3) patients with a CAC score of 0 should be excluded from primary prevention randomized controlled trials.