Complicating factors in evaluating coronary artery atherosclerosis.

The most commonly used morphological descriptors of coronary artery atherosclerosis are cross-sectional intimal area and "percent stenosis." Cross-sectional intimal area, i.e. plaque area, describes lesion size, without normalizing for differences in arterial size. "Percent stenosis" describes the percentage of the area within the internal elastic lamina that is occupied by plaque. When using intimal area and percent lumen stenosis data from atherosclerosis regression experiments there may be interpretational difficulties not only in determining the extent to which atherosclerosis has regressed, but also in whether or not regression has occurred. Specifically, if there if a minimal decrease in intimal area, i.e. little or no regression of atherosclerisis, and the artery becomes larger, percent lumen stenosis will decrease, in some cases substantially, indicating improvement or "regression" of the disease. In experiments where the age, body and heart weights of baseline animals are different from those of the regression animals, part of the improvement that is seen in "percent stenosis" may be attributable to animal growth and part to an actual decrease in intimal area. A particularly interesting, complicating factor is the apparent effect of atherosclerosis on arterial size. In an atherosclerosis progression experiment we compared coronary arteries from cynomolgus monkeys fed either a control diet or an atherogenic diet for 36 months. Ages, body weights and heart weights were similar between the groups. The animals fed the atherogenic diet had much larger coronary artery intimal areas, but also had considerably larger coronary arteriese as indicated both by area enclosed by the internal elastic lamina and lumen area. These findings suggest that in growing animals atherosclerosis may result in increased arterial size and thereby complicate interpretations of atherosclerosis progression and regression experiments.