Effect of vascular risk factors on increase in carotid and femoral intima-media thickness. Identification of a risk scale

Abstract

Background: The well established correlation between intima-media thickness (IMT) and the risk of cardiovascular and cerebrovascular events and death is usually measured in subjects with multiple vascular risk factors, which makes it difficult, after application of the usual analysis-of-variance linear combination of effects model, to establish whether each cardiovascular risk factor has, per se, an effect on IMT.

Method and results: In this study we investigated five "pure" groups of patients (865), i.e. each presenting only one of the following risk factors: hypertension, obesity, overweight, smoking, hypercholesterolaemia and a control group of 37 healthy subjects. We measured, both as discrete and as continuous variables, the following indices: intima-media thickening of the common carotid artery (IMT(C)) and of the common femoral artery (IMT(F)) and the ankle-brachial index (ABI). Descriptive statistics were used to analyse the prevalence of pathological values for the three indices in the different groups. Subsequently the entire group of 902 subjects was included in a correlation analysis in which the Pearson correlation coefficient for each pair of variables was computed. In order to assign the risk factors a continuous ranking, and obtain a more general idea of the correlation structure, principal component analysis (PCA) was used. The scores obtained from PCA made it possible to build a scale of severity of the vascular risk factors considered. All the risk factors considered were demonstrated to strongly affect the studied indices. Overweight was shown to be the least important risk factor with regard to intima-media thickening, followed by smoking, hypercholesterolaemia, hypertension and finally obesity, which emerged as the greatest risk factor.

Conclusions: The strong correlation between the indices made it possible to compute a composite general score, which provides an univocal risk estimation at single-patient level. IMT(F) was demonstrated to be the most sensitive descriptor. The construction of this risk scale has implications for preventive treatment and the frequency of instrumental examinations, allowing clear quantitative definition of the extent of the damage.