Interchangeability of carotid and femoral intima-media thickness in risk stratification

Background. Carotid intima-media thickness (c-IMT) is an intermediate pheno type not only for the local but also the global arteriosclerotic status, a concept which has been validated by its ability to act as a marker for futu re cardiovascular and cerebrovascular events. Whether the association betwe en c-IMT and risk factors, distant atherosclerotic disease and prognosis ar e the sole prerogative of the carotid artery, or whether these findings can be extrapolated to other arterial sites is less well studied. In view of t he concept of vascular heterogeneity, we measured the IMT in a muscular, lo wer extremity artery, the common femoral (f-IMT), and in elastic upper extr emity artery, the common carotid, in apparently healthy individuals and exp lored the relationship with risk factors and the individuals' 10-year cardi ovascular (CV) risk, calculated using the Framingham systolic blood pressur e equation. Methods. A population of 156 apparently healthy normotensive Caucasian volu nteers between 18 and 65 years was studied (mean age 43 +/- 13 years; 68 me n, 88 women; mean arterial blood pressure 126 +/- 15/70 +/- 10 mmHg). The c -IMT and f-IMT were measured using a 10 MHz vascular linear array transduce r at the far walls 1 to 2 centimetres proximal to the right common carotid and right common femoral artery bifurcations, respectively. Risk factors we re assessed and the 10-year cardiovascular risk was calculated using the Fr amingham systolic blood pressure equation. Results. The median c-IMT was 0. 52 mm (interquartile range 0.45-0.62 mm) and f-IMT was 0.52 mm (0.39-0.67). Both parameters were significantly correlated (r=0.363; p <0.01) and both were significantly correlated to the calculated 10-year CV risk (r=0.519; p <0.01 and r=0.574; p <0.01 for the carotid and c-IMT and f-IMT, respective ly). Median risk was low: 2.11% (0.27-5.50). Although measures of agreement were higher for the f-IMT versus risk (0.47) than for the c-IMT versus ris k (0.30), the former showed a significantly wider scatter with increasing a ge and with quartiles of CV risk. The c-IMT and f-IMT do not share determin ant risk factors to the same extent and with only 20% of mutual variance ex plained, cannot be regarded as interchangeable. Conclusions. Although the c -IMT and f-IMT are significantly intercorrelated and correlate to the calcu lated 10-year CV risk, they are not interchangeable. While the f-IMT is les s suited as a continuous variable for risk stratification in a low-risk pop ulation, our data suggest its possible use as a dichotomised risk marker.