Is carotid artery intima-media thickening a reliable marker of early atherosclerosis?

BACKGROUND It is widely believed that carotid artery intima-media thickening represents an early marker for the development of atheroma. However, carotid intima-media thickening might also be expected to occur in response to an increased tensile stress and decreased wall shear stress which may accompany physical exercise. DESIGN, METHODS, AND RESULTS In order to test this hypothesis 24 athletes (professional footballers) were compared to 14 age and sex matched control subjects. Each subject underwent carotid and femoral ultrasonography and echocardiography. The athletes had a greater left ventricular mass index compared with the controls: 135 (127-143) vs. 104 (91-116) g/m2, p < 0.001. In addition, they had a greater carotid intima-media thickness (IMT): 0.55 (0.52-0.57) vs. 0.51 (0.48-0.54) mm, p < 0.05. However, carotid artery diameters, femoral IMT and femoral artery diameters were similar: 6.0 (5.9-6.2) vs. 5.8 (5.6-6.1) mm, 0.43 (0.42-0.45) vs. 0.43 (0.41-0.45) mm and 8.3 (8.0-8.6) vs. 8.4 (8.0-8.7) mm, respectively. CONCLUSIONS The increased carotid IMT of the athletes may result from intermittent exposure to markedly elevated systemic arterial pressures during exercise, resulting in intermittent elevations in carotid wall tensile stress. The lack of a disparity between athletes and controls for femoral IMT may be explained by the intermittent elevation of femoral wall tensile stress being accompanied by increased femoral artery blood flow and wall shear stress, which would tend to reduce any wall thickening. This is an important observation, since it suggests that an increased carotid IMT cannot be relied on solely as a marker of early atherosclerosis.