Internal Carotid Artery Angle of Origin: A Novel Risk Factor for Early Carotid Atherosclerosis

Background and Purpose— Established “systemic” vascular risk factors do not fully explain the occurrence of atherosclerosis at the carotid bifurcation. Local anatomic and hemodynamic factors may also influence the initiation of the atherosclerotic process. We determined whether the angle of internal carotid artery (ICA) origin is a risk factor for early atherosclerosis. Methods— In 1300 individuals from a normal population aged 40 to 70 years, we measured both carotid intima-media thickness (IMT) at 3 arterial sites (common carotid artery; carotid bifurcation; ICA bulb) and the presence of any atherosclerotic plaque within the ICA bulb bilaterally by means of high-resolution ultrasound. A standardized transverse insonation was used to determine the angle of ICA origin, expressed as the angle of rotation relative to the external carotid artery. Results— This angle was positively associated with ICA bulb IMT but not with IMT at other sites. After we controlled for age, sex, and other cardiovascular risk factors, a dorsal/dorsomedial ICA origin (angle ≥60°) conferred an odds ratio for having an ICA bulb IMT in the highest quartile of 2.99 (95% CI, 1.86 to 4.83) on the left and 2.01 (95% CI, 1.31 to 3.09) on the right side (both P <0.001). A similar relationship was found for plaque; odds ratios on multivariate analysis were 3.67 (95% CI, 1.49 to 9.03) on the left and 2.07 (95% CI, 1.10 to 4.83) on the right side (both P =0.035). Conclusions— This study suggests that the angle of ICA origin may be an independent risk factor for early atherosclerotic changes at the ICA bulb. This new hypothesis should be tested in prospective studies.