To propose a carotid index (CI) and leverage it in combination with conventional measurement parameters to evaluate the structural characteristics of the carotid arteries and their influencing factors in subjects without carotid atherosclerosis (CAS).

The results of carotid artery ultrasound examinations between September 2020 and December 2021 from the multicenter "standardized evaluation for cerebral vascular ultrasound screening in the high-risk population of stroke" database, led by Xuanwu Hospital Capital Medical University, were continuously included. The participants without CAS [intima-media thickness (IMT) ≤ 1 mm] and without cardiovascular risk factors (CRFs) were assigned to the no-CRF group (573 cases), while those with only one CRF were assigned to the CRF group (573 cases), which was further divided into hypertension (159 cases), hyperlipidemia (78 cases), diabetes (69 cases), smoking (240 cases), and coronary heart disease subgroups (27 cases). Ultrasonography was performed to measure and record IMT, common carotid artery diameter (D_CCA), carotid bulb diameter (D_CB), and internal carotid artery diameter (D_ICA). CI₁ was calculated as D_CB/D_CCA, and CI₂ was calculated as D_CB/D_ICA. Analysis of covariance was used to compare the differences in carotid structure between each CRF subgroup and the no-CRF group, and pairwise comparisons between groups were performed using the LSD test. Simple and multiple linear regression analyses were performed to identify the influencing factors of carotid structure in subjects without CAS.

Compared with the no-CRF group, the hypertension subgroup had larger D_CCA [(6.344±0.038) mm vs (6.232±0.021) mm] and D_ICA [(4.833±0.041) mm vs (4.716±0.022) mm] and smaller CI₁ (1.106±0.008 vs 1.135±0.004) and CI₂ (1.459±0.012 vs 1.511±0.006), the hyperlipidemia subgroup had larger CI₁ (1.175±0.012 vs 1.135±0.004) and CI₂ (1.553±0.017 vs 1.135±0.004), and the diabetes subgroup had smaller D_CB [(6.820±0.076) mm vs (7.040±0.028) mm] and CI₂ (1.466±0.017 vs 1.511±0.006); the differences were all statistically significant (P_hypertension=0.011, 0.012, 0.002, and 0.011; P_{hyperlipidemia}=0.002 and 0.017; P_diabetes=0.007 and 0.015, respectively). Simple linear regression analysis showed that D_CCA, D_CB, and D_ICA were all significantly and positively correlated with IMT (β=1.139, 0.847, and 0.749, respectively, all P<0.001). Multiple linear regression analysis showed that IMT, age, male gender, body mass index (BMI), and hypertension were independent influencing factors of D_CCA (β_IMT=0.490, β_age=0.013, β_male=0.202, β_BMI=0.017, β_hypertension=0.094, all P<0.05); age, male gender, BMI, and diabetes were independent influencing factors of D_CB (β_age=0.014, β_male=0.280, β_BMI=0.017, β_diabetes=-0.225, all P<0.05); IMT, age, male gender, and hypertension were independent influencing factors of D_ICA (β_IMT=0.268, β_age=0.008, β_male=0.136, β_hypertension=0.108, all P<0.05); IMT, left side, hypertension, and hyperlipidemia were independent influencing factors of CI₁ (β_IMT=-0.061, β_left=0.016, β_hypertension=-0.027, β_{hyperlipidemia}=0.041, all P<0.05); and hypertension, hyperlipidemia, and diabetes were independent influencing factors of CI₂ (β_hypertension=-0.050, β_{hyperlipidemia}=0.043, β_diabetes=-0.043, all P<0.05).

The CI may serve as a novel parameter for quantitatively assessing carotid artery structure with potential clinical value. Among subjects without CAS, carotid artery diameters are segmentally affected by age, sex, BMI, side, hypertension, hyperlipidemia, and diabetes.