The results of this large prospective study of middle-aged and older Chinese indicate that elevated carotid IMT measurements significantly predict an increase risk of CHD and stroke in healthy Chinese, independent of other cardiovascular risk factors. These data provide useful information on the potential utility of IMT measurements and carotid sonography in screening subclinical cardiovascular disease in populations with relatively low CHD but high stroke risk.
Carotid sonography has been recommended as a screening tool for future cardiovascular events among high-risk populations, such as elderly adults
, type 2 diabetics
or stable CHD patients
. Updated consensus has proposed the standards for measurement of IMT and plaque in the carotid artery
. However, there is a disagreement regarding the use of these measurements as screening tool in the general population
. And it has been recommended that more data need to be collected for different ethnic groups. Our study has partially filled this gap.
Carotid artery IMT and plaque stenosis, as markers of subclincial atherosclerosis, reflect not only early atherosclerosis but also compensatory enlargement with medial hypertrophy as a result of smooth muscle cell proliferation reactions
. Because atherosclerosis develops in men at an earlier stage, carotid IMT is greater in men than in women. Common and internal carotid artery IMT progression has been related to several cardiovascular risk factors including smoking, hypertension and hyperglycemia 
. In the stiffer arteries such as ICA, systolic blood pulse is augmented by fast travel of pulse wave and the blood flow velocity is reduced in diastole, further accelerating lipid deposition and local inflammation and results in increasing thickness of intima medial layers in ICA
Clinical observations suggested that the higher blood pressure and vascular wall shear stress on the left carotid artery resulted in higher common carotid IMT on left side
; however, the side difference was only limited to CCA and did not affect the prediction of subsequent cardiovascular events
. Our study did not show differential effects of measurements from different sides on CVD risk. Also, there were no appreciable gender, age, smoking, hypertension, obesity and hyperlipidemia differences in the role of IMT for predicting risk of CHD and stroke. Nevertheless, our findings showed a slightly higher risk for CHD and stroke for ICA than for CCA, but the difference was small.
Several cohort studies have explored the association between carotid artery IMT and the incidence of CHD and stroke in Western populations
. After one year follow-up among 1257 middle-aged Finnish men, common carotid IMT was associated a 3.3-fold increased risk for CHD event
. In the Rotterdam Elderly Study including 7983 participants older than 55 years and follow up for 6 years, common carotid IMT was a significant predictor for stroke and CHD
. Chambless and colleagues demonstrated that the combined CCA and ICA measurements were significant predictors of CHD among 15792 middle-aged adults in the Atherosclerosis Risk in Community cohort
. In another study based on 5858 older adults (65 years of age or older) and 6 year of follow-up , O'Leary and colleagues demonstrated that both common and internal carotid IMT measurements were significant predictors of CHD and stroke
Few studies have examined the role of carotid IMT in predicting CVD events in Asian populations
. In a study of Japanese diabetic patients, carotid IMT was associated with increased CHD events during a 3-year follow up 
. Among 298 elderly Japanese (older than 75 years, average 80 years), carotid IMT was associated with increased cardiovascular death and total mortality during 3 years of follow-up
. Our study provided strong evidence that carotid IMT significantly predicts CHD and stroke in a community-based healthy Chinese population. Furthermore, our findings were compatible with a recent meta-analysis results which showed one standard deviation of IMT difference increased a 1.26-fold risk for CHD and a 1.32-fold risk for stroke 
Carotid plaque provided additional information for cardiovascular risk prediction because the plaque score reflects the severity of irregular morphology and lumen narrowing
. Carotid plaque was reported to be associated with local inflammation and biomechanical stress
and was considered as a marker of advanced atherosclerosis. Furthermore, ethnic variation in carotid plaque severity has been demonstrated and African Americans men appear to have appreciably lower carotid plaque than white men.
Cross-sectional studies found that carotid plaque was significantly associated with prevalence of CHD
, and the prospective cohort data suggested that carotid plaque predicted future risk of ischemic stroke among 1939 U.S. adults
and among 1289 elderly Japanese men
. Our findings suggested that the carotid plaque was significantly associated with risk of CHD and stroke, but the association was largely explained by IMT.
To our knowledge, this is the first extensive investigation of carotid artery structure and risk of CHD and stroke among Chinese. Because of the prospective cohort design, the baseline measurements of our cohort members were unlikely to be affected by disease status. Furthermore, the use of a community-based population could reduce the possibility of selection bias. We also included important covariates including socioeconomic status, lifestyle factors, and well-established CVD risk factors including hypertension, diabetes, blood lipid profiles and the metabolic syndrome. Adjustment for these variables did not diminish the role of IMT in predicting CHD or stroke.
Our study had several potential limitations. First, the number of incident cases of CHD and stroke events was relatively small, even with more than a decade's follow up, which would reduce the power to detect the subtle differences between common and internal carotid artery IMT and make the relative risk estimation unstable. However, the 95% confidence intervals for the estimated relative risks were narrow and tests for linear trends were significant for our exposure variables. Second, we did not measure functional parameters such as resistance index, which might be useful for further risk stratification. In addition, there was no formal comparison of our results to those from other racial/ethnic groups. Nonetheless, our findings added to the existing literature about the role of carotid atherosclerosis for further cardiovascular risk.
In conclusion, we demonstrate that IMT and carotid plaque were associated the risks of CHD and stroke among Chinese. Because of only moderate correlation coefficients between carotid artery measurements and traditional vascular risk factors, the carotid artery measurements especially IMT can be useful for comprehensive evaluation of cardiovascular risk in Asian populations.