The incidence of subclinical atherosclerosis in subjects with low and moderate cardiovascular risk

Abstract Background The cardiovascular risk models and subclinical atherosclerotic indicators are both recommended for cardiovascular risk stratification. The accordance between the incidence of subclinical atherosclerosis and subjects with low and moderate cardiovascular risk is unclear. Hypothesis Subjects with low and moderate cardiovascular risk have a lower incidence of subclinical atherosclerosis compared with subjects with high risk. Methods Brachial‐ankle pulse wave velocity (BaPWV) and brachial flow‐mediated dilation (BFMD) were measured in 421 subjects without a history of atherosclerotic cardiovascular disease (ASCVD) from October 2016 to January 2020. All subjects were classified into low, moderate, and high risk based on Framingham and China‐par risk models respectively. Results Mean age was 57.05 ± 9.35 years and 248 (58.9%) were male. In subjects with low, moderate, and high risk assessed by Framingham and China‐par risk models, the percentage of abnormal BaPWV ( > 1400 cm/s) was 42.9%, 70.1%, 85.7%, and 40.4%, 71.4%, 89.7%, respectively. Meanwhile, the percentage of abnormal BFMD ( ≤ 7%) was 43.8%, 68.5%, 77.3%, and 44.9%,72.1%, and 76.6%. According to Framingham‐based high‐risk categories, positive predictive value (PPV), negative predictive value (NPV), sensitivity and specificity for BaPWV abnormality were 85.7%, 39.4%, 36.1%, and 87.5%, respectively. For BFMD abnormality, the values were 77.3%, 40.1%, 34.1%, and 81.8%, respectively. According to China‐par high‐risk categories, the values for BaPWV abnormality were 89.7%, 43.8%, 45.6%, and 89.0%, respectively. For BFMD abnormality, the values were 76.6%, 41.3%, 40.7%, and 77%, respectively. In multivariate analysis, age and blood pressure were the independent predictors for subclinical atherosclerosis in subjects with low‐moderate risk. Conclusions More than one‐half of subjects with low and moderate risk already have detectable subclinical atherosclerosis, indicating higher cardiovascular risk beyond the traditional stratification.


| INTRODUCTION
2][3] To prevent ASCVD, risk stratification models have been recommended in the current guidelines to guide the primary prevention. 4,5For example, the Framingham Heart Study developed the first ASCVD risk model based on traditional risk factors in the American population in 1976, 6,7 which has been widely used in primary prevention.Recently, the China-par risk model has been validated in the prediction for 10-year ASCVD risk in Chinese population. 80][11] For example, Murphy et al. found that 75%-87% of myocardial infarction (MI) or coronary death occurred in populations with low and moderate risk. 9Brindle and Orford reported that about 40% of major adverse cardiovascular and cerebrovascular events (MACCEs) occurred in individuals with Framingham model-based low and moderate risk. 10,11 recent years, some subclinical atherosclerotic indicators, reflecting either structural or functional damage in the arterial wall, have been demonstrated to effectively predict future cardiovascular risk in individuals without prior history of ASCVD.
For example, a meta-analysis showed that arterial stiffness, expressed as pulse wave velocity (PWV), predicts the incidence of future cardiovascular disease (CVD), and improves risk classification. 12Moreover, the abnormal flow-mediated dilation (FMD), which reflects endothelial dysfunction, may present higher cardiovascular risk in the future. 13Therefore, a series of subclinical atherosclerotic indicators have been used to improve the accuracy of risk stratification. 5,14 this study, subjects without ASCVD were classified into low-, moderate-, and high-risk groups by the Framingham and China-par risk models separately.PWV and FMD were measured as subclinical atherosclerotic parameters.We aim to investigate the accordance between the incidence of subclinical atherosclerosis and subjects with low and moderate cardiovascular risk.

| Study population
Subjects, who had measurements of brachial-ankle pulse wave velocity (BaPWV), and brachial flow-mediated dilation (BFMD) in Health Management Center, Xuanwu hospital Capital Medical University from October 2016 to January 2020, were included in the current study.
Subjects were excluded if (1) subjects were younger than 30 years old or older than 74 years old; (2) subjects had a history of MI, percutaneous coronary intervention, ischemic stroke, hemorrhagic stroke, transient ischemic attack which were acquired by subjects' medical records; (3) lumen diameter stenosis is higher than 50% in coronary artery as determined by coronary angiography (CAG); (4) lumen diameter stenosis is higher than 50% in intracranial artery as determined by transcranial color doppler ultrasound (TCCD); (5) lumen diameter stenosis is higher than 50% in peripheral artery as determined by peripheral arterial ultrasonography.Informed consent forms were signed by all subjects.

| Measurement of BaPWV
We measured BaPWV by a volume plethysmographic method using automatic waveform analyzer.Before measurements, patients were required to be in the supine position and rest for at least 5 min.Cuffs were wrapped around both upper arms and ankles.BaPWV was calculated by measuring the time for the pulse wave to travel between the brachial and posterior tibial arteries. 15The maximum value of the left and right BaPWV was used in the statistical analyses.BaPWV＞1400 cm/s was regarded as abnormal BaPWV. 16

| Measurement of BFMD
The subjects remained supine throughout the study.Vasodilator responses in the brachial arteries were measured using B-mode ultrasound images with a 7.5-MHz linear array transducer.The brachial artery was scanned in the antecubital fossa in a longitudinal fashion.After baseline measurements of the diameter and flow velocity in the brachial artery, a blood pressure (BP) cuff was placed around the forearm and inflated to a pressure of 250-300 mmHg for 5 min, and then released.Diameter measurements during reactive hyperemia were taken 45-90 s after cuff deflation.The changes in vessel diameter in response to reactive hyperemia (FMD) were expressed as a percentage increase in diameter from the baseline value. 17BFMD ≤ 7% was seen as abnormal BFMD. 18

| Calculation of ASCVD risk scores
Framingham general CVD risk model was designed for 10-year risk prediction about ASCVD events including coronary death, MI, coronary insufficiency, angina, ischemic stroke, hemorrhagic stroke, transient ischemic attack, peripheral artery disease, heart failure.Risk categories were defined as low-risk ( ≤ 6%), moderate-risk (6%-20%), and high-risk ( > 20%) groups according to the Framingham Heart Study. 7China-par risk model evaluated ASCVD (nonfatal acute MI or coronary heart disease death or fatal or nonfatal stroke) events during the next 10 years.

| Statistical analysis
Continuous variables were described as mean ± standard deviation or median (interquartile range), and differences among the groups were assessed by the independent t test or the Wilcoxon rank-sum test.Categorical variables were described as number (n) with percentage (%), and differences were analyzed by the χ 2 test or Fisher exact test.For subclinical atherosclerosis, the sensitivity and specificity of ASCVD risk models were evaluated by receiver operating characteristic curve analysis.The relationship between subclinical atherosclerosis and risk factors was evaluated by multivariable logistic regression analysis.We included the following covariates in the multivariate analysis: age, gender, SBP, DBP, hypertension, smoking, diabetes mellitus, TC, HDL-C.SPSS version 22.0 (IBM Corp.) was used for statistical analysis, and a p value < .05 was defined as the threshold of statistical significance.
T A B L E 1 Clinical characteristics of subjects.

| DISCUSSION
In this study, we evaluated ASCVD risks through risk models and measured BaPWV and BFMD in each risk category.In the high-risk group, the majority of subjects (76.6-89.7%)had abnormal BaPWV and BFMD.More importantly, the abnormal BaPWV and BFMD also appeared in 40.4%-44.9% of the low-risk group and 68.5%-72.1% of the moderate-risk group, indicating the existence of structural or functional damage in the artery.We also found age and BP were independent predictors for abnormal BaPWV and BFMD in the lowto moderate-risk group.
The relationship between subclinical atherosclerotic parameters and China-par risk groups.

T A B L E 2
The accuracy of subclinical atherosclerosis among low-to moderate-risk group and high-risk group.ASCVD risk models, such as Framingham and China-par risk models, have been recommended in the current guidelines to predict the risk of future cardiovascular events and guide the primary prevention. 4,50][11] Orford et al. found the Framingham risk model underestimated the incidence of cardiovascular events in the very low-risk group ( < 5%). 11By comparing observed events rates with events rates predicted by the Framingham risk model in 1700 subjects, the Whickham (UK) study found the two rates were similar in the highrisk population, but the events rates were underestimated by the Framingham risk model in those at low-and moderate-risk populations. 19Moreover, recent studies investigated the relationship between predicted cardiovascular risk and subclinical atherosclerotic injury. 20,21According to Eleid's study, 43% of subjects in the low-risk group and 62% of subjects in the moderate-risk group had carotid plaque or thickening of carotid intima-media. 20Canpolat et al. also found that 33.8% of subjects with low-risk scores had coronary atherosclerotic plaque. 21In our study, Framingham and China-par risk models were used to predict cardiovascular risk, and the abnormal BaPWV and BFMD, reflecting arterial stiffness and endothelial dysfunction separately, were defined as subclinical atherosclerosis.The majority of subjects in the high-risk group had abnormal BaPWV and BFMD.Whereas more than half of the subjects in the low-to moderate-risk group also had subclinical

atherosclerosis. Previous studies have demonstrated that abnormal
BaPWV was closely associated with twofold risk of coronary heart disease and stroke, 16 and per percent point decreasing in BFMD indicated a significant 10% higher risk of cardiovascular events. 22nce, the low-and moderate-risk populations with subclinical atherosclerosis may have higher cardiovascular risk than that initially assessed by ASCVD risk models.
The reasons for the poor performance of ASCVD risk models in subjects with low-and moderate risk are still uncertain.Generally, risk models were developed based on traditional risk factors, including age, gender, waist circumference, diabetes, smoking, BP, TC, and HDL cholesterol.It is likely that the existence of nontraditional risk factors, such as inflammatory and metabolic abnormality, may contribute to subclinical atherosclerotic injury and subsequent higher risk of cardiovascular events. 23For example, higher levels of high sensitivity C-reactive protein (hsCRP) and | 1265 5][26] High level of lipoprotein (a) (Lp[a]), an indicator of remnant metabolic risk, is an independent predictor for subclinical coronary atherosclerosis 27 and is associated with a 48% increased risk of MI after adjustment for traditional risk factors. 28In addition, risk scores are modifiable.The scores vary with the changes in traditional risk factors, such as BP, blood lipid, and other parameters.A single risk score only reflects the cardiovascular risk at that time, but cannot reveal the dynamic changes of cardiovascular risk.Whereas subclinical atherosclerosis directly reflects the injury of comprehensive risk factors on the artery wall.Previous studies have demonstrated that subclinical atherosclerosis was closely associated with the higher risk of future ASCVD events. 16,22Thus, the combination of ASCVD risk models and subclinical atherosclerotic parameters may be more accurate to predict cardiovascular risk than applying ASCVD risk models alone.
The risk models were used to classify populations into low-, moderate-, and high-risk groups in current guidelines.Then, the primary prevention strategies were offered respectively. 5,14Intensive interventions are required for high-risk populations to reduce cardiovascular risk.
For low-to moderate-risk subjects, routine prevention strategies were appropriate to maintain their low-to moderate-risk status. 5 However, for those low-and moderate-risk populations with subclinical atherosclerosis, intensive interventions may also be needed to slow, halt, or even reverse the progression of atherosclerotic injury. 29Takamitsu et al. 30 showed that after achieving the optimal goals of traditional risk factors, subjects with improvement in either BaPWV or BFMD alone tended to reduce 69% risk for cardiovascular events, and subjects with improvement in both BaPWV and BFMD had 86% reduced risks.
Therefore, it may be reasonable to combine ASCVD risk models and subclinical atherosclerotic parameters to guide prevention strategies, especially for subjects with low and moderate cardiovascular risk.
According to our findings, age and BP were independent predictors for subclinical atherosclerosis in low-to moderate-risk population after adjustment for various risk factors.were consistent with our study. 31In addition, our study found that low levels of BP were closely associated with low incidence of subclinical atherosclerosis.The systolic blood pressure intervention trial study 32 and the strategy of blood pressure intervention in the elderly hypertensive patients) trial 33 have demonstrated that targeting lower levels of systolic BP resulted in lower rates of MACCEs.Future studies and more evidence are needed to determine whether controlling BP strictly can reduce the risk of subclinical atherosclerosis.
In our study, more than half of the populations with no evidence of atherosclerosis, evaluated by vascular imaging tests, already have abnormal BaPWV or BFMD.Populations with abnormal BaPWV and BFMD had a higher risk of cardiovascular events in the future. 12,13us, those people, who had abnormal BaPWV and BFMD, may need more strict prevention strategies, even if they did not have <50% stenosis atherosclerosis.

| Limitations
The current study examines the incidence of subclinical atherosclerosis in subjects with low and moderate cardiovascular risk assessed by ASCVD risk models.However, this study has some limitations.First, this was a single-center observational study, which may lead to data bias.Second, we do not have follow-up data for subclinical atherosclerosis.Thus, we are not sure whether intensive interventions can improve subclinical atherosclerotic indicators.Third, subclinical atherosclerosis includes various parameters, such as BaPWV, BFMD, coronary artery calcium (CAC), and carotid plaque.Our study only analyzed the BaPWV and BFMD.Fourth, 114 of the included subjects did not finish the vascular imaging tests, and we were not sure whether these subjects have <50% stenosis atherosclerosis.

| CONCLUSIONS
Considerable subjects with low-to moderate cardiovascular risk already have abnormal BaPWV and BFMD, indicating higher cardiovascular risk beyond the stratification based on ASCVD risk models.The combination of ASCVD risk models and subclinical atherosclerotic parameters may be more accurate to predict cardiovascular risk and guide prevention strategies than applying ASCVD risk models alone.
We collected demographic characteristics (including age, sex, body mass index [BMI], waist circumference, state of smoking and history of diseases [family history of ASCVD, hypertension, diabetes mellitus]), systolic blood pressure (SBP), diastolic blood pressure (DBP), laboratory results (blood glucose, blood uric acid, total cholesterol [TC], triglyceride, high-density lipoprotein cholesterol [HDL-C], low-density lipoprotein cholesterol [LDL-C]) and subclinical atherosclerotic parameters (BaPWV and BFMD) from subjects' medical records and questionnaires.Laboratory examinations were conducted when subjects were fasting for at least 8 h.
T A B L E 3 Relationship between subclinical atherosclerosis with risk factors in low-to moderate-risk population.
Tomiyama et al. included 12 517 subjects to evaluate the influences of age on BaPWV and the results