Participants
This cross-sectional survey was conducted from June 2016 to June 2017. We prospectively recruited patients with hypertension who visited clinics. Each participant was required to complete an interviewer-led questionnaire and performed carotid artery ultrasound examinations in Anzhen Hospital, Beijing, China. The inclusion criteria were as follows: (1) patients aged 35–74 years; and (2) patients with a medical history of hypertension for a minimum of 3 months. The exclusion criteria were as follows: (1) patients with familial hypercholesterolemia; and (2) patients suffering from serious congestive heart failure, renal insufficiency and requiring dialysis treatment, and/or cancer patients. In total, 4500 subjects met the selection criteria, and 3998 subjects completed traditional risk factors survey and carotid ultrasound measurements[22]. Written informed consent was obtained from participants.
Data collection
The questionnaire concerned demographic information, medical history, and details of lifestyle. The information was collected by trained research staff. Height, weight, waist circumference and blood pressure (BP) were measured. Systolic BP (SBP) and diastolic BP (DBP) were measured using a standard mercury sphygmomanometer cuff placed on the right arm, supported at the level of the heart. Participants rested for at least 5 min in a seated position, then BP was measured twice, with a 60 s interval, and the mean of these two measurements was recorded and averaged[17, 18]. Total cholesterol (TC) and low-density lipoprotein-cholesterol (LDL-C) during the last three months were recorded in the questionnaire, or were measured if records could not be provided.
Color Doppler ultrasonography was used for carotid artery plaque. The carotid ultrasound scanning and measuring protocol was carried out using a previously described method[20, 23]. The distance between the lumen-intima and the media-adventitia ultrasound interface was measured using Hitachi Preirus Color Doppler ultrasound machine with linear array probe (at a frequency of 3 ~ 7 MHz). All subjects were scanned at six carotid sites [including 1 cm length of both side of the common carotid artery (CCA), the carotid artery bulb (bulb) and the proximal internal carotid artery (ICA)]. 12 sites were visited and measured for CCA, bulb and ICA (three sites within 1 cm for the far and the near wall of each carotid artery was measured). Intima-media thickness (IMT) was an average of 12 measurements. Three-dimensional ultrasound imaging system is Vasqscan system developed by University of Western Ontario. All operators had good experience in ultrasound scanning and measurement, and high-quality data were collected. The result was valid if subjects performed carotid artery ultrasound examinations in Anzhen Hospital within the last year.
Measurement and diagnostic criteria
Current smokers were defined as those who reported having smoked ≥ 100 cigarettes during their lifetime and were smoking every day or some days at the time of interview. Obesity was defined as a waist circumference ≥ 80 cm for women and ≥ 85 cm for men. Ischemic cardiovascular disease (ISCVD) includes ischemic stroke and coronary heart disease (CHD). A history of ischemic stroke was defined as a history of symptoms/signs such as numbness, abnormal speech, transient blindness, vertigo, nausea, deviated eyes and mouth, hemiplegia, or dribbling; consistent signs on brain computed tomography or magnetic resonance imaging; or the diagnosis of ischemic stroke by a neurologist (including cerebral thrombosis or lacunar infarction). A clinical diagnosis of CHD based on patient symptoms, electrocardiogram changes, and highly sensitive biochemical markers, as well as information gleaned from various imaging techniques, which includes history of stable angina, unstable angina and myocardial infarction. Controlled hypertension was defined as a mean SBP < 140 mmHg and a mean DBP < 90 mmHg. Cardiovascular risk score was calculated using Chinese Risk Tables, which estimate the 10-year risk of suffering CVD. The risk score for each subject classified into 0–5% risk (low risk), 5–10% risk (intermediate risk), ≥ 10% risk (high risk) [5]. A carotid plaque was defined as carotid IMT (≥ 1.5 mm, or thicker than the normal IMT value by 0.5 mm or thicker than the normal IMT value by 50%[20, 23].
Statistical analysis
Non-normally distributed variable (duration of hypertension) was presented as median (interquartile range). Normally distributed continuous variables are presented as means ± standard deviations, and independent two-sample t-test was used to compare the difference between two means. Categorical variables are presented as frequencies and percentages, and the chi-square test were used to compare differences in proportions between groups. All analyses were performed by SPSS statistical software (Version18.0, SPSS Inc., Chicago). P values of < 0.05 were considered statistically significant.