Population
All residents who lived in the Shi Jing Shan District of Beijing and who were aged > 40 years were invited to participate. The investigation methods have been published previously [6]. Of 5593 subjects, 1069 volunteered to participate. The investigation started in 2004 and ended in 2005. Participants who underwent echocardiography were recruited, while participants who had regional wall movement abnormalities, moderate or severe aortic valve stenosis, rheumatic heart disease, or congenital heart disease were excluded. Finally, 1032 participants were included. The study was approved by the institutional review board of Peking University First Hospital, and informed consent was obtained from all participants.
Definition of cardiovascular risk factors and disease
The methods used to measure height, weight, blood pressure, heart rate, fasting blood glucose, oral glucose tolerance, and blood lipid concentrations have been described previously [7]. Current smokers and participants with a history of smoking were defined as smokers. Hypertension was defined as a systolic blood pressure of ≥ 140 mmHg and/or a diastolic blood pressure of ≥ 90 mmHg or a history or usage of antihypertensive drugs. Diabetes mellitus was diagnosed according to each participant’s history. Participants with a fasting blood glucose concentration of ≥ 7.0 mmol/L and a 2 h glucose concentration of ≥ 11.1 mmol/L were also defined as having diabetes mellitus. BMI ≥ 28 kg/m2 was defined as obesity. Stroke, including intracerebral hemorrhage, cerebral infarction, and transient ischemic attack, was defined by the patient’s history. A history of myocardial infarction, percutaneous coronary intervention, and coronary artery bypass grafting were all included in coronary heart disease (CHD).
Echocardiography
Echocardiography was performed using a 3 MHz transducer and an ultrasound system (Vivid-7; General Electric). According to previously published guidelines [8], standard images were collected and stored. One experienced clinician who was blinded to the clinical picture of the participants measured the echocardiography parameters at the central laboratory of Peking University First Hospital.
For the patients without BSH, LV end-diastolic dimension (LVEDD), LV end-systolic dimension and wall thicknesses (LVESD) including middle IVS thickness (MIVST), and LV posterior wall thickness (LVPWT) were measured at the mitral chordae level by parasternal long-axis view by 2 D method according to ASE guideline [8], basal interventricular septal thickness (BIVST) was measured simultaneously. For the patients with BSH, MIVST, LVPWT, LVEDD and LVESD were measured below the basal hypertrophy where the septal thickness was uniform, maximal BIVST thickness was measured simultaneously. LVEF was calculated by Teichholtz method. Left atrial diameter (LAD) was anteroposterior (AP) linear dimension obtained from the parasternal long-axis view in 2D image according to ASE guideline [8]. LV mass (LVM) was calculated as follows: LVM = 0.8 × 1.04 × ([PWTd + SWTd + LVIDd]3 − [LVIDd]3) + 0.6 g, where PWTd and SWTd are the posterior and middle septal wall thicknesses at LV end-diastole, respectively, and LVIDd is the LV dimension at end-diastole. LVM index (LVMI) was then calculated, as previously described [8].Relative wall thickness (RWT) was calculated using the following formula: (2 × LV PWT) ÷ LVEDD. An LVMI > 115 g/m2 (male) or > 95 g/m2 (female) was defined as increased LVMI, and RWT > 0.42 was defined as increased RWT as well. Normal geometry is defined as increased LVMI = 'NO' and increased RWT = 'NO' while concentric remodeling as increased LVMI = 'NO' and increased RWT = 'YES'. Concentric hypertrophy is defined as increased LVMI = = 'YES' and increased RWT = = 'YES' while eccentric hypertrophy as increased LVMI = 'YES' and increased RWT = 'NO' [8]
BSH was defined when all three of the following criteria were fulfilled [8]: (1) a basal IVS thickness ≥ 14 mm; (2) a basal IVS thickness/mid IVS thickness ≥ 1.3; and (3) no wall motion abnormalities or scarring in the middle septum that could result in isolated septal thickening.
Statistical analysis
Continuous data with normal distribution are presented as mean ± standard deviation, while presented as median plus quartile when the data are abnormal distribution. Count data are presented as percentages. Student t test was used to compare between the two groups when continuous data are normal distribution. Continuous data were compared between the two groups using non-parametric test (Median Test for k samples) when the data are abnormal distribution. Categorical data were compared between the two groups using the Chi square test or the Fisher’exact test if needed.
Multivariable logistic regression was used to analyze the relationship between BSH, the increase in LVMI, and the increase in RWT, adjusting for age, sex, obesity, hypertension, diabetes mellitus, and heart rate concerned about univariable logistic regression analysis results and clinical significance. Subgroup analyses and interaction tests were used to examine the relationship between BSH and the increase in RWT according to age (< 60 years and ≥ 60 years), sex (male and female), BMI (< 24 kg/m2 and ≥ 24 kg/m2), diabetes mellitus (yes or no), CHD (yes or no), stroke (yes or no), and smoking status (yes or no) by multivariable logistic regression. The intraclass correlation coefficient was used to evaluate intra-observer consistency. A two-sided p value of < 0.05 was considered statistically significant for all tests. All analyses were performed using statistical software (Empower (R) [www.empowerstats.com]; X&Y solutions, Inc., Boston, MA, USA; R [http://www.R-project. org] v3.4.3; SPSS v13.0).
