Prevalence of left atrial enlargement and its risk factors in general Chinese population

Study population

From January 2012 to August 2013, a representative sample of participants aged ?35 years
was selected to characterize the prevalence and risk factors in rural areas of Liaoning
Province, located in China. The study adopted a multi-stage, stratified, random-cluster
sampling scheme. In the first stage, three counties (Dawa, Zhangwu and Liaoyang County)
were randomly selected from Liaoning province. In the second stage, one town was randomly
selected from each county (for a total of three towns). In the third stage, 8–10 rural
villages from each town were randomly selected (for a total of 26 rural villages).
Participants who were pregnant or had malignant tumors or mental disorders were excluded
from the study, comprising a potential pool of 14,016 people. Of these, 11,956 participants
agreed and completed the present study, yielding a response rate of 85.3 %. In this
report, we used only the data from participants who completed the study, which provided
a final sample size of 10,574 subjects (4768 men and 5806 women). For the present
analysis, participants with atrial fibrillation showed by Electrocardiogram that made
diastolic function and diameter assessment unreliable with conventional Doppler technique
were also excluded.

The study was approved by the Ethics Committee of China Medical University (Shenyang,
China). All procedures were performed in accordance with ethical standards. Written
consent was obtained from all participants after they had been informed of the objectives,
benefits, medical items and confidentiality agreement regarding their personal information.
For participants who were illiterate, we obtained written informed consent from their
proxies.

Data collection and measurements

Data were collected during a single visit to the clinic by cardiologists and trained
nurses using a standard questionnaire in a face-to-face interview. Before the survey
was performed, we invited all eligible investigators to attend an organized training
session. The training included the purpose of this study, how to administer the questionnaire,
the standard method of measurement, the importance of standardization and the study
procedures. A strict test was administered after this training, and only those who
scored perfectly on the test were accepted as investigators in this study. During
data collection, our inspectors gave some further instructions and support. Data regarding
the demographic characteristics, lifestyle risk factors, dietary habits, family income
and family history of chronic diseases were obtained during the interview using the
standardized questionnaire. The study was guided by a central steering committee with
a subcommittee for quality control.

According to American Heart Association protocol, BP was measured three times at 2-min
intervals after at least 5 min of rest using a standardized automatic electronic sphygmomanometer
(HEM-907; Omron), which had been validated according to the British Hypertension Society
protocol 10] . The participants were advised to avoid caffeinated beverages and exercise for at
least 30 min before the measurement. During the measurement, the participants were
seated with their arms supported at the level of the heart. The mean of three BP measurements
was calculated and used in all analyses. Weight and height were measured to the nearest
0.1 kg and 0.1 cm, respectively, with the participants wearing light-weight clothing
and without shoes. Body mass index (BMI) was calculated as the weight in kilograms
divided by the square root of the height in meters. Fasting blood samples were collected
in the morning after at least 12 h of fasting. Blood samples were obtained from an
antecubital vein into Vacutainer tubes containing ethylenediaminetetraacetic acid
(EDTA). Fasting plasma glucose (FPG), total cholesterol (TC), low-density lipoprotein
cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), triglycerides (TGs)
and other routine blood biochemical indexes were analyzed enzymatically using an autoanalyzer.
All laboratory equipments were calibrated, and blinded duplicate samples were used
for these analyses.

Echocardiographic measurements

Echocardiograms were obtained using a commercially available Doppler echocardiograph
(Vivid, GE Healthcare, United States), with a 3.0-MHz transducer. The transthoracic
echocardiogram examinations included M-mode, two-dimensional, spectral and color Doppler,
and were performed with subjects resting in the supine position. Echocardiogram analyses
and readings were performed by three doctors specialized in echocardiography. Consultations
were made to two other specialists if any questions or uncertainty arose. The parasternal
acoustic window was used to record two-dimensional and M-mode images of the left ventricular
(LV) internal diameter, wall thickness, aortic root and left atrium (LA). The apical
acoustic window was used to record 4- and 5-chamber images. Color Doppler recordings
were adopted to identify valvular regurgitation. The correct orientation of imaging
planes and Doppler recordings were verified using previously described procedures
11], 12]. The left ventricular end-diastolic dimension (LVIDd) was obtained in the LV minor
axis at end-diastole, internal dimensions and interventricular septal thickness (IVST)
and posterior wall thickness (PWT) were measured at end of the diastole and systole
according to the recommendations of the American Society of Echocardiography 13], 14]. The LV mass was estimated by Devereux’s formula 0.8?×?[1.04 {(LVIDd?+?PWT+ SWT)
³
???LVIDd
³
}]?+?0.6 g 15] and normalized to body surface area (BSA). Left ventricular ejection fraction (LVEF)
was measured from the four-chamber apical projection by the area product?×?the ventricular
length. Two-dimensional guided M-mode measurements of the LA posteroanterior dimension
were performed from the parasternal long-axis view according to the standards of the
American Society of Echocardiography.

Definitions

Left atrial enlargement was defined as an LA diameter exceeding 4.0 cm in men and
3.8 cm in women 16]. LAE as the index by body surface area (iLAE) was defined as indexed LA diameter
exceeding 2.3 cm/m2 in both sexes 16]. Higher left ventricular myocardial index (LVMI) was defined as LVMI exceeding 115 g/m
²
in men and 95 g/m
²
in women 16]. According JNC-7 report 17], Hypertension was defined as systolic blood pressure (SBP) ?140 mmHg and/or diastolic
blood pressure (DBP) ?90 mmHg and/or use of antihypertensive medications. BMI were
categorized into 2 groups as normal (BMI 30 kg/m
²
) and obesity (BMI ?30 kg/m
²
), according to the World Health Organization (WHO) criteria 18]. Dyslipidemia was defined according to the National Cholesterol Education Program-Third
Adult Treatment Panel (ATP III) criteria 19]. Diabetes mellitus was diagnosed according to the WHO criteria 20]: FPG???7 mmol/L (126 mg/dL) and/or being on treatment for diabetes. Anemia was defined
as an hemoglobin concentration lower than 110 g/L in women and lower than 120 g/L
in men according to the China expert consensus.

Statistical analysis

Descriptive statistics were calculated for all the variables, including continuous
variables (reported as mean values and standard deviations) and categorical variables
(reported as numbers and percentages). The differences between the LAE and non-LAE
groups were evaluated using the Student’s t-test, analysis of variance, non-parametric test or the ?²â€“test, as appropriate. Multivariate logistic regression analyses and linear regression
analysis were used to identify independent factors of LAE, and odds ratios (ORs).
Linear correlation coefficient ? and corresponding 95 % confidence intervals (CIs)
also were calculated. All the statistical analyses were performed using SPSS version
17.0 software (SPSS Inc, Chicago, Illinois, USA), and P values less than 0.05 were considered statistically significant.