Subjects
After a routine health check-up between September 2007 and January 2009, a total of 1,680 subjects were initially eligible for cross-sectional analysis. During the follow-up from February 2013 to September 2013, 181 people were lost to follow-up due to various reasons. Finally, 1,499 subjects with complete data were included in the 5-year follow-up analysis (follow-up rate 89.2%). During the follow-up from June 2017 to September 2018, 174 people were lost to follow-up, and eventually 1,325 subjects completed the follow-up (follow-up rate 89.2%). The research protocol of this project was approved by the ethics committee of the General Hospital of the PLA, and each subject provided informed written consent. The median follow-up interval for the original subjects was 9.5 years. During these visits, all participants received a questionnaire survey. Physical examinations, biochemical indicators, and biomarkers (including hs-cTnT) were reviewed at the same time. Any event reported was subject to verification through medical records, death certificates, pathological autopsy results and objective coronary angiographic examination results and were jointly judged by two clinically experienced doctors.
Clinical data collection
Height (cm) and weight (kg) were measured. Systolic and diastolic blood pressures (SBP and DBP) were measured in the right arm twice in a sitting position after 5 min of rest. Blood samples were collected from participants after an overnight fast. Concentrations of fasting blood glucose (FBG), total cholesterol (TC), triglycerides (TGs), low density lipoprotein cholesterol (LDL-C), high density lipoprotein cholesterol (HDL-C), homocysteine (Hcy), and uric acid The Roche Diagnostics GmbH (Roche Diagnostics GmbH, Mannheim, Germany) was used to detect on the Roche Diagnostics, Indianapolis, Indiana; the serum creatinine (Scr) was tested on the Hitachi 7600 by the Roche Diagnostics GmbH (Roche Diagnostics GmbH). (Hitachi, Tokyo, Japan); high-sensitivity C-reactive protein (hs-CRP) was detected on a Diension RxL Max analyzer (Siemens Healthcare Diagnostic) using an immunoassay method kit (Siemens Healthcare Diagnostic, USA, IN); N-terminal B-type brain natriuretic peptide (NT-proBNP) was detected on an autoanalyzer using the electroluminescence method using a Roche Diagnostics GmbH (Roche Diagnostics GmbH); hs-cTnT) was measured using the Elecsys Troponin T high-sensitivity kit (Roche Diagnostics GmbH, Mannheim, Germany) by a laboratory professional using an electroluminescence immunoassay method on a Modular Analytics E170 (Roche Diagnostics) instrument. The concentration unit of hs-cTnT is pg/mL, and the coefficient of variation between batches is 8% at 10 pg/mL and 2.5% at 100 pg/mL [9].
Definition of variables
Body mass index (BMI): weight (kg)/height2 (m2).
Hypertension: SBP ≥ 140 mmHg and/or DBP 90 mmHg or those who have taken antihypertensive drugs.
Diabetes mellitus: fasting venous blood glucose ≥ 7.0 mmol/L, OGTT test with 2 h blood glucose ≥ 11.1 mmol/L, symptoms of hyperglycemia and random blood glucose ≥ 11.1 mmol/L, or receiving hypoglycemic treatment [10].
Estimated glomerular filtration rate (eGFR): 141 × min (Scr/k,1)α × max (Scr/k,1)-1.209 × 0.993Age × 1.018 (if female) × 1.159 (if Black), where Scr is plasma creatinine (mg/dL), k is 0.7 for females and 0.9 for males, α is -0.329 for females and -0.411 for males, min indicates the minimum of Scr/k or 1, and max indicates the maximum of Scr/k or 1.
hs-cTnT: The lowest detectable concentration according to the kit instructions is 3 pg/mL (according to the reagent instructions), which is used as the cut-off value in this study. Therefore, hs-cTNT levels ≥ 3 pg/mL are considered measurable. The 99th percentile for the hs-cTnT of a group of healthy people aged 20 to 70 years was 14 pg/mL [11], and hs-cTnT concentrations ≥ 14 pg/mL were generally considered to be elevated.
All-cause mortality was determined by review of death certificates. The definition of MACE comprised nonfatal myocardial infarction, newly diagnosed CHD (identified by coronary artery imaging or receiving coronary revascularization), stroke (ischemic or hemorrhagic) and cardiovascular mortality.
Cardiovascular death was defined as deaths related to atherosclerotic heart disease (fatal myocardial infarction and definite fatal coronary heart disease), cerebrovascular disease deaths (fatal stroke), and causes including heart failure death from other atherosclerotic and cardiovascular diseases [12].
Cardiovascular events were defined as cardiovascular death, nonfatal myocardial infarction, coronary revascularization, coronary heart disease and stroke confirmed by coronary imaging [13].
Coronary heart disease events were defined as coronary heart disease death, nonfatal myocardial infarction, coronary revascularization, and coronary heart disease diagnosed by coronary imaging.
Stroke was defined as acute, focal damage to the central nervous system caused by vascular causes, which results in neurological deficits, including cerebral infarction (rather than internal hemorrhage) and subarachnoid hemorrhage [14].
Statistical analyses
Continuous variables are expressed as the mean or median (interquartile range) ± standard deviation (SD) and dichotomous variables are expressed as percentages. Analysis of continuous variables was performed by t test, and analysis of categorical variables was performed by χ2 test.
Pearson regression analysis and stepwise multivariate linear regression analysis were performed to evaluate the associations between baseline hs-cTnT and baseline traditional cardiovascular risk factors.
For the analyses of hs-cTnT as a categorical variable, subjects were divided into three groups according to their baseline hs-cTnT level: hs-cTnT < 3 pg/mL, hs-cTnT between 3 and 14 pg/mL, and hs-cTnT ≥ 14 pg/mL. The relationship between baseline hs-cTnT levels and MACE and coronary events and mortality were analyzed by Cox proportional hazards models. Models were defined as follows: model 1 = adjusted for age and gender; model 2 = adjusted for model 1 + presence of hypertension or diabetes mellitus, current smoking status, SBP, postprandial blood glucose, TC, HDL-C, antihypertensive medication use and antidiabetic medication use; model 3 = adjusted for model 2 + eGFR; model 4 = adjusted for model 3 + hs-CRP and NT-proBNP (both after logarithmic transformation).
We also analyzed the relationship between hs-cTnT as a continuous variable and endpoints, in which values of cTnT that were below the detection limit were assigned to 1.5 ng/L (i.e., one-half of the lower limit of detection).
SPSS17.0 software was used for all statistical analyses. P value < 0.05 was considered statistically significant.