DESIGN AND STUDY PARTICIPANTS
The HSCAA study is an ongoing single center cohort performed for a review of cardio-metabolic risk factors, including quantitatively measured sleep parameters, for elucidation of the clinical implications of cardiovascular and metabolic diseases [8]. From October 2010 to December 2018, 976 patients with at least 1 cardiovascular risk factor, including obesity, hypertension, dyslipidemia, diabetes mellitus, and chronic kidney diseases , were enrolled in that cohort study. Patients (n=240) with ischemic heart disease, moderate to severe valvular heart disease, hypertrophic cardiomyopathy, atrial fibrillation, HF, or cardiac diastolic dysfunction [transmitral early inflow velocity/early diastolic tissue velocity (E/e’ >14)], assessed according to the recommendations of the American Society of Echocardiography and European Association of Cardiovascular Imaging [9] were excluded. After excluding another 131 with missing baseline data for cardiac ultrasonography and 88 with a follow-up period <12 months, 517 of those patients were enrolled in the present study (Figure 1). A large majority of the participants (n=462) underwent apnomonitor monitoring for a review of sleep apnea. The HSCAA study was approved by an appropriate institutional ethical committee (approval No. 2351) and informed written consent was obtained from each participant.
ASSESSMENT OF CLASSICAL CARDIOVASCULAR RISK FACTORS
Body mass index (BMI) was calculated as weight in kilograms divided by the square of height in meters (kg/m2). Smoking status was based on self-reported cigarette smoking habit. Blood pressure and pulse rate were measured twice in a sitting position after a deep breath, with the mean values used for analysis. Type 2 diabetes was diagnosed based on results showing fasting plasma glucose ≥126 mg/dl, causal plasma glucose ≥200 mg/dl, or 2-hour plasma glucose ≥200 mg/dl during a 75-g oral glucose tolerance test, or previous therapy for diabetes [10]. Hypertension was defined as systolic BP ≥140 mmHg, diastolic BP ≥90 mmHg, or treatment for hypertension. Dyslipidemia was defined based on results showing low density lipoprotein (LDL) cholesterol (≥140 mg/dl), high density lipoprotein (HDL) cholesterol (≤40 mg/dl), elevated triglyceride level (≥150 mg/dl), or treatment for dyslipidemia.
ASSESSMENT OF LV DIASTOLIC FUNCTION
LV function was evaluated by echocardiography as previously described [11]. Examinations were repeated every 1-3 years to determine changes in LV function. To measure LV ejection fraction (LVEF), we used the modified Simpson’s method for patients with LV segmental asynergy or deformation, and Teichholz’s formula for patients without LV asynergy or deformation. LV mass index (LVMI) was calculated as follows: LVMI = 1.04 × {(LVDd + IVST + RWT)3 - (LVDd)3 - 13.6} / 1000 / BSA, in which RWT (relative wall thickness) = IVST + PWT/LVDd, BSA (body surface area) = height(cm)0.725 × weight(kg)0.425 × 0.7184 (LVDd: left ventricular diastolic dimension, IVST: intraventricular septal thickness, PWT: posterior wall thickness). Transmitral early inflow velocity (E-wave), late diastolic filling velocity (A-wave), and E-wave deceleration time (DcT) were determined using pulsed Doppler echocardiography [9]. Early diastolic tissue velocity (e´) was measured in the septal basal region using tissue Doppler imaging and the E/e′ ratio was then calculated to obtain estimated LV filling pressure. Among these parameters, E/e’ >14 was evaluated as LV diastolic dysfunction as recommended [9]. Annual change in E/e’ was estimated by using the slope (b) of the linear regression line calculated from at least 3 echocardiographic measurements with the following equation: E/e’ = a + b x months.
ASSESSMENT OF SLEEP APNEA
To examine the presence of sleep apnea, we used an apnomonitor device (SAS-2100®, Teijin, Tokyo, Japan) to determine apnea hypopnea index (AHI), as previously described [8]. Percutaneous oxygen saturation was recorded using a pulse oximeter. Apnea was defined as complete cessation of air flow lasting ≥10 seconds, hypopnea as a ≥50% reduction in air flow lasting ≥10 seconds associated with a 4% decrease in oxygen saturation, and AHI as the average number of apnea and hypopnea episodes per hour.
PLASMA BIOCHEMICAL PARAMETERS
Blood samples were obtained in the morning after an overnight fast and then quickly centrifuged to obtain plasma. Whole blood was used for hemoglobin A1c, EDTA-plasma for glucose, and lipids, and serum for other biochemical assays. Glucose was measured using a glucose oxidase method. Insulin was determined by chemiluminesce enzyme immunoassay results and serum creatinine concentration with an enzymatic method. Estimated glomerular filtration rate (eGFR) in each subject was calculated using an equation for Japanese subjects, as follows: eGFR (ml/min/1.73 m2) = 194×age(years)-0.287×S-creatinine-1.094 (if female, ×0.739).
STATISTICAL ANALYSES
To compare mean and median values among the groups, Student’s t-test and a Mann-Whitney test were used. A chi-square test was used for comparisons for dichotomous variables. To analyze associations between factors, parameters with skewed distribution were natural logarithm-transformed (ln) to normalize skewed distribution. For this study, the primary outcome was LV diastolic dysfunction, which as defined as E/e’ >14, as previously recommended [9]. Outcome rates for the groups were compared using Kaplan-Meier analysis and a log-rank test. Prognostic variables for primary outcome were examined using a Cox proportional hazards regression model. Predictors for annual changes of E/e’ were examined using Pearson’s correlation coefficient and logistic regression analysis. To compare each logistic model in aggregate, we constructed receiver operating characteristic (ROC) curves and determined the area under the curve (AUC). All statistical analyses were performed using the Statistical Package for Social Sciences software package (PASW Statistics version 18.0). All reported p values are 2-tailed and were considered statistically significant at <0.05.