Study population
This study was approved by the Biomedical Research Ethics Committee of our hospital and was conducted in accordance with the Declaration of Helsinki.The need for informed consent was waived given the retrospective design of the study.
The study cohort comprised patients diagnosed with T2DM based on the current American Diabetes Association guidelines who underwent CMR examination at our institution between January 2015 and October 2023. The patients were divided into the healthy control, T2DM (AR−), and T2DM (AR+) groups. The exclusion criteria were as follows: patients with ischemic heart disease, rheumatic heart disease, congenital heart disease, primary cardiomyopathy, coexistence of other significant valvular disease, acute AR, and previous history of aortic valve surgery; those with incomplete clinical data; and those with CMR contraindications, poor image quality, and incomplete scans. Finally, 317 patients, including 229 with T2DM (AR−) and 88 with T2DM (AR+), were eligible for this study. Based on the echocardiographic findings, the T2DM (AR +) group was further classified into three subgroups, which were as follows: the mild AR (n = 41, 44.6%), moderate AR (n = 25, 28.4%), and severe AR (n = 22, 25%) groups. The healthy control group comprised patients who underwent cardiac MRI but did not present with a previous history of cardiac disease or symptoms and T2DM or impaired fasting glucose levels and inadequate cardiac MRI image quality (n = 122).
Data on the demographic characteristics, clinical history, cardiovascular risk factors, and laboratory test results of the patients were recorded in the Hospital Information System and Laboratory Information Management System.
MRI protocol
All patients were placed in the supine position, and they underwent imaging using a 3.0-T whole-body magnetic resonance scanner (TrioTim or MAGNETOM Skyra, Siemens Medical Solutions, Erlangen, Germany) equipped with 32-channel body-phased array coils and standard ECG trigger equipment. Balanced steady-state free precession cine images were obtained during breath-holding at the end of expiration with retrospective cardiac gating. Moreover, they comprised standard long-axis views and a short-axis stack that encompassed the entirety of the left and right ventricles. The following parameters were used for the two scanners: temporal time = 39.34/40 ms; echo time = 1.22/1.20 ms; slice thickness = 8.0 mm; field of view = 234 × 280/250 × 300 mm2; matrix size = 208 × 139/256 × 166 pixels; and flip angle = 40°/50°.
Image analysis
The CMR images were uploaded to an offline commercial software (Cvi42, v.5.11.2; Circle Cardiovascular Imaging, Calgary, Canada). Next, they were analyzed by two radiologists who were blinded to the clinical data of the participants. Both radiologists had > 3 years of experience in CMR imaging. The endo- and epicardial contours of both ventricles were automatically delineated at the end-diastolic and end-systolic phases on the short-axis cine images in the short three-dimensional module. Then, the two investigators manually adjusted the borders layer by layer, and the morphological and functional parameters, including LV and RV end-diastolic volume (EDV), end-systolic volume (ESV), stroke volume (SV), ejection fraction (EF), and myocardial masses (MM), were calculated automatically. The papillary muscle and trabeculae were excluded from MM but included in the ventricular volume analyses. The LV remodeling index and RV remodeling index were calculated as LVMM/LVEDV and RVMM/RVEDV, respectively.
The short-, long-axis four- and two-chamber cine images were used to evaluate the myocardial strain of both ventricles using the tissue tracking module. The endocardium and epicardium of both ventricles were manually outlined at the end diastole after cautious exclusion of the papillary muscles and trabeculae. The biventricular and interventricular septal (IVS) global radial (GRS), circumferential (GCS) and longitudinal peak strains (GLS), RV regional peak strain (including the basal, middle, and apical cavities), and LV regional peak strain were generated automatically (Fig. 1). The 2, 3, 8, 9, and 14 LV segments represented the area of the interventricular septum, according to the 16-segment model of the AHA. The interventricular septum thickness (IVST) on each patient’s CMR was measured using the four-chamber long-axis view at the midway between the base and apex of the left ventricle at the end diastole (Additional file 1).
Reproducibility analysis
To assess the intraobserver variability of the RV global and regional strains, 50 participants selected randomly were evaluated by comparing two measurements conducted by LT.S. and taken 1 month apart. Interobserver variability was assessed by comparing the two measurements of all participants, which were conducted by LT.S. and K.S. double-blindly and independently.
Statistical analysis
All statistical analyses were performed using the Statistical Package for the Social Sciences software (version 23.0, IBM, Armonk, New York, USA). Continuous variables with a normal distribution were presented as mean ± standard deviation. Meanwhile, variables with a non-normal distribution were expressed as median (interquartile range: 25–75%). One-way analysis of variance with Bonferroni post hoc correction was used to compare data with a normal distribution, and the Kruskal–Wallis test was used to compare data with a non-normal distribution among the healthy control, T2DM (AR−), and T2DM (AR+) groups. Categorical variables were expressed as frequencies (percentages) and analyzed using the chi-square test or the Fisher’s exact test based on the data distribution.
The associations between RV global strain, IVS global strain, RVEF, and LV geometric parameters and strains were assessed via Pearson’s or Spearman’s correlation coefficient analysis, as appropriate. Multivariate linear regression models adjusted for statistically significant parameters in the univariate analysis (p < 0.05) and traditional clinical risk factors (age, sex, body mass index, hyperlipidemia, fasting plasma glucose and hemoglobin A1c [HbA1c] levels, and diabetes duration) were used to determine the predictors of both ventricular global strains in the populations with T2DM and the independent effects of LV strains on RV strains. The intraobserver and interobserver variabilities of RV global and regional deformation were analyzed using the intraclass correlation coefficient. Two-tailed p values of < 0.05 were considered statistically significant.