Study Design: This prospective cohort study was performed in Peking University First Hospital and the Affiliated Hospital of Xuzhou Medical University. The study was approved by the Institutional Review Board of each participating center, and conformed to the Declaration of Helsinki and Good Clinical Practice Guidelines of the China Food and Drug Administration. All patients provided written informed consent.
Participants: The study cohort comprised 86 patients with STEMI treated with primary PCI comprising stent implantation in one of the two participating centers from February 2015 to September 2016. All patients underwent CMR imaging before discharge.
Exclusion criteria were: 1) atrial fibrillation, frequent premature contractions, persistent ventricular tachycardia, or other tachyarrhythmia; 2) previous cardiac surgery or myocardial infarction; 3) severe liver and/or kidney dysfunction; 4) malignancy; 5) life expectancy of less than 1 year; 6) pregnancy; and 7) contraindications to magnetic resonance imaging (e.g. contrast agent allergy, ferromagnetic objects in the body, claustrophobia).
CMR Imaging Measurements: CMR imaging was performed before discharge (generally 5–7 days after the index event). All patients were examined with a 1.5 Tesla GE magnetic resonance imaging scanner. Three long-axis views (four-, three-, and two-chamber orientation) and short-axis stacks were acquired using a balanced steady-state free-precession imaging technique for functional cardiac analyses. Native T2, T2-weighted, and post-contrast T1-weighted image sequences were used for the assessment of edema, infarction size, microvascular obstruction (MVO), and intramyocardial hemorrhage. T1-weighted images were obtained 15 minutes after the administration of gadolinium-based contrast agent.
CMR Imaging Analysis: The analysis was performed offline by two experienced radiologists. Infarct size, edema, MVO, and intramyocardial hemorrhage were quantified using CVI 42 software (Circle Cardiovascular Imaging Calgary, Canada) (13). CMR-FT strains (GLS, global circumferential strain (GCS), and global radial strain (GRS), LV end-diastolic volume (LVEDV), LV end-systolic volume, and LV ejection fraction (LVEF) were determined using the TomTec Imaging System (2D CPA MR, Cardiac Performance Analysis, version 1.1.2, TomTec Imaging Systems, Germany) (14,15). Briefly, LV contours were drawn semi-automatically at the end of diastole and systole. Subsequently, image features throughout an entire cardiac cycle were determined by the automatic border tracking algorithm of the software. Accurate tracking was confirmed by visual review of all borders and manual adjustments with consequent reapplication of the algorithm if necessary.
Follow-up Examination: The incidence of major adverse cardiac events (MACE), including cardiac death, reinfarction, unplanned revascularization, and heart failure within 6 months after STEMI was obtained from hospital records or face-to-face visits. Heart failure manifestations were deﬁned as the exacerbation of exertional dyspnea or pulmonary edema requiring hospital admission, initiation of diuretics, or an increase in an existing diuretic regimen. Follow-up CMR imaging was performed at 6 months after STEMI. Adverse LV remodeling was defined as an LVEDV of > 15% greater than the LVEDV before discharge from the hospital.
Statistical Analysis: Variables are denoted as mean ± standard deviation, and the independent t test or Fisher exact test was used to compare differences between groups. Variables that were not normally distributed (as determined by Kolmogorov–Smirnov tests) were expressed as medians with 25th and 75th percentiles, and were compared using the Mann-Whitney U test. Based on the ratio of the infarcted myocardial mass to the LV mass (IM%LV), patients were divided into group A (IM%LV < 10%), group B (10% ≤ IM%LV < 20%), and group C (IM%LV ≥ 20%).
A comparison of multiple variables was performed between patients with LV remodeling and patients without LV remodeling, and between patients who did and did not develop MACE during follow-up. Uni- and multivariate logistic backward stepwise regression analyses were performed to evaluate the potential correlations between clinical parameters and CMR imaging parameters to MACE and LV remodeling. Because of the small sample size, the parameters with a p value < 0.05 in comparisons between the MACE and no MACE groups (and between the LV remodeling and no LV remodeling groups), sex, and age were selected for the logistic regression analysis. If there were multiple parameters with high correlations, only the most clinically significant parameter was selected for the analysis. For example, as LVEDV, LV end-systolic volume, and LVEF were highly correlated, only LVEF was used in the analysis. Receiver operating-characteristic (ROC) curve analysis was used to determine the cutoff values of the GLS for predicting MACE. All statistical analyses were performed with a test significance level of 0.05 using SAS version 9.4 (SAS Institute, Inc., Cary, NC).