Study Design: This prospective cohort study was performed in two centers, i.e., Peking University First Hospital and Affiliated Hospital of Xuzhou Medical University. The study was approved by the Institutional Review Board (IRB) for each participating center, conforming 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 prospective cohort study included 86 STEMI patients treated with primary PCI with implantation of stents in the two centers from February 2015 to September 2016. All patients underwent CMR before discharge.
Exclusive criteria included: 1) complicated with atrial fibrillation, frequent premature contraction, persistent ventricular tachycardia, or other tachyarrhythmia; 2) previous cardiac surgery history or myocardial infarction; 3) severe liver and kidney dysfunction; 4) malignant tumors; 5) life expectancy less than one year; 6) pregnant women; and 7) those who had contraindications for magnetic resonance (e.g. contrast agent allergy, ferromagnetic objects in the body, claustrophobia, etc.).
CMR Measurements: CMR was performed in enrolled patients before discharge (5–7 days after the index event was recommended). All patients were examined with a 1.5 T GE magnetic resonance imaging scanner. Three long-axis views (4-, 3- and 2-chamber orientation) as well as short axis stacks were acquired using a balanced steady state free precession imaging technique for functional cardiac analyses. Native T2, T2 weighted image (T2WI), and post contrast T1 weighted image (T1WI) sequences were used for assessment of edema, infarction size, microvascular obstruction (MVO), and intramyocardial hemorrhage (IMH). T1 weighted images were obtained 15 minutes after administration of Gadolinium-based contrast agents.
CMR Analysis: The analysis was performed offline by two experienced radiologists. Infarct size, edema, MVO and IMH were quantified by using the CVI 42 software (Circle Cardiovascular Imaging Calgary, Canada) (13). CMR feature tracking strains (GLS, GCS and GRS: global longitudinal, circumferential and radial strains), left ventricular end-diastolic volume (LVEDV), left ventricular end-systolic volume (LVESV) and left ventricular ejection fraction (LVEF) were determined by using the TomTec Imaging Systems (2D CPA MR, Cardiac Performance Analysis, Version 1.1.2, TomTec Imaging Systems, Germany) (14, 15). Briefly, LV contours were first drawn semi-automatically at the end of diastole and systole. Subsequently, image features throughout an entire cardiac cycle were determined by the software’s automatic border tracking algorithm. Accurate tracking was finally assured by visual review of all borders and manual adjustments with consequent reapplication of the algorithm if necessary.
Follow-up Study: Major adverse cardiac events (MACE), including cardiac death, reinfarction, unplanned revascularization and heart failure, were obtained from hospital records or face-to-face visit in patients 6 months after STEMI. 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 was also performed in patients 6 months after STEMI. Adverse LV remodeling was defined as LVEDV > 15% than that before discharge from the hospital.
Statistical Analysis: Variables are denoted as mean ± SD (standard deviation), and independent t testing or Fisher exact testing is used to compare differences between groups. Variables that are not normally distributed (as determined by Kolmogorov–Smirnov tests) are expressed as medians with 25th and 75th percentiles and compared using the Mann–Whitney U test. Based on the ratio of infarcted myocardium mass to LV mass (IM%LV), patients are divided into three groups as: group A (IM%LV < 10%), group B (10%≤IM%LV < 20%), and group C (IM%LV ≥ 20%).
A comparison of multiple variables is demonstrated between patients with LV remodeling and patients without LV remodeling as well as between patients who did and did not show MACE during the follow-up study. The logistic backward stepwise regression analysis (two tailed and α of 0.05) was demonstrated to determine which variables are better predictors of MACE as well as LV remodeling. Receiver operating-characteristic (ROC) curve is used to determine the cutoff value of GLS. All statistical analyses were performed with a test significance level of 0.05 using the SAS version 9.4 (SAS Institute, Inc., Cary, North Carolina).