Background: ST-segment elevation myocardial infarction (STEMI) leads to transient impairment of left ventricular (LV) systolic function, which might or might not persist after myocardial healing. Cardiovascular magnetic resonance (CMR) derived infarct size (IS), microvascular obstruction (MVO) or intramyocardial hemorrhage (IMH) are independent predictors of persistent LV systolic impairment, adverse ventricular remodeling, re-hospitalization and mortality.  However, MVO or IMH do not occur regularly after STEMI, leaving the prediction of systolic functional regain in the majority of patients challenging. 

Aim: Therefore, we aimed to assess the ability of total infarct-territorial native T1 as an independent predictor of local and global systolic functional regain at 6 months follow-up after STEMI. 

Methods: Patients with STEMI and treatment according to current guidelines were prospectively recruited from January 2019 until December 2020 (n=262). CMR examination was conducted 5.0 ± 1.1 days after STEMI according to our study protocol (NCT03539133) in n=114 patients. 101 (89%) patients had a six month follow-up CMR examination and 99 (87%) completed a one-year follow-up telephone interview. T1 mapping was conducted with a 5(3)3-MOLLI sequence according to current guidelines in 3 slices. Regain of global systolic function was defined as a >= 20% increase in cardiac index (CI). Regain of regional systolic function was defined as an increase in wall thickening (WT) of >= 20%. 

Results: In the Youden-Index method a total infarct-territorial native T1 threshold of 1093 was identified best predictive of systolic functional regain. In multivariable regression, total infarct-territorial native T1 was independently of MVO or IMH associated with regain of local [odds ratio (OR: 5.3 (0.8, 9.8); p = 0.022) and global systolic function [odds ratio (OR: 6.3 (1.4, 11.2); p = 0.012). Sixty-one (62%) patients had a total infarct-territorial native T1 value above 1093 ms. Those patients failed to regain local (WT 5d vs 6m post STEMI – 36.3 ± 14.8 vs 31.8 ± 14.2; p = 0.089) and global systolic function (CI 5d vs 6m post STEMI – 2.9 ± 0.7 vs 2.6 ± 0.4; p = 0.004). Total infarct-territorial native T1 was also associated with scar transmurality. Nevertheless, it was not predictive of adverse LV remodeling. 

Conclusion: Total infarct-territorial native T1 is a predictor for regain of systolic function and scar transmurality 6 months after STEMI independent of MVO or IMH. Total infarct-territorial native T1 might be of additive value in the risk stratification of STEMI patients without MVO or IMH.