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BackgroundThe time course and relationships of myocardial hemorrhage and edema in patients after acute ST‐segment elevation myocardial infarction (STEMI) are uncertain.Methods and ResultsPatients with ST‐segment elevation myocardial infarction treated by primary percutaneous coronary intervention underwent cardiac magnetic resonance imaging on 4 occasions: at 4 to 12 hours, 3 days, 10 days, and 7 months after reperfusion. Myocardial edema (native T2) and hemorrhage (T2*) were measured in regions of interest in remote and injured myocardium. Myocardial hemorrhage was taken to represent a hypointense infarct core with a T2* value <20 ms. Thirty patients with ST‐segment elevation myocardial infarction (mean age 54 years; 25 [83%] male) gave informed consent. Myocardial hemorrhage occurred in 7 (23%), 13 (43%), 11 (33%), and 4 (13%) patients at 4 to 12 hours, 3 days, 10 days, and 7 months, respectively, consistent with a unimodal pattern. The corresponding median amounts of myocardial hemorrhage (percentage of left ventricular mass) during the first 10 days after myocardial infarction were 2.7% (interquartile range [IQR] 0.0–5.6%), 7.0% (IQR 4.9–7.5%), and 4.1% (IQR 2.6–5.5%; P<0.001). Similar unimodal temporal patterns were observed for myocardial edema (percentage of left ventricular mass) in all patients (P=0.001) and for infarct zone edema (T2, in ms: 62.1 [SD 2.9], 64.4 [SD 4.9], 65.9 [SD 5.3]; P<0.001) in patients without myocardial hemorrhage. Alternatively, in patients with myocardial hemorrhage, infarct zone edema was reduced at day 3 (T2, in ms: 51.8 [SD 4.6]; P<0.001), depicting a bimodal pattern. Left ventricular end‐diastolic volume increased from baseline to 7 months in patients with myocardial hemorrhage (P=0.001) but not in patients without hemorrhage (P=0.377).ConclusionsThe temporal evolutions of myocardial hemorrhage and edema are unimodal, whereas infarct zone edema (T2 value) has a bimodal pattern. Myocardial hemorrhage is prognostically important and represents a target for therapeutic interventions that are designed to preserve vascular integrity following coronary reperfusion.Clinical Trial Registration URL: https://clinicaltrials.gov/. Unique identifier: NCT02072850.

Smoking is associated with enhanced inflammation acutely, infarct-zone hemorrhage subsequently, and longer term adverse cardiac outcomes. Inflammation and irreversible myocardial hemorrhage post-MI represent mechanistic drivers for adverse long-term prognosis in smokers. (Detection and Significance of Heart Injury in ST Elevation Myocardial Infarction. [BHF MR-MI]; NCT02072850).