Impact of Initial Culprit Vessel Flow on Infarct Size, Microvascular Obstruction, and Myocardial Salvage in Acute Reperfused ST-Elevation Myocardial Infarction

Data on the impact of initial Thrombolysis In Myocardial Infarction (TIMI) flow in the culprit coronary artery on myocardial damage after ST-elevation myocardial infarction (STEMI) are limited. Aim of this multicenter study was, therefore, to elucidate the impact of TIMI flow grade before percutaneous coronary intervention (PCI) on infarct size (IS), myocardial salvage index (MSI), and microvascular obstruction (MVO) assessed by cardiac magnetic resonance (CMR) imaging in patients with STEMI. We enrolled 738 patients with STEMI reperfused by primary PCI within 12 hours after symptom onset at 8 centers. Impaired coronary flow was defined as an initial coronary TIMI flow grade ≤1, whereas preserved coronary flow was defined as an initial coronary TIMI flow grade ≥2. CMR was performed in median 3 days (interquartile range 2 to 4 days) after infarction using a standardized infarction protocol. IS, MVO, and MSI were determined in central core laboratory-masked analyses. The primary clinical end point of the study was the time to major adverse cardiac events defined as death, reinfarction, and new onset of heart failure within 12 months after infarction. TIMI flow ≤1 before PCI was present in 507 patients (68.7%) and was significantly associated with larger IS (19% left ventricular [LV] vs 9% LV; p <0.001), less MSI (0.46 vs 0.65; p <0.001), reduced left ventricular ejection fraction (49% vs 55%; p <0.001), and a higher extent of MVO (0.6% LV vs 0.0% LV; p <0.001). Moreover, TIMI flow before PCI was identified as an independent predictor of IS, MVO, and MSI. However, there were no significant differences in major adverse cardiac event rates between groups (6.1% vs 7.5%; p = 0.48). In conclusion, TIMI flow pre-PCI is reversely associated with myocardial injury and is an independent predictor of myocardial damage assessed by CMR.