Purpose. To study the relationship between the characteristics of acute myocardial infarction and ST-segment elevation (infarction size, microvascular obstruction) according to contrast cardiac MRI data with the features of coronary lesion and the time of percutaneous coronary intervention.

Methods. The study included 52 patients with acute ST-segment elevation myocardial infarction (MI) who were admitted to the hospital in the first 48 hours after the onset of the disease and underwent primary percutaneous coronary intervention (pPCI). On Days 3-7 contrast-enhanced cardiac MRI was done. Tissue analysis of scans was performed evaluating infarct size, presence and size of microvascular obstruction (MVO).

Results. Patients were divided into 2 groups separated by the median time to reperfusion treatment (3 hours). There were no significant differences between groups in MRI-measured ejection fraction (EF) (in the group with later pPCI >3 hours of symptom onset EF was 49.0 ± 11.0%, and in the comparison group – 45.7 ± 10.5%, р=0,2). MRI-measured infarct size was significantly higher in the group where pPCI was done >3 hours of symptom onset: 18.1 ± 1.7% of the left ventricular mass, compared to the early reperfusion group – 10.9 ± 1.9% (р=0.009). MVO magnitude was also higher in the later pPCI group (2.6 ± 0.64% vs 0.03 ± 0.3% in the comparator group), (р<0,027). Correlation analysis also revealed a reliable relationship between infarct size and time to reperfusion (R 0.381, p=0.006). LAD lesions were associated with higher infarct size values (p=0.02) and higher risk of MVO (odds ratio 2.9, CI 0.83-10.0, р=0.03).

Complete occlusion of infarct-related artery (IRA) was associated with higher infarct size (16,97±3.3 vs 12.05±1.4, р=0.02). There was no reliable correlations between IRA patientcy and MVO magnitude (р=0.7).

Conclusions. In this study timing primary percutaneous coronary intervention, in groups of below and more than 3 hours after symptom onset, had no significant impact on ejection fraction, as determined by MRI. However, primary percutaneous coronary intervention timing exceeding 3 hours significantly influenced infarct size, the occurrence and magnitude of microvascular obstruction. LAD being the infarct-related artery was associated with larger infarct size, higher risks of microvascular obstruction development. The absence of complete occlusion of the infarct-related artery was associated with a smaller myocardial infarction size according to MRI data.