The study intends to provide important data on whether the noval method using quantitative flow ratio could predict microvascular dysfunction.

Microvascular dysfunction (MVD) is a serious complication of PCI, which happens frequently after STEMI and always correlates with a poor prognosis. However, precise and simplified assessment of MVD is difficult, especially in the acute phase of STEMI patients. Resent studies suggested that FFR could be overestimated when MVD exists. But whether the overestimated value of FFR caused by CMR defined MVO could reflect microcirculation function is still unclear.

This study is a retrospective study using STEMI patients with TFG 2/3 of the infarct vessel on initial angiography and presumed culprit lesion ≥50% as the population. Contrast-enhanced CMR was performed 5 days after PCI as the reference standard.

Inclusion Criteria:

• STEMI patients treated with revasculation within 12 hours from onset of symptoms to PCI time and received CMR 5 days afterwards. STEMI was defined as a combination of the following: chest pain for more than 30min, electrocardiographic (ECG) changing with ST segment elevation of >2 mm in at least 2 precordial leads and >1 mm in limb leads, and abnormal troponin levels or CKMB levels higher than twice the upper limit of normal.
• Patients with TFG 2/3 in the initial angiography of the culprit vessel.

Exclusion Criteria:

• Patients with left bundle branch block in the presenting ECG, cardiogenic shock, PCI or bypass surgery history.
• Patients with residual stenosis <50%.
• Patients with unqualified coronary angiographic images with problems such as ostial lesion, severe vessel tortuosity and diffuse long lesions.

STEMI patients who underwent successful reperfusion therapy with TFG 2/3 of the infarct vessel on initial angiography and presumed culprit lesion ≥50%.