Assessment of Microvascular Obstruction by Cardiac Magnetic Resonance Imaging (MRI) in patients with ST–Elevation Myocardial Infarction Managed by Primary PCI

Abstract

Microvascular obstruction (MVO) is an independent predictor of left ventricular remodeling and mortality following ST-segment-elevation myocardial infarction (STEMI). Cardiac Magnetic Resonance (CMR) Imaging is a reliable method for quantitative evaluation of myocardial blood flow (MBF) and MVO. The prevalence and predictors of MVO after successful Primary Percutaneous Coronary Intervention (PCI) are largely unknown. We sought to assess MVO in patients with STEMI after successful Primary PCI achieving TIMI-3 flow using CMR. Moreover, to delineate the possible factors related to MVO in such patient group. Thirty Patients presented to our facility with acute STEMI successfully reperfused by Primary PCI with final TIMI 3 flow in the infarct-related artery (IRA) were included. Following PCI, angiographic assessment of microvascular perfusion was performed with Myocardial Blush Grade (MBG). Assessment of CMR-derived MVO was performed on day 2 - 4 after primary PCI using 1.5 Tesla machine. MVO and infarction size volumes were evaluated in late gadolinium enhancement (LGE) CMR. Echocardiography was done within 48 hours after Primary PCI and repeated after 3 months for assessment of the Left Ventricular ejection fraction (LVEF) by biplane Simpson’s method. Patients were followed up clinically for Major Adverse Cardiac Events (MACE) during hospital stay and up to 3 months. The mean age was 49 ± 7 years (84% males). The prevalence of MVO in patients successfully re-perfused was 46.6 %. There was a strong positive correlation between infarction size and MVO volume (p-value 0.001) (r=0.802). There was more delayed peaking of Creatine Kinase (CK) total and (CK)-MB in patients with MVO with Mean ± SD (16.11 ± 5.54 hours) compared to (11.63 ± 4.03 hours) in non-MVO group (p=0.016). MVO presence is associated with less improvement in LVEF at 90 days (p=0.034) than non-MVO group. MVO volume assessed by CMR had negative correlation with LVEF at 90 days (p = 0.007) (r = -0.686). MVO had a positive association with MACE (p = 0.02). MBG showed no correlation to CMR-derived MVO. The only procedural predictor of CMR-derived MVO was Pre-stenting balloon angioplasty (p value <0.05). Factors predicting the presence of CMR-derived MVO include: Time to peak cardiac enzymes more than 12 hours (78.6% sensitivity and 62% specificity), CK-MB more than 308 IU/dL (57% sensitivity and 69% specificity), Infarction size more than 20465 ml (78.6% sensitivity and 75% specificity), Follow up echocardiography with EF less than 45% (71.4% sensitivity and 68.8% specificity). In conclusion, MVO in patients with successful Primary PCI achieving TIMI-3 flow is fairly common. CMR-derived MVO is associated with a lower LVEF, increased ventricular volumes and infarct size, greater risk of MACE and predicts less improvement of LVEF after Primary PCI. Pre-stenting Balloon Angioplasty fairly predicts increased incidence of MVO after primary PCI.