Angio-IMR and Cardiac MR-derived MVO in STEMI Patients

Coronary microcirculatory dysfunction has been known to be prevalent even after successful revascularization of ST-segment elevation myocardial infarction (STEMI) patients. Microvascular obstruction (MVO) in cardiac magnetic resonance (CMR) is significant prognostic indicator in STEMI patients after primary percutaneous coronary intervention (PCI). Although current gold-standard method to assess microvascular damage or dysfunction in STEMI patients is CMR and assessment of MVO, previous study presented that index of microcirculatory resistance (IMR) in culprit vessel of STEMI patients showed significant association with the presence of MVO in CMR and the risk of cardiac death or heart failure admission. Nevertheless, the need for pressure-temperature sensor wire and hyperemic agents significantly limits adoption of IMR in daily practice. Recent technical development enabled angiographic derivation of IMR without pressure wire, hyperemic agents, or thermodilution method. In this regard, the current study will evaluate the feasibility of functional angiography-derived IMR (angio-IMR) in the evaluation of MVO after successful primary PCI for STEMI. The study population will be derived from the prospective institutional AMI registry of Samsung Medical Center between December 2007 and July 2014. Main results from this registry were published elsewhere (PLoS One. 2017 Jan 12;12(1):e0170115 and Sci Rep. 2019 Jul 4;9(1):9646). In this registry, 515 consecutive patients who presented with acute myocardial infarction and underwent CMR were prospectively enrolled. AMI was defined as evidence of myocardial injury (defined as elevation of cardiac troponin values, with at least one value above the 99th percentile upper reference limit) with necrosis in a clinical setting, consistent with myocardial ischemia. Among the total patients, STEMI patients (n = 332), whose electrocardiogram showed ST-segment elevation more than 1 mm in two or more contiguous leads or a presumably new-onset left bundle branch block, will be analyzed for the current study. For the study purpose, patients with failed primary PCI (n=1), treated by medical treatment alone without PCI (n=4), and no available coronary angiographic images (n=3) will be excluded. Among the remaining 324 patients, functional coronary angiography core laboratory (Shanghai Institute of Cardiovascular Diseases, Shanghai, China) evaluated the quality of angiographic images and additionally exclude patients with insufficient image quality for angio-IMR calculation (n=37). All patients also underwent baseline and 1-year follow-up echocardiography. The Institutional Review Board of Samsung Medical Center approved this study, and all patients provided written informed consent. The association of Angio-IMR with CMR-derived quantitative parameters (extent of MVO, infarct size, area at risk) and qualitative parameter (presence of MVO) will be analyzed. The discrimination ability of angio-IMR to predict the presence of MVO in CMR will be compared with conventional angiographic measures of culprit vessel reperfusion (TIMI flow grade, myocardial blush grade).