Infarct‐Related Myocardial Resistance Before Reperfusion in Patients With Acute Myocardial Infarction to Predict Microvascular Injury and Clinical Outcomes

Background: Microvascular injury (MVI) increases the risk of heart failure and mortality in patients with ST-elevation myocardial infarction (STEMI). Therefore, it is important to detect these patients at an early stage for additional (experimental) therapies to improve outcomes. Currently, there are no methods to diagnose MVI in STEMI patients before reperfusion. The objective of this study was to assess the invasively measured infarct-related absolute myocardial resistance (Rinfarction) to predict MVI before reperfusion. Cardiac magnetic resonance imaging (CMR) characterizes MVI, in the forms of microvascular obstruction (MVO) and intramyocardial hemorrhage (IMH) with IMH being at the “extreme” end of the injury spectrum. Methods: In this substudy of the EURO-ICE trial, Rinfarction was calculated as the change in distal coronary pressure during saline infusion in the occluded culprit artery, divided by the flow rate of the infused saline. The primary endpoint was to assess the diagnostic performance of Rinfarction to predict MVO on CMR performed at 2–7 days. The secondary endpoint was a composite of all-cause mortality or hospitalization for heart failure up to 5 years. Results: A total of 82 patients were included. The area under the Receiver-Operating Characteristic curve of Rinfarction to predict MVO and IMH was 0.84 and 0.78, respectively. The optimal cut-off value for both MVO and IMH was 1000 Wood units (WU). The composite endpoint of all-cause mortality or hospitalization for heart failure occurred in 15.6% and 2.3% in the Rinfarction ≥ 1000 WU and Rinfarction < 1000 WU groups, respectively (p = 0.06). Conclusions: Rinfarction is able to predict MVI in STEMI before reperfusion and may serve as a tool in future trials to select patients that might benefit most from experimental therapies.