Index of Microcirculatory Resistance to predict microvascular obstruction in STEMI: A systematic review and meta‐analysis

Abstract Background Microvascular obstruction (MVO) is an independent predictor of adverse cardiac events after ST‐elevation myocardial infarction (STEMI). The Index of Microcirculatory Resistance (IMR) may be a useful marker of MVO, which could simplify the care pathway without the need for Cardiac Magnetic Resonance (CMR). We assessed whether the IMR can predict MVO in STEMI patients. Methods and Results We conducted a systematic review and meta‐analysis, including articles where invasive IMR was performed post primary percutaneous coronary intervention (PCI) in addition to MVO assessment with cardiac MRI. We searched PubMed, Scopus, Embase, and Cochrane databases from inception until January 2023. Baseline characteristics, coronary physiology and cardiac MRI data were extracted by two independent reviewers. The random‐effects model was used to pool the data. Among 15 articles identified, nine articles ( n = 728, mean age 61, 81% male) contained IMR data stratified by MVO. Patients with MVO had a mean IMR of 41.2 [95% CI 32.4−50.4], compared to 25.3 [18.3−32.2] for those without. The difference in IMR between those with and without MVO was 15.1 [9.7−20.6]. Meta‐regression analyses demonstrated a linear relationship between IMR and TIMI grade ( β = 0.69 [0.13−1.26]), as well as infarct size ( β = 1.18 [0.24−2.11]) or ejection fraction at 6 months ( β = −0.18 [−0.35 to −0.01]). Conclusion In STEMI, patients with MVO had 15‐unit higher IMR than those without. IMR also predicts key prognostic endpoints such as infarct size, MVO, and long‐term systolic function.