Prognostic Impact of Infarct Size and Coronary Microvascular Function Via Cardiovascular Magnetic Resonance and Coronary Angiography‐Derived Index of Microcirculatory Resistance in Myocardial Infarction With Nonobstructive Coronary Arteries

Background Infarct size (IS) and microvascular obstruction (MVO), measured by cardiovascular magnetic resonance, are key prognostic markers after myocardial infarction (MI). The index of microcirculatory resistance (IMR) predicts MVO and IS; however, its role in MI with nonobstructive coronary arteries (MINOCA) is unclear. This study explored the relationship between coronary angiography‐derived IMR, MVO, and IS in true MINOCA and assessed the prognostic value of coronary microvascular dysfunction (CMD), IS, and MVO. Methods Patients with suspected MINOCA who completed cardiovascular magnetic resonance and coronary angiography‐derived IMR were included. CMD was defined as coronary angiography‐derived IMR >25, and IS as a percentage of left ventricular mass (IS%LV) measured by late gadolinium enhancement. True MINOCA was identified by cardiovascular magnetic resonance evidence of ischemia or infarction. Individuals with true MINOCA were divided into 3 groups: non‐CMD and IS%LV <16.78%, CMD or IS%LV ≥16.78%, and CMD with IS%LV ≥16.78%. Follow‐up for major adverse cardiovascular events was conducted. Results Of 317 patients, 102 had true MINOCA (91.2% non–ST‐segment–elevation MI). CMD was similarly distributed across all suspected MINOCA. Coronary angiography‐derived IMR did not predict MVO or IS among true MINOCA. Over a median 27 months, 33.3% of patients with true MINOCA experienced major adverse cardiovascular events, with a higher risk in patients with CMD or IS%LV ≥16.78%. Multivariate Cox analysis revealed that CMD combined with IS%LV ≥16.78% had a hazard ratio (HR) of 7.40 (95% CI, 1.94–28.23), and either CMD or IS%LV ≥16.78% had an HR of 8.77 (95% CI, 2.57–29.94), but MVO did not. Sensitivity analyses excluding ST‐segment–elevation MI supported these findings. Conclusions CMD with larger IS strongly predicts major adverse cardiovascular events in MINOCA, underscoring their utility in risk stratification, especially for non–ST‐segment–elevation MI. REGISTRATION URL: https://clinicaltrials.gov . Unique identifier: NCT06502899.