Prognostic Value of Coronary Angiography-Derived Index of Microcirculatory Resistance in Patients With Intermediate Coronary Stenosis

BACKGROUND The association between coronary microcirculation and clinical outcomes in patients with intermediate stenosis remains unclear. OBJECTIVES The aim of this study was to assess the prognostic significance of angiography-derived index of micro- circulatory resistance (angio-IMR) in patients with intermediate coronary stenosis. METHODS This post hoc analysis included 1,658 patients from the FLAVOUR (Fractional Flow Reserve and Intravascular Ultrasound for Clinical Outcomes in Patients with Intermediate Stenosis) trial, with angio-IMR measured in each vessel exhibiting intermediate stenosis. The primary endpoint was a patient-oriented composite outcome (POCO), a composite of all-cause death, myocardial infarction, or revascularization over a 2-year period. RESULTS The median follow-up period was 24.8 months (Q1-Q3: 24.4-26.4 months). Over the 2-year follow-up period, patients with angio-IMR >25 exhibited a significantly higher POCO rate in both the percutaneous coronary intervention (PCI) group (35.06% [27 of 77] vs 7.2% [51 of 708]; P < 0.001) and the non-PCI group (17.95% [21 of 117] vs 4.23% [32 of 756]; P < 0.001). After adjusting for potentially related risk factors, angio-IMR >25 remained an independent predictor of the POCO in the PCI group (HR: 6.235; 95% CI: 3.811-10.203; P <0.001) and the non-PCI group (HR: 5.282; 95% CI: 2.948-9.462; P < 0.001). The addition of angio-IMR demonstrated incremental prognostic value in both an angiographic risk factor model (C-index 0.710 [95% CI: 0.663-0.756] vs 0.615 [95% CI: 0.563-0.664] [P < 0.001]; net reclassification index 0.268 [95% CI: 0.191-0.362; P < 0.001]; integrated discrimination improvement 0.055 [95% CI: 0.030-0.108; P < 0.001]) and a clinical risk factor model (C-index 0.705 [95% CI: 0.658-0.751] vs 0.594 [95% CI: 0.544-0.644] [P < 0.001]; net reclassification index 0.268 [95% CI: 0.171-0.350; P < 0.001]; integrated discrimination improvement 0.057 [95% CI: 0.027-0.102; P < 0.001]). CONCLUSIONS In individuals with intermediate coronary stenosis, elevated angio-IMR is linked to an adverse prognosis. Using angio-IMR significantly enhanced the capability to reclassify patients and accurately estimate the risk for the POCO. (JACC Cardiovasc Interv. 2025;18:171-183) (c) 2025 The Authors. Published by Elsevier on behalf of the American College of Cardiology Foundation. This is an open access article under the CC BY-NC-ND license (http://creativecommons. org/licenses/by-nc-nd/4.0/).