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 microcirculatory 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.