Coronary Flow Reserve and Microcirculatory Resistance in Patients with Intermediate Coronary Stenosis

Background The prognostic impact of microvascular status in patients with high fractional flow reserve (FFR) is not clear. Objectives The goal of this study was to investigate the implications of coronary flow reserve (CFR) and the index of microcirculatory resistance (IMR) in patients who underwent FFR measurement. Methods Patients with high FFR (>0.80) were grouped according to CFR (≤2) and IMR (≥23 U) levels: Group A, high CFR with low IMR; group B, high CFR with high IMR; group C, low CFR with low IMR; and group D, low CFR with high IMR. Patient-oriented composite outcome (POCO) of any death, myocardial infarction, and revascularization was assessed. The median follow-up was 658 days (interquartile range: 503.8 to 1,139.3 days). Results A total of 313 patients (663 vessels) were assessed with FFR, CFR, and IMR. Correlation (r = 0.201; p < 0.001) and categorical agreement (kappa value = 0.178; p < 0.001) between FFR and CFR were modest. Low CFR was associated with higher POCO than high CFR (p = 0.034). There were no significant differences in clinical and angiographic characteristics among groups. Patients with high IMR with low CFR had the highest POCO (p = 0.002). Overt microvascular disease (p = 0.008), multivessel disease (p = 0.033), and diabetes mellitus (p = 0.033) were independent predictors of POCO. Inclusion of a physiological index significantly improved the discriminant function of a predictive model (relative integrated discrimination improvement 0.467 [p = 0.037]; category-free net reclassification index 0.648 [p = 0.007]). Conclusions CFR and IMR improved the risk stratification of patients with high FFR. Low CFR with high IMR was associated with poor prognosis.