Clinical Implications of Coronary Flow Reserve and Index of Microcirculatory Resistance in Patients with Intermediate Coronary Stenosis and High Fractional Flow Reserve

Abstract

Background: The clinical manifestations and prognostic impact of microvascular status in patients with high fractional flow reserve (FFR) have not yet been clearly defined. Objectives: We sought to investigate the clinical implications of coronary flow reserve (CFR) and index of microcirculatory resistance (IMR) in patients who underwent fractional flow reserve (FFR) measurement. Methods: Anatomical lesion severity was evaluated by Gensini and SYNTAX scores. Patients with high FFR (>0.80) were divided into 4 groups according to CFR (≤2) and IMR (≥23U) levels: high CFR and low IMR (61.3%), high CFR and high IMR (18.3%), low CFR and low IMR (13.5%), and low CFR and high IMR (7.0%). Clinical outcome was assessed by the patient-oriented composite outcome (POCO, a composite of any death, any myocardial infarction, and any revascularization). The median follow-up duration was 658.0 (IQR 503.8–1139.3) days. Results: The physiologic characteristics of 313 patients (663 vessels) were assessed with FFR, CFR, and IMR. Mean FFR and CFR values were 0.85±0.09 and 2.81±1.02, respectively. The mean angiographic percent diameter stenosis was 41.0±17.2%. The median IMR was 16.0U. Among patients with high FFR, those with low CFR had a higher POCO than did those with high CFR (HR, 4.189

95% confidence interval [CI], 1.117–15.715

P=0.034). There were no significant differences in clinical and angiographic characteristics and FFR values among the 4 groups. Patients with high IMR and low CFR (overt microvascular disease) showed the highest POCO of all groups (P=0.002). Overt microvascular disease (HR, 4.845

95% CI, 1.509–15.557

P=0.008), multivessel disease (HR, 3.254

95% CI, 1.082–9.787

P=0.033), and diabetes mellitus (HR, 2.828

95% CI, 1.088–7.349

P=0.033) were independent predictors of POCO in patients with high FFR. Conclusion: CFR and IMR can provide additional information on coronary circulation and improve risk stratification of patients with high FFR. Overt microvascular disease (low CFR and high IMR) was associated with poor prognosis.