Prognostic implication of thermodilution coronary flow reserve in patients with indeterminate pressure-bounded coronary flow reserve

Background: Recently, the concept of pressure-bounded coronary flow reserve (PB-CFR) has been introduced. However, using pressure-only data, a substantial proportion of patients could not be classified into high or low PB-CFR and remained as indeterminate PB-CFR. The current study evaluated the prognostic implication of thermodilution-based CFR (thermo-CFR) in patients with indeterminate PB-CFR. Methods: Among 199 patients (211 lesions) with indeterminate PB-CFR, 170 patients (179 lesions) with deferral of revascularization were analyzed for the current study. The rates of patient-oriented composite outcomes (POCO, a composite of all-cause mortality, any myocardial infarction, and any ischemia-driven revascularization) were compared according to thermo-CFR. All patients underwent fractional flow reserve (FFR) and thermo-CFR measurements. Thermo-CFR ≤ 2.0 was classified as low thermo-CFR. The median follow-up duration was 1350.0 (Q1-Q3 1252.0–1468.0) days. Results: Mean angiographic percent diameter stenosis, FFR, and thermo-CFR were 42.3 ± 13.9, 0.84 ± 0.06, and 3.10 ± 1.15, respectively. Among 170 patients, 36 patients (21.2%) showed low thermo-CFR. Patients with low thermo-CFR showed significantly higher rate of POCO compared to those with high thermo-CFR (30.6% vs. 3.0%, HR 12.117, 95% CI 3.854–38.091, p < 0.001). Adding thermo-CFR to a prediction model with FFR significantly increased discrimination and reclassification index for the risk of POCO (c-index 0.545 vs. 0.766, p = 0.002, category-free net reclassification index 1.169, p < 0.001, relative integrated discrimination index 31.828, p < 0.001). Conclusions: Patients with low thermo-CFR showed a significantly higher risk of POCO compared to those with high thermo-CFR among patients with indeterminate PB-CFR. Thermo-CFR showed additional prognostic implication, in addition to FFR, in patients with indeterminate PB-CFR.