Diagnostic Agreement and Threshold Correspondence Between Resting Full‐Cycle Ratio and Nicorandil‐Based Fractional Flow Reserve in Intermediate Coronary Stenosis: A Prospective Single‐Center Registry

BACKGROUND: RFR has shown good aggregate agreement with FFR, including in prior Asian cohorts using intracoronary nicorandil. Where RFR-FFR disagreement is concentrated relative to the FFR 0.80 decision boundary, and how the two binary thresholds correspond, remain incompletely characterized. METHODS: In a prospective single-center registry, 300 patients (399 lesions) underwent sequential RFR and nicorandil-based FFR measurement. Diagnostic accuracy was assessed with patient-level cluster bootstrap CIs across post hoc FFR and RFR strata. Threshold correspondence used ordinary least squares and Deming regression. Univariable logistic regression evaluated correlates of discordance (exploratory). RESULTS: Overall threshold-based agreement was 85.0% (95% CI 81.1%-88.5%; κ = 0.684) with AUC 0.932 (95% CI 0.906-0.954). RFR exceeded FFR by +0.067 (patient-mean limits of agreement -0.040 to +0.173). Agreement was 91.6-92.8% away from the FFR 0.80 decision boundary but 72.0-73.5% in the two flanking strata. RFR 0.89 corresponded to an FFR of approximately 0.823, similar with Deming regression. Agreement exceeded 92% outside RFR 0.87-0.91 but was 63.2% within this exploratory band and 68.8% within the 0.86-0.92 interval of previous hybrid strategies. LAD territory was an exploratory univariable correlate of discordance, which likely reflected the FFR distribution of LAD lesions. CONCLUSIONS: RFR showed high agreement with nicorandil-based FFR, consistent with prior cohorts. Disagreement was concentrated near the FFR decision boundary, as expected for two correlated continuous indices dichotomized at fixed thresholds, and this study quantifies its frequency. Agreement was lowest near the RFR cut-off (0.87-0.91), an exploratory interval that overlaps with previous hybrid gray zones and requires validation in outcome studies.