Comparison of Flow Ratio Derived From Intravascular Ultrasound with Coronary Angiography in Complex Coronary Artery Lesions: Correlation with Fractional Flow Reserve

BackgroundAccurate assessment of coronary artery disease is essential for guiding clinical decision-making, particularly in cases involving complex coronary lesions. Fractional Flow Reserve (FFR) remains the reference standard for lesion-specific ischemia evaluation; however, it is invasive and requires pharmacologically induced hyperemia. Emerging non-invasive alternatives, including Quantitative Flow Ratio (QFR) derived from coronary angiography (CAG) and Ultrasonic Flow Ratio (UFR) derived from intravascular ultrasound (IVUS), offer promising diagnostic value. This study aimed to compare the diagnostic performance of UFR and QFR against FFR in the assessment of complex coronary lesions. MethodsIn this retrospective, multicenter study, 217 patients (220 vessels) with coronary artery lesions who underwent both intravascular ultrasound (IVUS) and FFR measurement were included. UFR was derived from IVUS imaging, while QFR was computed using coronary angiography (CAG) data. Correlation coefficients, agreement analyses, and diagnostic metrics including sensitivity and specificity were employed to evaluate the performance of UFR and QFR against FFR, with receiver operating characteristic (ROC) curve analysis used to assess diagnostic accuracy. ResultsUFR demonstrated a stronger correlation with FFR (r = 0.79, p < 0.001) compared to QFR (r = 0.68, p < 0.001). Moreover, UFR exhibited superior diagnostic performance, with an area under the ROC curve (AUC) of 0.91, exceeding that of QFR (AUC = 0.86). In subsets of complex lesions--specifically diffuse, bifurcation, and heavily calcified lesions-- UFR consistently outperformed QFR, with the most pronounced difference observed in bifurcation and calcified lesions where QFR accuracy was significantly reduced (72.5% vs. 86.8%, p = 0.001). ConclusionUFR provides enhanced diagnostic accuracy compared to QFR for complex coronary lesions and represents a reliable, non-invasive alternative to FFR, particularly in challenging anatomical scenarios such as bifurcation and heavily calcified lesions. The clinical integration of UFR may reduce the reliance on invasive FFR measurements while preserving diagnostic precision.