Diagnostic Accuracy and Feasibility of Quantitative Flow Ratio at Low Frame Rate Angiography: The Prospective Multicentre Australian AVALON Study

BACKGROUND: Quantitative Flow Ratio (QFR) is a well-established, non-hyperemic, angiographic, wire-free predictor of ischemia when compared to Fractional Flow Reserve (FFR). However, its diagnostic accuracy at low frame rates (< 10 frames/second), commonly used in contemporary practice to minimize radiation exposure, has not been evaluated. AIMS: To assess the diagnostic accuracy of QFR when acquired at lower frame rates in line with contemporary practice. METHODS: The AVALON trial-a prospective, multi-center, Australian study-included patients undergoing invasive coronary angiography (ICA) and FFR assessment for stable coronary artery disease (CAD). QFR analysis was performed using Medis QAngio XA QFR 2.2.2.4 software. Significant QFR and FFR were defined as < 0.80. RESULTS: Among 1054 patients (66.8 ± 10.4 years, 585 males, 797 vessels), the mean FFR was 0.81 ± 0.10, with 312 vessels (39%) classified as FFR significant. The mean QFR was 0.81 ± 0.10, and 352 vessels (44%) were QFR significant. QFR demonstrated strong diagnostic performance in predicting significant FFR with AUC of 0.92 (p < 0.001). It exhibited sensitivity of 85%, specificity 89%, positive predictive value (PPV) 83%, negative predictive value (NPV) 90%, and diagnostic accuracy 87%. Interobserver reliability for QFR was excellent (ICC = 0.92, p < 0.001). Using the established QFR-FFR hybrid approach, where FFR was performed only if QFR ranged between 0.77 and 0.87, FFR could be safely deferred in 58% of cases, achieving a diagnostic accuracy of 93.8%. CONCLUSION: QFR remains highly accurate in predicting significant FFR, even when angiography is acquired at low frame rates. The QFR-FFR hybrid approach effectively minimizes the need for invasive FFR measurements, with the potential to enhance clinical efficiency while maintaining high diagnostic precision.