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Introduction In patients with coronary artery disease (CAD), ischaemia driven-revascularisation is recommended for intermediate-grade stenoses. 1Quantitative flow ratio (QFR) is a wire-free, non-hyperemic computational method to assess coronary flow from standard angiographic cines, and demonstrates good agreement with fractional flow reserve (FFR).2 A QFR threshold of ≤0.80 is recommended to guide revascularisation, however, validation against established non-invasive functional imaging modalities is limited.1 We examined the ability of QFR to discriminate significant CAD as determined by stress-perfusion cardiovascular magnetic resonance (CMR).Methods In this single-centre prospective study, consecutive adult patients with suspected CAD were recruited, with CMR performed prior to clinically indicated invasive coronary angiography. All participants underwent adenosine stress-perfusion CMR at 3-Tesla as previously described. 3 CMR images were analysed blinded to participant and angiographic details, by two experienced observers. For the primary analysis, significant CAD was determined on a per-territory basis by the presence of ischaemia and/or infarction. For secondary quantitative-only perfusion analysis, a regional myocardial perfusion reserve (MPR) threshold <1.96 was used at the coronary territory level to define significant CAD.4 Blinded QFR computation was performed on epicardial vessels ≥2mm diameter with visually determined ≥25% (mild) stenosis, with subtotal and complete occlusions excluded.5 Receiver operator characteristic analyses were performed to determine diagnostic performance, with reporting of area under the curve (AUC ± standard error [95% confidence interval]).Results One-hundred and twelve patients were recruited. Baseline characteristics are presented in table 1. QFR was performed on 232 vessels (median QFR 0.83 [Q1-Q3: 0.63–0.93] with 112 vessels ≤0.80). Overall, CAD prevalence by CMR was 53%, with infarction evident in 20% of patients, affecting a total of 57 myocardial segments.Abstract 7-037 Table 1Baseline characteristics Patients with CAD, n=112 Demographics Age, years 66 ± 10 Male 86 (77%) Body mass index, kg/m2 30.0 ± 4.5 Risk factors Ever smoked tobacco 59 (53%) Type II diabetes 23 (21%) Hypertension 73 (65%) Hypercholesterolemia 53 (47%) Previous myocardial infarction 1 (0.9%) Family history of premature CAD 44 (39%) Data presented as mean±SD or absolute value (%)For the primary analysis, there was a high diagnostic performance of QFR to detect significant CAD (AUC 0.84±0.03 [0.78–0.89]), with an optimal threshold ≤0.80 giving sensitivity 90% and specificity 68% (figure 1). With quantitative-only perfusion analysis, the diagnostic performance of QFR was moderate (AUC 0.68±0.04 [0.59–0.76]), with an optimal threshold ≤0.82 giving sensitivity 76% and specificity 58%. There was a modest but significant correlation between QFR and MPR at the coronary territory level: rs=0.303, p<0.001 (figure 2).Abstract 7-037 Figure 1Panel A Comparison of QFR between coronary territories with and without CAD. Panel B: ROC analysis demonstrating the diagnostic performance of QFR to detect significant CADAbstract 7-037 Figure 2Correlation of quantitative flow ratio with myocardial perfusion reserveConclusions This prospective study using CMR as the reference standard confirms that QFR accurately detects significant CAD. Furthermore, our findings support a QFR threshold of ≤0.80 as being appropriate to detect significant CAD. Wire-free, coronary flow assessment with QFR may prove a useful and cost-effective tool to aid decision-making, particularly in cases of diagnostic uncertainty regarding the significance of intermediate-grade stenoses.References Vrints C, Andreotti F, Koskinas KC, et al. 2024 ESC Guidelines for the management of chronic coronary syndromes: Developed by the task force for the management of chronic coronary syndromes of the European Society of Cardiology (ESC) Endorsed by the European Association for Cardio-Thoracic Surgery (EACTS). European Heart Journal. 2024;45(36):3415–537.Hwang D, Choi KH, Lee JM, et al. Diagnostic agreement of quantitative flow ratio with fractional flow reserve and instantaneous wave-free ratio. Journal of the American Heart Association. 2019;8(8):e011605.Yeo JL, Dattani A, Bilak JM, et al. Sex differences and determinants of coronary microvascular function in asymptomatic adults with type 2 diabetes. Journal of Cardiovascular Magnetic Resonance. 2024:101132.Kotecha T, Martinez-Naharro A, Boldrini M, et al. Automated pixel-wise quantitative myocardial perfusion mapping by CMR to detect obstructive coronary artery disease and coronary microvascular dysfunction: validation against invasive coronary physiology. J Am Coll Cardiol Img. 2019;12(10):1958–69.van Diemen PA, de Winter RW, Schumacher SP, et al. The diagnostic performance of quantitative flow ratio and perfusion imaging in patients with prior coronary artery disease. European Heart Journal-Cardiovascular Imaging. 2024;25(1):116–26.