Objectives:Quantitative flow ratio(QFR)is a coronary angiography-derived functional test without the need of guidewire use.Fractional flow reserve(FFR)is used as the reference standard to verify the diagnostic value of QFR in patients with non-ST-segment elevation acute coronary syndrome(NSTE-ACS)with coronary critical lesion(40%-70%stenosis)and functional stenosis. Methods:This retrospective analysis included patients with NSTE-ACS who were admitted to Fuwai Central China Cardiovascular Hospital from June 1,2018 to February 1,2023 and underwent coronary FFR examination.QFR values of target vessels were analyzed offline by AngioPlus(Shanghai Pulsation Medical Imaging Technology Co.,LTD.),the second-generation QFR detector,and anatomical parameters of the diseased vessels were recorded as follows:minimal luminal diameter(MLD),percent diameter stenosis(DS%),minimal luminal area(MLA),percent area stenosis(AS%).Functional coronary artery stenosis is defined as FFR≤0.80. Results:Using FFR as the gold standard,the AUC values of contrast-flow QFR(cQFR)and fixed-flow QFR(fQFR)for identifying functional coronary artery stenosis in NSTE-ACS patients were 0.829(95%CI:0.773-0.885,P<0.001)and 0.821(95%CI:0.766-0.875,P<0.001),respectively.The diagnostic accuracy,sensitivity and specificity of cQFR and fQFR were 81.30%,56.00%,98.63%and 76.83%,59.00%,99.04%,respectively.DeLong test showed that diagnostic performance of cQFR was significantly better than fQFR in diagnosing functional stenosis of coronary critical lesions in patients with NSTE-ACS. Conclusions:With FFR as the gold standard,QFR(especially cQFR)has certain diagnostic value in patients with NSTE-ACS with functional stenosis of coronary critical lesions.