Repeatability and quality assessment of QFR in the FAVOR III Europe trial: the REPEAT-QFR study

BACKGROUND: Quantitative flow ratio (QFR) is a guideline-recommended angiography-based estimation of fractional flow reserve (FFR) for functional lesion evaluation. The FAVOR III Europe trial raised concerns regarding the safety and efficacy of QFR compared with FFR. Whether the poor clinical outcomes in the trial were attributable to software limitations or suboptimal in-procedure QFR analysis is unknown. AIMS: We aimed to compare in-procedure and core laboratory QFR, and to evaluate the quality of in-procedure QFR analyses. METHODS: The 1,008 patients randomised to QFR in FAVOR III Europe were assessed for eligibility. Core laboratory QFR analyses were performed by two blinded observers. The quality of in-procedure QFR analyses were evaluated during patient enrolment. Quality scores from 1 (very poor) to 5 (very good) were assigned based on adherence to the standard operating procedure (SOP). RESULTS: Of 1,233 vessels with in-procedure QFR, 1,191 (96.6%) were analysable in the core laboratory and were included in the paired analysis. The median in-procedure QFR was 0.81 (interquartile range [IQR] 0.71-0.90) and core laboratory QFR was 0.84 (IQR 0.73-0.91). The mean difference was 0.02 (95% limits of agreement: -0.26 to 0.29). Spearman's rank correlation coefficient was 0.58, and diagnostic agreement was 72%. Most in-procedure QFR analyses demonstrated very good (19%), good (45%), or acceptable (28%) SOP adherence, while 8% were rated as poor or very poor. Suboptimal angiographic quality, poor in-procedure QFR analysis quality, high SYNTAX score, and diabetes were predictors of increased variability. CONCLUSIONS: In FAVOR III Europe, agreement between in-procedure and core laboratory QFR was modest. Measurement variability increased with reduced angiographic quality, poor in-procedure QFR analysis quality, and more advanced coronary artery disease.