Applicability of quantitative flow ratio for rapid evaluation of intermediate coronary stenosis: comparison with instantaneous wave-free ratio in clinical practice

Quantitative flow ratio (QFR) is an image-based fractional flow reserve (FFR) computed by three-dimensional quantitative coronary angiography and estimated flow velocity. Several studies have reported that QFR was rapidly computed within approximately 5 min and had a good diagnostic performance as compared with FFR. However, studies comparing QFR with instantaneous wave-free ratio (iFR) as an index with a prognostic value comparable to that of FFR are limited. Thus, we investigated the applicability of QFR with respect to iFR, both being easy-to-measure indices not requiring pharmacological hyperaemic induction. We computed QFR in prospectively enrolled 150 coronary lesions (including 50 lesions for onsite QFR analysis) in consecutive patients with intermediate stenosis evaluated by iFR. The correlation and diagnostic performance of QFR were compared using iFR as a reference. The mean QFR and iFR were 0.81 ± 0.12 and 0.89 ± 0.11, respectively. QFR and iFR exhibited a good correlation in all subjects (R = 0.70, p < 0.0001) and the onsite-analysed vessels (R = 0.74, p < 0.0001). In the receiver-operating characteristics analysis, the area under the curve of QFR predicting iFR ≤ 0.89 was 0.91. Applying the cut-off value of QFR ≤ 0.80 and iFR ≤ 0.89, the sensitivity, specificity, positive and negative predictive values were 85%, 83%, 72%, and 91%, respectively, in all subjects, and 82%, 82%, 78%, and 85%, respectively, in the onsite-analysed vessels. QFR including onsite analysis demonstrated a good correlation with iFR and a diagnostic performance comparable to that of iFR in consecutive patients with intermediate coronary stenosis, suggesting its potential as a rapidly derived index for evaluating myocardial ischaemia in clinical settings.