Quantitative flow ratio and non-hyperemic pressure ratio in patients with intermediate coronary lesions

Quantitative flow ratio (QFR) is a recent, non-invasive method for functional coronary assessment, providing estimates of lesion-specific ischemia without the need for pressure wires or hyperemic agents. While its diagnostic concordance with fractional flow reserve (FFR) has been previously explored, data comparing QFR to non-hyperemic pressure ratios (NHPRs), such as instantaneous wave-free ratio (iwFR) and resting full-cycle ratio (RFR), remain limited.

This study aimed to evaluate the diagnostic agreement between QFR and NHPRs in real-world patients undergoing physiological assessment for intermediate coronary stenoses.

Lesions from the CAST registry with available iwFR or RFR and analyzable angiograms for QFR computation were included. Ischemia was defined as NHPRs ≤0.89 or QFR ≤0.80. Diagnostic performance was assessed using sensitivity, specificity, predictive values, and ROC analysis (AUC via DeLong's method). Agreement was evaluated with Cohen's kappa and Bland-Altman analysis. McNemar's test assessed asymmetry in discordant pairs. Spearman's correlation and logistic univariate and multivariable regressions identified predictors of QFR-NHPRs discordance.

A total of 174 lesions from 142 patients were included in the final analysis. QFR demonstrated a diagnostic accuracy of 79 %, with a sensitivity of 90 % and a negative predictive value of 82 %, in respect of NHPRs. Specificity and positive predictive value were 63 % and 78 %, respectively. The area under the ROC curve was 0.80 (95 % CI, 0.733-0.867). QFR underestimated ischemia in 14.9 % of lesions (false negatives), and overall diagnostic discordance with NHPRs occurred in 20.7 % of cases. Longer lesion length was independently associated with higher concordance (OR 0.95, 95 % CI 0.91-0.99, p = 0.012), while bifurcation lesions were predictors of discordance (OR 4.81, 95 % CI 1.30-21.12, p = 0.024).

QFR shows moderate concordance with NHPRs and may serve as a useful, wire-free alternative for excluding functionally significant stenoses. While it demonstrated high sensitivity, the risk of false negatives in certain anatomical subsets highlights the value of a cautious, individualized approach, possibly integrating QFR with invasive indices or imaging modalities in selected cases.