Contrast medium Pd/Pa ratio in comparison to fractional flow reserve, quantitative flow ratio and instantaneous wave-free ratio for evaluation of intermediate coronary lesions

Introduction
Contrast medium Pd/Pa ratio (cFFR) was introduced as an alternative to fractional flow reserve (FFR). To assess the accuracy of cFFR in predicting of FFR, quantitative flow ratio (QFR) and instantaneous wave-free ratio (iFR).

Material and methods
Resting Pd/Pa, cFFR, FFR, QFR, and iFR were measured in 110 intermediate coronary lesions. cFFR was obtained after intracoronary injection of contrast medium. FFR was measured after the intravenous administration of adenosine. QFR was derived from fixed empiric hyperemic flow velocity based on coronary angiography. iFR was calculated by measuring the resting pressure gradient across a coronary lesion during diastole.

Results
Forty-four patients with 110 intermediate coronary lesions were enrolled. Mean baseline Pd/Pa was 0.93 ±0.05. Mean cFFR value was similar to FFR value (0.83 ±0.09 vs. 0.81 ±0.09; p = 0.13) and QFR (0.81 ±0.1; p = 0.69) and iFR (0.90 ±0.07; p = 0.1). A total of 46 vessels (41.8%) had FFR ≤ 0.80, 50 (45.5%) vessels had cFFR ≤ 0.83, 44 (40.0%) vessels had QFR ≤ 0.80, and 38 (34.5%) vessels had iFR ≤ 0.89. An excellent agreement between cFFR and resting Pd/Pa, FFR, QFR, and iFR was confirmed (intraclass correlation coefficients of 0.83, 0.99, 0.98, and 0.88, respectively). The optimal cutoff value of cFFR was 0.83 for prediction of FFR ≤ 0.80 with sensitivity, specificity, and accuracy of 96.9%, 97.8%, and 97.3%, respectively. 100% sensitivity was observed for a cutoff value of 0.82 and 100% specificity for a cutoff value of 0.84; AUC = 0.998 (0.995–1.00); p < 0.001.

Conclusions
Contrast medium Pd/Pa ratio seems to be accurate in predicting the functional significance of borderline coronary lesions assessed with FFR, iFR, and QFR.