Comparison of Resting Full-Cycle Ratio and Fractional Flow Reserve in a German Real-World Cohort

Abstract

Objective: The aim of this study was to evaluate non-hyperemic resting pressure ratios (NHPRs), especially the novel "resting full-cycle ratio" (RFR; lowest pressure distal to the stenosis/aortic pressure during the entire cardiac cycle), compared to the gold standard fractional flow reserve (FFR) in a "real-world" setting. Methods: The study included patients undergoing coronary pressure wire studies at one German University Hospital. No patients were excluded based on any baseline or procedural characteristics, except for insufficient quality of traces. The diagnostic performance of four NHPRs vs. FFR ≤ 0.80 was tested. Morphological characteristics of stenoses were analyzed by quantitative coronary angiography. Results: 617 patients with 712 coronary lesions were included. RFR showed a significant correlation with FFR (r = 0.766, p < 0.01). Diagnostic accuracy, sensitivity, specificity, positive predictive value, and negative predictive value of RFR were 78% (95% confidence interval = 75; 81), 72% (65; 78), 81% (77; 84), 63% (57; 69), and 86% (83; 89). Relevant predictors for discordance of RFR ≤ 0.89/FFR > 0.8 were LAD lesions, peripheral artery disease, age, female sex and non-focal stenoses. Predictors for discordance of RFR > 0.89/FFR ≤ 0.8 included non-LCX lesions, percent diameter stenosis and previous percutaneous coronary intervention in the target vessel. RFR and all other NHPRs were highly correlated with each other. Conclusion: All NHPRs have a similar correlation with the gold standard FFR and may facilitate the acceptance and implementation of physiological assessments of lesion severity. However, we found ~20% discordant results between NHPRs and FFR in our "all-comers" German cohort.

Keywords: coronary artery disease (CAD); coronary physiology; fractional flow reserve (FFR); invasive coronary angiography (ICA); resting full-cycle ratio (RFR).

Figure 1

Schematic explanation of the NHPRs and FFR. Diastole starts at the nadir of the dicrotic notch. The dPR[entire] is defined as mean Pd/Pa over the entire diastole. The dPR[WFP] is defined as the mean Pd/Pa value in the wave-free period for 5 heart cycles (from 25% of the entire diastole to 5 ms before the end of diastole; equivalent to the definition of iFR). Whole cycle resting Pd/Pa was calculated continuously throughout the entire cardiac cycle for three heart cycles. FFR is defined as the lowest, artifact-free Pd/Pa during maximal hyperemia over at least three heart cycles (Pd/Pa and FFR are calculated in the same way, just under different conditions, i.e. resting conditions vs hyperemic conditions). RFR is defined as the lowest Pd/Pa value in systole and diastole (mean of 5 consecutive cardiac cycles). dPR[entire], diastolic pressure ratio during entire diastole; dPR[WFP], diastolic pressure ratio during wave-free period; FFR, fractional flow reserve; NHPR, non-hyperemic pressure ratio; Pa, aortic pressure; Pd, distal coronary pressure; RFR, resting full-cycle ratio.

Figure 2

Concordance and discordance among NHPRs and FFR. (A) FFR and RFR showed a significant correlation (r = 0.766; p < 0.01), but 21.0% of lesions showed discordant classifications with FFR and RFR cutoff values of ≤0.80 and ≤0.89, respectively. (B–D) The correlation of FFR and dPR[entire], dPR[WFP] and Pd/Pa was also significant with a similar correlation coefficient. The frequency of discordant indices was comparable, too. dPR[entire], diastolic pressure ratio during entire diastole; dPR[WFP], diastolic pressure ratio during wave-free period; FFR, fractional flow reserve; NHPR, non-hyperemic pressure ratio; Pa, aortic pressure; Pd, distal coronary pressure; RFR, resting full-cycle ratio.

Figure 3

Bland-Altman plots of differences against the means are displayed for RFR (A), dPR[entire] (B), dPR[WFP] (C) and Pd/Pa (D). Solid lines represent the mean bias, enclosed by the limits of agreement (dashed lines). The Bland-Altman plots demonstrate a good agreement between FFR and NHPRs. dPR[entire], diastolic pressure ratio during entire diastole; dPR[WFP], diastolic pressure ratio during wave-free period; FFR, fractional flow reserve; NHPR, non-hyperemic pressure ratio; Pa, aortic pressure; Pd, distal coronary pressure; RFR, resting full-cycle ratio.

Figure 4

ROC curves. (A) ROC curves for RFR, dPR[entire], dPR[WFP] and Pd/Pa showed a similar performance of all NHPRs tested against an FFR ≤ 0.80. (B) ROC curves for dPR[WFP], dPR[entire], and Pd/Pa tested against RFR ≤ 0.89. All three indexes showed an excellent prediction for RFR defined ischemia, supporting the similar performance of all NHPRs. dPR[entire], diastolic pressure ratio during entire diastole; dPR[WFP], diastolic pressure ratio during wave-free period; FFR, fractional flow reserve; NHPR, non-hyperemic pressure ratio; Pa, aortic pressure; Pd, distal coronary pressure; RFR, resting full-cycle ratio.