Korean Circ J.  2021 Feb;51(2):126-139. 10.4070/kcj.2020.0375.

Association of Quantitative Flow Ratio with Lesion Severity and Its Ability to Discriminate Myocardial Ischemia

• Dai N
• Hwang D
• Lee JM
• Zhang J
• Tong Y
• Jeon KH
• Paeng JC
• Cheon GJ
• Koo BK
• Ge J

• KMID: 2512450
• DOI: http://doi.org/10.4070/kcj.2020.0375

Abstract

Background and Objectives
Quantitative flow ratio (QFR) is an angiography-based technique for functional assessment of coronary artery stenosis. This study investigated the response of QFR to different degree of stenosis severity and its ability to predict the positron emission tomography (PET)-defined myocardial ischemia.
Methods
From 109 patients with 185 vessels who underwent both 13 N-ammonia PET and invasive physiological measurement, we compared QFR, fractional flow reserve (FFR) and instantaneous wave-free ratio (iFR) for the responses to the different degree of anatomical (percent diameter stenosis [%DS]) and hemodynamic (relative flow reserve [RFR], coronary flow reserve, hyperemic stenosis resistance, and stress myocardial flow) stenosis severity and diagnostic performance against PET-derived parameters.
Results
QFR, FFR, and iFR showed similar responses to both anatomic and hemodynamic stenosis severity. Regarding RFR, the diagnostic accuracy of QFR was lower than FFR (76.2% vs. 83.2%, p=0.021) and iFR (76.2% vs. 84.3%, p=0.031). For coronary flow capacity (CFC), QFR showed a lower accuracy than iFR (74.1% vs. 82%, p=0.031) and lower discriminant function than FFR (area under curve: 0.74 vs. 0.79, p=0.044). Discordance between QFR and FFR or iFR was shown in 14.6% of cases and was driven by the difference in %DS and heterogeneous distribution of PET-derived RFR and stress myocardial blood flow.
Conclusions
QFR demonstrated a similar response to different anatomic and hemodynamic stenosis severity as FFR or iFR. However, its diagnostic performance was inferior to FFR and iFR when PET-derived RFR and CFC were used as a reference.

Keyword

Coronary artery disease; Myocardial ischemia; Positron emission tomography

Figure

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  Figure 1 Correlations between angiographic severity and pressure-derived physiologic indices.Correlations between 2D and 3D %DS and FFR, iFR and QFR are shown. There were significant correlations between 2D %DS and FFR, iFR and QFR, as well as 3D %DS and FFR, iFR and QFR. Redline was drawn using polynomial regression.2D = 2-dimensional; 3D = 3-dimensional; FFR = fractional flow reserve; iFR = instantaneous wave-free ratio; %DS = percent diameter stenosis; QCA = quantitative coronary angiography; QFR = quantitative flow ratio.

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  Figure 2 Pressure-derived physiologic indices according to hemodynamic severity groups.This figure shows the values of FFR, iFR, and QFR, according to RFR, CFR, HSR and stress MBF. Solid circle and error bar mean the mean value and standard error, respectively.FFR = fractional flow reserve; iFR = instantaneous wave-free ratio; RFR = relative flow reserve; CFR = coronary flow reserve; HSR = hyperemic stenosis resistance; MBF = myocardial blood flow; QFR = quantitative flow ratio.

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  Figure 3 Discriminant functions of QFR, FFR and iFR against PET-derived indices.Comparison of ROC curves of FFR, iFR, and QFR to predict RFR, CFR, and CFC are shown and AUCs are presented.AUC = area under curve; CFC = coronary flow capacity; CFR = coronary flow reserve; CI = confidence interval; FFR = fractional flow reserve; iFR = instantaneous wave-free ratio; PET = positron emission tomography; QFR = quantitative flow ratio; RFR = relative flow reserve; ROC = receiver operating characteristic.

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  Figure 4 Anatomical and physiological severity according to QFR and FFR or iFR agreement.The different distribution patterns of stenosis severity indices are shown in QFR and FFR agreement groups (A) and QFR and iFR agreement groups (B). The red star means a p value of <0.05. Each box ranges from upper quartile to lower quartile of the parameters and line inside the box indicates the location of the median value. The whiskers expand from the box to upper (upper quartile + 1.5×IQR) and lower (lower quartile − 1.5×IQR) extreme and outliers are plotted as individual dots.FFR = fractional flow reserve; iFR = instantaneous wave-free ratio; IQR = interquartile range; QCA = quantitative coronary angiography; QFR = quantitative flow ratio.

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