Relative Flow Reserve Derived From Quantitative Perfusion Imaging May Not Outperform Stress Myocardial Blood Flow for Identification of Hemodynamically Significant Coronary Artery Disease

Abstract

Background— Quantitative myocardial perfusion imaging is increasingly used for the diagnosis of coronary artery disease. Quantitative perfusion imaging allows to noninvasively calculate fractional flow reserve (FFR). This so-called relative flow reserve (RFR) is defined as the ratio of hyperemic myocardial blood flow (MBF) in a stenotic area to hyperemic MBF in a normal perfused area. The aim of this study was to assess the value of RFR in the detection of significant coronary artery disease. Methods and Results— From a clinical population of patients with suspected coronary artery disease who underwent oxygen-15–labeled water cardiac positron emission tomography and invasive coronary angiography, 92 patients with single- or 2-vessel disease were included. Intermediate lesions (diameter stenosis, 30%–90%; n=75) were interrogated by FFR. Thirty-eight (41%) vessels were deemed hemodynamically significant (>90% stenosis or FFR ≤0.80). Hyperemic MBF, coronary flow reserve, and RFR were lower for vessels with a hemodynamically significant lesion (2.01±0.78 versus 2.90±1.16 mL·min −1 ·g −1 ; P <0.001, 2.27±1.03 versus 3.10±1.29; P <0.001, and 0.67±0.23 versus 0.93±0.15; P <0.001, respectively). The correlation between RFR and FFR was moderate ( r =0.54; P <0.01). Receiver operator characteristic curve analysis showed an area under the curve of 0.82 for RFR, which was not significantly higher compared with that for hyperemic MBF and coronary flow reserve (0.76; P =0.32 and 0.72; P =0.08, respectively). Conclusions— Noninvasive estimation of FFR by quantitative perfusion positron emission tomography by calculating RFR is feasible, yet only a trend toward a slight improvement of diagnostic accuracy compared with hyperemic MBF assessment was determined.

Physiologic Stenosis Severity, Binary Thinking, Revascularization, and “Hidden Reality”

“…7,8 The lower right quadrant of Figure 3 in this article 1 shows a different kind of discordance-a high FFR with low coronary flow capacity characterizing diffuse CAD 4-7 associated with high risk of coronary events; its natural history may be improved by coronary artery bypass surgery, 9 but that hypothesis remains untested in a randomized trial. The present study used FFR as the standard reference of severity based on the profoundly important FAME randomized trials that moved interventional thinking from anatomic to physiological stenosis severity as the optimal guide to percutaneous coronary intervention (PCI).…”

“…T he interesting study by Stuijfzand et al 1 in this issue of Circulation: Cardiovascular Imaging compares positron emission tomography (PET)-measured coronary flow reserve (CFR), maximum absolute stress perfusion (MBF) in cc/ min/g, and relative CFR (RFR) for predicting pressure-derived fractional flow reserve (FFR) in patients undergoing coronary angiography for suspected CAD. 2,3 RFR was determined as the ratio of regional MBF of stenotic arteries to MBF of nonstenotic arteries.…”

Integrated Myocardial Perfusion Imaging Diagnostics Improve Detection of Functionally Significant Coronary Artery Stenosis by 13 N-ammonia Positron Emission Tomography

“…Sensitivity analyses were subsequently performed to determine whether diagnostic performance was alterable through other methods of calculating RFR. On reanalysis of our data, applying the RFR calculation method of Stuijfzand et al, 22 correlation between FFR and RFR (correlation coefficient: 0.78 versus 0.407; P<0.001) and diagnostic performance of RFR to determine low FFR were significantly low (Table I in In addition, the magnitude of correlation between FFR and RFR was higher in patients whose reference segment was assigned as FFR-guided method (FFR ≥0.95), regardless of stenosis degree, than in patients whose reference segment was solely assigned by angiography-guided method (<30% luminal stenosis; correlation coefficient: 0.788 versus 0.708; interaction P<0.001; Figure III in the Data Supplement).…”

“…PET-derived CFR was calculated as the ratio of stress MBF to resting MBF 20,21 and RFR, as the ratio of stress MBF in target myocardial territories to that of a reference vascular territory. 22 Parametric stress MBF polar maps were visually referenced to delineate defect areas in target myocardial territories, obtaining MBF values of target vessels in defects only. 23 The averaged stress MBF in 3 segments with highest MBF was used as reference hyperemic MBF.…”

Flow-Based Functional Assessment of Coronary Artery Disease by Myocardial Perfusion Positron Emission Tomography in the Era of Fractional Flow Reserve

“…It was initially introduced as an invasive surrogate marker of relative severity of myocardial ischemia, and validated by comparison with PET-derived relative coronary flow reserve (CFR) (11). Ironically, however, novel flowbased functional assessment parameters measured by PET should be validated by comparison with FFR as a reference test these days (16,17).…”