Abstract Background The relative flow reserve (RFR) derived from quantitative myocardial perfusion imaging (MPI), defined as the ratio of absolute myocardial perfusion in a stenotic area to the perfusion in a normally perfused area, is considered the non-invasive equivalent of the invasive fractional flow reserve (FFR). In patients without prior CAD, RFR does not outperform hyperemic myocardial blood flow (hMBF) in detecting hemodynamically significant coronary artery disease (CAD). However, studies in patients with prior CAD found high MPI false positive rates when referenced against FFR, potentially attributed to microvascular disease. Therefore, we studied the diagnostic value of RFR over absolute perfusion in patients with prior CAD. Methods The PACIFIC-2 trial included symptomatic patients with prior myocardial infarction and/or percutaneous coronary intervention who underwent 15OH2O position emission tomography (PET) perfusion imaging and invasive coronary angiography with three-vessel FFR. We performed RFR analysis on two cohorts: 1) an overall cohort including all patients of PACIFIC-2 stress PET; and 2) an optimal cohort consisting of patients with angiographic 1- or 2 vessel disease and a healthy reference vessel. RFR was calculated as the ratio between the lowest to highest regional hMBF (overall cohort) or the lowest hMBF of a stenotic area to the regional hMBF of the healthy reference area (optimal cohort). Results The overall cohort included 187 patients (63±9.3 years, 36 19% female), and the optimal cohort included 80 patients (62±9.6 years, 19 24% female). Significant CAD was present in 87 (47%) and 43 (54%) vessels, respectively. Correlation between RFR and FFR for both cohorts were 0.60 and 0.66 (P0.001) (Figure 1). Areas under the curve for RFR and hMBF were comparable in the overall (0.78 vs 0.81, P=0.288) and the optimal (0.79 vs 0.82, P=0.512) cohort (Figure 2). Conclusions RFR proves applicable in a clinical setting without the need of optimizing patient selection for improvement of diagnostic performance. However, RFR does not improve diagnostic performance over absolute myocardial perfusion for the detection of FFR-defined significant CAD in a population with prior CAD and recurrence of symptoms.Correlation between hMBF and RFR Areas under the curve of hMBF and RFR
Hoek et al. (Sat,) studied this question.