Retrospective comparison of Resting Full-cycle Ratio (RFR) and Fractional Flow Reserve (FFR) in a coronary artery disease cohort

Abstract Background The fractional flow reserve (FFR) is the gold standard for the assessment of the physiological severity of coronary artery disease. Measurement of FFR requires administration of a vasodilator (commonly adenosine) to achieve maximum hyperemia. The development of resting indices that do not require the administration of adenosine is of great importance. A novel hyperemia-free resting index is the “resting full cycle ratio” (RFR), which corresponds to the lowest pressure distal to the stenosis in relation to the aortic pressure during the entire cardiac cycle. The aim of the present study was to examine the diagnostic accuracy of RFR compared to FFR. Methods The study included consecutive patients undergoing pressure wire studies for standard indications at our university hospital from March 9, 2015 to February 15, 2019. Lesions with FFR ≤0.80 were classified as functionally significant. The RFR values were calculated retrospectively from the curves of the FFR measurements, using a point in time before adenosine administration, so that non-hyperemic resting conditions were present. Results A total of 635 patients with 733 coronary lesions were investigated using FFR. The average age of the subjects was 68.1±10.7 years. 459 (72.3%) were male. The distribution of the lesions was as follows: LAD: 444 (60.5%), RCA: 140 (19.1%), RCX: 127 (17.3%), RIM: 12 (1.6), LM: 6 (0.9%) and bypasses: 4 (0.5). Overall, the FFR and RFR values were 0.841±0.08 and 0.91±0.06. The RFR showed a significant correlation with the FFR (Table 1). Diagnostic accuracy of the RFR compared to the FFR was highest at a cut-off value of 0.89. This could be demonstrated using the receiver operating characteristic curve (Picture 1). In 408 measurements, coronary stenoses that were not hemodynamically relevant were found (FFR>0.8 and RFR>0.89). 164 measurements showed hemodynamically relevant coronary stenoses (FFR ≤0.8 and RFR ≤0.89). In 66 lesions, the FFR measurement showed hemodynamic relevance and the RFR measurement did not, whereas in 95 patients the RFR measurement showed hemodynamic relevance and the FFR values were normal. Conclusions The RFR as a new resting index has a significant correlation with the FFR after adenosine administration. In 22% of the measurements, a different therapeutic decision would have been made based on the RFR vs. the FFR. A randomized study should therefore investigate whether a RFR-guided approach is non-inferior to a FFR-guided approach in