LAUSR

Fractional flow reserve (FFR) is a recommended tool to assess the hemodynamic relevance of borderline stenosis of epicardial coronary arteries but requires costly pressure wires and administration of a hyperemic agent [1]. A novel approach enabling rapid computation of FFR pullbacks from three-dimensional quantitative coronary angiography (3D QCA) has recently been developed [2, 3]. The computational FFR, known as quantitative flow ratio (QFR), may be obtained from 3D QCA using an advanced computer algorithms [2]. However, so far, data on the clinical performance of QFR are rather limited. Thus, the aim herein, was to assess the accuracy of QFR and correlation between QFR and FFR in the assessment of borderline coronary artery stenoses. Consecutive patients with stable angina, who were scheduled for FFR, were prospectively enrolled. Ethics approval was granted by the institutional ethics review process. Details of FFR procedure were previously described [4, 5]. Computation of QFR was performed offline, using a software package (Medis Suite 2.1.12.2, Medis Medical Imaging System, Leiden, the Netherlands) by two independent corelab analyzers who were blinded to FFR results. The analysis was conducted twice by each analyzer and the mean value (from four calculations) was used for further analysis. The software computed QFR pullback was performed with frame count analysis separately on two diagnostic angiographic projections without pharmacologically induced hyperemia, and empiric hyperemic flow velocities were derived from software computed with two new QFR pullbacks. The QFR pullbacks were chosen based on the best image quality (most well-defined contrast flow) in the frame count analysis as the QFR pullback to compare with the pressure wire-based FFR. The QFR value at the position that matched the location of the pressure transducer on the pressure wire was used for comparison with the FFR value measured by the pressure wire. The flow velocity was derived by dividing the arterial segment length from 3D QCA and the corresponding dye flow time from the frame count analysis. The software allowed for selection of a subsegment of the reconstructed artery with good visualization of the dye flow for calculation of flow velocity. Using the guide catheter for calibration and an edge detection system (CAAS 5.7 QCA system, Pie Medical), the reference vessel diameter and minimum lumen diameter were measured, and the percent diameter stenosis (DS%) was calculated. A total of 50 patients with 123 borderline coronary artery stenoses were enrolled. Overall, mean age was 66.0 ± 9.3 years, and 72% of patients were male. The left anterior descending artery was the most commonly assessed vessel (39%). Mean angiographic DS% was 44.2 ± 11.7%. The mean FFR assessed with the femoral vein adenosine infusion at 140 μg/kg/min was 0.82 ± ± 0.10 and 49 (39.8%) vessels had FFR ≤ 0.80, 24 (19.5%) vessels — FFR ≤ 0.75. Figure 1A shows the distribution of the FFR values. Mean QFR value was 0.82 ± 0.09. Forty-seven (38.2%) vessels had QFR value ≤ 0.80 and 30 (24.4%) vessels had QFR ≤ 0.75. A limited intraand interobserver variability for measuring the QFR was confirmed by intraclass correlation coefficient of 0.991 (95% confidence interval [CI] 0.988–0.993) and 0.990 (95% CI 0.987–0.992), respectively. More importantly, an excellent agreement between FFR and