Background: Contrast-flow quantitative flow ratio (QFR) is a novel, software-based noninvasive method for the quantitative evaluation of coronary physiology using computational fluid dynamics, based on 3D vessel reconstruction in coronary angiograms. Computing this 3D-model of the vessel using a specialized algorithm, the software computes the virtual FFR. This new technique has shown a high accuracy in determining the functional significance of coronary stenosis of the three main epicardial coronary arteries using the gold standard FFR as reference. However, QFR data for the evaluation of coronary side branches (SB) are scarce. Therefore, the study aimed to determine the feasibility of this novel method to analyze SB and to characterize optimal viewing angles for the evaluation using QFR.  

Methods: A total of 87 patients with suspected CCS, who underwent a coronary angiography with routine core lab projections, were enrolled and were analyzed retrospectively by two certified experts with the software QAngio XA 3D 3.2 (Medis, Leiden, The Netherlands). In addition, 37 patients were enrolled prospectively using coronary angiography projections recommended for the virtual QFR-Analysis. Quantitative Analysis was performed only for SB with a maximum lumen diameter (MLD) of >2mm. The following outcome parameters were analyzed: baseline characteristics, SB parameters such as MLD and vessel length and procedure parameters, such as use of applicated contrast medium, procedure time and fluoroscopy time.

Results: 187 side branches (obtuse marginal, diagonal branch, intermediate ans posterior descending artery and posterolateral branch) were analyzed using QFR. Out of 87 patients undergoing a coronary angiography with routine projections with 224 SB > 2mm, 123 SB (55%) were computable with the use of QFR. In the prospective cohort of 37 patients with recommended angiographic projections of main branches, 75 SB > 2mm were found. 64 of the 75 SB (85%) were computable with the use of QFR. The use of recommended projections led to an overall significant higher evaluability of SB compared to the use of routine cath lab projections (85% vs. 55%, p<0.001). The data show that the fluoroscopy time for recommended QFR projections was not significantly different to the time for routine projections (3.7±2.2 vs. 4.6±3, p = 2.69). The study shows a significant increase of the amount of contrast medium used for QFR projections (55.4±24.2 vs. 87.95±43.7, p < 0.01).  The study shows a significant increase of the procedure time used for the QFR-recommended projections (23.2±16.4 vs. 36.1±17.2, p<0.01).

 
Fig. 1: A QFR evaluability in overall of SD with routine projections and B QFR evaluability of SD with recommended projections

Conclusion: To our knowledge this is the first study evaluating QFR for SB analysis. QFR is feasible for the routine assessment of side branches (SD) with MLD> 2mm. The use of recommended projections significantly improved the quality of the QFR SB analysis apart from PDA and IA, without increasing the fluoroscopy time during coronary angiography. Overall QFR could increase the use of physiologically guided coronary interventions, not only for the main epicardial vessels, but also for the big and potentially relevant SB, leading to the Chance of a targeted, patient friendly examination on the future.