Quantitative flow ratio as a new tool for angiography-based physiological evaluation of coronary artery disease: a review

Coronary Artery Disease and Transcatheter Aortic Valve Replacement

Concomitant coronary artery disease (CAD) and severe aortic stenosis (AS) are frequently encountered in patients evaluated for transcatheter aortic valve replacement (TAVR). Invasive coronary angiography remains the mainstay for anatomical assessment of CAD, whereas coronary computed tomography angiography may be used in patients with a low pretest probability of CAD. Adjunctive functional evaluation of coronary lesions has proven safe in the presence of AS, but uncertainty remains over the impact of AS on the results of functional testing. For patients with CAD, revascularization of significant lesions (≥90% stenosis, fractional flow reserve ≤0.80) is associated with improved clinical outcomes compared to medical therapy. However, the optimal timing of percutaneous coronary intervention (PCI) remains unclear with no clear benefit to revascularization in advance of TAVR. When planning post-TAVR PCI, careful consideration should be given to the type of valve implanted, with short-frame valves having more favorable coronary access after TAVR. Planning for future coronary access is particularly relevant for patients who have either unrevascularized obstructive coronary lesions or unknown coronary anatomy in advance of TAVR. Moreover, post-TAVR PCI will likely increase, given the younger age profile of patients being treated and the trend to defer revascularization until after valve replacement.

Prognostic implications of quantitative flow ratio and optical coherence tomography-guided neointimal characteristics in drug-coated balloon treatment for in-stent restenosis

The aim of this study was to investigate the relationship between quantitative flow ratio (QFR) after drug-coated balloon (DCB) treatment for in-stent restenosis (ISR) and between neointimal characteristics assessed by optical coherence tomography (OCT) and clinical outcomes. This single-center, retrospective, observational cohort study included ISR patients who underwent DCB angioplasty under OCT guidance. The primary outcome of the study was a target vessel failure (TVF), defined as a composite endpoint of cardiovascular death, target vessel myocardial infarction and target vessel revascularization. During a median follow-up of 756 days (IQR: 443.25, 1134.50), 204 ISR patients underwent OCT-guided DCB angioplasty, resulting in TVF development in 27 patients. At the post-procedural DCB angioplasty, the vessel-level QFR was significantly lower in the TVF group (0.89 [IQR: 0.87, 0.93] vs. 0.93 [IQR: 0.91, 0.96]; P < 0.001) than in the non-TVF group. Analysis of the qualitative characteristics of ISR lesions showed a significantly higher incidence of heterogeneous neointima in the TVF group compared with the non-TVF group (13 [48.15%] vs. 32 [18.08%]; P < 0.001). In the multivariable Cox regression analysis, low vessel-level QFR (HR per 0.1 increase: 0.11; 95% CI: 0.03-0.41; P < 0.001) and heterogeneous neointima were independently associated with TVF. The TVF rate of vessels with the 2 features was 10.69 times higher than that of all other vessels (95%CI [2.05-55.79]; log-rank P < 0.0001). Vessel-level QFR and heterogeneous neointima were independent factors associated with TVF in ISR patients after DCB angioplasty. Adding the QFR measure-ment to OCT findings may enable better discrimination of patients with subsequent TVF post-DCB angioplasty for ISR.

Impact of trans-stent gradient on outcome after PCI: results from a HAWKEYE substudy

To test whether quantitative flow ratio (QFR)-based trans-stent gradient (TSG) is associated with adverse clinical events at follow-up. A post-hoc analysis of the multi-center HAWKEYE study was performed. Vessels post-PCI were divided into four groups (G) as follows: G1: QFR ≥ 0.90 TSG = 0 (n = 412, 54.8%); G2: QFR ≥ 0.90, TSG > 0 (n = 216, 28.7%); G3: QFR < 0.90, TSG = 0 (n = 37, 4.9%); G4: QFR < 0.90, TSG > 0 (n = 86, 11.4%). Cox proportional hazards regression model was used to analyze the effect of baseline and prognostic variables. The final reduced model was obtained by backward stepwise variable selection. Receiver operating characteristic (ROC) was plotted and area under the curve (AUC) was calculated and reported. Overall, 449 (59.8%) vessels had a TSG = 0 whereas (40.2%) had TSG > 0. Ten (2.2%) vessel-oriented composite endpoint (VOCE) occurred in vessels with TSG = 0, compared with 43 (14%) in vessels with TSG > 0 (p < 0.01). ROC analysis showed an AUC of 0.74 (95% CI: 0.67 to 0.80; p < 0.001). TSG > 0 was an independent predictor of the VOCE (HR 2.95 [95% CI 1.77–4.91]). The combination of higher TSG and lower final QFR (G4) showed the worst long-term outcome while low TSG and high QFR showed the best outcome (G1) while either high TSG or low QFR (G2, G3) showed intermediate and comparable outcomes. Higher trans-stent gradient was an independent predictor of adverse events and identified a subgroup of patients at higher risk for poor outcomes even when vessel QFR was optimal (> 0.90).

Diagnostic comparison of automatic and manual TIMI frame-counting-generated quantitative flow ratio (QFR) values

Quantitative flow ratio (QFR) is a computational measurement of FFR (fractional flow reserve), calculated from coronary angiography. Latest QFR software automates TIMI frame counting (TFC), which occurs during the flow step of QFR analyses, making the analysis faster and more reproducible. The objective is to determine the diagnostic performance of QFR values obtained from analyses using automatic TFC compared to those obtained from analyses using manual TFC. This was a single-arm clinical trial that used the prospective analysis of the coronary angiographic image series of 97 patients who underwent evaluation of stable coronary artery disease with FFR/iFR at MedStar Washington Hospital Center in Washington, DC, USA. Automatic and manual TFC QFR values were obtained from the analyses of each of the 97 patients' image series, with manual TFC QFR values as the current gold standard for comparison. The diagnostic performance of automatic TFC QFR values was measured as follows: sensitivity was 0.87 (95% CI 0.66-0.97) and specificity was 1.00 (95% CI 0.9514-1.00), positive predictive value (PPV) was 1.00 (95%CI 1.00-1.00), while the NPV was 0.96 (95% CI 0.96-0.99). Overall accuracy was 96.91% (95% CI 91.23%-99.36%). The agreement as illustrated by the Bland-Altman plot shows a bias of 0.0023 (SD 0.0208) and narrow limits of agreement (LOA): Upper LOA 0.0573 and Lower LOA - 0.0528. The area under curve (AUC) was 0.996. QFR values generated from automatic TFC are comparable to those generated from manual TFC in diagnostic capability. The most recent software update produces values equivalent to those of the previous manual option, and can therefore be used interchangeably.

Comparison of quantitative flow ratio and invasive physiology indices in a diverse population at a tertiary United States hospital

BACKGROUND

Quantitative flow ratio (QFR) is a technology to evaluate the coronary stenosis significance on 3-dimensional quantitative coronary angiography. The aim of this study is to evaluate and compare the QFR versus fractional flow reserve (FFR) and/or instantaneous free-wave ratio (iFR) in a US population with a fair African American population representation.

METHODS AND RESULTS

This was a retrospective, observational and single center study which enrolled 100 patients who underwent coronary angiography. The diagnostic performance of QFR in terms of sensitivity was 0.80 (95%CI 0.64-0.97) and specificity was 0.95 (95%CI 0.90-1.00), the positive predictive value (PPV) was 0.83 (0.68-0.98), while the NPV was 0.94 (0.88-0.99). The overall accuracy was 0.91 and area under curve (AUC) was 0.92 (95% CI 0.87-0.97). The R-squared was 0.54 and the Bland-Altman plot showed a bias of 0.0016 (SD 0.063) and limits of agreement (LOA): Upper LOA 0.13 and Lower LOA -0.12. In African Americans (n = 33), accuracy, AUC, sensitivity, specificity (94%; 0.90 (0.80-1.00); 0.90 (0.71-1.00); 0.96 (0.87-1.00), respectively) were better than those for the overall population.

CONCLUSIONS

In a US based representative population, vessel QFR accuracy and agreement with FFR as reference is high. Diagnostic performance of QFR in African Americans is also excellent.