Quantitative Flow Ratio Based on Murray Fractal Law: Accuracy of Single Versus Two Angiographic Views

Angiography-Derived Fractional Flow Reserve: Newer Data and Future Directions

Several novel software systems have been developed for the reconstruction of the coronary artery tree and the calculation of fractional flow reserve (FFR) from coronary artery angiography images without coronary artery instrumentation: FFRangio, Computational pressure-flow dynamics derived FFR, quantitative flow ratio (QFR), and vessel FFR. In this report, we review the current evidence on each software, their contemporary use, and future directions.

Main Coronary Flow Calculation With the Assistance of Physiological Side Branch Flow

OBJECTIVE

Fractional flow reserve (FFR) derived from coronary angiography, referred to as ICA-FFR, is a less-invasive alternative for invasive FFR measurement based on computational fluid dynamics. Blood flow into side branches influences the accuracy of ICA-FFR. However, properly compensating for side branch flow in ICA-FFR analysis is challenging. In this study, we proposed a physiological side branch flow model to comprehensively compensate side branch flow for ICA-FFR analysis with no need for reconstructing side branch geometry.

METHODOLOGY

the physiological side branch flow model employed a reduced-order model to calculate the pressure distribution in vessel segments. The main coronary artery (without side branches) was delineated and divided based on bifurcation nodes. The model compensates for flow to invisible side branches within each segment and flow to visible side branches at each bifurcation node. Lastly, ICA-FFR based on physiological side branch flow model (ICA-FFR) was calculated from a single angiographic view. Functional stenosis is defined by FFR 0.80.

RESULT

Our study involved 223 vessels from 172 patients. Using invasive FFR as a reference, the Pearson correlation coefficient of ICA-FFR was 0.93. ICA-FFR showed a high AUC (AUC = 0.96) and accuracy (91.9) in predicting functional stenosis.

CONCLUSION

The proposed model accurately compensates for flow to side branches without their geometry in ICA-FFR analysis. ICA-FFR analysis exhibits high feasibility and diagnostic performance in identifying functional stenosis.

Physiological Performance of Drug-Coated Balloons in Small Coronary Arteries PICCOLETO II μFR

BACKGROUND

Drug-coated balloons (DCB) are emerging as an alternative to permanent implants for managing de novo coronary artery disease, particularly in small vessels (SVD). This sub-analysis of the PICCOLETO II study aimed to compare the performance of DCB and DES in terms of Murray's law-based quantitative flow ratio (μFR) changes between baseline, post-percutaneous coronary intervention (PCI), and follow-up.

METHODS

Patients with a clinical indication for PCI were assigned to receive either Xience DES or Elutax SV/Emperor DCB. Coronary angiograms were blindly analyzed by an independent Core Laboratory (Consorzio Futuro in Ricerca, University of Ferrara, Italy).

RESULTS

Among 232 patients, 59 were included in this analysis. Pre-PCI μFR was comparable between groups (0.65 ± 0.29 vs. 0.58 ± 0.25; p = 0.20). Post-PCI, the DCB group had a lower acute functional gain compared to DES (+0.21 vs. +0.31; p = 0.064), with lower μFR values (0.86 ± 0.36 vs. 0.89 ± 0.3; p = 0.074). At 6-month follow-up, μFR values were similar between groups (0.84 ± 0.29 vs. 0.84 ± 0.31, p = 0.93), with a comparable late functional loss (-0.02 vs. -0.05; p = 0.93). Angiographic late lumen loss was significantly lower in the DCB group (-0.03 vs. +0.29 mm; p = 0.027).

CONCLUSIONS

DCB-based PCI showed a trend toward less favorable immediate post-PCI functional result but a comparable performance at follow-up, suggesting its potential in treating de novo SVD.

Integrated Assessment of Coronary Physiology Based on Coronary Angiography in Heart Transplant Patients

BACKGROUND

Early detection of cardiac allograft vasculopathy after heart transplant (HTx) with invasive coronary angiography is challenging.

AIMS

The study aimed to determine if computational techniques able to assess epicardial lesions, by means of Murray's law-based quantitative flow ratio (μFR), and microvascular physiology, by means of angiography microvascular resistance (AMR), enhance risk stratification in HTx patients with nonsignificant coronary artery disease.

METHODS

The cohort consisted of 86 consecutive HTx patients (200 epicardial vessels) with stenosis < 50% at baseline. μFR ≤ 0.80 indicated coronary ischemia, while AMR ≥ 2.5 suggested microvascular dysfunction. Clinical events were assessed over a median follow-up of 43 months, focusing on the relationship between μFR and target vessel failure (TVF), and between AMR and heart failure (HF) hospitalizations.

RESULTS

At baseline, mean μFR was 0.94 ± 0.08, with eight vessels (4.0%) disclosing flow-limiting lesions, while AMR was 2.4 ± 0.7, with 80 vessels/40 patients (40.0%/46.5%) having microvascular dysfunction. TVF-related segments were associated with lower mean μFR values (0.89 ± 0.14 vs. 0.95 ± 0.05; p < 0.007) compared TVF-free segments. At the receiver operating characteristic curve a μFR ≤ 0.93 demonstrated an area under the curve of 0.632 (95% CI: 0.562-0.699) in predicting TVF occurrence, showing an accuracy of 76.0%, a sensitivity of 46.9%, a specificity of 81.6%, a negative predictive value of 89.0%, and a positive predictive value of 32.6%. μFR ≤ 0.93 showed a significant interaction with TVF occurrence at 43 months (32.6% vs. 11.0%; HR: 2.96; 95% CI: 1.26-6.96; p = 0.013). Microvascular dysfunction showed a significant interaction with HF hospitalizations occurence (AMR: 2.8 ± 4.4 vs. 2.4 ± 4.5; p = 0.001; CMD: 27.5% vs. 4.3%; HR: 7.36; 95% CI: 2.45-22.07; p = 0.002).

CONCLUSIONS

Angiography-derived epicardial and microvascular physiology computation may improve risk stratification of heart transplanted patients.

Validation of angiography-derived Murray law-based quantitative flow reserve (μQFR) against pressure-derived instantaneous wave-free ratio for assessing coronary lesions, a single-center study in Egypt

BACKGROUND

Instantaneous wave-free ratio (iwFR) is a well-validated method for functional evaluation of intermediate coronary lesions. A recently developed Murray law-based QFR (µQFR) allows wire-free FFR estimation using a high-quality single angiographic projection. We aim to determine the diagnostic accuracy of µQFR as compared to wire-based iwFR for physiological assessment of coronary lesions in a sample of Egyptian patients.

RESULTS

Over a one-year period, patients who previously underwent iwFR assessment of an intermediate coronary stenosis (40-90%) were retrospectively included. μQFR analysis was then performed offline using a dedicated artificial intelligence (AI)-aided computation software. All the measurements were performed blinded to iwFR results, and the agreement between iwFR and μQFR values was tested. Forty-nine patients (mean age 57.9 ± 9 years, 72.9% males) were included. Mean value of iwFR and μQFR was 0.90 ± 0.075 and 0.79 ± 0.129, respectively. There was a significant moderate positive linear correlation between μQFR and iwFR (r = 0.47, p = 0.001; 95% CI 0.22-0.68) with moderate-to-substantial agreement between the two methods (Kappa 0.6). In assessing the diagnostic accuracy of μQFR, the receiver operating characteristic (ROC) curve yielded an area under the curve (AUC) of 0.84 (95% CI 0.717-0.962) for predicting functionally significant lesions defined as iwFR < 0.89. The sensitivity and specificity of μQFR < 0.8 for detecting physiological significance of coronary lesions were 89% and 74% with positive and negative predictive values of 70 and 91%, respectively.

CONCLUSION

µQFR has good diagnostic accuracy for predicting functionally significant coronary lesions with moderate correlation and agreement with the gold standard iwFR. Angiography-derived µQFR could be a promising tool for improving the utilization of physiology-guided revascularization.

Rationale and design of a comparison of angiography-derived fractional flow reserve-guided and intravascular ultrasound-guided intervention strategy for clinical outcomes in patients with coronary artery disease: a randomised controlled trial (FLAVOUR II)

INTRODUCTION

Percutaneous coronary intervention (PCI) guided by coronary angiography-derived fractional flow reserve (FFR) or intravascular ultrasound (IVUS) has shown improved clinical outcomes compared with angiography-only-guided PCI. In patients with intermediate stenoses, FFR resulted in fewer coronary interventions and was non-inferior to IVUS with respect to clinical outcomes. However, whether this finding can be applied to angiography-derived FFR in significant coronary artery disease (CAD) remains unclear.

METHOD AND ANALYSIS

The comparison of angiography-derived FFR-guided and IVUS-guided intervention strategies for clinical outcomes in patients with coronary artery disease (FLAVOUR II) trial is a multicentre, prospective, randomised controlled trial. A total of 1872 patients with angiographically significant CAD (stenoses of at least 50% as estimated visually through angiography) in a major epicardial coronary artery will be randomised 1:1 to receive either angiography-derived FFR-guided or IVUS-guided PCI. Patients will be treated with second-generation drug-eluting stent according to the predefined criteria for revascularisation: angiography-derived FFR≤0.8 and minimal lumen area (MLA)≤3 mm2 or 3 mm270%. The primary endpoint is a composite of all-cause death, myocardial infarction and revascularisation at 12 months after randomisation. We will test the non-inferiority of the angiography-derived FFR-guided strategy compared with the IVUS-guided decision for PCI and the stent optimisation strategy.The FLAVOUR II trial will provide new insights into optimal evaluation and treatment strategies for patients with CAD.

ETHICS AND DISSEMINATION

FLAVOUR II was approved by the institutional review board at each participating site (The Second Affiliated Hospital of Zhejiang University School of Medicine Approval No: 2020LSYD410) and will be conducted in line with the Declaration of Helsinki. Informed consent would be obtained from each patient before their participation. The study results will be submitted to a scientific journal.

TRIAL REGISTRATION NUMBER

NCT04397211.

Post-procedural and long-term functional outcomes of jailed side branches in stented coronary bifurcation lesions assessed with side branch Murray law-based quantitative flow ratio

Introduction

In coronary bifurcation lesions treated with percutaneous coronary intervention (PCI) using a 1-stent strategy, the occurrence of side branch (SB) compromise may lead to long-term myocardial ischemia in the SB territory. Murray law-based quantitative flow ratio (μQFR) is a novel angiography-based approach estimating fractional flow reserve from a single angiographic view, and thus is more feasible to assess SB compromise in routine practice. However, its association with long-term SB coronary blood flow remains unknown.

Methods

A total of 146 patients with 313 non-left main bifurcation lesions receiving 1-stent strategy with drug-eluting stents was included in this retrospective study. These lesions had post-procedural Thrombolysis in Myocardial Infarction (TIMI) flow grade 3 in SBs, and documented angiographic images of index procedure and 6- to 24-month angiographic follow-up. Post-procedural SB μQFR was calculated. Long-term SB coronary blood flow was quantified with the TIMI grading system using angiograms acquired at angiographic follow-up.

Results

At follow-up, 8 (2.6%), 16 (5.1%), 61 (19.5%), and 228 (72.8%) SBs had a TIMI flow grade of 0, 1, 2, and 3, respectively. The incidences of long-term SB TIMI flow grade ≤1 and ≤2 both tended to decrease across the tertiles of post-procedural SB μQFR. The receiver operating characteristic curve analyses indicated the post-procedural SB μQFR ≤0.77 was the optimal cut-off value to identify long-term SB TIMI flow grade ≤1 (specificity, 37.50%; sensitivity, 87.20%; area under the curve, 0.6673; P = 0.0064), and it was independently associated with 2.57-fold increased risk (adjusted OR, 2.57; 95% CI, 1.02-7.25; P = 0.045) in long-term SB TIMI flow grade ≤1 after adjustment.

Discussion

Post-procedural SB μQFR was independently associated with increased risk in impaired SB TIMI flow at long-term follow-up. Further investigations should focus on whether PCI optimization based on μQFR may contribute to improve SB flow in the long term.