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IntroductionThe use of non-invasive Fractional Flow Reserve derived from CT coronary angiography ( i.e. FFR-CT) is increasingly becoming the mainstay in the investigation and thus management of patients with intermediate-risk chest pain in the United Kingdom. The UK National Institute of Care Excellence (NICE) recommends the use of FFR-CT to assess the functional significance of stenosis found on computed tomographic coronary angiogram( CTCA). This is expected to save cost and reduce unnecessary invasive coronary angiography . FFR-CT was introduced routinely in the cardiology service of our hospital in 2019. Our aims is to describe our experience and to assess the utility of FFR-CT on evaluating the functional significance of stenotic lesions on CT coronary angiography among our patient population.MethodsThe hospital’s electronic medical record and the FFR-CT provider company's portal were queried for data on all patients who were referred for CT-FFR analysis from May 2019 to June 2022 . Significant coronary stenosis was defined as FFRCT of ≤ 0.8 in at least 1 vessel. This was correlated with the rates of invasive angiography and revascularization. We also looked at this rates in cases that were not analysed due to CT image qualityResultsA total of 90 cases were referred for FFR CT analysis in the period under review. 25 cases ( 27%) were rejected or not analysed due to artifacts or image quality .65 cases were thus analysed of which 35 patients (53.8%) had a FFRCT≤ 0.80 and 30 patients(46.1%) had FFRCT≥ 0.80. Invasive angiograph was performed on 15 patients(42.8%) with FFRCT≤0.08 and of these,9 had a revascularization procedure done. Of the Patients with FFRCT≥0.08, Invasive angiography was performed on 3 patients(10%), 2 of which had revascularisation. Also we noted that 18 of the 25 patients(72%) who did not have their CTCA analysed due to image quality had invasive angiography done. Four of these patients did have revascularisation .ConclusionThe use of FFR-CT allows some intermediate-risk patients with chest pain to be managed without being subjected to the risks of invasive coronary angiography. However, this modality relies on the quality of CTCA . Poor quality image is a factor that may undermine the patient safety and cost saving benefit that the implementation of FFR-CT is meant to provideAbstract 189 Figure 1Sanky chart showing FFR-CT referrals and downstream analysusConflict of InterestNil

Purpose of ReviewThree-dimensional quantitative coronary angiography-based methods of fractional flow reserve (FFR) derivation have emerged as an appealing alternative to conventional pressure-wire-based physiological lesion assessment and have the potential to further extend the use of physiology in general. Here, we summarize the current evidence related to angiography-based FFR and perspectives on future developments.Recent FindingsGrowing evidence suggests good diagnostic performance of angiography-based FFR measurements, both in chronic and acute coronary syndromes, as well as in specific lesion subsets, such as long and calcified lesions, left main coronary stenosis, and bifurcations. More recently, promising results on the superiority of angiography-based FFR as compared to angiography-guided PCI have been published.SummaryCurrently available angiography -FFR indices proved to be an excellent alternative to invasive pressure wire-based FFR. Dedicated prospective outcome data comparing these indices to routine guideline recommended PCI including the use of FFR are eagerly awaited.

Background: The noninvasive computed tomography angiography–derived fractional flow reserve (CT-FFR) can be used to diagnose coronary ischemia. With advancements in associated software, the diagnostic capability of CT-FFR may have evolved. This study evaluates the effectiveness of a novel deep learning-based software in predicting coronary ischemia through CT-FFR. Methods: In this prospective study, 138 subjects with suspected or confirmed coronary artery disease were assessed. Following indication of 30%–90% stenosis on coronary computed tomography (CT) angiography, participants underwent invasive coronary angiography and fractional flow reserve (FFR) measurement. The diagnostic performance of the CT-FFR was determined using the FFR as the reference standard. Results: With a threshold of 0.80, the CT-FFR displayed an impressive diagnostic accuracy, sensitivity, specificity, area under the receiver operating characteristic curve (AUC), positive predictive value (PPV), and negative predictive value (NPV) of 97.1%, 96.2%, 97.7%, 0.98, 96.2%, and 97.7%, respectively. At a 0.75 threshold, the CT-FFR showed a diagnostic accuracy, sensitivity, specificity, AUC, PPV, and NPV of 84.1%, 78.8%, 85.7%, 0.95, 63.4%, and 92.8%, respectively. The Bland–Altman analysis revealed a direct correlation between the CT-FFR and FFR (p < 0.001), without systematic differences (p = 0.085). Conclusions: The CT-FFR, empowered by novel deep learning software, demonstrates a strong correlation with the FFR, offering high clinical diagnostic accuracy for coronary ischemia. The results underline the potential of modern computational approaches in enhancing noninvasive coronary assessment.

Objective To assess the accuracy of a virtual stenting tool based on coronary CT angiography (CCTA) and fractional flow reserve (FFR) derived from CCTA (FFR CT Planner) across different levels of image quality. Materials and methods Prospective, multicenter, single-arm study of patients with chronic coronary syndromes and lesions with FFR ≤ 0.80. All patients underwent CCTA performed with recent-generation scanners. CCTA image quality was adjudicated using the four-point Likert scale at a per-vessel level by an independent committee blinded to the FFR CT Planner. Patient- and technical-related factors that could affect the FFR CT Planner accuracy were evaluated. The FFR CT Planner was applied mirroring percutaneous coronary intervention (PCI) to determine the agreement with invasively measured post-PCI FFR. Results Overall, 120 patients (123 vessels) were included. Invasive post-PCI FFR was 0.88 ± 0.06 and Planner FFR CT was 0.86 ± 0.06 (mean difference 0.02 FFR units, the lower limit of agreement (LLA) − 0.12, upper limit of agreement (ULA) 0.15). CCTA image quality was assessed as excellent (Likert score 4) in 48.3%, good (Likert score 3) in 45%, and sufficient (Likert score 2) in 6.7% of patients. The FFR CT Planner was accurate across different levels of image quality with a mean difference between FFR CT Planner and invasive post-PCI FFR of 0.02 ± 0.07 in Likert score 4, 0.02 ± 0.07 in Likert score 3 and 0.03 ± 0.08 in Likert score 2, p  = 0.695. Nitrate dose ≥ 0.8mg was the only independent factor associated with the accuracy of the FFR CT Planner (95%CI − 0.06 to − 0.001, p  = 0.040). Conclusion The FFR CT Planner was accurate in predicting post-PCI FFR independent of CCTA image quality. Clinical relevance statement Being accurate in predicting post-PCI FFR across a wide spectrum of CT image quality, the FFR CT Planner could potentially enhance and guide the invasive treatment. Adequate vasodilation during CT acquisition is relevant to improve the accuracy of the FFR CT Planner. Key Points • The fractional flow reserve derived from coronary CT angiography (FFR CT ) Planner is a novel tool able to accurately predict fractional flow reserve after percutaneous coronary intervention. • The accuracy of the FFR CT Planner was confirmed across a wide spectrum of CT image quality. Nitrates dose at CT acquisition was the only independent predictor of its accuracy. • The FFR CT Planner could potentially enhance and guide the invasive treatment. Graphical abstract

IntroductionMurray’s law relates blood flow (Q) to vessel diameter (D) (Q ∝ D3) in coronary trees. As a fundamental physiological law, it is used to inform various computational techniques for deriving coronary physiology, including virtual fractional flow reserve (vFFR), absolute distal flow (Qd) and microvascular resistance (CMVR). However, the cubed exponent of 3.0 is disputed; the Huo Kassab law suggests that it is 2.33. The aim of this study was to assess the sensitivity of the flow-diameter exponent in deriving computed coronary physiology.MethodsUsing an established 1D model of coronary flow, we evaluated vFFR, Qd and CMVR in 403 idealised coronary arteries, derived from angiography and invasive physiology data. The flow-diameter exponent was used to determine the magnitude of side-branch flow, which was sequestered along the length of the vessel according to local taper and pressure.ResultsMedian vFFR was 0.87 [0.75 – 0.94] using an exponent of 2.33 and 0.90 [0.79 – 0.95] using an exponent of 3.0. Correlation was strong (r = 0.985, p < 0.0001). Relative to an exponent of 2.33, Murray’s original exponent of 3.0 overestimated vFFR by +0.02 (95% CI 0.00 to +0.10) and resulted in a change in management (vFFR ≤ 0.80) in 28 (6.9%) cases. Correlation was also significant for both Qd and CMVR (r = 0.992, p < 0.0001 and r = 0.997, p < 0.0001 respectively). However, compared with vFFR, agreement was relatively poorer for Qd (-15 mL/min, 95% CI -5 to -28 mL/min) and CMVR (+361 WU, 95% CI +40 to +2176 WU).DiscussionThe flow-diameter exponent influences the diagnostic accuracy of vFFR, with even more pronounced implications for advanced measures of coronary physiology. Determination of the optimum flow-diameter exponent for human coronary arteries is, therefore, an important question in clinical cardiology.Abstract 220 Figure 1Scatter plot comparing vFFR with exponents 2.33 versus 3.0Abstract 220 Figure 2Bland Altman plot comparing vFFR with exponents 2.33 versus 3.0Conflict of InterestNone

The energy sector is currently undergoing a rapid transformation with the integration of power electronic converter (PEC)-interfaced renewable energy sources (RES), such as wind and solar photovoltaic (PV) systems, at both the transmission and distribution networks. Power system stability has been significantly influenced by this power grid transformation. This paper comprehensively reviews major power system stability issues affected due to large-scale integration of PEC-interfaced RES in power grids, with some example case studies relevant for each stability category. According to the review, stability issues are mainly originating from reduction in synchronous inertia, reduction in reactive power reserve, low short-circuit strength of the power network, and fault ride-through (FRT) strategy/capability of the PEC-interfaced RES. Decrease in synchronous inertia could affect both the rotor angle stability and the frequency stability, while decrease in short-circuit strength and reactive power reserve could cause voltage stability and rotor angle stability issues in power networks. Sub-synchronous control interactions are also receiving a lot of attention by the power industry due to increasing oscillatory stability incidents reported in power networks with PEC-interfaced RES. FRT capabilities/strategies of PEC-interfaced RES are also playing a pivotal role in power grid stability due to its influence on active and reactive power, hence more emphasis should be placed on FRT schemes of PEC-interfaced RES, since future power grids are expected to operate with 100% PEC-interfaced generation sources. Stability improvement strategies could be implemented to address multiple stability issues in PEC-interfaced power networks; however, rigorous stability studies are required to identify the optimal conditions to implement these improvement strategies. Furthermore, ongoing structural changes in power grids to accommodate remotely sited PEC-interfaced RES are also influencing the stability of power grids. Therefore, all these factors must be carefully considered by system operators when planning and operating power grids in a secure and stable manner with high penetration levels of PEC-interfaced RES.

Purpose of Review The goal of this article is to review the data supporting the use of fractional flow reserve derived from coronary computed tomography angiography (FFR CT ) in patients with chest pain. Review Findings Numerous clinical trials have demonstrated that the diagnostic accuracy of coronary computed tomography angiography (CCTA) can be improved with the use of FFR CT , primarily due to its superior specificity when compared to CCTA alone. This promising development may help reduce the need for invasive angiography in patients presenting with chest pain. Furthermore, some studies have indicated that incorporating FFR CT into decision-making is safe, with an FFR CT value of ≥ 0.8 being associated with favorable outcomes. While FFR CT has been shown to be feasible in patients with acute chest pain, further large-scale studies are warranted to confirm its utility. Summary The emergence of FFR CT as a tool for the management of patients with chest pain is promising. However, potential limitations require the interpretation of FFR CT in conjunction with clinical context.

The current management of acute coronary syndromes (ACS) is with an invasive strategy to guide treatment. However, identifying the lesions which are physiologically significant can be challenging. Non-invasive imaging is generally not appropriate or timely in the acute setting, so the decision is generally based upon visual assessment of the angiogram, supplemented in a small minority by invasive pressure wire studies using fractional flow reserve (FFR) or related indices. Whilst pressure wire usage is slowly increasing, it is not feasible in many vessels, patients and situations. Limited evidence for the use of FFR in non-ST elevation (NSTE) ACS suggests a 25% change in management, compared with traditional assessment, with a shift from more to less extensive revascularisation. Virtual (computed) FFR (vFFR), which uses a 3D model of the coronary arteries constructed from the invasive angiogram, and application of the physical laws of fluid flow, has the potential to be used more widely in this situation. It is less invasive, fast and can be integrated into catheter laboratory software. For severe lesions, or mild disease, it is probably not required, but it could improve the management of moderate disease in 'real time' for patients with non-ST elevation acute coronary syndromes (NSTE-ACS), and in bystander disease in ST elevation myocardial infarction. Its practicability and impact in the acute setting need to be tested, but the underpinning science and potential benefits for rapid and streamlined decision-making are enticing.

Assessing fractional flow reserve (FFR) with a pressure wire is frequently underused due to the invasiveness of guide wire insertion and the necessity for a hyperemic agent. This study aimed to assess the diagnostic accuracy of the CAAS-vessel FFR (vFFR) software tool compared to pressure wire (pw) FFR in evaluating coronary stenotic lesions. A single-center, prospective study was conducted at Clinique Saint Clotilde, Reunion Island, from August 2023 to March 2024. All patients undergoing coronary angiograms with pwFFR assessment of lesion severity of 40%-70% were included. Diagnostic accuracy, sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of vFFR were calculated using pwFFR as the reference standard. The cutoff value of 0.80 was used for both modalities. A total of 116 patients with 146 lesions were included. The mean age was 67±9years old, with 19% being female. Patients had an average of 1.3±0.4 lesions each, with a mean pwFFR of 0.79±0.09 and a mean vFFR of 0.79±0.28. The overall diagnostic accuracy of vFFR was 77%, with sensitivity/specificity of 85%/71% and PPV/NPV of 67%/87%. For the left anterior descending coronary artery, the accuracy was 78%, with a sensitivity/specificity of 81%/78%. In the grey zone (invasive FFR 0.75-0.85), the accuracy dropped to 70%. vFFR is a reliable noninvasive alternative to pwFFR, showing acceptable diagnostic accuracy in line with current literature.

ObjectivesAs stipulated by the 2016 NICE Chest Pain of recent onset guidelines, Computed Tomography Coronary Angiography (CTCA) is the recommended first line investigation when stable angina cannot be excluded by clinical assessment alone (1). Non-invasive Computed Fractional Flow Reserve (CT-FFR; Heartflow) is a method which utilises CT data as a diagnostic tool in identification of patients that may benefit from coronary revascularisation (2). We aimed to evaluate the diagnostic utility of CT-FFR in a district general setting in predicting significant coronary disease, defined as a positive functional test or the need for revascularisation (percutaneous or coronary artery bypass grafting).Method:This was a single centre, retrospective study of patients who had CTCA with subsequent FFR analysis from July 2019 to February 2021 (n=106). Electronic records were used to determine subsequent downstream testing and revascularisation. Lesions were documented as concordant or discordant; the former indicating an FFR result that was in keeping with the reported anatomical severity and the latter indicated discrepant results. Due to the intermediate nature of CAD-RADS 3 results, CT-FFR findings could not be defined as either concordant or discordant. Positive and negative predictive values of both CTCA and CT-FFR in identifying significant coronary pathology were calculated.Results:106 patients underwent CTCA with FFR analysis. 15 were excluded from this study due to suboptimal image quality preventing reliable FFR results. The Positive Predictive Value (PPV) and Negative Predictive Value (NPV) for CTCA alone in predicting functionally significant coronary disease was 41.3% and 86.9%, respectively. When the CAD-RADS 3 cohort was eliminated, PPV increased to 71.4% and the NPV remained unchanged (86.9%). The combination of CTCA with FFR gives a Positive and Negative Predictive Value of 48.4% and 83.3%, respectively. With elimination of the CAD-RADS 3 group, PPV was 85.7% and NPV of 80%.Abstract 152 Figure 1Revascularisation in the discordant and concordant CT-FFR groupsAbstract 152 Figure 2Outcomes of FFR analysis in the CAD-RADS 3 cohortConclusionAs supported by previously published literature, the negative predictive value of both CTCA in isolation, and when combined with FFR remains consistently reliable. Our study demonstrated that the positive predictive value is less reliable for both tests and supports the notion that these tests tend to over-estimate the severity of coronary lesions. However, at the extremes of the CAD-RADS spectrum, PPV is a much more robust variable, as highlighted by the increase in this value when CAD-RADS 3 results are removed from the cohort. This reiterates the importance of not letting test results detract from robust clinical assessment and symptom correlation, particularly in the context of discordant or intermediate results.References1. National Institute for health and care excellence (NICE) guidance for the assessment and diagnosis of recent-onset chest pain of suspected cardiac origin (clinical guideline 95 (CG95)).2. Pijls NH, van Schaardenburgh P, Manoharan G, et al. Percutaneous coronary intervention of functionally non-significant stenosis: 5-year follow-up of the defer study. J Am Coll Cardiol. 2007;49:2105–2111.Conflict of Interestnone