Novel Indices of Coronary Physiology

Review and Key Takeaways of the 2021 Percutaneous Coronary Intervention Guidelines

The 2021 Percutaneous Coronary Intervention guidelines completed by American College of Cardiology/American Heart Association/Society for Cardiovascular Angiography and Interventions provide a set of guidelines regarding revascularization strategies. With emphasis on equity of care, multidisciplinary heart team use, revascularization for acute coronary syndrome, and stable ischemic heart disease, the guidelines create a thorough framework with recommendations regarding therapeutic strategies. In this comprehensive review, our aim is to summarize the 2021 revascularization guidelines and analyze key points regarding each recommendation.

OUFR Versus FFR for Functional Assessment of Coronary Artery Stenosis in Patients With Unstable Angina

BACKGROUND

Hybrid intravascular ultrasound-optical coherence tomography (IVUS-OCT) imaging can integrate both advantages. Optical ultrasonic flow ratio (OUFR) was recently developed for functional assessment.

OBJECTIVES

This study aimed to verify the diagnostic performance of OUFR using fractional flow reserve (FFR) as the reference standard.

METHODS

From February 2023 to June 2023, 80 patients (126 vessels) with unstable angina pectoris were assessed with FFR and either hybrid IVUS-OCT or stand-alone IVUS imaging before percutaneous coronary intervention in a prospective series. OUFR based on OCT alone (OUFRO) or based on both (OUFROI) were derived from hybrid IVUS-OCT imaging in 61 patients (86 vessels). OUFR based on IVUS alone (OUFRI) was derived from single modality IVUS imaging in 58 patients (80 vessels). In all cases, wire-based FFR was measured in the same vessels for comparison.

RESULTS

All 3 computed OUFR indexes achieved high agreement with FFR, with OUFROI and OUFRO showing higher correlation with FFR (r = 0.88; P < 0.001; r = 0.85; P < 0.001, respectively) than OUFRI (r = 0.73; P < 0.001). Compared with OUFRO, the integration of both IVUS and OCT (OUFROI) further improved the diagnostic accuracy for predicting FFR ≤0.80 with accuracy, sensitivity, and specificity being 95%, 94%, and 96%, respectively. The area under the curve of OUFROI to predict FFR ≤0.80 was 0.99, higher than that for OUFRO (0.95) and OUFRI (0.91).

CONCLUSIONS

OUFROI is feasible and accurate in the prospective study, resulting in excellent agreement with FFR, superior to single imaging modality-based physiology indexes.

Coronary Physiological Indexes to Evaluate Myocardial Ischemia in Patients With Aortic Stenosis Undergoing Valve Replacement

BACKGROUND

The evaluation of myocardial ischemia in patients with aortic valve stenosis (AS) with concomitant coronary artery disease (CAD) and possible microvascular dysfunction (MVD) is challenging because fractional flow reserve (FFR) and the resting full-cycle ratio (RFR) have not been validated in this clinical setting.

OBJECTIVES

The aims of this study in patients with AS and CAD were: 1) to describe the relationship between hyperemic and resting indexes; 2) to investigate the acute and long-term effects of aortic valve replacement (AVR) on epicardial indexes and microvascular function; 3) to assess the impact of these changes on clinical decision making; and 4) to determine FFR/RFR ischemia cutoff points in AS.

METHODS

In this prospective multicentric study, we performed serial measurements of FFR and RFR and evaluated MVD by means of coronary flow reserve, the index of microvascular resistance, and microvascular resistance reserve in patients with severe AS and intermediate to severe CAD before and 6 months after AVR. Patients underwent myocardial perfusion single-photon emission computed tomography before AVR.

RESULTS

In total, 146 coronary lesions in 116 patients were included. Before AVR, we observed high FFR/RFR discordance according to standard cutoff values (FFR negative [>0.80]/RFR positive [≤0.89] in 42.3% [68/137] of these lesions). Acutely after AVR, FFR decreased significantly (-0.0120 ± 0.0192; P = 0.0045), whereas RFR remained stable (0.0140 ± 0.0673; P = 0.3089). Six months after AVR, FFR decreased (-0.0279 ± 0.0368), whereas RFR increased significantly (+0.0410 ± 0.0487) (P < 0.0001 for both), resulting in 21.5% (21/98) and 39.8% (39/98) of lesions crossing traditional FFR and RFR cutoff lines, respectively. Left ventricular mass decreased significantly (153.68 ± 44.22 g before vs 134.66 ± 37.26 g after; P < 0.0001). MVD was frequently observed at baseline (32.1% abnormal index of microvascular resistance and 68.6% abnormal microvascular resistance reserve) with all microvascular parameters improving after AVR. The most accurate cutoffs to predict ischemia were FFR ≤0.83 and RFR ≤0.85 with comparable accuracy (75%-80%).

CONCLUSIONS

In patients with severe AS and CAD, FFR ≤0.83 and RFR ≤0.85 appear to predict myocardial ischemia more accurately. Six months after AVR, FFR decreases, whereas RFR increases significantly with a simultaneous decrease of left ventricular mass and an improvement of microvascular function.

Diagnostic Accuracy of Computational Fluid Dynamics-Based Fractional Flow Reserve Derived From Coronary Angiography: The ACCURATE Study

BACKGROUND

Although fractional flow reserve (FFR) is the contemporary standard to detect hemodynamically significant coronary stenosis, it remains underused for the need of pressure wire and hyperemic stimulus. Coronary angiography-derived FFR could break through these barriers. The aim of this study was to assess the feasibility and performance of a novel diagnostic modality deriving FFR from invasive coronary angiography (AccuFFRangio) for coronary physiological assessment.

METHODS AND RESULTS

The ACCURATE (Angiography-Derived Fractional Flow Reserve for Functional Evaluation of Coronary Artery Disease) study was a prospective, multicenter study conducted at 5 centers. Patients who had at least 1 lesion with a diameter stenosis of 30% to 90% were eligible. AccuFFRangio was measured on site in real time and compared with invasive FFR measurements in a blinded fashion. Primary end point was the diagnostic accuracy of AccuFFRangio in identifying functional relevant lesions. Between November 2020 and June 2021, pairwise analyses of AccuFFRangio and FFR were performed in 304 coronary arteries. AccuFFRangio showed good correlation (r=0.89; P<0.001) and agreement (mean difference: 0.01±0.06) with FFR. The diagnostic accuracy was 95.07% (95% CI, 91.99%-97.21%), which were significantly exceeded the prespecified target value (P<0.001). The sensitivity, specificity, and area under the receiver operating characteristic curve of 95.83% (95% CI, 89.67%-98.85%), 94.71% (95% CI, 90.73%-97.33%), and 0.972 (95% CI, 0.947-0.988), respectively.

CONCLUSIONS

AccuFFRangio derived from coronary angiography alone has high diagnostic accuracy, sensitivity, and specificity compared with FFR. AccuFFRangio bears the potential for increasing the adoption of functional assessment of coronary artery stenosis and improving the use of physiological guided decision-making.

REGISTRATION

URL: https://www.clinicaltrials.gov; Unique identifier: NCT04814550.

Association of vessel fractional flow reserve (vFFR) with luminal obstruction and plaque characteristics as detected by optical coherence tomography (OCT) in patients with NSTE-ACS: the FAST OCT study

AIMS

There is a paucity of data on the performance of angiography-derived vessel fractional flow reserve (vFFR) in coronary artery lesions of patients presenting with non-ST-segment elevation acute coronary syndrome (NSTE-ACS). Optical coherence tomography (OCT) allows for visualization of lumen dimensions and plaque integrity with high resolution. The aim of this study was to define the association between vFFR and OCT findings in intermediate coronary artery lesions in patients presenting with NSTE-ACS.

METHODS AND RESULTS

The FAST OCT study was a prospective, multicenter, single-arm study. Patients presenting with NSTE-ACS with intermediate to severe coronary artery stenosis in one or multiple vessels with TIMI 3 flow suitable for OCT imaging were eligible. Complete pre-procedural vFFR and OCT data were available in 226 vessels (in 188 patients). A significant association between vFFR and minimal lumen area (MLA) was observed, showing an average decrease of 20.4% (95% CI -23.9% to -16.7%) in MLA per 0.10 decrease in vFFR (adjusted P < 0.001). vFFR ≤ 0.80 showed a sensitivity of 56.7% and specificity of 92.5% to detect MLA ≤ 2.5 mm2. Conversely, vFFR had a poor to moderate discriminative ability to detect plaque instability (sensitivity, 46.9%; specificity, 71.6%).

CONCLUSION

In patients with NSTE-ACS, vFFR is significantly associated with OCT-detected MLA, and vFFR ≤ 0.80 is highly predictive of the presence of significant disease based on OCT. Conversely, the sensitivity of vFFR ≤ 0.80 to detect OCT-assessed significant disease was low, indicating that the presence of significant OCT findings cannot be ruled out based on a negative vFFR.

Development and validation of a novel angiography-derived index of absolute coronary blood flow and resistance

Intracoronary continuous thermodilution has been recently proposed as an invasive method to quantify absolute coronary flow (Qabs) and resistance (Rabs) in vivo. The aim of the present study is to develop and validate of a novel pressure-wire- and microcatheter-free surrogate of coronary flow and resistance derived from a standard coronary angiogram. Angiography derived coronary flow (Qangio) and resistance (Rangio) was prospectively validated in a two-center cohort of patients from Oxford Heart Centre and the Essex Cardiothoracic Centre. Qabs and Rabs were measured during resting and hyperemic conditions with continuous thermodilution using the Rayflow microcatheter. Qangio and Rangio were computed from the diagnostic coronary angiogram in a blinded fashion in resting and hyperemic conditions. A total of 62 patients and 115 vessels were included in the present analysis. The median Qabs at rest was 75 ml/min (53-95) and 151 ml/min (105-203) during hyperemia; Qangio at rest was 84 ml/min (66-108) and 154 ml/min (115-195) during hyperemia. There was a strong correlation between Qabs and Qangio (R = 0,72; p < 0.001, R = 0,86; p < 0.001 respectively) with satisfactory interclass correlation (0.841, 95% CI 0.509-0.957; p = 0.0003). The median Rabs was 1111 mmHg/(L/min) (830-1581.4) at rest and 454 mmHg/(L/min) (348-610) during hyperemia; angiographic resistance (Rangio) was 937.4 mmHg/(L/min) (695.4-1261.9) at rest and 492.4 mmHg/(L/min) (406-697) during hyperemia. There was a strong correlation between Rabs and Rangio in both conditions (R = 0,81; p < 0.001 and R = 0,78; p < 0.001 respectively). The was a good correlation between absolute coronary flow reserve (CFR) and angiography-derived CFR (R = 0,61; p < 0.001) and between absolute microvascular resistance reserve (MRR) and angiography-derived MRR (R = 0,49; p < 0.001).

Predictive value of the inconsistency between the residual and post-PCI QFR for prognosis in PCI patients

Introduction

To investigate the prognostic value of the consistency between the residual quantitative flow ratio (QFR) and postpercutaneous coronary intervention (PCI) QFR in patients undergoing revascularization.

Methods

This was a single-center, retrospective, observational study. All enrolled patients were divided into five groups according to the ΔQFR (defined as the value of the post-PCI QFR minus the residual QFR): (1) Overanticipated group; (2) Slightly overanticipated group; (3) Consistent group; (4) Slightly underanticipated group; and (5) Underanticipated group. The primary outcome was the 5-year target vessel failure (TVF).

Results

A total of 1373 patients were included in the final analysis. The pre-PCI QFR and post-PCI QFR were significantly different among the five groups. TVF within 5 years occurred in 189 patients in all the groups. The incidence of TVF was significantly greater in the underanticipated group than in the consistent group (P = 0.008), whereas no significant differences were found when comparing the underanticipated group with the other three groups. Restricted cubic spline regression analysis showed that the risk of TVF was nonlinearly related to the ΔQFR. A multivariate Cox regression model revealed that a ΔQFR≤ -0.1 was an independent risk factor for TVF.

Conclusions

The consistency between the residual QFR and post-PCI QFR may be associated with the long-term prognosis of patients. Patients whose post-PCI QFR is significantly lower than the residual QFR may be at greater risk of TVF. An aggressive PCI strategy for lesions is anticipated to have less functional benefit and may not result in a better clinical outcome.

Intravascular Imaging-Derived Physiology-Basic Principles and Clinical Application

Intravascular imaging-derived physiology is emerging as a promising tool allowing simultaneous anatomic and functional lesion assessment. Recently, several optical coherence tomography-based and intravascular ultrasound-based fractional flow reserve (FFR) indices have been developed that compute FFR through computational fluid dynamics, fluid dynamics equations, or machine-learning methods. This review aims to provide an overview of the currently available intravascular imaging-based physiologic indices, their diagnostic performance, and clinical application.

Non-invasive fractional flow reserve derived from reduced-order coronary model and machine learning prediction of stenosis flow resistance

BACKGROUND AND OBJECTIVE

Recently, computational fluid dynamics enables the non-invasive calculation of fractional flow reserve (FFR) based on 3D coronary model, but it is time-consuming. Currently, machine learning technique has emerged as an efficient and reliable approach for prediction, which allows saving a lot of analysis time. This study aimed at developing a simplified FFR prediction model for rapid and accurate assessment of functional significance of stenosis.

METHODS

A reduced-order lumped parameter model (LPM) of coronary system and cardiovascular system was constructed for rapidly simulating coronary flow, in which a machine learning model was embedded for accurately predicting stenosis flow resistance at a given flow from anatomical features of stenosis. Importantly, the LPM was personalized in both structures and parameters according to coronary geometries from computed tomography angiography and physiological measurements such as blood pressure and cardiac output for personalized simulations of coronary pressure and flow. Coronary lesions with invasive FFR ≤ 0.80 were defined as hemodynamically significant.

RESULTS

A total of 91 patients (93 lesions) who underwent invasive FFR were involved in FFR derived from machine learning (FFRML) calculation. Of the 93 lesions, 27 lesions (29.0%) showed lesion-specific ischemia. The average time of FFRML simulation was about 10 min. On a per-vessel basis, the FFRML and FFR were significantly correlated (r = 0.86, p < 0.001). The diagnostic accuracy, sensitivity, specificity, positive predictive value and negative predictive value were 91.4%, 92.6%, 90.9%, 80.6% and 96.8%, respectively. The area under the receiver-operating characteristic curve of FFRML was 0.984.

CONCLUSION

In this selected cohort of patients, the FFRML improves the computational efficiency and ensures the accuracy. The favorable performance of FFRML approach greatly facilitates its potential application in detecting hemodynamically significant coronary stenosis in future routine clinical practice.

The influence of flow distribution strategy for the quantification of pressure- and wall shear stress-derived parameters in the coronary artery: A CTA-based computational fluid dynamics analysis

For image-based computational fluid dynamics (CFD) analysis to characterize the local coronary hemodynamic environment, the accuracy depends on the flow rate which is in turn associated with outlet branches' morphology. A good flow distribution strategy is important to mitigate the effect when certain branches cannot be considered. In this study, stenotic coronary arteries from 13 patients were used to analyze the effect of missing branches and different flow distribution strategies. Pressure- and wall shear stress (WSS)-derived parameters around the stenotic region (ROI) were compared, including fractional flow reserve (CT-FFR), instantaneous wave-free ratio (CT-iFR), resting distal to aortic coronary pressure (CT-Pd/Pa), time-averaged WSS, oscillatory shear index (OSI) and relative residence time (RRT). Three flow distribution strategies were the Huo-Kassab model at distal outlets (Type I), flow distribution based on outlet resistances (Type II), and a developed algorithm distributing flow at each bifurcation until the final outlets (Type III). Results showed that Type III strategy for models with truncated branch(es) had a good agreement in both pressure- and WSS-related results (interquatile range less than 0.12% and 4.02%, respectively) with the baseline model around the ROI. The relative difference of pressure- and WSS-related results were correlated with the flow differences in the ROI to the baseline mode. Type III strategy had the best performance in maintaining the flow in intermediate branches. It is recommended for CFD analysis. Removal of branches distal to a stenosis can be undertaken with an improved performance and maintained accuracy, while those proximal to the ROI should be kept.

Contemporary Use of Coronary Physiology in Cardiology

Coronary angiography has a limited ability to predict the functional significance of intermediate coronary lesions. Hence, physiological assessment of coronary lesions, via fractional flow reserve (FFR) or instantaneous wave-free ratio (iFR), has been introduced to determine their functional significance. An accumulating body of evidence has consolidated the role of physiology-guided revascularization, particularly among patients with stable ischemic heart disease. The use of FFR or iFR to guide decision-making in patients with stable ischemic heart disease and intermediate coronary lesions received a class I recommendation from major societal guidelines. Nevertheless, the role of coronary physiology testing is less clear among certain patients' groups, including patients with serial coronary lesions, acute coronary syndromes, aortic stenosis, heart failure, as well as post-percutaneous coronary interventions. In this review, we aimed to discuss the utility and clinical evidence of coronary physiology (mainly FFR and iFR), with emphasis on those specific patient groups.

#FullPhysiology: a systematic step-by-step guide to implement intracoronary physiology in daily practice

#FullPhysiology is a comprehensive and systematic approach to evaluate patients with suspected coronary disease using PressureWire technology (Abbott Vascular, Santa Clara, CA, USA). This advancement in technology enables the investigation of each component of the coronary circulation, including epicardial, microvascular, and vasomotor function, without significantly increasing procedural time or technical complexity. By identifying the predominant physiopathology responsible for myocardial ischemia, #FullPhysiology enhances precision medicine by providing accurate diagnosis and facilitating tailored interventional or medical treatments. This overview aims to provide insights into modern coronary physiology and describe a systematic approach to assess epicardial flow-limiting disease, longitudinal physiological vessel analysis, microvascular and vasomotor dysfunction, as well as post- percutaneous coronary intervention (PCI) physiological results.

Diagnostic performance of angiography-derived fractional flow reserve analysis based on bifurcation fractal law for assessing hemodynamic significance of coronary stenosis

OBJECTIVES

Blood flow into the side branch affects the calculation of coronary angiography-derived fractional flow reserve (FFR), called Angio-FFR. Neglecting or improperly compensating for the side branch flow may decrease the diagnostic accuracy of Angio-FFR. This study aims to evaluate the diagnostic accuracy of a novel Angio-FFR analysis that considers the side branch flow based on the bifurcation fractal law.

METHODS

A one-dimensional reduced-order model based on the vessel segment was used to perform Angio-FFR analysis. The main epicardial coronary artery was divided into several segments according to the bifurcation nodes. Side branch flow was quantified using the bifurcation fractal law to correct the blood flow in each vessel segment. In order to verify the diagnostic performance of our Angio-FFR analysis, two other computational methods were taken as control groups: (i) FFR_s: FFR calculated by delineating the coronary artery tree to consider side branch flow, (ii) FFR_n: FFR calculated by just delineating the main epicardial coronary artery and neglecting the side branch flow.

RESULTS

The analysis of 159 vessels from 119 patients showed that our Anio-FFR calculation method had comparable diagnostic accuracy to FFR_s and provided significantly higher diagnostic accuracy than that of FFR_n. In addition, using invasive FFR as a reference, the Pearson correlation coefficients of Angio-FFR and FFRs were 0.92 and 0.91, respectively, while that of FFR_n was only 0.85.

CONCLUSIONS

Our Angio-FFR analysis has demonstrated good diagnostic performance in assessing the hemodynamic significance of coronary stenosis by using the bifurcation fractal law to compensate for side branch flow.

CLINICAL RELEVANCE STATEMENT

Bifurcation fractal law can be used to compensate for side branch flow during the Angio-FFR calculation of the main epicardial vessel. Compensating for side branch flow can improve the ability of Angio-FFR to diagnose stenosis functional severity.

KEY POINTS

• The bifurcation fractal law could accurately estimate the blood flow from the proximal main vessel into the main branch, thus compensating for the side branch flow. • Angiography-derived FFR based on the bifurcation fractal law is feasible to evaluate the target diseased coronary artery without delineating the side branch.

Fast Computational Approaches to Derive Fractional Pressure Ratio in Patients with Extracranial or Intracranial Symptomatic Stenosis

OBJECTIVE

We aimed to evaluate the performance of fast and straightforward Murray law-based quantitative flow ratio (μQFR) computation in cerebrovascular stenosis.

METHODS

A total of 30 patients with symptomatic stenosis of 50%-70% luminal stenosis and underwent fractional pressure ratio (FPR) assessment at our hospital were included in the present study. μQFR was applied to the interrogated vessel. An artificial intelligence algorithm was proposed for automatic delineation of lumen contours of cerebrovascular stenosis. We used invasive FPRs as a reference standard. Pearson's correlation coefficient (r) was used to assess the correlation strength between the μQFR and FPR, and Bland-Altman plots were used to evaluate the agreement between the μQFR and FPR. An analysis of the receiver operating characteristic was used to evaluate the performance of μQFR.

RESULTS

Our results displayed a strong positive correlations (r = 0.92; P < 0.001) between the μQFR and pressure wire FPR. Excellent agreement was observed between the μQFR and FPR with a mean difference of 0.01 ± 0.08 (range, -0.16 to 0.14; P = 0.263). The overall accuracy for identifying an FPR of ≤0.7 was 92% (95% confidence interval [CI], 85%-100%). The area under the receiver operating characteristic curve was higher for the μQFR (0.92; 95% CI, 0.81-0.98) than for diameter stenosis (0.88; 95% CI, 0.75-0.95). The positive likelihood ratio was 3.9 for the μQFR with a negative likelihood ratio of 0.

CONCLUSIONS

The μQFR computation has a strong correlation and agrees with the FPR calculated from the pressure wire. Therefore, the μQFR might provide an essential therapeutic aid for patients with symptomatic stenosis.

Management of Residual Risk in Chronic Coronary Syndromes. Clinical Pathways for a Quality-Based Secondary Prevention

Chronic coronary syndrome (CCS), which encompasses a broad spectrum of clinical presentations of coronary artery disease (CAD), is the leading cause of morbidity and mortality worldwide. Recent guidelines for the management of CCS emphasize the dynamic nature of the CAD process, replacing the term "stable" with "chronic", as this disease is never truly "stable". Despite significant advances in the treatment of CAD, patients with CCS remain at an elevated risk of major cardiovascular events (MACE) due to the so-called residual cardiovascular risk. Several pathogenetic pathways (thrombotic, inflammatory, metabolic, and procedural) may distinctly contribute to the residual risk in individual patients and represent a potential target for newer preventive treatments. Identifying the level and type of residual cardiovascular risk is essential for selecting the most appropriate diagnostic tests and follow-up procedures. In addition, new management strategies and healthcare models could further support available treatments and lead to important prognostic benefits. This review aims to provide an overview of the diagnostic and therapeutic challenges in the management of patients with CCS and to promote more effective multidisciplinary care.

Fractional flow reserve and non-hyperemic indices: Essential tools for percutaneous coronary interventions

Hemodynamical evaluation of a coronary artery lesion is an important diagnostic step to assess its functional impact. Fractional flow reserve (FFR) received a class IA recommendation from the European Society of Cardiology for the assessment of angiographically moderate stenosis. FFR evaluation of coronary artery disease offers improvement of the therapeutic strategy, deferring unnecessary procedures for lesions with a FFR > 0.8, improving patients' management and clinical outcome. Post intervention, an optimal FFR > 0.9 post stenting should be reached and > 0.8 post drug eluting balloons. Non-hyperemic pressure ratio measurements have been validated in previous studies with a common threshold of 0.89. They might overestimate the hemodynamic significance of some lesions but remain useful whenever hyperemic agents are contraindicated. FFR remains the gold standard reference for invasive assessment of ischemia. We illustrate this review with two cases introducing the possibility to estimate also non-invasively FFR from reconstructed 3-D angiograms by quantitative flow ratio. We conclude introducing a hybrid approach to intermediate lesions (DFR 0.85-0.95) potentially maximizing clinical decision from all measurements.

Coronary Physiologic Assessment Based on Angiography and Intracoronary Imaging

Intracoronary physiology testing has evolved as a promising diagnostic approach in the management of patients with coronary artery disease. The value of hyperemic translesional pressure ratios to estimate the functional relevance of coronary stenoses is supported by a wealth of outcomes data. The continuing drive to further simplify this approach led to the development of non-hyperemic pressure-based indices. Recent attention has focused on estimating functional significance without invasively measuring coronary pressure through the measurement of virtual indices derived from the coronary angiogram. By offering a routine assessment of the physiology of all the major epicardial coronary vessels, angiogram-derived physiology has the potential to modify current practice by facilitating more accurate patient-level, vessel-level, and even lesion-level decision making. This article reviews the current state of angiogram-derived physiology and speculates on its potential impact on clinical practice, in continuation to the previously published article on coronary physiology in this journal.

Culprit versus Complete Revascularization during the Initial Intervention in Patients with Acute Coronary Syndrome Using a Virtual Treatment Planning Tool: Results of a Single-Center Pilot Study

Background and Objectives: The revascularization strategy for percutaneous coronary intervention (PCI) in patients with multivessel (MV) acute coronary syndrome (ACS) remains controversial. Certain gaps in the evidence are related to the optimal timing of non-culprit lesion revascularization and the utility of instantaneous wave-free ratio (iFR) in the management of MV ACS intervention. The major benefits of iFR utilization in MV ACS patients in one-stage complete revascularization are: (1) the possibility to virtually plan the PCI, both the location and the extension of the necessary stenting to achieve the prespecified final hemodynamic result; (2) the opportunity to validate the final hemodynamic result of the PCI, both in culprit artery and all non-culprit arteries and (3) the value of obliviating the uncomfortable, costly, time consuming and sometimes deleterious effects from Adenosine, as there is no requirement for administration. Thus, iFR use fosters the achievement of physiologically appropriate complete revascularization in MV ACS patients during acute hospitalization. Materials and Methods: This pilot study was aimed to test the feasibility of a randomized trial research protocol as well as to assess patient safety signals of co-registration iFR-guided one-stage complete revascularization compared with that of standard staged angiography-guided PCI in de novo patients with MV ACS. This was a single-center, prospective, randomized, open-label clinical trial consecutively screening patients with ACS for MV disease. The intervention strategy of interest was iFR-guided physiologically complete one-stage revascularization, in which the virtual PCI planning of non-culprit lesions and the intervention itself were performed in one stage directly following treatment of the culprit lesion and other critical stenosis of more than ninety percent. Seventeen patients were recruited and completed the 3-month follow-up. Results: Index PCI duration was significantly longer while the volume of contrast media delivered in index PCI was significantly greater in the iFR-guided group than in the angiography-guided group (119.4 ± 40.7 vs. 47 ± 15.5 min, p = 0.004; and 360 ± 97.9 vs. 192.5 ± 52.8 mL, p = 0.003). There were no significant differences in PCI-related major adverse cardiovascular events (MACE) between the groups during acute hospitalization and at 3-months follow-up. One-stage iFR-guided PCI requires fewer PCI attempts until complete revascularization than does angiography-guided staged PCI. Conclusions: Complete revascularization with the routine use of the virtual planning tool in one-stage iFR-guided PCI is a feasible practical strategy in an everyday Cath lab environment following the protocol designed for the study. No statistically significant safety signals were documented in the number of PCI related MACE during the 3-month follow-up.

Intravascular Imaging-Derived Physiology-Basic Principles and Clinical Application

Intravascular imaging-derived physiology is emerging as a promising tool allowing simultaneous anatomic and functional lesion assessment. Recently, several optical coherence tomography-based and intravascular ultrasound-based fractional flow reserve (FFR) indices have been developed that compute FFR through computational fluid dynamics, fluid dynamics equations, or machine-learning methods. This review aims to provide an overview of the currently available intravascular imaging-based physiologic indices, their diagnostic performance, and clinical application.

Comparison between the diagnostic performance of vessel fractional flow reserve and nonhyperemic pressure ratio for functionally significant coronary stenosis severity as assessed by fractional flow reserve

BACKGROUND

Fractional flow reserve (FFR) and nonhyperemic pressure ratios (NHPRs) have been widely used to assess the functional severity of coronary stenosis. However, their measurement requires using a pressure wire, making their use in all patients difficult. The recently developed vessel fractional flow reserve (vFFR), derived from three-dimensional quantitative coronary angiography, is expected to serve as a surrogate for pressure wire assessment.

METHODS

This retrospective study was conducted on patients with intermediate coronary stenosis who underwent FFR and NHPR measurements. The vFFR and NHPR values were compared for diagnosing coronary stenosis as defined by an FFR of ≤0.80, and the number of patients not requiring wire-based assessment was estimated.

RESULTS

In a total of 90 lesions from 74 patients (median [SD] age 75 [12] years; men 80%), the median FFR was 0.78 (0.72-0.84), and 57% of these lesions (N = 51) exhibited an FFR of ≤0.80. vFFR provided high discrimination for coronary stenosis (area under the curve 0.80, 95% confidence interval 0.70-0.90), which was comparable to that of NHPRs (p = 0.42). High diagnostic accuracy was consistently observed across a variety of clinical presentations (i.e., old age, diabetes, target coronary artery, and left ventricular hypertrophy) (p_interaction  > 0.05). In total, 55 lesions (61%) demonstrated positive or negative likelihood of coronary stenosis when vFFR was <0.73 (specificity 90%) or >0.87 (sensitivity 88%), respectively.

CONCLUSION

vFFR demonstrated excellent diagnostic performance for detecting functionally significant coronary stenosis as evaluated by FFR. vFFR may be used as a surrogate for pressure wire assessment.

The impact of deep learning reconstruction on image quality and coronary CT angiography-derived fractional flow reserve values

OBJECTIVES

To explore the impact of deep learning reconstruction (DLR) on image quality and machine learning-based coronary CT angiography (CTA)-derived fractional flow reserve (CT-FFR_ML) values.

METHODS

Thirty-three consecutive patients with known or suspected coronary artery disease who underwent coronary CTA and subsequent invasive coronary angiography were enrolled. DLR was compared with filtered back projection (FBP), statistical-based iterative reconstruction (SBIR), model-based iterative reconstruction (MBIR) Cardiac, and MBIR Cardiac sharp for objective image qualities of coronary CTA. Invasive fractional flow reserve (FFR) and quantitative flow ratio (QFR) were used as the reference standards. The diagnostic performances of different reconstruction approach-based CT-FFR_ML were calculated.

RESULTS

A total of 182 lesions in 33 patients were enrolled for analysis. The image quality of DLR was superior to the others. There were no significant differences in the CT-FFR_ML values among these five approaches (all p > 0.05). Of the 182 lesions, 17 had invasive FFR results, and 70 had QFR results. Using FFR as a reference, MBIR Cardiac, MBIR Cardiac sharp, and DLR achieved equal diagnostic performance, slightly higher than the other reconstruction approaches (MBIR Cardiac, MBIR Cardiac sharp, and DLR: AUC = 0.82, FBP and AIDR: AUC = 0.78, all p > 0.05). Using QFR as a reference, the AUCs of FBP, SBIR, MBIR Cardiac, MBIR Cardiac sharp, and DLR were 0.83, 0.81, 0.86, 0.84, and 0.83, respectively (all p > 0.05).

CONCLUSIONS

Our study showed that the DLR algorithm improved image quality, but there were no significant differences in the CT-FFR_ML values and diagnostic performance among different reconstruction approaches.

KEY POINTS

• Deep learning-based image reconstruction (DLR) improves the image quality of coronary CTA. • CT-FFR_ML values and diagnostic performance of DLR revealed no significant differences compared to other reconstruction approaches.

Coronary physiology in the catheterisation laboratory: an A to Z practical guide

Coronary revascularisation, either percutaneous or surgical, aims to improve coronary flow and relieve myocardial ischaemia. The decision-making process in patients with coronary artery disease (CAD) remains largely based on invasive coronary angiography (ICA), even though until recently ICA could not assess the functional significance of coronary artery stenoses. Invasive wire-based approaches for physiological evaluations were developed to properly assess the ischaemic relevance of epicardial CAD. Fractional flow reserve (FFR) and later, instantaneous wave-free ratio (iFR), were shown to improve clinical outcomes in several patient subsets when used for coronary revascularisation guidance or deferral and for procedural optimisation of percutaneous coronary intervention (PCI) results. Despite accumulating evidence and positive guideline recommendations, the adoption of invasive physiology has remained quite low, mainly due to technical and economic issues as well as to operator-resistance to change. Coronary image-based computational physiology has been recently developed, with promising results in terms of accuracy and a reduction in computational time, costs, radiation exposure and risks for the patient. Lastly, the integration of intracoronary imaging and physiology allows for individualised PCI treatment, aiming at complete relief of ischaemia through optimised morpho-functional immediate procedural results. Instead of a conventional state-of-the-art review, this A to Z dictionary attempts to provide a practical guide for the application of coronary physiology in the catheterisation laboratory, exploring several methods, their pitfalls, and useful tips and tricks.

Functional Evaluation of Intermediate Coronary Lesions with Integrated Computed Tomography Angiography and Invasive Angiography in Patients with Stable Coronary Artery Disease

Background and objectives

The hemodynamic evaluation of coronary stenoses undergoes a transition from wire-based invasive measurements to image-based computational assessments. However, fractional flow reserve (FFR) values derived from coronary CT angiography (CCTA) and angiography-based quantitative flow ratio have certain limitations in accuracy and efficiency, preventing their widespread use in routine practice. Hence, we aimed to investigate the diagnostic performance of FFR derived from the integration of CCTA and invasive angiography (FFR_CT-angio) with artificial intelligence assistance in patients with stable coronary artery disease (CAD).

Methods

Forty stable CAD patients with 67 target vessels (50%-90% diameter stenosis) were included in this single-center retrospective study. All patients underwent CCTA followed by coronary angiography with FFR measurement within 30 days. Both CCTA and angiographic images were combined to generate a three-dimensional reconstruction of the coronary arteries using artificial intelligence. Subsequently, functional assessment was performed through a deep learning algorithm. FFR was used as the reference.

Results

FFR_CT-angio values were significantly correlated with FFR values (r = 0.81, P < 0.001, Spearman analysis). Per-vessel diagnostic accuracy of FFR_CT-angio was 92.54%. Sensitivity and specificity in identifying ischemic lesions were 100% and 88.10%, respectively. Positive predictive value and negative predictive value were 83.33% and 100%, respectively. Moreover, the diagnostic performance of FFR_CT-angio was satisfactory in different target vessels and different segment lesions.

Conclusions

FFR_CT-angio exhibits excellent diagnostic performance of identifying ischemic lesions in patients with stable CAD. Combining CCTA and angiographic imaging, FFR_CT-angio may represent an effective and practical alternative to invasive FFR in selected patients.

Case Report: Invasive and Non-invasive Hemodynamic Assessment of Coronary Artery Disease: Strengths and Weaknesses

Coronary angiography has been the gold standard for assessment of coronary artery disease (CAD) and guidance for percutaneous coronary interventions (PCI). Physiology-guided PCI has shown increased safety and efficacy, improved resource utilization, and better clinical outcomes in patients with stable angina and acute coronary syndromes. The three cases presented and discussed in this report illustrate the strengths and weaknesses of the available invasive and non-invasive methods for the physiological assessment of CAD. As technology evolves, invasive non-wire-based (angiography-derived FFR) and non-invasive (FFR_CT) modalities for the hemodynamic assessment of CAD appear to provide reliable and user-friendly alternatives to the gold standard invasive wire-based techniques. Interventional cardiologists and cardiovascular healthcare providers should be familiar with the strengths and weaknesses of the available hemodynamic assessment modalities.

Deceleration Capacity Improves Prognostic Accuracy of Relative Increase and Final Coronary Physiology in Patients With Non-ST-Elevation Acute Coronary Syndrome

Background

Both coronary physiology and deceleration capacity (DC) showed prognostic efficacy for patients with acute coronary syndrome (ACS). This retrospective cohort study was performed to evaluate the prognostic implication of DC combined with the relative increase and final coronary physiology as detected by quantitative flow ratio (QFR) for patients with non-ST-elevation ACS (NSTE-ACS) who underwent complete and successful percutaneous coronary intervention (PCI).

Methods

Patients with NSTE-ACS who underwent PCI with pre- and post-procedural QFR in our department between January 2018 and November 2019 were included. The 24-hour deceleration capacity (DC 24h) was obtained via Holter monitoring. The incidence of major adverse cardiac and cerebrovascular events (MACCEs) during follow up was defined as the primary outcome. The optimal cutoffs of the relative increase, final QFR, and DC 24h for prediction of MACCEs were determined via receiver operating characteristic (ROC) analysis and the predictive efficacies were evaluated with multivariate Cox regression analysis.

Results

Overall, 240 patients were included. During a mean follow up of 21.3 months, 31 patients had MACCEs. Results of multivariate Cox regression analyses showed that a higher post-PCI QFR [adjusted hazard ratio (HR): 0.318; 95% confidence interval (CI): 0.129–0.780], a higher relative QFR increase (HR: 0.161; 95% CI: 0.066–0.391], and a higher DC (HR: 0.306; 95% CI: 0.134–0.701) were all independent predictors of lower risk of MACCEs. Subsequently, incorporating low DC (≤2.42) into the risk predicting model with clinical variables, the predictive efficacies of low relative QRS increase (≤23%) and low post-PCI QFR (≤0.88) for MACCEs were both significantly improved.

Conclusions

The DC combined with relative increase and final coronary physiology may improve the predictive efficacy of existing models based on clinical variables for MACCEs in NSTE-ACS patients who underwent complete and successful PCI.

Effects of diabetes mellitus on post-intervention coronary physiological assessment derived by quantitative flow ratio in patients with coronary artery disease underwent percutaneous coronary intervention

AIMS

To compare the prognostic implication of post-percutaneous coronary intervention (PCI) quantitative flow ratio (QFR) assessment in patients with and without diabetes enrolled in the all-comers, multicenter, randomized controlled PANDA III trial.

METHODS

All treated vessels in PANDA III trial were retrospectively assessed for post-PCI QFR. Vessels with available post-PCI QFR were further stratified into DM and non-DM cohorts, and prognostic performance of post-PCI QFR was compared in 2 cohorts. The primary outcome was 2-year vessel-oriented composite endpoint (VOCE), defined as composite of vessel-related cardiac death, vessel-related non-procedural myocardial infarction, and ischemia-driven target vessel revascularization.

RESULTS

Of 2,989 treated vessels, 2,227 (74.5%) with available post-PCI QFR were included, while 548 were presence of DM and 1,679 were not. The performance of post-PCI QFR to predict 2-year VOCE were moderate in both DM (area under the curve [AUC] 0.77, 95% confidence interval [CI]: 0.68 to 0.87) and non-DM cohorts (AUC 0.74, 95% CI: 0.67 to 0.82), while between-cohorts AUC difference was not significant (ΔAUC 0.03, P = 0.65). After multivariate adjustment, vessels with suboptimal post-PCI QFR results (≤0.92) were associated with higher risk of 2-year VOCE in both DM (adjusted HR 6.24, 95% CI: 2.40 to 16.2) and non-DM cohorts (adjusted HR 5.92, 95% CI: 3.28 to 10.7) without significant interaction (P for interaction 0.91).

CONCLUSIONS

This study, the first to directly compare clinical value of post-PCI QFR assessments in patients with and without DM, showed that a higher post-PCI QFR value was associated with improved long-term prognosis regardless of the presence of DM. Clinical Trial Registration Information URL: https://www.

CLINICALTRIALS

gov; Unique identifier: NCT02017275.

Outcomes of quantitative flow ratio-based percutaneous coronary intervention in an all-comers study

BACKGROUND

Quantitative flow ratio (QFR) is a novel angiography-based physiological index for fast computation of fractional flow reserve without the use of a pressure wire or induction of hyperaemia.

AIMS

We sought to investigate the prevalence and prognostic implications of achieving physiology-consistent percutaneous coronary intervention (PCI) according to the baseline angiographic QFR in an all-comers cohort.

METHODS

QFR was retrospectively analysed from the angiograms of 1,391 patients enrolled in the randomised PANDA III trial. Patients in whom all functionally ischaemic vessels (baseline QFR ≤0.80) were treated and in whom all non-ischaemic vessels (baseline QFR >0.80) were deferred were termed as having had QFR-consistent treatment; otherwise, they were termed as having had QFR-inconsistent treatment. The major outcome was two-year major adverse cardiac events (MACE; a composite of all-cause death, all myocardial infarction (MI), or any ischaemia-driven revascularisation).

RESULTS

Overall, 814 (58.5%) patients had QFR-consistent PCI, while 577 (41.5%) patients received QFR-inconsistent PCI. Patients with QFR-consistent versus those with QFR-inconsistent treatment had a lower risk of two-year MACE (8.4% vs 14.7%; hazard ratio [HR] 0.56, 95% confidence interval [CI]: 0.41-0.78). After adjusting for differences in baseline covariates, two-year rates of MACE remained significantly lower in the QFR-consistent group (8.8% vs 13.6%; adjusted HR 0.64, 95% CI: 0.44-0.93), due mainly to reduced ischaemia-driven revascularisation (2.9% vs 8.0%; adjusted HR 0.35, 95% CI: 0.20-0.60).

CONCLUSIONS

In this post hoc analysis of an all-comers PCI trial, approximately 60% of patients were treated in accordance with what the QFR measurement would have recommended, the achievement of which was associated with improved two-year clinical outcomes. ClinicalTrials.gov identifier: NCT02017275.

The Role of Coronary Physiology in Contemporary Percutaneous Coronary Interventions

Invasive assessment of coronary physiology has radically changed the paradigm of myocardial revascularization in patients with coronary artery disease. Despite the prognostic improvement associated with ischemia-driven revascularization strategy, functional assessment of angiographic intermediate epicardial stenosis remains largely underused in clinical practice. Multiple tools have been developed or are under development in order to reduce the invasiveness, cost, and extra procedural time associated with the invasive assessment of coronary physiology. Besides epicardial stenosis, a growing body of evidence highlights the role of coronary microcirculation in regulating coronary flow with consequent pathophysiological and clinical and prognostic implications. Adequate assessment of coronary microcirculation function and integrity has then become another component of the decision-making algorithm for optimal diagnosis and treatment of coronary syndromes. This review aims at providing a comprehensive description of tools and techniques currently available in the catheterization laboratory to obtain a thorough and complete functional assessment of the entire coronary tree (both for the epicardial and microvascular compartments).

Angiographic quantitative flow ratio-guided coronary intervention (FAVOR III China): a multicentre, randomised, sham-controlled trial

BACKGROUND

Compared with visual angiographic assessment, pressure wire-based physiological measurement more accurately identifies flow-limiting lesions in patients with coronary artery disease. Nonetheless, angiography remains the most widely used method to guide percutaneous coronary intervention (PCI). In FAVOR III China, we aimed to establish whether clinical outcomes might be improved by lesion selection for PCI using the quantitative flow ratio (QFR), a novel angiography-based approach to estimate the fractional flow reserve.

METHODS

FAVOR III China is a multicentre, blinded, randomised, sham-controlled trial done at 26 hospitals in China. Patients aged 18 years or older, with stable or unstable angina pectoris or patients who had a myocardial infarction at least 72 h before screening, who had at least one lesion with a diameter stenosis of 50-90% in a coronary artery with a reference vessel of at least 2·5 mm diameter by visual assessment were eligible. Patients were randomly assigned to a QFR-guided strategy (PCI performed only if QFR ≤0·80) or an angiography-guided strategy (PCI based on standard visual angiographic assessment). Participants and clinical assessors were masked to treatment allocation. The primary endpoint was the 1-year rate of major adverse cardiac events, a composite of death from any cause, myocardial infarction, or ischaemia-driven revascularisation. The primary analysis was done in the intention-to-treat population. The trial was registered with ClinicalTrials.gov (NCT03656848).

FINDINGS

Between Dec 25, 2018, and Jan 19, 2020, 3847 patients were enrolled. After exclusion of 22 patients who elected not to undergo PCI or who were withdrawn by their physicians, 3825 participants were included in the intention-to-treat population (1913 in the QFR-guided group and 1912 in the angiography-guided group). The mean age was 62·7 years (SD 10·1), 2699 (70·6%) were men and 1126 (29·4%) were women, 1295 (33·9%) had diabetes, and 2428 (63·5%) presented with an acute coronary syndrome. The 1-year primary endpoint occurred in 110 (Kaplan-Meier estimated rate 5·8%) participants in the QFR-guided group and in 167 (8·8%) participants in the angiography-guided group (difference, -3·0% [95% CI -4·7 to -1·4]; hazard ratio 0·65 [95% CI 0·51 to 0·83]; p=0·0004), driven by fewer myocardial infarctions and ischaemia-driven revascularisations in the QFR-guided group than in the angiography-guided group.

INTERPRETATION

In FAVOR III China, among patients undergoing PCI, a QFR-guided strategy of lesion selection improved 1-year clinical outcomes compared with standard angiography guidance.

FUNDING

Beijing Municipal Science and Technology Commission, Chinese Academy of Medical Sciences, and the National Clinical Research Centre for Cardiovascular Diseases, Fuwai Hospital.

Impact of physiologically diffuse versus focal pattern of coronary disease on quantitative flow reserve diagnostic accuracy

Background

Fractional flow reserve (FFR) and instantaneous wave‐free ratio (iFR) disagree in about 20% of intermediate coronary lesions. As the physiological pattern of coronary artery disease has a significant influence on FFR‐iFR discordance, we sought to assess it may impact on the diagnostic accuracy of quantitative flow reserve (QFR).

Methods

One hundred and ninety‐four patients with 224 intermediate coronary lesions were investigated with iFR, FFR, and QFR. The physiological pattern of disease was assessed with iFR Scout pullback and QFR virtual pullback in all the cases.

Results

A predominantly physiologically focal pattern was observed in 81 (36.2%) lesions, whereas a predominantly physiologically diffuse was observed in 143 (63.8%) cases. QFR demonstrated a significant correlation (r = 0.581, p < 0.001) and a substantial agreement with iFR, both in diffuse (AUC = 0.798) and in focal (AUC = 0.812) pattern of disease. Discordance between QFR and iFR was observed in 51 (22.8%) lesions, consisting of iFR+/QFR− (64.7%) and iFR−/QFR+ (35.3%). Notably, the physiological pattern of disease was the only variable significantly associated with iFR/QFR discordance. QFR virtual pullback demonstrated an excellent agreement (83.9%) with iFR Scout pullback in classifying the physiological pattern of disease.

Conclusions

QFR has a good diagnostic accuracy in assessing myocardial ischemia independently of the pattern of coronary disease. However, the physiological pattern of disease has an influence on the QFR/iFR discordance, which occurs in ~20% of the cases. The QFR virtual pullback correctly defined the physiological pattern of disease in the majority of the cases using the iFR pullback as reference.

Relationship Between Immunoinflammation and Coronary Physiology Evaluated by Quantitative Flow Ratio in Patients With Coronary Artery Disease

Background: The association between coronary physiology and immunoinflammation has not been investigated. We performed a retrospective study using quantitative flow ratio (QFR) to evaluate the interaction between immunoinflammatory biomarkers and coronary physiology.

Methods: A total of 172 patients with CAD who underwent coronary arteriography (CAG) and QFR were continuously enrolled from May 2020 to February 2021. As a quantitative indicator of coronary physiology, QFR can reflect the functional severity of coronary artery stenosis. The target vessel measured by QFR was defined as that with the most severe lesions. Significant coronary anatomical stenosis was defined as 70% stenosis in the target vessel.

Results: Compared with the QFR > 0.8 group, interleukin (IL)-6, IL-10, tumor necrosis factor (TNF)-α, and interferon (IFN)-γ were increased and CD3⁺ and CD4⁺ T lymphocyte counts were decreased in the QFR ≤ 0.8 group. In addition, patients with DS ≤ 70% had higher IL-6, IL-10, and TNF-α levels and decreased CD3⁺ and CD4⁺ T lymphocyte counts than those with DS > 70%. Logistic regression analysis indicated IL-6 to be an independent predictor of significant coronary functional and anatomic stenosis (odds ratio, 1.125; 95% CI, 1.059–1.196; P < 0.001). Receiver operating characteristic (ROC) analyses showed that IL-6 > 6.36 was predictive of QFR ≤ 0.8 of the target vessel. The combination of IL-6, IL-10 and CD4 improved the value for predicting QFR ≤ 0.8 of the target vessel (AUC, 0.737; 95% CI, 0.661–0.810).

Conclusion: Among immunoinflammatory biomarkers, IL-6 was independently associated with a higher risk of QFR ≤ 0.8 of the target vessel. The combination of immunoinflammatory biomarkers was highly predictive of significant coronary functional and anatomic stenosis.

An improved reduced-order model for pressure drop across arterial stenoses

Quantification of pressure drop across stenotic arteries is a major element in the functional assessment of occlusive arterial disease. Accurate estimation of the pressure drop with a numerical model allows the calculation of Fractional Flow Reserve (FFR), which is a haemodynamic index employed for guiding coronary revascularisation. Its non-invasive evaluation would contribute to safer and cost-effective diseases management. In this work, we propose a new formulation of a reduced-order model of trans-stenotic pressure drop, based on a consistent theoretical analysis of the Navier-Stokes equation. The new formulation features a novel term that characterises the contribution of turbulence effect to pressure loss. Results from three-dimensional computational fluid dynamics (CFD) showed that the proposed model produces predictions that are significantly more accurate than the existing reduced-order models, for large and small symmetric and eccentric stenoses, covering mild to severe area reductions. FFR calculations based on the proposed model produced zero classification error for three classes comprising positive (≤ 0.75), negative (≥ 0.8) and intermediate (0.75 − 0.8) classes.

Comparison Between 5- and 1-Year Outcomes Using Cutoff Values of Pressure Drop Coefficient and Fractional Flow Reserve for Diagnosing Coronary Artery Diseases

Background

The current pressure-based coronary diagnostic index, fractional flow reserve (FFR), has a limited efficacy in the presence of microvascular disease (MVD). To overcome the limitations of FFR, the objective is to assess the recently introduced pressure drop coefficient (CDP), a fundamental fluid dynamics-based combined pressure–flow index.

Methods

We hypothesize that CDP will result in improved clinical outcomes in comparison to FFR. To test the hypothesis, chi-square test was performed to compare the percent major adverse cardiac events (%MACE) at 5 years between (a) FFR < 0.75 and CDP > 27.9 and (b) FFR < 0.80 and CDP > 25.4 groups using a prospective cohort study. Furthermore, Kaplan–Meier survival curves were compared between the FFR and CDP groups. The results were considered statistically significant for p < 0.05. The outcomes of the CDP arm were presumptive as clinical decision was solely based on the FFR.

Results

For the complete patient group, the %MACE in the CDP > 27.9 group (10 out of 35, 29%) was lower in comparison to the FFR < 0.75 group (11 out of 20, 55%), and the difference was near significant (p = 0.05). The survival analysis showed a significantly higher survival rate (p = 0.01) in the CDP > 27.9 group (n = 35) when compared to the FFR < 0.75 group (n = 20). The results remained similar for the FFR = 0.80 cutoff. The comparison of the 5-year MACE outcomes with the 1-year outcomes for the complete patient group showed similar trends, with a higher statistical significance for a longer follow-up period of 5 years.

Conclusion

Based on the MACE and survival analysis outcomes, CDP could possibly be an alternate diagnostic index for decision-making in the cardiac catheterization laboratory.

Clinical Trial Registration

www.ClinicalTrials.gov, identifier NCT01719016.

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.

Deep learning for prediction of fractional flow reserve from resting coronary pressure curves

BACKGROUND

It would be ideal for a non-hyperaemic index to predict fractional flow reserve (FFR) more accurately, given FFR's extensive validation in a multitude of clinical settings.

AIMS

The aim of this study was to derive a novel non-hyperaemic algorithm based on deep learning and to validate it in an internal validation cohort against FFR.

METHODS

The ARTIST study is a post hoc analysis of three previously published studies. In a derivation cohort (random 80% sample of the total cohort) a deep neural network was trained (deep learning) with paired examples of resting coronary pressure curves and their FFR values. The resulting algorithm was validated against unseen resting pressure curves from a random 20% sample of the total cohort. The primary endpoint was diagnostic accuracy of the deep learning-derived algorithms against binary FFR ≤0.8. To reduce the variance in the precision, we used a fivefold cross-validation procedure.

RESULTS

A total of 1,666 patients with 1,718 coronary lesions and 2,928 coronary pressure tracings were included. The diagnostic accuracy of our convolutional neural network (CNN) and recurrent neural networks (RNN) against binary FFR ≤0.80 was 79.6±1.9% and 77.6±2.3%, respectively. There was no statistically significant difference between the accuracy of our neural networks to predict binary FFR and the most accurate non-hyperaemic pressure ratio (NHPR).

CONCLUSIONS

Compared to standard derivation of resting pressure ratios, we did not find a significant improvement in FFR prediction when resting data are analysed using artificial intelligence approaches. Our findings strongly suggest that a larger class of hidden information within resting pressure traces is not the main cause of the known disagreement between resting indices and FFR. Therefore, if clinicians want to use FFR for clinical decision making, hyperaemia induction should remain the standard practice.

From anatomy to function and then back to anatomy: invasive assessment of myocardial ischemia in the catheterization laboratory based on anatomy-derived indices of coronary physiology

For many decades, the severity of coronary artery disease (CAD) and the indication to proceed with either percutaneous coronary intervention (PCI) or surgical revascularization has been based on anatomically derived parameters of vessel stenosis, and typically on the percentage of lumen diameter stenosis (DS%) as determined by invasive coronary angiography (CA). However, it is currently a well-accepted concept that pre-specified thresholds of DS% have a weak correlation with the ischemic and functional potential of an epicardial coronary stenosis. In this regard, the introduction of fractional-flow reserve (FFR) has represented a paradigm-shift in the understanding, diagnosis, and treatment of CAD, but the adoption of FFR into the clinical practice remains surprisingly limited and sub-standard, probably because of the inherent drawbacks of pressure-wire-based technology such as additional costs, prolonged procedural time, invasive instrumentation of the target vessel, and use of vaso-dilatory agents causing side effects for patients. For this reason, new modalities are under development or validation to derive FFR from computational fluid dynamics (CFD) applied to a three-dimensional model (3D) of the target vessel obtained from CA, intravascular imaging, or coronary computed tomography angiography. The purpose of this review was to describe the technical details of these anatomy-derived indices of coronary physiology with a special focus on summarizing their workflow, available evidence, and future perspectives about their application in the clinical practice.

Aortic Valve Disease and Associated Complex CAD: The Interventional Approach

Coronary artery disease (CAD) is highly prevalent in patients with severe aortic stenosis (AS). The management of CAD is a central aspect of the work-up of patients undergoing transcatheter aortic valve implantation (TAVI), but few data are available on this field and the best percutaneous coronary intervention (PCI) practice is yet to be determined. A major challenge is the ability to elucidate the severity of bystander coronary stenosis independently of the severity of aortic valve stenosis and subsequent impact on blood flow. The prognostic role of CAD in patients undergoing TAVI is being still debated and the benefits and the best timing of PCI in this context are currently under evaluation. Additionally, PCI in the setting of advanced AS poses some technical challenges, due to the complex anatomy, risk of hemodynamic instability, and the increased risk of bleeding complications. This review aims to provide a comprehensive synthesis of the available literature on myocardial revascularization in patients with severe AS undergoing TAVI. This work can assist the Heart Team in individualizing decisions about myocardial revascularization, taking into account available diagnostic tools as well as the risks and benefits.

Accuracy of Intravascular Ultrasound-Based Fractional Flow Reserve in Identifying Hemodynamic Significance of Coronary Stenosis

BACKGROUND

Ultrasonic flow ratio (UFR) is a novel method for fast computation of fractional flow reserve (FFR) from intravascular ultrasound images. The objective of this study is to evaluate the diagnostic performance of UFR using wire-based FFR as the reference.

METHODS

Post hoc computation of UFR was performed in consecutive patients with both intravascular ultrasound and FFR measurement in a core lab while the analysts were blinded to FFR.

RESULTS

A total of 167 paired comparisons between UFR and FFR from 94 patients were obtained. Median FFR was 0.80 (interquartile range, 0.68-0.89) and 50.3% had a FFR≤0.80. Median UFR was 0.81 (interquartile range, 0.69-0.91), and UFR showed strong correlation with FFR (r=0.87; P<0.001). The area under the curve was higher for UFR than intravascular ultrasound-derived minimal lumen area (0.97 versus 0.89, P<0.001). The diagnostic accuracy, sensitivity, specificity, positive predictive value, negative predictive value, positive likelihood ratio, and negative likelihood ratio for UFR to identify FFR≤0.80 was 92% (95% CI, 87-96), 91% (95% CI, 82-96), 96% (95% CI, 90-99), 96% (95% CI, 89-99), 91% (95% CI, 93-96), 25.0 (95% CI, 8.2-76.2), and 0.10 (95% CI, 0.05-0.20), respectively. The agreement between UFR and FFR was independent of lesion locations (P=0.48), prior myocardial infarction (P=0.29), and imaging catheters (P=0.22). Intraobserver and interobserver variability of UFR analysis was 0.00±0.03 and 0.01±0.03, respectively. Median UFR analysis time was 102 (interquartile range, 87-122) seconds.

CONCLUSIONS

UFR had a strong correlation and good agreement with FFR. The fast computational time and excellent analysis reproducibility of UFR bears the potential of a wider adoption of integration of coronary imaging and physiology in the catheterization laboratory.

Short- and long-term functional results following drug-coated balloons versus drug- eluting stents in small coronary vessels: The RESTORE quantitative flow ratio study

Background Immediate and long-term functional outcomes after percutaneous treatment of small vessel disease (SVD) with drug-coated balloon (DCB) versus drug-eluting stent (DES) remain unknown. The study sought to investigate whether treatment of de novo SVD with DCB yields similar functional results compared with DES, as judged with angiography-based quantitative flow ratio (QFR). Methods and results QFR was measured at pre-procedural, post-procedural and 9-month angiography in all available subjects from the non-inferiority RESTORE SVD China trial, in which patients were randomized to Restore DCB (n = 116) or Resolute DES (n = 114) study arms. Primary outcome of this analysis was 9-month QFR. Pre-procedural, post-procedural and 9-month QFR was performed in 84.8% (195/230), 83.0% (191/230) and 93.8% (181/193) cases, respectively. At 9 months, the QFR of DCB showed no significant difference to DES (0.88 ± 0.23 vs. 0.92 ± 0.12, p = 0.12). Both 9-month QFR and the QFR difference between post-procedure and 9-month follow-up were correlated with angiographic percentage of diameter stenosis and late loss, and predictive of 2-year clinical outcome. Conclusions Treatment of coronary SVD with DCB resulted in similar 9-month functional results compared with DES. This study provides evidences to the value of QFR as a mean of evaluating device performance after coronary revascularization. Clinical trial registration URL: https://www.clinicaltrials.gov; ClinicalTrial.gov: Identifier: NCT02946307.

After ISCHEMIA: is invasive physiology the only remaining gatekeeper for myocardial revascularization in chronic coronary syndromes?

The International Study of Comparative Health Effectiveness With Medical And Invasive Approaches (ISCHEMIA) has the potential to be a game changer in terms of the diagnostic and management approach to patients presenting with chronic coronary syndrome, suggesting that coronary revascularization may become almost like a "bail-out" strategy in the treatment of these patients. However, invasive perfusion assessment as a means of detecting the source of myocardial ischaemia at a lesion level, such as fractional flow reserve (FFR), has been validated in the past and established beyond doubt as a key diagnostic tool. The complementary role of the two approaches will be discussed here.