Abnormal epicardial coronary resistance in patients with diffuse atherosclerosis but "Normal" coronary angiography

The role of advanced physiological guidance in contemporary coronary artery disease management

PURPOSE OF REVIEW

This review evaluates the emerging role of the pullback pressure gradient (PPG) as a standardized metric for assessing coronary artery disease (CAD) patterns and its implications for clinical decision-making when managing patients undergoing percutaneous coronary interventions (PCIs). By integrating PPG with existing physiological assessments, this review highlights the potential benefits of PPG in predicting treatment outcomes and refining therapeutic strategies for CAD.

RECENT FINDINGS

Recent studies, particularly the PPG Global study have demonstrated a strong correlation between PPG values and post-PCI outcomes, revealing that focal disease is associated with improved fractional flow reserve (FFR) and lower rates of adverse events than vessels with diffuse disease (low PPG). Additionally, PPG has been linked to specific atherosclerotic plaque characteristics, indicating its utility in identifying high-risk plaques. The integration of PPG with advanced imaging techniques further enhances the understanding of CAD patterns and their implications for treatment planning.

SUMMARY

The PPG represents a significant advancement in the management of CAD, providing a reproducible and objective assessment of coronary artery disease patterns that can inform clinical decision-making. As research continues to explore the relationship among PPG, atherosclerotic characteristics, and patient outcomes, its integration into routine practice is expected to improve the effectiveness of PCI and optimize patient management strategies. Future studies are warranted to establish specific PPG thresholds and further investigate its potential in identifying vulnerable plaques and guiding treatment decisions.

Interrater Variability of ML-Based CT-FFR in Patients without Obstructive CAD before TAVR: Influence of Image Quality, Coronary Artery Calcifications, and Location of Measurement

Objectives: CT-derived fractional flow reserve (CT-FFR) can improve the specificity of coronary CT-angiography (cCTA) for ruling out relevant coronary artery disease (CAD) prior to transcatheter aortic valve replacement (TAVR). However, little is known about the reproducibility of CT-FFR and the influence of diffuse coronary artery calcifications or segment location. The objective was to assess the reliability of machine-learning (ML)-based CT-FFR prior to TAVR in patients without obstructive CAD and to assess the influence of image quality, coronary artery calcium score (CAC), and the location of measurement within the coronary tree. Methods: Patients assessed for TAVR, without obstructive CAD on cCTA were evaluated with ML-based CT-FFR by two observers with differing experience. Differences in absolute values and categorization into hemodynamically relevant CAD (CT-FFR ≤ 0.80) were compared. Results in regard to CAD were also compared against invasive coronary angiography. The influence of segment location, image quality, and CAC was evaluated. Results: Of the screened patients, 109/388 patients did not have obstructive CAD on cCTA and were included. The median (interquartile range) difference of CT-FFR values was -0.005 (-0.09 to 0.04) (p = 0.47). Differences were smaller with high values. Recategorizations were more frequent in distal segments. Diagnostic accuracy of CT-FFR between both observers was comparable (proximal: Δ0.2%; distal: Δ0.5%) but was lower in distal segments (proximal: 98.9%/99.1%; distal: 81.1%/81.6%). Image quality and CAC had no clinically relevant influence on CT-FFR. Conclusions: ML-based CT-FFR evaluation of proximal segments was more reliable. Distal segments with CT-FFR values close to the given threshold were prone to recategorization, even if absolute differences between observers were minimal and independent of image quality or CAC.

Illusion of revascularization: does anyone achieve optimal revascularization during percutaneous coronary intervention?

This Perspective article is a form of 'pastiche', inspired by the 1993 review by Lincoff and Topol entitled 'Illusion of reperfusion', and explores how their concept continues to apply to percutaneous revascularization in patients with coronary artery disease and ischaemia. Just as Lincoff and Topol argued that reperfusion of acute myocardial infarction was facing unresolved obstacles that hampered clinical success in 1993, we propose that challenging issues are similarly jeopardizing the potential benefits of stent-based angioplasty today. By analysing the appropriateness and efficacy of percutaneous coronary intervention (PCI), we emphasize the limitations of relying solely on visual angiographic guidance, which frequently leads to inappropriate stenting and overtreatment in up to one-third of patients and the associated increased risk of periprocedural myocardial infarction. The lack of optimal revascularization observed in half of patients undergoing PCI confers risks such as suboptimal physiology after PCI, residual angina and long-term stent-related events, leaving an estimated 76% of patients with an 'illusion of revascularization'. These outcomes highlight the need to refine our diagnostic tools by integrating physiological assessments with targeted intracoronary imaging and emerging strategies, such as co-registration systems and angiography-based computational methods enhanced by artificial intelligence, to achieve optimal revascularization outcomes.

The Influence of Epicardial Resistance on Microvascular Resistance Reserve

BACKGROUND

The optimal index of microvascular function should be specific for the microvascular compartment. Yet, coronary flow reserve (CFR), despite being widely used to diagnose coronary microvascular dysfunction (CMD), is influenced by both epicardial and microvascular resistance. Conversely, microvascular resistance reserve (MRR) adjusts for fractional flow reserve (FFR), and thus is theoretically independent of epicardial resistance.

OBJECTIVES

The authors tested the hypothesis that MRR, unlike CFR, is not influenced by increasing epicardial resistance, and thus is a more specific index of microvascular function.

METHODS

In a cohort of 16 patients who had undergone proximal left anterior descending artery stenting, we created 4 grades of artificial stenosis (no stenosis, mild, moderate, and severe) using a coronary angioplasty balloon inflated to different degrees within the stent. For each stenosis grade, we calculated CFR and MRR using continuous thermodilution (64 measurements of each) to assess their response to changing epicardial resistance.

RESULTS

Graded balloon inflation resulted in a significant sequential decrease in mean FFR (no stenosis: 0.82 ± 0.05; mild: 0.72 ± 0.04; moderate: 0.61 ± 0.05; severe: 0.48 ± 0.09; P < 0.001). This translated into a linear decrease in mean hyperemic coronary flow (no stenosis: 170.5 ± 66.8 mL/min; mild: 149.8 ± 58.8 mL/min; moderate: 124.4 ± 53.0 mL/min; severe: 94.0 ± 45.2 mL/min; P < 0.001). CFR exhibited a marked linear decrease with increasing stenosis (no stenosis: 2.5 ± 0.9; mild: 2.2 ± 0.8; moderate: 1.8 ± 0.7; severe: 1.4 ± 0.6), corresponding to a decrease of 0.3 for a decrease in FFR of 0.1 (P < 0.001). In contrast, MRR exhibited a negligible decrease across all stenosis grades (no stenosis: 3.0 ± 1.0; mild: 3.0 ± 1.0; moderate: 2.9 ± 1.0; severe: 2.8 ± 1.0), corresponding to a decrease of just 0.05 for a decrease in FFR of 0.1 (P < 0.001).

CONCLUSIONS

MRR, unlike CFR, is minimally influenced by epicardial resistance, and thus should be considered the more specific index of microvascular function. This suggests that MRR can also reliably evaluate microvascular function in patients with significant epicardial disease.

Development and Validation of a Quantitative Coronary CT Angiography Model for Diagnosis of Vessel-Specific Coronary Ischemia

BACKGROUND

Noninvasive stress testing is commonly used for detection of coronary ischemia but possesses variable accuracy and may result in excessive health care costs.

OBJECTIVES

This study aimed to derive and validate an artificial intelligence-guided quantitative coronary computed tomography angiography (AI-QCT) model for the diagnosis of coronary ischemia that integrates atherosclerosis and vascular morphology measures (AI-QCTISCHEMIA) and to evaluate its prognostic utility for major adverse cardiovascular events (MACE).

METHODS

A post hoc analysis of the CREDENCE (Computed Tomographic Evaluation of Atherosclerotic Determinants of Myocardial Ischemia) and PACIFIC-1 (Comparison of Coronary Computed Tomography Angiography, Single Photon Emission Computed Tomography [SPECT], Positron Emission Tomography [PET], and Hybrid Imaging for Diagnosis of Ischemic Heart Disease Determined by Fractional Flow Reserve) studies was performed. In both studies, symptomatic patients with suspected stable coronary artery disease had prospectively undergone coronary computed tomography angiography (CTA), myocardial perfusion imaging (MPI), SPECT, or PET, fractional flow reserve by CT (FFRCT), and invasive coronary angiography in conjunction with invasive FFR measurements. The AI-QCTISCHEMIA model was developed in the derivation cohort of the CREDENCE study, and its diagnostic performance for coronary ischemia (FFR ≤0.80) was evaluated in the CREDENCE validation cohort and PACIFIC-1. Its prognostic value was investigated in PACIFIC-1.

RESULTS

In CREDENCE validation (n = 305, age 64.4 ± 9.8 years, 210 [69%] male), the diagnostic performance by area under the receiver-operating characteristics curve (AUC) on per-patient level was 0.80 (95% CI: 0.75-0.85) for AI-QCTISCHEMIA, 0.69 (95% CI: 0.63-0.74; P < 0.001) for FFRCT, and 0.65 (95% CI: 0.59-0.71; P < 0.001) for MPI. In PACIFIC-1 (n = 208, age 58.1 ± 8.7 years, 132 [63%] male), the AUCs were 0.85 (95% CI: 0.79-0.91) for AI-QCTISCHEMIA, 0.78 (95% CI: 0.72-0.84; P = 0.037) for FFRCT, 0.89 (95% CI: 0.84-0.93; P = 0.262) for PET, and 0.72 (95% CI: 0.67-0.78; P < 0.001) for SPECT. Adjusted for clinical risk factors and coronary CTA-determined obstructive stenosis, a positive AI-QCTISCHEMIA test was associated with aHR: 7.6 (95% CI: 1.2-47.0; P = 0.030) for MACE.

CONCLUSIONS

This newly developed coronary CTA-based ischemia model using coronary atherosclerosis and vascular morphology characteristics accurately diagnoses coronary ischemia by invasive FFR and provides robust prognostic utility for MACE beyond presence of stenosis.

Angiography-based Fractional Flow Reserve for the Prediction of Clinical Outcomes After Drug-coated Balloon or Plain Old Balloon Angioplasty

BACKGROUND

AccuFFRangio is a novel method for fast computation of fractional flow reserve (FFR) based on coronary angiography and computational fluid dynamics. The association between the AccuFFRangio and clinical outcomes after drug-coated balloon (DCB) or plain old balloon angioplasty (POBA) remains to be investigated.

METHODS

This study included consecutive patients who underwent balloon angioplasty from December 2016 to October 2020. AccuFFRangio was calculated retrospectively based on the post-procedural angiography obtained immediately after angioplasty. The primary endpoint was major adverse cardiac events (MACE), defined as a composite of all-cause death, vessel-related myocardial infarction, and repeat target vessel revascularization.

RESULTS

A total of 169 patients were retrospectively analyzed in this study. Post-procedural AccuFFRangio (hazard ratio [HR] per 0.1 increase 0.33, 95% confidence interval [CI] 0.22-0.48, p < 0.001) was an independent predictor for MACE at 2-year follow-up. Post-procedural AccuFFRangio ≤ 0.87 was determined as the optimal cutoff value to predict MACE with an area under the curve (AUC) of 0.872 (95% CI 0.813-0.919, p < 0.001).

CONCLUSIONS

AccuFFRangio measured immediately after balloon angioplasty is a promising predictor of unfavorable clinical outcomes.

PET/CT Assessment of Flow-Mediated Epicardial Vasodilation in Obesity and Severe Obesity

Background

It is not known whether the transition from obesity and severe obesity, as 2 different metabolic disease entities, affect flow-mediated and, thus, endothelium-dependent epicardial vasodilation.

Objectives

The purpose of this study was to investigate the effect of obesity and severe obesity on flow-mediated epicardial vasomotion with positron emission tomography/computed tomography-determined longitudinal decrease in myocardial blood flow (MBF) from the base-to-apex direction of the left ventricle or gradient.

Methods

13N-ammonia positron emission tomography/computed tomography evaluated global MBF during pharmacologically induced hyperemia and at rest for assessment of coronary microvascular function. In addition, the Δ longitudinal MBF gradient (hyperemia minus rest) was determined. Patients were then grouped according to the body mass index (BMI) into normal weight (NW) (BMI 20.0-24.9 kg/m2, n = 27), overweight (OW) (BMI 25.0-29.9 kg/m2, n = 29), obesity (OB) (BMI 30.0-39.9 kg/m2, n = 53), and severe obesity (morbid obesity: BMI ≥40 kg/m2, n = 43).

Results

Compared to NW, left ventricular Δ longitudinal MBF gradient progressively declined in OW and OB (0.04 ± 0.09 mL/g/min vs -0.11 ± 0.14 mL/g/min and -0.15 ± 0.11 mL/g/min; P ≤ 0.001, respectively) but not significantly in SOB (-0.01 ± 0.11 mL/g/min, P = 0.066). Regadenoson-induced global hyperemic MBF was lower in OB than in NW (1.88 ± 0.40 mL/g/min vs 2.35 ± 0.32 mL/g/min; P ≤ 0.001), while comparable between NW and SOB (2.35 ± 0.32 mL/g/min vs 2.26 ± 0.40 mL/g/min; P = 0.302). The BMI of the study population was associated with the Δ longitudinal MBF gradient in a U-turn fashion (r = 0.362, standard error of the estimate = 0.124; P < 0.001).

Conclusions

Increased body weight associates with abnormalities in coronary circulatory function that advances from an impairment flow-mediated, epicardial vasodilation in overweight and obesity to coronary microvascular dysfunction in obesity, not observed in severe obesity. The U-turn of flow-mediated epicardial vasomotion outlines obesity and severe obesity to affect epicardial endothelial function differently.

Understanding the pathogenesis of coronary slow flow: Recent advances

Coronary slow flow is taken to be indicative of delayed filling of terminal vessels of the coronary arteries in the absence of coronary stenosis, as detected using coronary angiography. Patients suffering from coronary slow flow typically experience recurrent chest pain, thereby markedly affecting their quality of life. The etiology and pathogenesis of coronary slow flow, which is gradually attracting clinical attention, have yet to be sufficiently established, although it is currently believed that they may be associated with endothelial dysfunction in the coronary arteries, inflammatory response, abnormalities in microvascular reserve function, subclinical atherosclerosis, blood cell and platelet abnormalities, and genetic factors. In this review, we provide a brief overview of recent progress in research on the pathogenesis of coronary slow flow with a view toward elucidating the possible underlying pathogenesis and identify targets and directions for the treatment of this condition.

Impact of vessel morphology on CT-derived fractional-flow-reserve in non-obstructive coronary artery disease in right coronary artery

OBJECTIVES

Computed tomography (CT)-derived fractional flow reserve (FFRCT) decreases continuously from proximal to distal segments of the vessel due to the influence of various factors even in non-obstructive coronary artery disease (NOCAD). It is known that FFRCT is dependent on vessel-length, but the relationship with other vessel morphologies remains to be explained.

PURPOSE

To investigate morphological aspects of the vessels that influence FFRCT in NOCAD in the right coronary artery (RCA).

METHODS

A total of 443 patients who underwent both FFRCT and invasive coronary angiography, with < 50% RCA stenosis, were evaluated. Enrolled RCA vessels were classified into two groups according to distal FFRCT: FFRCT ≤ 0.80 (n = 60) and FFRCT > 0.80 (n = 383). Vessel morphology (vessel length, lumen diameter, lumen volume, and plaque volume) and left-ventricular mass were assessed. The ratio of lumen volume and vessel length was defined as V/L ratio.

RESULTS

Whereas vessel-length was almost the same between FFRCT ≤ 0.80 and > 0.80, lumen volume and V/L ratio were significantly lower in FFRCT ≤ 0.80. Distal FFRCT correlated with plaque-related parameters (low-attenuation plaque, intermediate-attenuation plaque, and calcified plaque) and vessel-related parameters (proximal and distal vessel diameter, vessel length, lumen volume, and V/L ratio). Among all vessel-related parameters, V/L ratio showed the highest correlation with distal FFRCT (r = 0.61, p < 0.0001). Multivariable analysis showed that calcified plaque volume was the strongest predictor of distal FFRCT, followed by V/L ratio (β-coefficient = 0.48, p = 0.03). V/L ratio was the strongest predictor of a distal FFRCT ≤ 0.80 (cut-off 8.1 mm3/mm, AUC 0.88, sensitivity 90.0%, specificity 76.7%, 95% CI 0.84-0.93, p < 0.0001).

CONCLUSIONS

Our study suggests that V/L ratio can be a measure to predict subclinical coronary perfusion disturbance.

CLINICAL RELEVANCE STATEMENT

A novel marker of the ratio of lumen volume to vessel length (V/L ratio) is the strongest predictor of a distal CT-derived fractional flow reserve (FFRCT) and may have the potential to improve the diagnostic accuracy of FFRCT.

KEY POINTS

• Physiological FFRCT decline depends not only on vessel length but also on the lumen volume in non-obstructive coronary artery disease in the right coronary artery. • FFRCT correlates with plaque-related parameters (low-attenuation plaque, intermediate-attenuation plaque, and calcified plaque) and vessel-related parameters (proximal and distal vessel diameter, vessel length, lumen volume, and V/L ratio). • Of vessel-related parameters, V/L ratio is the strongest predictor of a distal FFRCT and an optimal cut-off value of 8.1 mm3/mm.

Implementation of Microcirculation Examination in Clinical Practice-Insights from the Nationwide POL-MKW Registry

Background and Objectives: The assessment of coronary microcirculation may facilitate risk stratification and treatment adjustment. The aim of this study was to evaluate patients' clinical presentation and treatment following coronary microcirculation assessment, as well as factors associated with an abnormal coronary flow reserve (CFR) and index of microcirculatory resistance (IMR) values. Materials and Results: This retrospective analysis included 223 patients gathered from the national registry of invasive coronary microvascular testing collected between 2018 and 2023. Results: The frequency of coronary microcirculatory assessments in Poland has steadily increased since 2018. Patients with impaired IMR (≥25) were less burdened with comorbidities. Patients with normal IMR underwent revascularisation attempts more frequently (11.9% vs. 29.8%, p = 0.003). After microcirculation testing, calcium channel blockers (CCBs) and angiotensin-converting enzyme inhibitors were added more often for patients with IMR and CFR abnormalities, respectively, as compared to control groups. Moreover, patients with coronary microvascular dysfunction (CMD, defined as CFR and/or IMR abnormality), regardless of treatment choice following microcirculation assessment, were provided with trimetazidine (23.2%) and dihydropyridine CCBs (26.4%) more frequently than those without CMD who were treated conservatively (6.8%) and by revascularisation (4.2% with p = 0.002 and 0% with p < 0.001, respectively). Multivariable analysis revealed no association between angina symptoms and IMR or CFR impairment. Conclusions: The frequency of coronary microcirculatory assessments in Poland has steadily increased. Angina symptoms were not associated with either IMR or CFR impairment. After microcirculation assessment, patients with impaired microcirculation, expressed as either low CFR, high IMR or both, received additional pharmacotherapy treatment more often.

Computed Tomography-Derived Physiology Assessment: State-of-the-Art Review

Coronary computed tomography angiography (CCTA) and CCTA-derived fractional flow reserve (FFRCT) are the best non-invasive techniques to assess coronary artery disease (CAD) and myocardial ischemia. Advances in these technologies allow a paradigm shift to the use of CCTA and FFRCT for advanced plaque characterization and planning myocardial revascularization.

Diffuse non-obstructive coronary artery disease: two clinical faces of the same disease-a case report

Background

Coronary artery disease has a long preclinical phase before manifesting itself clinically due to diffuse non-obstructive disease, stenoses, or thrombosis.

Case summary

We present a case of a middle-aged male complaining of atypical chest pain, then severe retrosternal pain, and, eventually, effort angina. We performed non-invasive testing, coronary angiography, intravascular imaging, and flow reserve tests, each as appropriate. Cardiovascular risk control, optimization of drug therapy, and percutaneous coronary intervention were considered trying to comply with the best clinical practice.

Discussion

Diffuse non-obstructive coronary artery disease may present clinically in different ways. Exercise stress test might be sufficient to assess effort angina before a potential angiography. Flow reserve tests across the diseased vessel can distinguish between diffuse and focal pattern of the disease and assist in the adequate selection of therapy. Finally, intravascular imaging is invaluable for the assessment of the plaque risk features.

Current status and perspectives of nuclear cardiology

Nuclear cardiology has long been used to identify myocardial ischemia for appropriate treatment strategies for stable coronary artery disease (CAD). After the Ischemia Trial, it is time to reevaluate the significance of ischemia assessment. Functional imaging continues to play pivotal role in detecting microcirculatory disturbances. PET provides a clear image of blood flow distribution and is useful for the quantitative evaluation of myocardial flow reserve (MFR), which plays an important role in predicting treatment strategies and improving prognosis in CAD. Heart failure has become a major area of focus in cardiovascular medicine. Radionuclide imaging has been widely applied in this field. FDG PET is useful in identifying cardiac sarcoidosis and active inflammation. Clinical values of I-123 MIBG and BMIPP SPECT have been reported worldwide from Japan. Additionally, clinical experiences of Tc-99m pyrophosphate imaging have recently gained attention for assessing cardiac amyloidosis. Cardiac PET/CT and PET/MR imaging permit combined assessment of metabolic/functional/structural analyses of various cardiac diseases. While other non-invasive imaging modalities have rapidly been developed, the roles of radionuclide imaging remain to be valuable for early and accurate diagnosis and patient management in most cases of chronic CAD and various cardiovascular diseases.

Preprocedural physiological assessment of coronary disease patterns to predict haemodynamic outcomes post-PCI

BACKGROUND

Even with intracoronary imaging-guided stent optimisation, suboptimal haemodynamic outcomes post-percutaneous coronary intervention (PCI) can be related to residual lesions in non-stented segments. Preprocedural assessment of pathophysiological coronary artery disease (CAD) patterns could help predict the physiological response to PCI.

AIMS

The aim of this study was to assess the relationship between preprocedural pathophysiological haemodynamic patterns and intracoronary imaging findings, as well as their association with physiological outcomes immediately post-PCI.

METHODS

Data from 206 patients with chronic coronary syndrome enrolled in the ASET-JAPAN study were analysed. Pathophysiological CAD patterns were characterised using Murray law-based quantitative flow ratio (μQFR)-derived indices acquired from pre-PCI angiograms. The diffuseness of CAD was defined by the pullback pressure gradient (PPG) index. Intracoronary imaging in stented segments after stent optimisation was also analysed.

RESULTS

In the multivariable analysis, diffuse disease - defined by the pre-PCI μQFR-PPG index - was an independent factor for predicting a post-PCI μQFR <0.91 (per 0.1 decrease of PPG index, odds ratio 1.57, 95% confidence interval: 1.07-2.34; p=0.022), whereas the stent expansion index (EI) was not associated with a suboptimal post-PCI μQFR. Among vessels with an EI ≥80% and post-PCI μQFR <0.91, 84.0% of those vessels had a diffuse pattern preprocedure. There was no significant difference in EI between vessels with diffuse disease and those with focal disease. The average plaque burden in the stented segment was significantly larger in vessels with a preprocedural diffuse CAD pattern.

CONCLUSIONS

A physiological diffuse pattern preprocedure was an independent factor in predicting unfavourable immediate haemodynamic outcomes post-PCI, even after stent optimisation using intracoronary imaging. Preprocedural assessment of CAD patterns could identify patients who are likely to exhibit superior immediate haemodynamic outcomes following PCI.

Rationale and design of the pullback pressure gradient (PPG) global registry

INTRODUCTION

Diffuse disease has been identified as one of the main reasons leading to low post-PCI fractional flow reserve (FFR) and residual angina after PCI. Coronary pressure pullbacks allow for the evaluation of hemodynamic coronary artery disease (CAD) patterns. The pullback pressure gradient (PPG) is a novel metric that quantifies the distribution and magnitude of pressure losses along the coronary artery in a focal-to-diffuse continuum.

AIM

The primary objective is to determine the predictive capacity of the PPG for post-PCI FFR.

METHODS

This prospective, large-scale, controlled, investigator-initiated, multicenter study is enrolling patients with at least 1 lesion in a major epicardial vessel with a distal FFR ≤ 0.80 intended to be treated by PCI. The study will include 982 subjects. A standardized physiological assessment will be performed pre-PCI, including the online calculation of PPG from FFR pullbacks performed manually. PPG quantifies the CAD pattern by combining several parameters from the FFR pullback curve. Post-PCI physiology will be recorded using a standardized protocol with FFR pullbacks. We hypothesize that PPG will predict optimal PCI results (post-PCI FFR ≥ 0.88) with an area under the ROC curve (AUC) ≥ 0.80. Secondary objectives include patient-reported and clinical outcomes in patients with focal vs. diffuse CAD defined by the PPG. Clinical follow-up will be collected for up to 36 months, and an independent clinical event committee will adjudicate events.

RESULTS

Recruitment is ongoing and is expected to be completed in the second half of 2023.

CONCLUSION

This international, large-scale, prospective study with pre-specified powered hypotheses will determine the ability of the preprocedural PPG index to predict optimal revascularization assessed by post-PCI FFR. In addition, it will evaluate the impact of PPG on treatment decisions and the predictive performance of PPG for angina relief and clinical outcomes.

Practical Application of Coronary Physiologic Assessment: Asia-Pacific Expert Consensus Document: Part 1

Coronary physiologic assessment is performed to measure coronary pressure, flow, and resistance or their surrogates to enable the selection of appropriate management strategy and its optimization for patients with coronary artery disease. The value of physiologic assessment is supported by a large body of evidence that has led to major recommendations in clinical practice guidelines. This expert consensus document aims to convey practical and balanced recommendations and future perspectives for coronary physiologic assessment for physicians and patients in the Asia-Pacific region based on updated information in the field that including both wire- and image-based physiologic assessment. This is Part 1 of the whole consensus document, which describes the general concept of coronary physiology, as well as practical information on the clinical application of physiologic indices and novel image-based physiologic assessment.

Quantitative flow ratio derived pullback pressure gradient and CZT-SPECT measured longitudinal flow gradient for hemodynamically significant coronary artery disease

BACKGROUND

Whether physiological coronary diffuseness assessed by quantitative flow reserve (QFR) pullback pressure gradient (PPG) correlates with longitudinal myocardial blood flow (MBF) gradient and improves diagnostic performances for myocardial ischemia remains unknown.

METHODS AND RESULTS

MBF was measured in mL g-1 min-1 with 99mTc-MIBI CZT-SPECT at rest and stress, corresponding myocardial flow reserve (MFR = MBF stress/MBF rest) and relative flow reserve (RFR = MBF stenotic area/MBF reference) were calculated. Longitudinal MBF gradient was defined as apical and basal left ventricle MBF gradient. △longitudinal MBF gradient was calculated by longitudinal MBF gradient at stress and rest. QFR-PPG was acquired from virtual QFR pullback curve. QFR-PPG significantly correlated with hyperemic longitudinal MBF gradient (r = 0.45, P = 0.007) and △longitudinal MBF gradient (stress-rest) (r = 0.41, P = 0.016). Vessels with lower RFR had lower QFR-PPG (0.72 vs. 0.82, P = 0.002), hyperemic longitudinal MBF gradient (1.14 vs. 2.22, P = 0.003) and △longitudinal MBF gradient (0.50 vs. 1.02, P = 0.003). QFR-PPG, hyperemic longitudinal MBF gradient and △longitudinal MBF gradient showed comparable diagnostic performances for predicting decreased RFR (area under curve [AUC]: 0.82 vs. 0.81 vs. 0.75, P = NS) or QFR (AUC: 0.83 vs. 0.72 vs. 0.80, P = NS). In addition, QFR-PPG and QFR in combination showed incremental value compared with QFR for predicting RFR (AUC = 0.83 vs. 0.73, P = 0.046, net reclassification index = 0.508, P = 0.001).

CONCLUSION

QFR-PPG significantly correlated with longitudinal MBF gradient and △longitudinal MBF gradient when used for physiological coronary diffuseness assessment. All three parameters had high accuracy in predicting RFR or QFR. Adding physiological diffuseness assessment increased accuracy for predicting myocardial ischemia.

Diagnostic accuracy of optical flow ratio: an individual patient-data meta-analysis

BACKGROUND

Optical flow ratio (OFR) is a novel method for the fast computation of fractional flow reserve (FFR) from optical coherence tomography.

AIMS

We aimed to evaluate the diagnostic accuracy of OFR in assessing intermediate coronary stenosis using wire-based FFR as the reference.

METHODS

We performed an individual patient-level meta-analysis of all available studies with paired OFR and FFR assessments. The primary outcome was vessel-level diagnostic concordance of the OFR and FFR, using a cut-off of ≤0.80 to define ischaemia and ≤0.90 to define suboptimal post-percutaneous coronary intervention (PCI) physiology. This meta-analysis was registered in PROSPERO (CRD42021287726).

RESULTS

Five studies were finally included, providing 574 patients and 626 vessels (404 pre-PCI and 222 post-PCI) with paired OFR and FFR from 9 international centres. Vessel-level diagnostic concordance of the OFR and FFR was 91% (95% confidence interval [CI]: 88%-94%), 87% (95% CI: 82%-91%), and 90% (95% CI: 87%-92%) in pre-PCI, post-PCI, and overall, respectively. The overall sensitivity, specificity, and positive and negative predictive values were 84% (95% CI: 79%-88%), 94% (95% CI: 92%-96%), 90% (95% CI: 86%-93%), and 89% (95% CI: 86%-92%), respectively. Multivariate logistic regression indicated that a low pullback speed (odds ratio [OR] 7.02, 95% CI: 1.68-29.43; p=0.008) was associated with a higher risk of obtaining OFR values at least 0.10 higher than FFR. Increasing the minimal lumen area was associated with a lower risk of obtaining an OFR at least 0.10 lower than FFR (OR 0.39, 95% CI: 0.18-0.82; p=0.013).

CONCLUSIONS

This individual patient data meta-analysis demonstrated a high diagnostic accuracy of OFR. OFR has the potential to provide an improved integration of intracoronary imaging and physiological assessment for the accurate evaluation of coronary artery disease.

Investigation of the Relationship Between Triglycerides-Glucose İndex and Coronary Slow Flow: A Retrospective Case-Control Study

BACKGROUND

Coronary slow flow (CSF) refers to delayed distal vessel opacification in the absence of epicardial coronary artery stenosis. The etiopathogenic mechanism of CSF is still unclear.

OBJECTIVES

This study investigates the relationship between CSF and the triglyceride-glucose (TyG) index.

METHODS

The study sample consisted of 118 CSF patients and 105 patients with normal coronary flow (NCF). The coronary flow rate was measured via the Thrombolysis in Myocardial Infarction (TIMI) frame count (TFC) method in all patients. The TyG index was calculated as the logarithm of the [fasting triglyceride (mg/dL)×fasting glucose (mg/dL)]/2 value. A significance level of < 0.05 was adopted as statistically significant.

RESULTS

The TyG index, low-density lipoprotein (LDL), body mass index (BMI), neutrophil-to-lymphocyte ratio (NLR) and TFC values, male ratio, and the ratio of smokers were higher, whereas high-density lipoprotein (HDL) levels were significantly lower in the CSF group compared to the NCF group (p<0,05). The correlation analysis revealed that CSF was significantly correlated with TyG index, BMI, NLR, and HDL values. The strongest of these correlations was between CSF and TyG index (r= 0.57, p<0.001). Additionally, the multivariate analysis revealed that TyG index, BMI, NLR ratio, and male gender were independent predictors for CSF (p<0.05). Receiver operating characteristic (ROC) curve analysis indicated that a cut-off value of ≥ 9.28 for the TyG index predicted CSF with a sensitivity of 78% and a specificity of 78.1% [Area under the curve (AUC): 0.868 and 95% Confidence Interval (CI): 0.823-0.914].

CONCLUSION

The findings of this study revealed a very strong relationship between CSF and TyG index.

Progressive Perception Learning for Main Coronary Segmentation in X-Ray Angiography

Main coronary segmentation from the X-ray angiography images is important for the computer-aided diagnosis and treatment of coronary disease. However, it confronts the challenge at three different image granularities (the semantic, surrounding, and local levels). The challenge includes the semantic confusion between the main and collateral vessels, low contrast between the foreground vessel and background surroundings, and local ambiguity near the vessel boundaries. The traditional hand-crafted feature-based methods may be insufficient because they may lack the semantic relationship information and may not distinguish the main and collateral vessels. The existing deep learning-based methods seem to have issues due to the deficiency in the long-distance semantic relationship capture, the foreground and background interference adaptability, and the boundary detail information preservation. To solve the main coronary segmentation challenge, we propose the progressive perception learning (PPL) framework to inspect these three different image granularities. Specifically, the PPL contains the context, interference, and boundary perception modules. The context perception is designed to focus on the main coronary vessel based on the semantic dependence capture among different coronary segments. The interference perception is designed to purify the feature maps based on the foreground vessel enhancement and background artifact suppression. The boundary perception is designed to highlight the boundary details based on boundary feature extraction through the intersection between the foreground and background predictions. Extensive experiments on 1085 subjects show that the PPL is effective (e.g., the overall Dice is greater than 95%), and superior to thirteen state-of-the-art coronary segmentation methods.

Impact of coronary disease patterns, anatomical factors, micro-vascular disease and non-coronary cardiac factors on invasive coronary physiology

Invasive coronary physiology has been applied by interventional cardiologists to guide the management of coronary artery disease (CAD), with well-defined thresholds applied to determine whether CAD should be managed with optimal medical therapy (OMT) alone or OMT and percutaneous coronary intervention (PCI). There are multiple modalities in clinical use, including hyperaemic and non-hyperaemic indices. Despite endorsement in the major guidelines, there are various factors which impact and confound the readings of invasive coronary physiology, both within the coronary tree and beyond. This review article aims to summarise the mechanisms by which these factors impact invasive coronary physiology, and distinguish factors that contribute to ischaemia from confounding factors. The potential for mis-classification of ischaemic status is highlighted. Lastly, the authors identify targets for future research to improve the precision of physiology-guided management of CAD.

Integration of fractional flow reserve derived from CT into clinical practice

Fractional flow reserve (FFR) is currently considered as the gold standard for revascularization decision-making in patients with stable coronary artery disease (CAD). The application of computational fluid dynamics to coronary computed tomography (CT) angiography (CCTA) enables calculation of FFR without additional testing, radiation exposure, contrast medium injection, and hyperemia (FFR_CT). Although multiple diagnostic and clinical studies have enriched the scientific evidence, it is still challenging to integrate FFR_CT into clinical practice. Both meticulous scientific backgrounds and precise anatomical data derived from CCTA are fundamental for FFR_CT computation, and there are numerous factors impacting on FFR_CT calculation and interpretation: coronary artery stenosis, calcium, atherosclerosis, luminal volume, and left ventricular myocardial mass. Further, there is a gap that clinicians using FFR_CT need to recognize in interpretation of FFR_CT results between diagnostic studies and clinical studies. In this review, we summarize multiple evidence related to FFR_CT computation and interpretation to refine the FFR_CT strategy in patients with stable CAD.

Diagnostic performance of exercise stress tests for detection of epicardial and microvascular coronary artery disease: the UZ Clear study

BACKGROUND

Cardiac stress tests remain the cornerstone for evaluating patients suspected of having obstructive coronary artery disease (CAD). Coronary microvascular dysfunction (CMD) can lead to abnormal non-invasive tests.

AIMS

We sought to assess the diagnostic performance of exercise stress tests with indexes of epicardial and microvascular resistance as reference.

METHODS

This was a prospective, single-arm, multicentre study of patients with an intermediate pretest probability of CAD and positive exercise stress tests who were referred for invasive angiography. Patients underwent an invasive diagnostic procedure (IDP) with measurement of fractional flow reserve (FFR) and index of microvascular resistance (IMR) in at least one coronary vessel. Obstructive CAD was defined as diameter stenosis (DS) >50% by quantitative coronary angiography (QCA). The objective was to determine the false discovery rate (FDR) of cardiac exercise stress tests with both FFR and IMR as references.

RESULTS

One hundred and seven patients (137 vessels) were studied. The mean age was 62.1±8.7, and 27.1% were female. The mean diameter stenosis was 37.2±27.5%, FFR was 0.84±0.10, coronary flow reserve was 2.74±2.07, and IMR 20.3±11.9. Obstructive CAD was present in 39.3%, whereas CMD was detected in 20.6%. The FDR was 60.7% and 62.6% with QCA and FFR as references (p-value=0.803). The combination of FFR and IMR as clinical reference reduced the FDR by 25% compared to QCA (45.8% vs 60.7%; p-value=0.006).

CONCLUSIONS

In patients with evidence of ischaemia, an invasive functional assessment accounting for the epicardial and microvascular compartments led to an improvement in the diagnostic performance of exercise tests, driven by a significant FDR reduction.

Incorporating coronary artery calcium scoring in the prediction of obstructive coronary artery disease with myocardial ischemia: a study with sequential use of coronary computed tomography angiography and positron emission tomography imaging

BACKGROUND

Additional strategies are needed to refine the referral for diagnostic testing of symptomatic patients with suspected coronary artery disease (CAD). We aimed to compare various models to predict hemodynamically obstructive CAD.

METHODS AND RESULTS

Symptomatic patients with suspected CAD who underwent coronary artery calcium scoring (CACS) and sequential coronary computed tomography angiography (CCTA) and [15O]H2O positron emission tomography (PET) myocardial perfusion imaging were analyzed. Obstructive CAD was defined as a suspected coronary artery stenosis on CCTA with myocardial ischemia on PET (absolute stress myocardial perfusion ≤ 2.4 mL/g/min in ≥ 1 segment). Three models were developed to predict obstructive CAD-induced myocardial ischemia using logistic regression analysis: (1) basic model: including age, sex and cardiac symptoms, (2) risk factor model: adding number of risk factors to the basic model, and (3) CACS model: adding CACS to the risk factor model. Model performance was evaluated using discriminatory ability with area under the receiver-operating characteristic curves (AUC). A total of 647 patients (mean age 62 ± 9 years, 45% men) underwent CACS and sequential CCTA and PET myocardial perfusion imaging. Obstructive CAD with myocardial ischemia on PET was present in 151 (23%) patients. CACS was independently associated with myocardial ischemia (P < .001). AUC for the discrimination of ischemia for the CACS model was superior over the basic model and risk factor model (P < .001).

CONCLUSIONS

Adding CACS to the model including age, sex, cardiac symptoms and number of risk factors increases the accuracy to predict obstructive CAD with myocardial ischemia on PET in symptomatic patients with suspected CAD.

Relationship between tissue characteristics and mechanical properties of coronary plaques: a comparison between integrated backscatter intravascular ultrasound (IVUS) and speckle-tracking IVUS

High-risk coronary plaques have certain morphological characteristics. Thus, comprehensive assessment is needed for the risk stratification of plaques in patients with coronary artery disease. Integrated backscatter intravascular ultrasound (IB-IVUS) has been used successfully used to evaluate the tissue characteristics of coronary plaques; however, the mechanical properties of plaques have been rarely assessed. Therefore, we developed Speckle-tracking IVUS (ST-IVUS) to evaluate the mechanical properties of coronary plaque. This study aimed to evaluate the relation between the tissue characteristics of coronary plaques using IB-IVUS and their mechanical properties using ST-IVUS. We evaluated 95 non-targeted plaques in 95 patients undergoing elective percutaneous coronary intervention to the left anterior descending artery. We set regions of interest (ROIs) in the cross-sectional images of coronary plaques where we divided 120 degree plaques into four quadrants (every 30 degrees), with the center at the area of maximum atheroma thickness. We measured relative calcification area (%CA, relative fibrous area (%FI) and relative lipid pool area (%LP) in a total of 380 ROIs. In ST-IVUS analysis, we measured strain in the circumferential direction of the lumen area (LA strain: %), the external elastic membrane area strain (EEM strain: %), and strain in the radial direction (radial strain: %). On global cross-sectional area IB-IVUS analysis, the %CA was 1.2 ± 1.2%; the %FI was 49.0 ± 15.9%, and the %LP was 49.7 ± 16.5%. In ST-IVUS analysis, the LA strain was 0.67 ± 0.43%; the EEM strain was 0.49 ± 0.33%, and the radial strain was 2.02 ± 1.66%. On regional analysis, the %LP was not associated with the LA strain (r = - 0.002 p = 0.97), the EEM strain (r = - 0.05 p = 0.35), or with the radial strain (r = - 0.04 p = 0.45). These trends were seen between the %FI and the LA strain (r = 0.02 p = 0.74), the %FI and the EEM strain (r = 0.05 p = 0.35), and the %FI and the radial strain (r = 0.04 p = 0.50). A significant correlation was only observed between the %CA and the LA strain (r = - 0.15 p = 0.0038). Our findings indicate that the associations between mechanical properties and tissue characteristics lacked statistical significance, more often than not, and that it is necessary to evaluate the mechanical properties as well as plaque characteristics for risk stratification of coronary plaques.

Computed Tomography-Derived Physiology Assessment: State-of-the-Art Review

Coronary computed tomography angiography (CCTA) and CCTA-derived fractional flow reserve (FFRCT) are the best non-invasive techniques to assess coronary artery disease (CAD) and myocardial ischemia. Advances in these technologies allow a paradigm shift to the use of CCTA and FFRCT for advanced plaque characterization and planning myocardial revascularization.

Non-Dipper Blood Pressure Impact on Coronary Slow Flow in Hypertensive Patients With Normal Coronary Arteries

OBJECTIVE

Coronary slow flow (CSF) is linked to myocardial ischemia, malignant arrhythmias, and cardiovascular mortality. On the other hand, hypertension (HTN) is an important risk factor for vascular disorders. There is limited research on the relationship between CSF and HTN. This study aimed to investigate TIMI frame count (TFC), which is an indicator of CSF, in dipper and non-dipper hypertensive individuals with normal coronary arteries.

METHODS

The study was conducted as a retrospective observational study. Patients diagnosed with CSF and dipper or non-dipper hypertension were included in this study. Blood tests were routinely conducted for all patients. ECG was conducted for each patient, and echocardiography was performed. Coronary artery images were obtained in the CAG laboratory. Blood pressure (BP) measurements were obtained from the ambulatory Holter records. The patients were separated into two groups based on ambulatory Holter monitoring. The relationship between CSF and HTN was also examined.

RESULTS

A total of 71 patients, comprising 25 women (37.2%) and 46 men (62.8%) with an average age of 52.75±9.42 years, were enrolled in the research. Based on ambulatory BP, the individuals were separated into two groups: non-dipper (n=36) and dipper (n=35). The pulse rate was significantly higher in the non-dipper group (p<0.001). In terms of mean systolic and diastolic blood pressure, there were no substantial differences across the groups (p = 0.326 and p = 0.654, respectively). The daytime mean systolic and diastolic BP did not significantly differ across the groups (p = 0.842 and p = 0.421). The dipper group had substantially lower nighttime systolic and diastolic BP values (p <0.001). The LAD, Cx, and RCA TIMI frame scores were significantly lower in the dipper group (p<0.001).

CONCLUSION

In this study, non-dipper patients had a greater CSF rate than dipper.

Clinical Relevance of Impaired Physiological Assessment After Percutaneous Coronary Intervention: A Meta-analysis

Background

Despite the optimal angiographic result of percutaneous coronary intervention (PCI), residual disease at the site of the culprit lesion can lead to major adverse cardiac events. Post-PCI physiological assessment can identify residual stenosis. This meta-analysis aims to investigate data of studies examining post-PCI physiological assessment in relation to long-term outcomes.

Methods

Studies were included in the meta-analysis after performing a systematic literature search on July 1, 2022. The primary end point was the incidence of major adverse cardiac events, vessel-orientated cardiac events, or target vessel failure.

Results

Low post-PCI fractional flow reserve, reported in 7 studies with fractional flow reserve cutoff values between 0.84 and 0.90, including 4017 patients, was associated with an increased rate of the primary end point (hazard ratio [HR], 2.06; 95% CI, 1.37-3.08). One study reported about impaired post-PCI instantaneous wave-free ratio with instantaneous wave-free ratio cutoff value of 0.95 in relation to major adverse cardiac events, showing a significant association (HR, 3.38; 95% CI, 0.99-11.6; P = .04). Low post-PCI quantitative flow ratio, reported in 3 studies with quantitative flow ratio cutoff value between 0.89 and 0.91, including 1181 patients, was associated with an increased rate of vessel-orientated cardiac events (HR, 3.01; 95% CI, 2.10-4.32). Combining data of all modalities, impaired physiological assessment showed an increased rate of the primary end point (HR, 2.32; 95% CI, 1.71-3.16) and secondary end points, including death (HR, 1.41; 95% CI, 1.04-1.89), myocardial infarction (HR, 2.70; 95% CI, 1.34-5.42) and target vessel revascularization (HR, 2.88; 95% CI, 1.91-4.35).

Conclusions

Impaired post-PCI physiological assessment is associated with increased adverse cardiac events and individual end points, including death, myocardial infarction, and target vessel revascularization. Therefore, prospective studies are awaited on whether physiology-based optimization of PCI results in better clinical outcomes.

Characterization of non-stenotic plaques in intracranial arteries with multi-contrast, multi-planar vessel wall image analysis

OBJECTIVES

Non-stenotic plaques have been observed in intracranial arteries but are less understood compared to those in coronary and carotid arteries. We sought to compare plaque distribution and morphology between stenotic and non-stenotic intracranial plaques with MR vessel wall imaging (VWI) and quantitative image analysis.

MATERIALS AND METHODS

Twenty-four patients with intracranial arterial stenosis or luminal irregularity on clinical imaging were scanned with a multi-contrast VWI protocol. Plaques were detected as focal wall thickening on co-registered multiplanar reformats of multi-contrast VWI, with assessment of the location and morphology. TOF-MRA was independently reviewed for any appreciable stenosis using the WAISD criteria.

RESULTS

Across 504 arterial segments, a total of 80 plaques were detected, including 23 (29%) with stenosis on TOF-MRA, 56 (70%) without, and 1 (1%) not covered by TOF-MRA. Plaques involving the ICA were more likely to be non-stenotic than those involving other segments (80% versus 55%, p = 0.030) whereas the basilar artery (40%) and PCA (33%) had the lowest proportions of non-stenotic plaques. Maximum wall thickness, indicative of plaque burden, correlated poorly with degree of stenosis (p = 0.10) and overlapped substantially between stenotic and non-stenotic plaques (1.9 [1.5, 2.4] versus 2.0 [1.5, 2.2] mm, p = 0.074).

CONCLUSIONS

Intracranial plaques without appreciable stenosis on TOF-MRA represent a large proportion of lesions throughout arterial segments but disproportionately affect the ICA. Morphological characterization of plaques with and without stenosis shows that luminal stenosis is a poor indicator of the underlying burden of intracranial atherosclerosis.

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.

Impact of overestimation of fractional flow reserve by adenosine on anatomical-functional mismatch

Adenosine occasionally results in overestimation of fractional flow reserve (FFR) values, compared with other hyperemic stimuli. We aimed to elucidate the association of overestimation of FFR by adenosine with anatomically significant but functionally non-significant lesions (anatomical-functional mismatch) and its influence on reclassification of functional significance. Distal-to-aortic pressure ratio (Pd/Pa) was measured using adenosine (Pd/PaADN) and papaverine (Pd/PaPAP) in 326 patients (326 vessels). The overestimation of FFR was calculated as Pd/PaADN-Pd/PaPAP. The anatomical-functional mismatch was defined as diameter stenosis > 50% and Pd/PaADN > 0.80. Reclassification was indicated by Pd/PaADN > 0.80 and Pd/PaPAP ≤ 0.80. The mismatch (n = 72) had a greater overestimation of FFR than the non-mismatch (n = 99): median 0.02 (interquartile range 0.01-0.05) versus 0.01 (0.00-0.04), p = 0.014. Multivariable analysis identified the overestimation of FFR (p = 0.003), minimal luminal diameter (p = 0.001), and non-left anterior descending artery (LAD) location (p < 0.001) as determinants of the mismatch. Reclassification was indicated in 29% of the mismatch and was more frequent in the LAD than in the non-LAD (52% vs. 20%, p = 0.005). The overestimation of FFR is an independent determinant of anatomical-functional mismatch. Anatomical-functional mismatch, specifically in the LAD, may suggest a false-negative result.

Importance of plaque volume and composition for the prediction of myocardial ischaemia using sequential coronary computed tomography angiography/positron emission tomography imaging

AIMS

Coronary atherosclerosis with a large necrotic core has been postulated to reduce the vasodilatory capacity of vascular tissue. In the present analysis, we explored whether total plaque volume and necrotic core volume on coronary computed tomography angiography (CCTA) are independently associated with myocardial ischaemia on positron emission tomography (PET).

METHODS AND RESULTS

From a registry of symptomatic patients with suspected coronary artery disease and clinically indicated CCTA with sequential [15O]H2O PET myocardial perfusion imaging, we quantitatively measured diameter stenosis, total and compositional plaque volumes on CCTA. Primary endpoint was myocardial ischaemia on PET, defined as an absolute stress myocardial blood flow ≤2.4 mL/g/min in ≥1 segment. Multivariable prediction models for myocardial ischaemia were consecutively created using logistic regression analysis (stenosis model: diameter stenosis ≥50%; plaque volume model: +total plaque volume; plaque composition model: +necrotic core volume). A total of 493 patients (mean age 63 ± 8 years, 54% men) underwent sequential CCTA/PET imaging. In 153 (31%) patients, myocardial ischaemia was detected on PET. Diameter stenosis ≥50% (P < 0.001) and necrotic core volume (P = 0.029) were independently associated with myocardial ischaemia, while total plaque volume showed borderline significance (P = 0.052). The plaque composition model (χ2 = 169) provided incremental value for the prediction of ischaemia when compared with the stenosis model (χ2 = 138, P < 0.001) and plaque volume model (χ2 = 164, P = 0.021).

CONCLUSION

The volume of necrotic core on CCTA independently and incrementally predicts myocardial ischaemia on PET, beyond diameter stenosis alone.

Cardiac computed tomography-derived coronary artery volume to myocardial mass

In the absence of disease impacting the coronary arteries or myocardium, there exists a linear relationship between vessel volume and myocardial mass to ensure balanced distribution of blood supply. This balance may be disturbed in diseases of either the coronary artery tree, the myocardium, or both. However, in contemporary evaluation the coronary artery anatomy and myocardium are assessed separately. Recently the coronary lumen volume to myocardial mass ratio (V/M), measured noninvasively using coronary computed tomography angiography (CTCA), has emerged as an integrated measure of myocardial blood supply and demand in vivo. This has the potential to yield new insights into diseases where this balance is altered, thus impacting clinical diagnoses and management. In this review, we outline the scientific methodology underpinning CTCA-derived measurement of V/M. We describe recent studies describing alterations in V/M across a range of cardiovascular conditions, including coronary artery disease, cardiomyopathies and coronary microvascular dysfunction. Lastly, we highlight areas of unmet research need and future directions, where V/M may further enhance our understanding of the pathophysiology of cardiovascular disease.

Comparison of fluid dynamics changes due to physical activity in 3D printed patient specific coronary phantoms with the Windkessel equivalent model of coronary flow

Background

3D printing (3DP) used to replicate the geometry of normal and abnormal vascular pathologies has been demonstrated in many publications; however, reproduction of hemodynamic changes due to physical activities, such as rest versus moderate exercise, need to be investigated. We developed a new design for patient specific coronary phantoms, which allow adjustable physiological variables such as coronary distal resistance and coronary compliance in patients with coronary artery disease. The new design was tested in precise benchtop experiments and compared with a theoretical Windkessel electrical circuit equivalent, that models coronary flow and pressure using arterial resistance and compliance.

Methods

Five phantoms from patients who underwent clinically indicated elective invasive coronary angiography were built from CCTA scans using multi-material 3D printing. Each phantom was used in a controlled flow system where patient specific flow conditions were simulated by a programmable cardiac pump. To simulate the arteriole and capillary beds flow resistance and the compliance for various physical activities, we designed a three-chamber outlet system which controls the outflow dynamics of each coronary tree. Benchtop pressure measurements were recorded using sensors embedded in each of the main coronary arteries. Using the Windkessel model, patient specific flow equivalent electrical circuit models were designed for each coronary tree branch, and flow in each artery was determined for known inflow conditions. Local flow resistances were calculated through Poiseuille’s Law derived from the radii and lengths of the coronary arteries using CT angiography based multi-planar reconstructions. The coronary stenosis flow rates from the benchtop and the electrical models were compared to the localized flow rates calculated from invasive pressure measurements recorded in the angio-suites.

Results

The average Pearson correlations of the localized flow rates at the location of the stenosis between each of the models (Benchtop/Electrical, Benchtop/Angio, Electrical/Angio) are 0.970, 0.981, and 0.958 respectively.

Conclusions

3D printed coronary phantoms can be used to replicate the human arterial anatomy as well as blood flow conditions. It displays high levels of correlation when compared to hemodynamics calculated in electrically-equivalent coronary Windkessel models as well as invasive angio-suite pressure measurements.

Development, validation, and reproducibility of the pullback pressure gradient (PPG) derived from manual fractional flow reserve pullbacks

Fractional flow reserve (FFR) pullbacks assess the location and magnitude of pressure drops along the coronary artery. The pullback pressure gradient (PPG) quantifies the FFR pullback curve and provides a numeric expression of focal versus diffuse coronary artery disease. This study aims (1) to validate the PPG using manual FFR pullbacks compared with motorized FFR pullbacks as a reference; and (2) to determine the intra- and interoperator reproducibility of the PPG derived from manual FFR pullbacks. Patients with stable coronary artery disease and an FFR ≤ 0.80 were included. All patients underwent FFR pullback evaluation either with a motorized device or manually, depending on the study cohort. The agreement of the PPG between repeated pullbacks was assessed using the Bland-Altman method. Overall, 116 FFR pullback maneuvers (96 manual and 20 motorized) were analyzed. There was excellent agreement between the PPG derived from manual and motorized pullbacks (mean difference -0.01 ± 0.07, 95% limits of agreement [LOA] -0.14 to 0.12). The intra- and interoperator reproducibility of PPG derived from manual pullbacks were excellent (mean difference <0.01, 95% LOA -0.11 to 0.12, and mean difference <0.01, 95% LOA -0.12 to 0.11, respectively). The duration of the pullback maneuver did not impact the reproducibility of the PPG (r = 0.12, 95% CI: -0.29 to 0.49, p = 0.567). Manual pullbacks allow for an accurate PPG calculation. The inter- and intraoperator reproducibility of PPG derived from manual pullbacks were excellent.

CT Fractional Flow Reserve: A Practical Guide to Application, Interpretation, and Problem Solving

CT fractional flow reserve (FFR_CT) is a physiologic simulation technique that models coronary flow from routine coronary CT angiography (CTA). To evaluate lesion-specific ischemia, FFR_CT is measured 2 cm distal to a stenotic lesion. FFR_CT greater than 0.8 is normal, 0.76-0.8 is borderline, and 0.75 or less is abnormal. FFR_CT should always be interpreted in correlation with clinical and anatomic coronary CTA findings. FFR_CT increases the specificity of coronary CTA in the evaluation of coronary artery disease, decreases the prevalence of nonobstructive disease in invasive coronary angiography (ICA), and helps with revascularization decisions and planning. Patients with intermediate-risk coronary anatomy at CTA and abnormal FFR_CT can undergo ICA and revascularization, whereas those with normal FFR_CT can be safely deferred from ICA. In borderline FFR_CT values, management is decided in the context of the clinical scenario, but many cases could be safely managed with medical treatment. There are some limitations and pitfalls of FFR_CT. Abnormal FFR_CT values can be seen in mild stenosis, and normal FFR_CTvalues can be seen in severe stenosis. Gradually decreasing or abnormal low FFR_CT values at the distal vessel without a proximal focal lesion could be due to diffuse atherosclerosis. Coronary stents, bypass grafts, coronary anomalies, coronary dissection, transcatheter aortic valve replacement, unstable angina, and acute or recent myocardial infarction are situations in which FFR_CT has not been validated and should not be used at this time. The authors provide a practical guide to the applications and interpretation of FFR_CT, focusing on common pitfalls and challenges. Online supplemental material is available for this article. ^©RSNA, 2022.

Combined Coronary CT-Angiography and TAVI Planning: Utility of CT-FFR in Patients with Morphologically Ruled-Out Obstructive Coronary Artery Disease

Background: Coronary artery disease (CAD) is a frequent comorbidity in patients undergoing transcatheter aortic valve implantation (TAVI). If significant CAD can be excluded on coronary CT-angiography (cCTA), invasive coronary angiography (ICA) may be avoided. However, a high plaque burden may make the exclusion of CAD challenging, particularly for less experienced readers. The objective was to analyze the ability of machine learning (ML)-based CT-derived fractional flow reserve (CT-FFR) to correctly categorize cCTA studies without obstructive CAD acquired during pre-TAVI evaluation and to correlate recategorization to image quality and coronary artery calcium score (CAC). Methods: In total, 116 patients without significant stenosis (≥50% diameter) on cCTA as part of pre-TAVI CT were included. Patients were examined with an electrocardiogram-gated CT scan of the heart and high-pitch scan of the torso. Patients were re-evaluated with ML-based CT-FFR (threshold = 0.80). The standard of reference was ICA. Image quality was assessed quantitatively and qualitatively. Results: ML-based CT-FFR was successfully performed in 94.0% (109/116) of patients, including 436 vessels. With CT-FFR, 76/109 patients and 126/436 vessels were falsely categorized as having significant CAD. With CT-FFR 2/2 patients but no vessels initially falsely classified by cCTA were correctly recategorized as having significant CAD. Reclassification occurred predominantly in distal segments. Virtually no correlation was found between image quality or CAC. Conclusions: Unselectively applied, CT-FFR may vastly increase the number of false positive ratings of CAD compared to morphological scoring. Recategorization was virtually independently from image quality or CAC and occurred predominantly in distal segments. It is unclear whether or not the reduced CT-FFR represent true pressure ratios and potentially signifies pathophysiology in patients with severe aortic stenosis.

Coronary Arterial Function and Disease in Women With No Obstructive Coronary Arteries

Ischemic heart disease (IHD) is the leading cause of mortality in women. While traditional cardiovascular risk factors play an important role in the development of IHD in women, women may experience sex-specific IHD risk factors and pathophysiology, and thus female-specific risk stratification is needed for IHD prevention, diagnosis, and treatment. Emerging data from the past 2 decades have significantly improved the understanding of IHD in women, including mechanisms of ischemia with no obstructive coronary arteries and myocardial infarction with no obstructive coronary arteries. Despite this progress, sex differences in IHD outcomes persist, particularly in young women. This review highlights the contemporary understanding of coronary arterial function and disease in women with no obstructive coronary arteries, including coronary anatomy and physiology, mechanisms of ischemia with no obstructive coronary arteries and myocardial infarction with no obstructive coronary arteries, noninvasive and invasive diagnostic strategies, and management of IHD.

Prognostic Value of Coronary Sinus Flow Quantification by Cardiac Magnetic Resonance Imaging in Patients With Acute Myocardial Infarction

Background This study aimed to evaluate the prognostic value of hyperemic coronary sinus flow (h-CSF) and global coronary flow reserve (g-CFR) obtained by phase-contrast cine-magnetic resonance imaging in patients with acute myocardial infarction (MI). Methods and Results This retrospective study analyzed patients with acute MI (n=523) who underwent primary (ST-segment-elevation MI) or urgent (non-ST-segment-elevation MI) percutaneous coronary intervention. Absolute coronary sinus blood flow (CSF) at rest and during vasodilator stress hyperemia was quantified at 30 days (24-36 days) after the index infarct-related lesion percutaneous coronary intervention and revascularization of functionally significant non-infarct-related lesions. We used Cox proportional hazards regression modeling to examine the association between h-CSF, g-CFR, and major adverse cardiac events defined as all-cause death, nonfatal MI, hospitalization for congestive heart failure, and stroke. Finally, 325 patients with ST-segment-elevation MI (62.1%) and 198 patients with non-ST-segment-elevation MI (37.9%) were studied over a median follow-up of 2.5 years. The rest CSF, h-CSF, and g-CFR were 0.94 (0.68-1.26) mL/min per g, 2.05 (1.42-2.73) mL/min per g, and 2.17 (1.54-3.03), respectively. Major adverse cardiac events occurred in 62 patients, and Cox proportional hazards analysis showed that h-CSF and g-CFR were independent predictors of major adverse cardiac events (h-CSF: hazard ratio [HR], 0.64; 95% CI, 0.47-0.88; P=0.005; g-CFR: HR, 0.62; 95% CI, 0.47-0.82; P=0.001). When stratified by h-CSF and g-CFR, cardiac event-free survival was the worst in patients with concordantly impaired h-CSF (<1.6 mL/min per g) and g-CFR (<1.7) (P<0.001). Conclusions Global coronary sinus flow quantification using phase-contrast cine-magnetic resonance imaging provided significant prognostic information independent of infarction size and conventional risk factors in patients with acute MI undergoing revascularization.

Fractional Flow Reserve and Instantaneous Wave-Free Ratio Predict Pathological Wall Shear Stress in Coronary Arteries: Implications for Understanding the Pathophysiological Impact of Functionally Significant Coronary Stenoses

Background

The pathophysiological mechanism behind adverse outcomes associated with ischemia‐inducing epicardial coronary stenoses and microcirculatory dysfunction remains unclear. Wall shear stress (WSS) plays an important role in atherosclerotic plaque progression and vulnerability. We aimed to evaluate the relationship between WSS, functionally significant epicardial coronary stenoses, and microcirculatory dysfunction.

Methods and Results

Patients undergoing invasive coronary physiology testing were included. Fractional flow reserve, instantaneous wave‐free ratio, and the index of microcirculatory resistance were measured. Quantitative coronary angiography was used to obtain the lesion percentage diameter stenosis. Computational fluid dynamics analysis was performed to calculate WSS parameters. Multiple regression analysis was performed to calculate the standardized regression coefficient (β) for the coronary physiology indices.

A total of 107 vessels from 88 patients were included. Fractional flow reserve independently predicted the total area of low WSS (β=−0.44; 95% CI, −0.62 to −0.25; P<0.001) and maximum lesion WSS (β=−0.53; 95% CI, −0.70 to −0.36; P<0.001) after adjusting for percentage diameter stenosis and index of microcirculatory resistance. Similarly, instantaneous wave‐free ratio also independently predicted the total area of low WSS (β=−0.45; 95% CI, −0.62 to −0.28; P<0.001) and maximum lesion WSS (β=−0.58; 95% CI, −0.73 to −0.43; P<0.001). The index of microcirculatory resistance did not predict either low or high WSS.

Conclusions

Fractional flow reserve and instantaneous wave‐free ratio independently predicted the total burden of low WSS and maximum lesion WSS in coronary arteries. No relationship was found between microcirculatory dysfunction and WSS.

Trans-lesional fractional flow reserve gradient as derived from coronary CT improves patient management: ADVANCE registry

BACKGROUND

The role of change in fractional flow reserve derived from CT (FFRCT) across coronary stenoses (ΔFFRCT) in guiding downstream testing in patients with stable coronary artery disease (CAD) is unknown.

OBJECTIVES

To investigate the incremental value of ΔFFRCT in predicting early revascularization and improving efficiency of catheter laboratory utilization.

MATERIALS

Patients with CAD on coronary CT angiography (CCTA) were enrolled in an international multicenter registry. Stenosis severity was assessed as per CAD-Reporting and Data System (CAD-RADS), and lesion-specific FFRCT was measured 2 ​cm distal to stenosis. ΔFFRCT was manually measured as the difference of FFRCT across visible stenosis.

RESULTS

Of 4730 patients (66 ​± ​10 years; 34% female), 42.7% underwent ICA and 24.7% underwent early revascularization. ΔFFRCT remained an independent predictor for early revascularization (odds ratio per 0.05 increase [95% confidence interval], 1.31 [1.26-1.35]; p ​< ​0.001) after adjusting for risk factors, stenosis features, and lesion-specific FFRCT. Among the 3 models (model 1: risk factors ​+ ​stenosis type and location ​+ ​CAD-RADS; model 2: model 1 ​+ ​FFRCT; model 3: model 2 ​+ ​ΔFFRCT), model 3 improved discrimination compared to model 2 (area under the curve, 0.87 [0.86-0.88] vs 0.85 [0.84-0.86]; p ​< ​0.001), with the greatest incremental value for FFRCT 0.71-0.80. ΔFFRCT of 0.13 was the optimal cut-off as determined by the Youden index. In patients with CAD-RADS ≥3 and lesion-specific FFRCT ≤0.8, a diagnostic strategy incorporating ΔFFRCT >0.13, would potentially reduce ICA by 32.2% (1638-1110, p ​< ​0.001) and improve the revascularization to ICA ratio from 65.2% to 73.1%.

CONCLUSIONS

ΔFFRCT improves the discrimination of patients who underwent early revascularization compared to a standard diagnostic strategy of CCTA with FFRCT, particularly for those with FFRCT 0.71-0.80. ΔFFRCT has the potential to aid decision-making for ICA referral and improve efficiency of catheter laboratory utilization.

Optical flow ratio for assessing stenting result and physiological significance of residual disease

BACKGROUND

Optical flow ratio (OFR) is a novel method for fast computation of fractional flow reserve (FFR) from optical coherence tomography (OCT) images.

AIMS

We aimed to evaluate the accuracy of OFR in predicting post-percutaneous coronary intervention (PCI) FFR and the impact of stent expansion on within-stent OFR pressure drop (in-stent OFR).

METHODS

Post-PCI OFR was computed in patients with both OCT and FFR interrogation immediately after PCI. Calculation of post-PCI OFR (called simulated residual OFR) from pre-PCI OCT pullbacks after elimination of the stenotic segment by virtual stenting was performed in a subgroup of patients who had pre-PCI OCT images. Stent underexpansion was quantified by the minimum expansion index (MEI) of the stented segment.

RESULTS

A total of 125 paired comparisons between post-PCI OFR and FFR were obtained in 119 patients, among which simulated residual OFR was obtained in 64 vessels. Mean post-PCI FFR was 0.92±0.05. Post-PCI OFR showed good correlation (r=0.74, p<0.001) and agreement (mean difference=-0.01±0.03, p=0.051) with FFR. The accuracy in predicting post-PCI FFR ≤0.90 was 84% for post-PCI OFR. Simulated residual OFR significantly correlated with post-PCI FFR (r=0.42, p<0.001). MEI showed a moderate correlation (r=-0.49, p<0.001) with in-stent OFR.

CONCLUSIONS

Post-PCI OFR showed good diagnostic concordance with post-PCI FFR. Simulated residual OFR significantly correlated with post-PCI FFR. Stent underexpansion significantly correlated with in-stent pressure drop.

Impact of vascular morphology and plaque characteristics on computed tomography derived fractional flow reserve in early stage coronary artery disease

BACKGROUND

Computed-tomography (CT) derived fractional-flow-reserve (FFR_CT) gradually may decrease from proximal to distal vessels even without apparent coronary artery disease (CAD). It may be unclear whether the decrease in FFR_CT at the distal coronal artery is physiological or due to stenosis. We decided to study predictive factors of an FFR_CT decline below the pathological value of 0.80 in no-apparent CAD.

METHODS

A total of 150 consecutive patients who had both CT angiography coupled to FFR_CT analysis and invasive angiogram showing < 20% coronary stenosis were included. Vessels were divided into two groups according to FFR_CT at the distal vessel: FFR_CT > 0.80 (n = 317) and FFR_CT ≤ 0.80 (n = 114). ΔFFR_CT was defined as the change in FFR_CT from proximal to distal vessel. Vessel morphology (vessel length and lumen volume) and plaque characteristics [low-attenuation plaque volume, intermediate-attenuation (IAP) plaque volume, and calcified plaque volume] were evaluated.

RESULTS

FFR_CT decreased from proximal to distal for the three major vessels in both FFR_CT > 0.80 and FFR_CT ≤ 0.80. Compared to FFR_CT > 0.80, IAP volume was significantly higher in all three major vessels in FFR_CT ≤ 0.80. ΔFFR_CT was correlated with vessel length and lumen volume in FFR_CT > 0.80, whereas ΔFFR_CT was correlated with IAP volume in FFR_CT ≤ 0.80. IAP volume above 44.8 mm³ was the strongest predictor of distal FFR_CT of ≤ 0.80.

CONCLUSIONS

The presence of IAP is a major predictor of gradual decrease of FFR_CT below 0.80 in no-apparent CAD vessels. Vessel morphology and plaque characteristics should be considered when interpreting FFR_CT.