Basic structure-function relations of the epicardial coronary vascular tree. Basis of quantitative coronary arteriography for diffuse coronary artery disease

Operator decision-making in angiography-only guided revascularization for lesions not indicated for FFR: a QFR-based functional assessment in chronic coronary syndrome

Background

Discordance between coronary angiographic findings and invasive functional significance is well-established. Yet, the prevalence of this mismatch in an era increasingly utilizing invasive functional assessments, such as fractional flow reserve (FFR), remains unclear. This study examines the extent of such discrepancies in current clinical practice.

Methods

This single-center prospective registry included consecutive patients with chronic coronary syndrome (CCS) who underwent elective coronary angiography, with or without revascularization. Coronary angiograms deemed not requiring FFR due to clear anatomical distinctions, either anatomically severe indicating a need for revascularization or mild suggesting no need for intervention, were selected for evaluation. These were then subjected to post-hoc analysis by three independent operators who were blinded to the definitive treatment strategies. Importantly, the post-hoc analysis was conducted in two distinct phases: firstly, a re-evaluation of coronary stenosis, and secondly, a separate functional assessment, each carried out independently. Coronary stenosis severity was assessed visually, while functional relevance was determined by quantitative flow ratio (QFR), calculated using a computational fluid dynamics algorithm applied to angiographic images. Analysis focused on discrepancies between QFR-based functional indications and revascularization strategies actually performed.

Results

In 191 patients, 488 vessels were analyzed. Average diameter stenosis (DS) was 37 ± 34%, and QFR was 0.87 ± 0.15, demonstrating a moderate correlation (r = -0.84; 95% CI: -0.86 to -0.81, p < 0.01). Agreement with QFR at conventional anatomical cutoffs was 88% for 50% DS and 91% for 70% DS. Mismatches between revascularization decisions and QFR indications occurred in 10% of cases. Discrepancies were more frequent in the left anterior descending artery (14%) compared to the left circumflex (6%) and the right coronary artery (9%; p = 0.07).

Conclusion

In a cardiac-center where FFR utilization is high, discordance between coronary angiography and functional significance persists, even when operators are confident in their decisions not to use functional interrogation. This gap, most evident in the left anterior descending artery, highlights the potential need for integrated angiography-based functional assessments to refine revascularization decisions in CCS.

Relationship between coronary volume, myocardial mass, and post-PCI fractional flow reserve

BACKGROUND

Fractional flow reserve (FFR) measured after percutaneous coronary intervention (PCI) carries prognostic information. Yet, myocardial mass subtended by a stenosis influences FFR. We hypothesized that a smaller coronary lumen volume and a large myocardial mass might be associated with lower post-PCI FFR.

AIM

We sought to assess the relationship between vessel volume, myocardial mass, and post-PCI FFR.

METHODS

This was a subanalysis with an international prospective study of patients with significant lesions (FFR ≤ 0.80) undergoing PCI. Territory-specific myocardial mass was calculated from coronary computed tomography angiography (CCTA) using the Voronoi's algorithm. Vessel volume was extracted from quantitative CCTA analysis. Resting full-cycle ratio (RFR) and FFR were measured before and after PCI. We assessed the association between coronary lumen volume (V) and its related myocardial mass (M), and the percent of total myocardial mass (%M) with post-PCI FFR.

RESULTS

We studied 120 patients (123 vessels: 94 left anterior descending arteries, 13 left Circumflex arteries, 16 right coronary arteries). Mean vessel-specific mass was 61 ± 23.1 g (%M 39.6 ± 11.7%). The mean post-PCI FFR was 0.88 ± 0.06 FFR units. Post-PCI FFR values were lower in vessels subtending higher mass (0.87 ± 0.05 vs. 0.89 ± 0.07, p = 0.047), and with lower V/M ratio (0.87 ± 0.06 vs. 0.89 ± 0.07, p = 0.02). V/M ratio correlated significantly with post-PCI RFR and FFR (RFR r = 0.37, 95% CI: 0.21-0.52, p < 0.001 and FFR r = 0.41, 95% CI: 0.26-0.55, p < 0.001).

CONCLUSION

Post-PCI RFR and FFR are associated with the subtended myocardial mass and the coronary volume to mass ratio. Vessels with higher mass and lower V/M ratio have lower post-PCI RFR and FFR.

Coronary Physiology: Modern Concepts for the Guidance of Percutaneous Coronary Interventions and Medical Therapy

Recent evidence on ischemia, rather than coronary artery disease (CAD), representing a major determinant of outcomes, has led to a progressive shift in the management of patients with ischemic heart disease. According to most recent guidelines, myocardial revascularization strategies based on anatomical findings should be progressively abandoned in favor of functional criteria for the guidance of PCI. Thus, emerging importance has been assigned to the assessment of coronary physiology in order to determine the ischemic significance of coronary stenoses. However, despite several indexes and tools that have been developed so far, the existence of technical and clinical conditions potentially biasing the functional evaluation of the coronary tree still cause debates regarding the strategy of choice. The present review provides an overview of the available methods and the most recent acquirements for the invasive assessment of ischemia, focusing on the most widely available indexes, fractional flow reserve (FFR) and instant-wave free ratio (iFR), in addition to emerging examples, as new approaches to coronary flow reserve (CFR) and microvascular resistance, aiming at promoting the knowledge and application of those "full physiology" principles, which are generally advocated to allow a tailored treatment and the achievement of the largest prognostic benefits.

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.

Procedural Outcomes After Percutaneous Coronary Interventions in Focal and Diffuse Coronary Artery Disease

Background Coronary artery disease (CAD) patterns play an essential role in the decision-making process about revascularization. The pullback pressure gradient (PPG) quantifies CAD patterns as either focal or diffuse based on fractional flow reserve (FFR) pullbacks. The objective of this study was to evaluate the impact of CAD patterns on acute percutaneous coronary intervention (PCI) results considered surrogates of clinical outcomes. Methods and Results This was a prospective, multicenter study of patients with hemodynamically significant CAD undergoing PCI. Motorized FFR pullbacks and optical coherence tomography (OCT) were performed before and after PCI. Post-PCI FFR >0.90 was considered an optimal result. Focal disease was defined as PPG >0.73 (highest PPG tertile). Overall, 113 patients (116 vessels) were included. Patients with focal disease were younger than those with diffuse CAD (61.4±9.9 versus 65.1±8.7 years, P=0.042). PCI in vessels with high PPG (focal CAD) resulted in higher post-PCI FFR (0.91±0.07 in the focal group versus 0.86±0.05 in the diffuse group, P<0.001) and larger minimal stent area (6.3±2.3 mm² in focal versus 5.3±1.8 mm² in diffuse CAD, P=0.015) compared withvessels with low PPG (diffuse CAD). The PPG was associated with the change in FFR after PCI (R²=0.51, P<0.001). The PPG significantly improved the capacity to predict optimal PCI results compared with an angiographic assessment of CAD patterns (area under the curve_PPG 0.81 [95% CI, 0.73-0.88] versus area under the curve_angio 0.51 [95% CI, 0.42-0.60]; P<0.001). Conclusions PCI in vessels with focal disease defined by the PPG resulted in greater improvement in epicardial conductance and larger minimal stent area compared with diffuse disease. PPG, but not angiographically defined CAD patterns, distinguished patients attaining superior procedural outcomes. Registration URL: https://clinicaltrials.gov/ct2/show/NCT03782688.

The quantitative relationship between coronary microcirculatory resistance and myocardial ischemia in patients with coronary artery disease

It was hypothesized that the microcirculatory resistance of resting state (R_m-res) might be a good predictor for ischemia. In this study, the quantitative relationship between R_m-res and myocardial ischemia in different stenosed degrees was explored and verified through retrospective analysis, and the diagnostic performance was evaluated. 136 patients were screened and divided into a training set (90 patients) and a validation set (46 patients). In the training set, R_m-res was calculated, and thresholds were determined by exploring the relationship between R_m-res and myocardial ischemia in different stenosed degrees. In the validation set, the diagnostic performance of the thresholds was verified. It was found that the 90 data mean difference (95%CI) of R_m-res between the ischemic group and the non-ischemic group was 63.03 (95 %CI: 25.72-100.34), p < 0.05. In the training set with stenosed degree 41-60%, 61-70%, 71-80%, and >81%, the average of R_m-res in the ischemic and non-ischemic groups were (80.79, 136.87), (96.41, 172.62), (128.99, 198.94) and (175.95, 310.79) mmHg/s/ml. The R_m-res thresholds were 87.18, 118.96, 142.35, and 177.39 mmHg/s/ml. In the validation set, the overall sensitivity, specificity, PPV, NPV, and accuracy were 73.3%, 77.4%, 61.1%, 85.7%, and 76.1%. In conclusion, R_m-res had a significant predictor on myocardial ischemia. As a smaller R_m-res represents greater myocardial mass perfusion, it is more likely that a stenosis will have a functional impact. Threshold analysis showed that R_m-res of different stenosed degrees was a quantitative predictor of myocardial ischemia, which could assist physicians with clinical treatment strategies.

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.

PERSONALIZED FLOW DIVISION METHOD BASED ON THE LEFT-RIGHT CORONARY CROSS-SECTIONAL AREA

This paper proposes a personalized method to estimate blood flow distribution based on the cross-sectional area of the left-right coronary artery openings. According to the cross-sectional area of the left-right coronary artery in 30 cases, a personalized flow distribution model was derived. A 0D/3D geometric multiscale model was used for the numerical simulation of FFR. To evaluate the accuracy of the cross-sectional area method, invasive FFR was used as the standard. The diagnostic efficiency of the proposed method was verified through the simulation results of the volume and the fixed ratio methods. The flow of the left-right coronary artery was proportional to the 3/4 power of the cross-sectional area. The 95% LOA between the cross-sectional area method, volume method, fixed ratio method and FFR were [Formula: see text]0.06 ([[Formula: see text]0.22, 0.10]), [Formula: see text]0.03 ([[Formula: see text]0.35, 0.28]), and [Formula: see text]0.05 ([[Formula: see text]0.30, 0.20]), the accuracy values were 94.44%, 77.78%, and 77.78%, respectively. Flow distribution based on the cross-sectional area represents the supply and demand relationship of the myocardium. The flow of the left-right coronary arteries is proportional to the 3/4 exponent of the cross-sectional area, which affects the accuracy of FFRCT by affecting the exit boundary conditions of the 0D/3D model.

Estimation of coronary stenosis severity based on flow distribution ratios

We suggest improving minimally-invasive stenosis severity estimation, using a combination of existing geometry-based methods with Transluminal Attenuation Gradient measurements. Instead of local flow values, the method uses flow distribution ratios along the entire tree. The tree geometry is used to derive a lumped model and predict the 'theoretical' ratios in each bifurcation, while attenuation measurements are used for extracting 'actual' ratios. The discrepancies between the measured and the theoretical values are utilized to assess a functional degree of stenosis. Our experimental and numerical analyses show that the quantitative value of discrepancy is proportional to stenosis severity, regardless of boundary conditions.

Branch flow distribution approach and its application in the calculation of fractional flow reserve in stenotic coronary artery

OBJECTIVE

To calculate fractional flow reserve (FFR) based on computed tomography angiography (i.e., FFRCT) by considering the branch flow distribution in the coronary arteries.

BACKGROUND

FFR is the gold standard to diagnose myocardial ischemia caused by coronary stenosis. An accurate and noninvasive method for obtaining total coronary blood flow is needed for the calculation of FFRCT.

METHODS

A mathematical model for estimating the coronary blood flow rate and two approaches for setting the patient-specific flow boundary condition were proposed. Coronary branch flow distribution methods based on a volume-flow approach and a diameter-flow approach were employed for the numerical simulation of FFRCT. The values of simulated FFRCT for 16 patients were compared with their clinically measured FFR.

RESULTS

The ratio of total coronary blood flow to cardiac output and the myocardial blood flow under the condition of hyperemia were 16.97% and 4.07 mL/min/g, respectively. The errors of FFRCT compared with clinical data under the volume-flow approach and diameter-flow approach were 10.47% and 11.76%, respectively, the diagnostic accuracies of FFRCT were 65% and 85%, and the consistencies were 95% and 90%.

CONCLUSIONS

The mathematical model for estimating the coronary blood flow rate and the coronary branch flow distribution method can be applied to calculate the value of clinical noninvasive FFRCT.

Effects of Mechanical Dyssynchrony on Coronary Flow: Insights From a Computational Model of Coupled Coronary Perfusion With Systemic Circulation

Mechanical dyssynchrony affects left ventricular (LV) mechanics and coronary perfusion. Due to the confounding effects of their bi-directional interactions, the mechanisms behind these changes are difficult to isolate from experimental and clinical studies alone. Here, we develop and calibrate a closed-loop computational model that couples the systemic circulation, LV mechanics, and coronary perfusion. The model is applied to simulate the impact of mechanical dyssynchrony on coronary flow in the left anterior descending artery (LAD) and left circumflex artery (LCX) territories caused by regional alterations in perfusion pressure and intramyocardial pressure (IMP). We also investigate the effects of regional coronary flow alterations on regional LV contractility in mechanical dyssynchrony based on prescribed contractility-flow relationships without considering autoregulation. The model predicts that LCX and LAD flows are reduced by 7.2%, and increased by 17.1%, respectively, in mechanical dyssynchrony with a systolic dyssynchrony index of 10% when the LAD's IMP is synchronous with the arterial pressure. The LAD flow is reduced by 11.6% only when its IMP is delayed with respect to the arterial pressure by 0.07 s. When contractility is sensitive to coronary flow, mechanical dyssynchrony can affect global LV mechanics, IMPs and contractility that in turn, further affect the coronary flow in a feedback loop that results in a substantial reduction of dP_LV/dt, indicative of ischemia. Taken together, these findings imply that regional IMPs play a significant role in affecting regional coronary flows in mechanical dyssynchrony and the changes in regional coronary flow may produce ischemia when contractility is sensitive to the changes in coronary flow.

Topologic and Hemodynamic Characteristics of the Human Coronary Arterial Circulation

Background

Many processes contributing to the functional and structural regulation of the coronary circulation have been identified. A proper understanding of the complex interplay of these processes requires a quantitative systems approach that includes the complexity of the coronary network. The purpose of this study was to provide a detailed quantification of the branching characteristics and local hemodynamics of the human coronary circulation.

Methods

The coronary arteries of a human heart were filled post-mortem with fluorescent replica material. The frozen heart was alternately cut and block-face imaged using a high-resolution imaging cryomicrotome. From the resulting 3D reconstruction of the left coronary circulation, topological (node and loop characteristics), topographic (diameters and length of segments), and geometric (position) properties were analyzed, along with predictions of local hemodynamics (pressure and flow).

Results

The reconstructed left coronary tree consisted of 202,184 segments with diameters ranging from 30 μm to 4 mm. Most segments were between 100 μm and 1 mm long. The median segment length was similar for diameters ranging between 75 and 200 μm. 91% of the nodes were bifurcations. These bifurcations were more symmetric and less variable in smaller vessels. Most of the pressure drop occurred in vessels between 200 μm and 1 mm in diameter. Downstream conductance variability affected neither local pressure nor median local flow and added limited extra variation of local flow. The left coronary circulation perfused 358 cm³ of myocardium. Median perfused volume at a truncation level of 100 to 200 μm was 20 mm³ with a median perfusion of 5.6 ml/min/g and a high local heterogeneity.

Conclusion

This study provides the branching characteristics and hemodynamic analysis of the left coronary arterial circulation of a human heart. The resulting model can be deployed for further hemodynamic studies at the whole organ and local level.

The Human Coronary Collateral Circulation, Its Extracardiac Anastomoses and Their Therapeutic Promotion

Cardiovascular disease remains the leading global cause of death, and the number of patients with coronary artery disease (CAD) and exhausted therapeutic options (i.e., percutaneous coronary intervention (PCI), coronary artery bypass grafting (CABG) and medical treatment) is on the rise. Therefore, the evaluation of new therapeutic approaches to offer an alternative treatment strategy for these patients is necessary. A promising research field is the promotion of the coronary collateral circulation, an arterio-arterial network able to prevent or reduce myocardial ischemia in CAD. This review summarizes the basic principles of the human coronary collateral circulation, its extracardiac anastomoses as well as the different therapeutic approaches, especially that of stimulating the extracardiac collateral circulation via permanent occlusion of the internal mammary arteries.

Comprehensive physiological evaluation of epicardial and microvascular coronary domains using vascular conductance and zero flow pressure

AIMS

Assessment of the coronary circulation has been based largely on pressure ratios (epicardial) and resistance (micro-vessels). Simultaneous assessment of epicardial (CEPI) and microvascular conductance (CMICRO) provides an intuitive approach using the same units for both coronary domains and expressing the actual deliverability of blood. The aim of this study was to develop a novel integral method for assessing the functional severity of epicardial and microvascular disease.

METHODS AND RESULTS

We performed intracoronary pressure and Doppler flow velocity measurements in 403 vessels in 261 patients with stable coronary artery disease. Hyperaemic mid-to-late diastolic pressure and flow velocity (PV) relationships were calculated. The slope of the aortic PV indicates the overall conductance and the slope of the distal PV relationship represents CMICRO. The intercept with the x-axis represents zero-flow pressure (Pzf). CEPI was derived from microvascular and overall conductance. Median CEPI was higher compared to CMICRO (4.2 [2.1-8.0] versus 1.3 [1.0-1.7] cm/s/mmHg, p<0.001). CMICRO was independent of stenosis severity (1.3 [1.0-1.7] in FFR ≤0.80 versus 1.4 [1.0-1.8] in FFR >0.8, p=0.797). ROC curves (using FFR and HSR concordant vessels as standard) demonstrated an excellent ability of CEPI to characterise significant stenoses (AUC 0.93). When CEPI<CMICRO, a decrease in flow velocity and coronary pressure (optimal cut-off value 0.97, AUC 0.90) was demonstrated.

CONCLUSIONS

A comprehensive assessment of separate CEPI and CMICRO was feasible. CEPI has a remarkable diagnostic efficiency to detect a clinically relevant stenosis. When CEPI<CMICRO, distal flow and pressure decrease steeply, indicating myocardial ischaemia. CMICRO can be used to explore the severity of microvascular disease.

Assessing the Haemodynamic Impact of Coronary Artery Stenoses: Intracoronary Flow Versus Pressure Measurements

Fractional flow reserve (FFR)-guided percutaneous coronary intervention results in better long-term clinical outcomes compared with coronary angiography alone in intermediate stenoses in stable coronary artery disease (CAD). Coronary physiology measurements have emerged for clinical decision making in interventional cardiology, but the focus lies mainly on epicardial vessels rather than the impact of these stenoses on the myocardial microcirculation. The latter can be quantified by measuring the coronary flow reserve (CFR), a combined pressure and flow index with a strong ability to predict clinical outcomes in CAD. However, combined pressure-flow measurements show 30-40 % discordance despite similar diagnostic accuracy between FFR and CFR, which is explained by the effect of microvascular resistance on both indices. Both epicardial and microcirculatory involvement has been acknowledged in ischaemic heart disease, but clinical implementation remains difficult as it requires individual proficiency. The recent introduced pressure-only index instantaneous wave-free ratio, a resting adenosine-free stenosis assessment, led to a revival of interest in coronary physiology measurements. This review focuses on elaborating the coronary physiological parameters and potential of combined pressure-flow measurements in daily clinical practice.

Fractional Flow Reserve or Coronary Flow Reserve for the Assessment of Myocardial Perfusion : Implications of FFR as an Imperfect Reference Standard for Myocardial Ischemia

Purpose of Review

Accumulating evidence exists for the value of coronary physiology for clinical decision-making in ischemic heart disease (IHD). The most frequently used pressure-derived index to assess stenosis severity, the fractional flow reserve (FFR), has long been considered the gold standard for this purpose, despite the fact that the FFR assesses solely epicardial stenosis severity and aims to estimate coronary flow impairment in the coronary circulation. The coronary flow reserve (CFR) directly assesses coronary blood flow in the coronary circulation, including both the epicardial coronary artery and the coronary microvasculature, but is nowadays less established than FFR. It is now recognized that both tools may provide insight into the pathophysiological substrate of ischemic heart disease, and that particularly combined FFR and CFR measurements provide a comprehensive insight into the multilevel involvement of IHD. This review discusses the diagnostic and prognostic characteristics, as well as future implications of combined assessment of FFR and CFR pressure and flow measurements as parameters for inducible ischemia.

Recent Findings

FFR and CFR disagree in up to 40% of all cases, giving rise to fundamental questions regarding the role of FFR in contemporary ischemic heart disease management, and implying a renewed approach in clinical management of these patients using combined coronary pressure and flow measurement to allow appropriate identification of patients at risk for cardiovascular events.

Summary

This review emphasizes the value of comprehensive coronary physiology measurements in assessing the pathophysiological substrate of IHD, and the importance of acknowledging the broad spectrum of epicardial and microcirculatory involvement in IHD. Increasing interest and large clinical trials are expected to further strengthen the potential of advanced coronary physiology in interventional cardiology, consequently inducing reconsideration of current clinical guidelines.

Myocardial Mass Contributes to the Discrepancy Between Anatomic Stenosis Severity Assessed by Intravascular Ultrasound and Fractional Flow Reserve in Intermediate Lesions of the Coronary Artery

OBJECTIVES

The present study investigated the major contributors to the discrepancy between the minimal lumen area (MLA) and fractional flow reserve (FFR).

BACKGROUND

There was considerable discrepancy between MLA or diameter stenosis (DS) and FFR.

METHODS

We enrolled 744 patients with intermediate stenoses of the left anterior descending artery (LAD). Summed epicardial coronary artery length distal to the target stenosis was obtained from each longest view of the vessels on the coronary angiograms. Mismatching was defined as a lesion with FFR of >0.80 and MLA smaller than the best cut-off value (BCV) for predicting FFR of ≤0.80. Reverse mismatching was defined as a lesion with FFR of ≤0.80 and MLA larger than the BCV.

RESULTS

Summed epicardial coronary artery length was longer at the lesions of proximal LAD than that of middle LAD (380 mm ± 82 mm vs. 341 mm ± 80 mm, P < 0.001). Reverse mismatching was found more frequently in the proximal than middle LAD (28.3% vs. 5.5%, P < 0.001). Independent predictors of FFR ≤ 0.80 were age, male, multi-vessel disease, proximal LAD lesion, MLA, DS, plaque burden at distal reference, lesion length and summed epicardial coronary artery length. Proximal LAD lesion was an independent predictor of reverse mismatching (hazard ratio 3.162, 1.858-5.382, P < 0.001).

CONCLUSIONS

Myocardial mass subtended by a lesion is an important factor predicting FFR ≤0.80 and discrepancy between FFR and MLA. Myocardial mass subtended by a lesion should be considered when determining the revascularization therapy by intravascular ultrasound parameters. © 2017 Wiley Periodicals, Inc.

The Coronary Artery Running Pattern is One of the Causes of Individual Differences in the Progression of Coronary Atherosclerosis in WHHLMI Rabbits, an Animal Model for Coronary Atherosclerosis

AIMS

The relationship between the coronary artery running pattern and development of coronary lesions was re-examined herein using WHHLMI rabbits, an animal model of spontaneous coronary atherosclerosis.

METHODS

The coronary artery running pattern was analyzed using an X-ray computed tomography (CT) apparatus after perfusion. Pathological sections were prepared (Victoria blue-HE staining) at 100 µm intervals from the origin of the left circumflex artery (LCX). The severity of coronary lesions was evaluated based on cross-sectional narrowing (lesion area/inner area of the internal elastic lamina).

RESULTS

In the CT analysis, the angle of the main curvature of the LCX negatively correlated with the percentage of sections with lesions and cross-sectional narrowing. The percentage of sections with lesions was significantly higher in acute angle-type LCX than in obtuse angle-type LCX. Cross-sectional narrowing was also significantly greater in acute angle-type LCX than in obtuse angle-type LCX. The percentage of fibrous lesions was high at the proximal region of LCX, whereas that of lipid-rich lesions was high at the curvature. In 24 months age group, the percentage of sections with calcification in acute angle-type LCX was about twice that in obtuse angle-type LCX.

CONCLUSIONS

Individual differences were observed in the angle of the main curvature of the LCX, which affected the occurrence and extension of atherosclerotic lesions.

Effect of the ratio of coronary arterial lumen volume to left ventricle myocardial mass derived from coronary CT angiography on fractional flow reserve

BACKGROUND

We hypothesize that in patients with suspected coronary artery disease (CAD), lower values of the ratio of total epicardial coronary arterial lumen volume to left ventricular myocardial mass (V/M) result in lower fractional flow reserve (FFR).

METHODS

V/M was computed in 238 patients from the NXT trial who underwent coronary computed tomography angiography (CTA), quantitative coronary angiography (QCA) and FFR measurement in 438 vessels. Nitroglycerin was administered prior to CT, QCA and FFR acquisition. The V/M ratio was quantified on a patient-level from CT image data by segmenting the epicardial coronary arterial lumen volume (V) and the left ventricular myocardial mass (M). Calcified and noncalcified plaque volumes were quantified using semi-automated software.

RESULTS

The median value of V/M (18.57 mm³/g) was used to define equal groups of low and high V/M patients. Patients with low V/M had greater diameter stenosis by QCA, more plaque and lower FFR (0.80 ± 0.12 vs. 0.87 ± 0.08; P < 0.0001) than those with high V/M. A total of 365 vessels in 202 patients had QCA stenosis ≤50% and measured FFR. In these patients, those with low V/M had higher percent diameter stenosis by QCA, greater total plaque volume and lower FFR (0.81 ± 0.12 vs. 0.88 ± 0.07; P < 0.0001) than those with high V/M. In multivariate logistic regression analysis, V/M was an independent predictor of FFR ≤0.80 (all p-values < 0.001).

CONCLUSIONS

Patients with a low V/M ratio have lower FFR overall and in non-obstructive CAD, independent of plaque measures.

Targeting the dominant mechanism of coronary microvascular dysfunction with intracoronary physiology tests

The coronary microcirculation plays a key role in modulating blood supply to the myocardium. Several factors like myocardial oxygen demands, endothelial and neurogenic conditions determine its function. Although there is available evidence supporting microvascular dysfunction as an important cause of myocardial ischaemia, with both prognostic and symptomatic implications, its diagnosis and management in clinical practice is still relegated to a second plane. Both diagnostic and therapeutic approaches are hampered by the broadness of the concept of microvascular dysfunction, which fails addressing the plurality of mechanisms leading to dysfunction. Normal microcirculatory function requires both structural integrity of the microcirculatory vascular network and preserved signalling pathways ensuring adequate and brisk arteriolar resistance shifts in response to myocardial oxygen demands. Pathological mechanisms affecting these requirements include structural remodelling of microvessels, intraluminal plugging, extravascular compression or vasomotor dysregulation. Importantly, not every diagnostic technique provides evidence on which of these pathophysiological mechanisms is present or predominates in the microcirculation. In this paper we discuss the mechanisms of coronary microvascular dysfunction and the intracoronary tools currently available to detect it, as well as the potential role of each one to unmask the main underlying mechanism.

Utility of stress perfusion-cardiac magnetic resonance in follow-up of patients undergoing percutaneous coronary interventions of the left main coronary artery

To assess the accuracy of cardiac magnetic resonance (CMR) for the diagnosis of angiographic stenosis after percutaneous coronary intervention (PCI) of left main coronary artery (LMCA). Patients undergone in the last year PCI of unprotected LMCA and scheduled for conventional X-ray coronary angiography (CXA) were evaluated with stress perfusion CMR within 2 weeks before CXA. Main contraindications to CMR were exclusion criteria. Stress perfusion CMR was performed to follow a bolus of contrast Gadobutrol after 3 min of adenosine infusion. Between the 50 patients enrolled, only 1 did not finish the CMR protocol and 49 patients with median age 71 (65-75) years (38 male, 11 female) were analyzed. Between 784 coronary angiographic segments evaluated we found 75 stenosis or occlusions (prevalence 9.5%), but only 13 stenosis or occlusions in proximal segments (prevalence 6.6%). Patients with coronary stenosis (n = 12, 24%) showed a significantly (p = 0.002) higher prevalence of diabetes (7 of 12, 58%). At CMR examination, late gadolinium enhancement was present in 25 (51%), reversible perfusion defects in 12 (24%), and fixed perfusion defects in 6 subjects (12%). The only patient with LMCA restenosis resulted positive at perfusion CMR. The accuracy of stress perfusion CMR in diagnosis of coronary stenosis was higher when the analysis was performed only in proximal coronary arteries (95%, CI 86-99) compared to overall vessels (84%, CI 70-92). Stress perfusion CMR could strongly reduce the need for elective CXA in follow up of LMCA PCI and should be validated in further multicenter prospective studies.

Coronary flow capacity: concept, promises, and challenges

The vasodilator capacity of the coronary circulation is an important diagnostic and prognostic characteristic, and its accurate assessment is therefore an important frontier. The coronary flow capacity (CFC) concept was introduced to overcome the limitations associated with the use of coronary flow reserve (CFR) for this purpose, which are related to the sensitivity of CFR to physiological alterations in systemic and coronary hemodynamics. CFC was developed from positron emission tomography, and was subsequently extrapolated to invasive coronary physiology. These studies suggest that CFC is a robust framework for the identification of clinically relevant coronary flow abnormalities, and improves identification of patients at risk for adverse events over the use of CFR alone. This Review will discuss the concept of CFC, its promises in the setting of ischaemic heart disease, and its challenges both in theoretical and practical terms.

Angiographic underestimation of disease severity in the left anterior descending artery: a fractional flow reserve analysis

OBJECTIVES

This study compared the prevalence of angiographic underestimation of left anterior descending artery (LAD) lesions with non-LAD lesions.

BACKGROUND

Coronary angiography cannot assess the functional severity of a coronary stenosis. Previous studies suggested that lesions of the LAD are more often angiographically underestimated, but evidence is limited.

MATERIALS AND METHODS

Fractional flow reserve (FFR) was performed in 335 coronary lesions (187 LAD lesions and 148 non-LAD lesions). A visually estimated diameter stenosis of at least 70% was considered functionally significant. An FFR value of up to 0.80 was considered significant. Multivariable analyses were carried out.

RESULTS

Angiographically, LAD lesions as well as non-LAD lesions were considered functionally significant in 29% (P=0.94). FFR showed significant stenosis of the LAD in 52% compared with 24% in non-LAD lesions (P<0.001). Underestimation was observed in 30% of LAD lesions compared with 11% in non-LAD lesions (P<0.001). The adjusted odds ratio for underestimation in LAD lesions in comparison with non-LAD lesions was 3.48 (95% confidence interval 1.89-6.41; P<0.001).

CONCLUSION

Underestimation of the functional severity of a coronary stenosis is more common in LAD lesions. FFR should be performed more often for intermediate stenosis of the LAD.

Hemodynamics in Coronary Arterial Tree of Serial Stenoses

Serial segmental narrowing frequently occurs in humans, which alters coronary hemodynamics and further affects atherosclerotic progression and plaque formation. The objective of this study was to understand the distribution of hemodynamic parameters in the epicardial left main coronary arterial (LMCA) tree with serial stenoses reconstructed from patient computer tomography angiography (CTA) images. A finite volume method was used in conjunction with the inlet pressure wave and outlet flow resistance. The time-averaged wall shear stress (TAWSS) and oscillatory shear index (OSI) were determined from the flow field. A stenosis at a mother vessel mainly deteriorated the hemodynamics near the bifurcation while a stenosis at a daughter vessel affected the remote downstream bifurcation. In comparison with a single stenosis, serial stenoses increased the peak pressure gradient along the main trunk of the epicardial left anterior descending arterial tree by > 50%. An increased distance between serial stenoses further increased the peak pressure gradient. These findings have important implications on the diagnosis and treatment of serial coronary stenoses.

Patient-Specific Computational Models of Coronary Arteries Using Monoplane X-Ray Angiograms

Coronary artery disease (CAD) is the most common type of heart disease in western countries. Early detection and diagnosis of CAD is quintessential to preventing mortality and subsequent complications. We believe hemodynamic data derived from patient-specific computational models could facilitate more accurate prediction of the risk of atherosclerosis. We introduce a semiautomated method to build 3D patient-specific coronary vessel models from 2D monoplane angiogram images. The main contribution of the method is a robust segmentation approach using dynamic programming combined with iterative 3D reconstruction to build 3D mesh models of the coronary vessels. Results indicate the accuracy and robustness of the proposed pipeline. In conclusion, patient-specific modelling of coronary vessels is of vital importance for developing accurate computational flow models and studying the hemodynamic effects of the presence of plaques on the arterial walls, resulting in lumen stenoses, as well as variations in the angulations of the coronary arteries.

Better Diagnosis of Functionally Significant Intermediate Sized Narrowings Using Intravascular Ultrasound-Minimal Lumen Area and Coronary Computed Tomographic Angiography-Based Myocardial Segmentation

Lesion morphology poorly predicts functional significance of intermediate coronary artery stenosis. The aim of this study was to determine whether a coronary artery-based myocardial segmentation method that quantifies subtended myocardium can improve the diagnostic accuracy of intravascular ultrasound (IVUS)-derived parameters for detecting ischemia-producing lesions. Coronary computed tomography angiography, IVUS, and fractional flow reserve (FFR) data were analyzed in 101 non-left main lesions (20% to 80% angiographic stenosis). Using the coronary artery-based myocardial segmentation method, total left ventricular myocardial volume (Vtotal), myocardial volume subtended by the stenotic coronary segment (Vsub), and Vratio (the ratio of the Vsub to the Vtotal) were assessed. Both Vsub >30.7 cm(3) and Vratio >25.4% were determinants of FFR ≤0.75 (area under the curve = 0.696 and 0.744). Overall, an IVUS-measured minimum lumen area (IVUS-MLA) ≤2.83 mm(2) predicted FFR ≤0.75 with a sensitivity 88% and specificity 73%. Among lesions with IVUS-MLA ≤2.83 mm(2) and FFR >0.75, 89% showed Vsub <30.7 cm(3). In 50 lesions with Vsub >30.7 cm(3), an IVUS-MLA ≤2.85 mm(2) predicted FFR ≤0.75 with sensitivity 85%, specificity 92%, positive predictive value 92%, and negative predictive value 85%. Conversely, in 51 lesions with a Vsub ≤30.7 cm(3), IVUS-MLA ≤2.67 mm(2) showed sensitivity 100%, specificity 69%, positive predictive value 38%, and negative predictive value 100% for predicting FFR ≤0.75. Body surface area, reference lumen diameter, and vessel area had modest correlations with Vsub. In those lesion subsets, IVUS-MLA ≈2.8 mm(2) accurately predicted an FFR ≤0.75, whereas the clinical relevance of assessing and treating lesions with a smaller myocardial territory may be limited (ClinicalTrials.gov number NCT1696006).

Dedicated bifurcation stents - Mechanistic, hardware, and technical aspects

Percutaneous coronary intervention (PCI) in bifurcation lesions is associated with lower success rate, higher acute complication rates and higher event rates in follow-up.

The reason for this higher than usual complication rate relates to the relationship between anatomy, flow, and atheroma distribution in bifurcation lesions.

Further, stenting these lesions can be a prolonged procedure and can be technically more demanding. The most common complication is the loss of significant side branch (SB). Main vessel (MV) stenting may enhance the carina displacement and atheroma shift across the SB ostium leading to SB ostium narrowing.

Finally, complications, if they occur, are more difficult to manage. Dedicated bifurcation stent has been developed to overcome the number of limitations associated with conventional bifurcation PCI. The main advantage of most dedicated bifurcation stents is to allow the operator to perform the procedure on a bifurcation lesion without the need to rewire the SB.

Growth, ageing and scaling laws of coronary arterial trees

Despite the well-known design principles of vascular systems, it is unclear whether the vascular arterial tree obeys some scaling constraints during normal growth and ageing in a given species. Based on the micro-computed tomography measurements of coronary arterial trees in mice at different ages (one week to more than eight months), we show a constant exponent of 3/4, but age-dependent scaling coefficients in a length-volume scaling law (Lc=K(length-volume) · Vc³/⁴; Lc is the crown length, Vc is the crown volume, K(length-volume) is the age-dependent scaling coefficient) during normal growth and ageing. The constant 3/4 exponent represents the self-similar fractal-like branching pattern (i.e. basic mechanism to regulate the development of vascular trees within a species), whereas the age-dependent scaling coefficients characterize the structural growth or resorption of vascular trees during normal growth or ageing, respectively. This study enhances the understanding of age-associated changes in vascular structure and function.

Coronary pressure and flow relationships in humans: phasic analysis of normal and pathological vessels and the implications for stenosis assessment: a report from the Iberian-Dutch-English (IDEAL) collaborators

Background

Our understanding of human coronary physiological behaviour is derived from animal models. We sought to describe physiological behaviour across a large collection of invasive pressure and flow velocity measurements, to provide a better understanding of the relationships between these physiological parameters and to evaluate the rationale for resting stenosis assessment.

Methods and results

Five hundred and sixty-seven simultaneous intracoronary pressure and flow velocity assessments from 301 patients were analysed for coronary flow velocity, trans-stenotic pressure gradient (TG), and microvascular resistance (MVR). Measurements were made during baseline and hyperaemic conditions. The whole cardiac cycle and the diastolic wave-free period were assessed. Stenoses were assessed according to fractional flow reserve (FFR) and quantitative coronary angiography DS%. With progressive worsening of stenoses, from unobstructed angiographic normal vessels to those with FFR ≤ 0.50, hyperaemic flow falls significantly from 45 to 19 cm/s, P_trend < 0.001 in a curvilinear pattern. Resting flow was unaffected by stenosis severity and was consistent across all strata of stenosis ( P_trend > 0.05 for all). Trans-stenotic pressure gradient rose with stenosis severity for both rest and hyperaemic measures ( P_trend < 0.001 for both). Microvascular resistance declines with stenosis severity under resting conditions ( P_trend < 0.001), but was unchanged at hyperaemia (2.3 ± 1.1 mmHg/cm/s; P_trend = 0.19).

Conclusions

With progressive stenosis severity, TG rises. However, while hyperaemic flow falls significantly, resting coronary flow is maintained by compensatory reduction of MVR, demonstrating coronary auto-regulation. These data support the translation of coronary physiological concepts derived from animals to patients with coronary artery disease and furthermore, suggest that resting pressure indices can be used to detect the haemodynamic significance of coronary artery stenoses.

Fractional Flow Reserve for the Evaluation of Tandem and Bifurcation Lesions, Left Main, and Acute Coronary Syndromes

Fractional flow reserve (FFR) is a well-established invasive tool to assess the physiologic significance of a coronary stenosis. Several randomized trials proved the safety of deferring revascularization based on FFR in subjects with stable coronary artery disease with single or multivessel disease. Subjects with tandem or bifurcations lesions, left main disease, and acute coronary syndromes were not included in these trials. Unique hemodynamic changes occur in each of these situations, making the measurement and interpretation of FFR challenging. This article reviews the technical aspects of assessing FFR and literature supporting FFR-guided revascularization in each of these situations.

Fundamentals in clinical coronary physiology: why coronary flow is more important than coronary pressure

Wide attention for the appropriateness of coronary stenting in stable ischaemic heart disease (IHD) has increased interest in coronary physiology to guide decision making. For many, coronary physiology equals the measurement of coronary pressure to calculate the fractional flow reserve (FFR). While accumulating evidence supports the contention that FFR-guided revascularization is superior to revascularization based on coronary angiography, it is frequently overlooked that FFR is a coronary pressure-derived estimate of coronary flow impairment. It is not the same as the direct measures of coronary flow from which it was derived, and which are critical determinants of myocardial ischaemia. This review describes why coronary flow is physiologically and clinically more important than coronary pressure, details the resulting limitations and clinical consequences of FFR-guided clinical decision making, describes the scientific consequences of using FFR as a gold standard reference test, and discusses the potential of coronary flow to improve risk stratification and decision making in IHD.

Pathophysiology of coronary collaterals

While the existence of structural adaptation of coronary anastomoses is undisputed, the potential of coronary collaterals to be capable of functional adaptation has been questioned. For many years, collateral vessels were thought to be rigid tubes allowing only limited blood flow governed by the pressure gradient across them. This concept was consistent with the notion that although collaterals could provide adequate blood flow to maintain resting levels, they would be unable to increase blood flow sufficiently in situations of increased myocardial oxygen demand.

However, more recent studies have demonstrated the capability of the collateral circulation to deliver sufficient blood flow even during exertion or pharmacologic stress. Moreover, it has been shown that increases in collateral flow could be attributed directly to collateral vasomotion.

This review summarizes the pathophysiology of the coronary collateral circulation, ie the functional adapation of coronary collaterals to acute alterations in the coronary circulation.

Relationship between intravascular ultrasound parameters and fractional flow reserve in intermediate coronary artery stenosis of left anterior descending artery: intravascular ultrasound volumetric analysis

OBJECTIVES

The objective of this study was to assess the relationship between intravascular ultrasound (IVUS) parameters, including volumetric analysis, and fractional flow reserve (FFR).

BACKGROUND

Although it is known that coronary atherosclerosis burden measured by IVUS volumetric analysis is related with clinical outcomes, its relationship with functional significance remains unknown.

METHODS

Both IVUS and FFR were performed in 206 cases of intermediate stenosis of the left anterior descending artery (LAD). Myocardial ischemia was assessed by FFR and maximal hyperemia was induced by continuous intracoronary adenosine infusion. FFR < 0.80 was considered as significant inducible myocardial ischemia. We performed standard IVUS parameter measurements and volumetric analyses. IVUS parameter comparison was performed in the presence (n = 90) or absence (n =116) of significant myocardial ischemia.

RESULTS

Lesions with minimal lumen area (MLA) ≥ 4.0 mm2 had FFR ≥ 0.80 in 91.4% of cases, while 50.9% of lesions with MLA < 4.0 mm2 had FFR < 0.80. The independent predictors of FFR < 0.80 were IVUS lesion length (odds ratio [OR]: 1.1, 95% confidence interval [CI] = 1.06–1.18, P < 0.001) and MLA significance according to the lesion location (OR: 7.01, 95% CI = 3.09–15.92, P = 0.001). FFR correlated with plaque volume (r = −0.345, P < 0.001) and percent atheroma volume (PAV) (r = −0.398, P < 0.001). Lesions with significant ischemia (FFR < 0.80) as compared to those with FFR > 0.80 were associated with larger plaque volume (181.8 ± 82.3 vs. 125.9 ± 77.9 mm3, P < 0.001) and PAV (58.9 ± 5.6 vs. 53.8 ± 7.9%, P < 0.001).

CONCLUSIONS

IVUS parameters representing severity and extent of atheromatous plaque correlated with functional significance in LAD lesions with intermediate stenosis.

Association of prediabetes with diffuse coronary narrowing and small-vessel disease

BACKGROUND

A significant number of patients may not benefit from conventional techniques of myocardial revascularization due to diffuse coronary artery disease (CAD) or small coronary arterial sizes because of smaller arteries causing anastomotic technical difficulties and poor run-off. Diabetic patients have a more severe and diffuse coronary atherosclerosis with smaller coronary arteries limiting the possibility to perform a successful and complete revascularization, but this has not been examined in prediabetics.

OBJECTIVE

To evaluate whether there is an association between prediabetes and the coronary arterial size.

METHODS

We prospectively studied 168 consecutive patients with CAD and 172 patients with normal coronary artery anatomy (NCA). Patients were divided into three groups according to hemoglobin (Hb) A1c levels as "normal," "prediabetic," and "diabetic" groups, and the coronary artery sizes and Gensini scores were analyzed.

RESULTS

There were 78 female patients and 90 male patients in the CAD group, and 87 female patients and 85 male patients in the NCA group. There was a statistically significant difference in distal and proximal total coronary arterial size among the CAD and NCA groups for both genders. There was a positive correlation between the HbA1c subgroups and Gensini score (Spearman's ρ: 0.489, p<0.001 in female group; Spearman's ρ: 0.252 p=0.016 in male group).

CONCLUSION

We found that prediabetic patients have a smaller coronary size and diffuse coronary narrowing for both genders, particularly in distal coronary arterial tree of left anterior descending coronary artery. The early detection of prediabetes in daily cardiology practice may provide more appropriate coronary lesion for percutaneous or surgical revascularization.

Women's exhaustion and coronary artery atherosclerosis progression: The Stockholm Female Coronary Angiography Study

OBJECTIVE

Vital exhaustion (VE) has been associated with incident and recurrent cardiac events. The present study investigated the impact of VE on coronary atherosclerosis progression for 3 years. We further aimed to detect the relative importance of the VE subcomponents, fatigue, and depressed mood.

METHODS

103 women (age range, 30-65 years) who had experienced an acute coronary event underwent quantitative coronary angiography at baseline and again after 3 years. VE and subcomponents were assessed using the Maastricht Questionnaire.

RESULTS

VE correlated significantly with coronary artery diameter change for 3 years (r = -0.239, p = .015). When analyzed in quartiles, women of the highest VE level showed the most pronounced coronary artery luminal diameter narrowing (mean = 0.21 mm, 95% confidence interval [CI] = 0.15-0.27), women in the third quartile were intermediate (mean = 0.11 mm, 95% CI = 0.05-0.17), and women within the two lower quartiles showed no significant change. High levels of the depressed mood and fatigue subscales were also associated with coronary artery diameter narrowing (mean = 0.19 mm, 95% CI = 0.12-0.26, p = .003; and mean = 0.17 mm, 95% CI = 0.08-0.26, p = .03, respectively). However, the associations were attenuated when both variables were entered into the model simultaneously: 0.17 mm (95% CI = 0.09-0.25, p = .05) and 0.14 mm (95% CI = 0.03-0.25, p = .67), respectively.

CONCLUSIONS

VE was associated with accelerated coronary atherosclerosis progression in relatively young women who had experienced an acute coronary event. This association was mainly driven by depressed mood.

CT-based diagnosis of diffuse coronary artery disease on the basis of scaling power laws

PURPOSE

To provide proof of concept for a diagnostic method to assess diffuse coronary artery disease (CAD) on the basis of coronary computed tomography (CT) angiography.

MATERIALS AND METHODS

The study was approved by the Cleveland Clinic Institutional Review Board, and all subjects gave informed consent. Morphometric data from the epicardial coronary artery tree, determined with CT angiography in 120 subjects (89 patients with metabolic syndrome and 31 age- and sex-matched control subjects) were analyzed on the basis of the scaling power law. Results obtained in patients with metabolic syndrome and control subjects were compared statistically.

RESULTS

The mean lumen cross-sectional area (ie, lumen cross-sectional area averaged over each vessel of an epicardial coronary artery tree) and sum of intravascular volume in patients with metabolic syndrome (0.039 cm(2) ± 0.015 [standard deviation] and 2.71 cm(3) ± 1.75, respectively) were significantly less than those in control subjects (0.054 cm(2)± 0.015 and 3.29 cm(3)± 1.77, respectively; P < .05). The length-volume power law showed coefficients of 27.0 cm(-4/3) ± 9.0 (R(2) = 0.91 ± 0.08) for patients with metabolic syndrome and 19.9 cm(-4/3) ± 4.3 (R(2) = 0.92 ± 0.07) for control subjects (P < .05). The probability frequency shows that more than 65% of patients with metabolic syndrome had a coefficient of 23 or more for the length-volume scaling power law, whereas approximately 90% of the control subjects had a coefficient of less than 23.

CONCLUSION

The retrospective scaling analysis provides a quantitative rationale for diagnosis of diffuse CAD.