Coronary artery wall shear stress is associated with endothelial dysfunction and expansive arterial remodelling in patients with coronary artery disease

Long-Term Intracoronary Structural and Vasomotor Assessment of the ABSORB Bioresorbable Vascular Scaffold

We systematically categorized the longer-term (≥3 years) structural and functional characteristics of the ABSORB bioresorbable vascular scaffold (BVS) using optical coherence tomography imaging and coronary vasomotor reactivity testing and further compared the functional characteristics of BVS stented versus remote coronary segments. A total of 92 patients (mean age 56.4 ± 9.7 years, 22.8% women) who underwent percutaneous coronary intervention (76% with acute coronary syndrome) using the ABSORB BVS (112 lesions) were included. Optical coherence tomography analysis (38,790 visible struts) comprised in-segment quantitative lumen/plaque and semiquantitative plaque composition analysis of the neointimal pattern. Epicardial endothelium-dependent and-independent vasomotion was defined as any vasodilatation at low/intermediate intracoronary dose of acetylcholine (ACh) and nitroglycerine, assessed using quantitative coronary angiography. At a median time of 3.2 years follow-up, 79.8% of BVS segments still demonstrated visible struts with a predominant neointimal fibrotic healing pattern in 84% of BVS segments, with 99.5% of struts demonstrating coverage with apposition. Compared with remote segments, BVS segments demonstrated less endothelium-dependent vasodilatation at low (p = 0.06) and intermediate ACh doses (p = 0.04). Hypertension, longer time interval from index percutaneous coronary intervention, and the degree of in-BVS segment neointimal volume (p <0.03 for all) were each independently associated with abnormal BVS endothelium-dependent vasomotor function. Endothelium-independent function was more likely preserved in non-BVS (remote) segments compared with BVS segments (p = 0.06). In conclusion, at 3+ years post-ABSORB BVS insertion, the rate of complete scaffold resorption was low and residual strut presence was high, with a dominant fibrous healing response contributing toward neointimal hyperplasia and endothelium-dependent and-independent vasomotor dysfunction.

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.

Automated Analysis of Choroidal Sublayer Morphologic Features in Myopic Children Using EDI-OCT by Deep Learning

Purpose

The purpose of this study was to analyze the choroidal sublayer morphologic features in emmetropic and myopic children using an automatic segmentation model, and to explore the relationship between choroidal sublayers and spherical equivalent refraction (SER).

Methods

We collected data on 92 healthy children (92 eyes) from the Ophthalmology Department of Peking University First Hospital. The data were allocated to three groups: emmetropia (+0.50 diopters [D] to -0.50 D), low myopia (-0.75 D to -3.00 D), and moderate myopia (-3.25 D to -5.75 D). We performed standardized optical coherence tomography (OCT) and developed a new segmentation technique to measure choroidal thickness (CT), large-vessel choroidal layer (LVCL), medium-vessel choroidal layer (MVCL), and small-vessel choroidal layer thickness (SVCL), and evaluated the choroidal vascular system (choroidal vascular volume [VV], choroidal vascular index [CVI], and choroidal vascular density [CVD]).

Results

All choroidal sublayers (LVCL, MVCL, and SVCL) were significantly thinner in myopic than in emmetropic eyes (P < 0.05), the thinnest choroidal region being the nasal outer subfield (P < 0.05). In all choroidal regions of SVCL, a positive correlation was found between SER and thickness ratio (P < 0.001). In most subfields of MVCL, a similar correlation was found (P < 0.050), the exceptions being the two nasal subfields (0.050 < P < 0.300). In contrast, the thickness ratio of LVCL decreased in all subfields (P < 0.050). VV correlated with SER negatively in LVCL in all subfields (all P < 0.001) and most subfields in MVCL except for two temporal subfields (0.050 < P < 0.200). However, no significant correlations were found between CVI and SER in LVCL (P > 0.050) and MVCL (with the exception being the temporal inner subfield, P = 0.011).

Conclusions

Thickness of choroidal sublayers was reduced with higher myopic SER, whereas changes in thickness ratio varied between sublayers. No significant correlations between CVI and SER suggested that both choroidal stromal and vascular volume decreases proportionately.

Translational Relevance

Automatic segmentation model will be helpful for future clinical trials to quantify choroidal sublayer morphologic features in myopia.

Abnormal shear stress and residence time are associated with proximal coronary atheroma in the presence of myocardial bridging

BACKGROUND

Atheromatous plaques tend to form in the coronary segments proximal to a myocardial bridge (MB), but the mechanism of this occurrence remains unclear. This study evaluates the relationship between blood flow perturbations and plaque formation in patients with an MB.

METHODS AND RESULTS

A total of 92 patients with an MB in the mid left anterior descending artery (LAD) and 20 patients without an MB were included. Coronary angiography, intravascular ultrasound, and coronary physiology measurements were performed. A moving-boundary computational fluid dynamics algorithm was used to derive wall shear stress (WSS) and peak residence time (PRT). Patients with an MB had lower WSS (0.46 ± 0.21 vs. 0.96 ± 0.33 Pa, p < 0.001) and higher maximal plaque burden (33.6 ± 15.0 vs. 14.2 ± 5.8%, p < 0.001) within the proximal LAD compared to those without. Plaque burden in the proximal LAD correlated significantly with proximal WSS (r = -0.51, p < 0.001) and PRT (r = 0.60, p < 0.001). In patients with an MB, the site of maximal plaque burden occurred 23.4 ± 13.3 mm proximal to the entrance of the MB, corresponding to the site of PRT.

CONCLUSIONS

Regions of low WSS and high PRT occur in arterial segments proximal to an MB, and this is associated with the degree and location of coronary atheroma formation.

Coronary Artery Disease and Endothelial Dysfunction: Novel Diagnostic and Therapeutic Approaches

Coronary artery disease is the leading cause of morbidity and mortality worldwide. The most common pathophysiologic substrate is atherosclerosis which is an inflammatory procedure that starts at childhood and develops throughout life. Endothelial dysfunction is associated with the initiation and progression of atherosclerosis and is characterized by the impaired production of nitric oxide. In general, endothelial dysfunction is linked to poor cardiovascular prognosis and different methods, both invasive and non-invasive, have been developed for its evaluation. Ultrasound evaluation of flow mediated dilatation of the branchial artery is the most commonly used method to assessed endothelial function while intracoronary administration of vasoactive agents may be also be used to test directly endothelial properties of the coronary vasculature. Endothelial dysfunction has also been the subject of therapeutic interventions. This review article summarizes the knowledge about evaluation of endothelial function in acute coronary syndromes and stable coronary artery disease and demonstrates the current therapeutic approaches against endothelial dysfunction.

Haemodynamic impacts of myocardial bridge length: A congenital heart disease

OBJECTIVES

There is an association between long and thick myocardial bridging (MB), haemodynamic perturbations and increased risk of myocardial infarction. This study aims to investigate the alteration in coronary haemodynamics with increasing the length of MB.

METHODS

Angiography and intravascular ultrasound were performed in 10 patients with varying length of MB in the left anterior descending (LAD) artery. In silico models of MB were developed based on the reconstructed three-dimensional model of the LAD. The entire LAD was divided into 3 segments, proximal (pre-bridge), bridge and distal (post-bridge). Transient computational fluid dynamics simulations were performed to derive distribution of blood residence time and wall shear stress (WSS) over entire vessel including proximal, bridge and distal segments.

RESULTS

With increasing the length of MB, a decreasing trend was observed in the WSS over proximal segment whereas an increasing trend was found in the WSS over bridge segment. When patients were divided into 2 groups based on the average length of MB in the whole cohort (L_ave = 23.92 mm), patients with bridges longer than L_ave had smaller WSS and higher residence time in the proximal segment compared to those with bridges shorter than L_ave (0.59 ± 0.31 vs 0.21 ± 0.14 Pa and 0.0021 ± 0.0015 vs 0.0045 ± 0.0021 s). In contrast, patients with bridges longer than L_ave had greater WSS in the bridge segment compared to those with bridges shorter than L_ave (1.37 ± 1.66 vs 2.53 ± 3.14 Pa). No significant difference was found in the distal WSS of patients with short and long bridges.

CONCLUSION

Our findings revealed a direct relationship between the length of MB and haemodynamic perturbations in the proximal segment such that the increased length of MB is associated with decreased WSS and increased residence time.

Coronary Plaque Geometry and Thoracic Fat Distribution in Patients with Acute Chest Pain – a CT Angiography Study

The aim of our study was to investigate the correlation between volumes of thoracic fat distributed in different compartments and the geometry of vulnerable coronary plaques assessed by coronary computed tomography angiography (CCTA), in patients with acute chest pain.

Methods: This was a non-randomized, observational, single-center study, including 50 patients who presented in the emergency department with acute chest pain who underwent 128-slice single-source CCTA. Plaque geometry was evaluated in transversal and longitudinal planes, and the assessment of adipose tissue was performed using the Syngo.via Frontier (Siemens AG, Healthcare Sector, Forchheim, Germany) research platform.

Results: Eccentric plaques presented a significantly higher incidence of spotty calcification (40% vs. 22%, p = 0.018), whereas positive remodeling, volume of low attenuation plaque, and incidence of napkin-ring sign were not significantly different between the study groups or in ascending versus descending plaques. The volume of pericoronary fat around the plaque was significantly larger near eccentric lesions (707.68 ± 454.08 mm3 vs. 483.25 ± 306.98 mm3, p = 0.046) and descendent plaques (778.26 ± 479.37 mm3 vs. 473.60 ± 285.27 mm3, p = 0.016). Compared to ascending lesions, descendent ones presented a significantly larger volume of thoracic fat (1,599.25 ± 589.12 mL vs. 1,240.71 ± 291.50 mL), while there was no significant correlation between thoracic fat and cross-sectional eccentricity.

Conclusions: The phenotype of plaque distribution and geometry seems to be associated with a higher vulnerability of coronary lesions and may be influenced by the local accumulation of inflammatory mediators released by the pericoronary epicardial adipose tissue.

Post-partum Spontaneous Coronary Artery Dissection: A Case Report

Spontaneous coronary artery dissection (SCAD) is a rare illness often misdiagnosed, that accounts for up to 4% of cases of acute coronary syndrome in young women. Interestingly, SCAD is the most common cause of myocardial infarction related to pregnancy. Here, we present a case of a 35-year old postpartum patient who presented in cardiac arrest due to ventricular fibrillation and was found to have a ST-segment elevation myocardial infarction. Cardiac catheterization revealed significant coronary vasospasm and dissection of the right circumflex and distal left anterior descending artery. We discuss clinical diagnosis and management of spontaneous coronary dissection along with literature review.

Impact of coronary plaque geometry on plaque vulnerability and its association with the risk of future cardiovascular events in patients with chest pain undergoing coronary computed tomographic angiography-the GEOMETRY study: Protocol for a prospective clinical trial

INTRODUCTION

Coronary computed tomography angiography (CCTA) has emerged as a valuable noninvasive imaging tool for assessing atheromatous plaque morphology and composition, and several CCTA features have been validated as reliable indicators of the plaque-associated risk. However, the role of lesion geometry as a CCTA feature of plaque vulnerability has not been investigated so far.

MATERIAL AND METHODS

Here we present the study protocol of the GEOMETRY trial, a prospective, single center, cohort study in which we aim to investigate the relationship between plaque geometry (as expressed by cross-sectional and longitudinal plaque eccentricity) and the risk for major adverse cardiac events (MACE) during 2 years of follow-up, in order to validate plaque eccentricity as a new CCTA marker of coronary plaque vulnerability. One thousand patients with suspected coronary artery disease (CAD) and pretest probability of CAD between 15% and 85%, who undergo CCTA and in whom CCTA identifies the presence of at least 1 significant coronary plaque (producing a luminal narrowing of at least 50%) will be enrolled in the study. Based on the results of complex image post-processing and plaque analysis, patients will be divided into 2 groups: group 1-patients in whom CCTA analysis identifies only non-eccentric coronary plaque; and group 2-patients in whom CCTA analysis reveals the presence of at least 1 eccentric significant coronary plaque producing a significant luminal narrowing. Study outcomes will consist in the rate of major cardiovascular events and the rate of plaque progression during follow-up.The study is funded by the Romanian Ministry of European Funds, the Romanian Government and the European Union, as part of the research grant number 103544/2016 - PlaqueIMAGE (contract number 26/01.09.2016).

CONCLUSION

In conclusion, GEOMETRY will be the first CCTA-based study that will investigate the impact of geometric distribution of coronary atheromatous plaque on the future risk of cardiovascular events and on the rate of plaque progression, introducing and validating a new potential feature of plaque vulnerability represented by plaque geometry.

The relationship between coronary lesion characteristics and pathologic shear in human coronary arteries

BACKGROUND

Pathological shear stress is associated with distinct pathogenic biological pathways relevant to coronary thrombosis and atherogenesis. Although the individual effects of lesion characteristics including stenosis severity, eccentricity and lesion length on coronary haemodynamics is known, their relative importance remains poorly understood.

METHODS

Computational fluid dynamics (CFD) was implemented for haemodynamic analysis of 104 coronary arteries. For each coronary artery, maximum shear stress at the site of maximal stenosis, average shear stress over the sites of maximal stenosis segment, average shear stress in the proximal segments and average shear stress in the distal segments were determined. In addition, the area of low wall shear stress (ALWSS) sites in post-stenotic regions were quantified as a proportion of the vessel segment.

RESULTS

With increasing stenosis severity, eccentricity and lesion length, maximal and average shear stress over the sites of maximal stenosis and ALWSS increased whereas average shear stress in the proximal segments decreased. Two-way ANCOVA analysis revealed that stenosis severity and lesion length were both independent predictors of maximum shear at the site of maximal stenosis [F (1, 104) = 10.94, P = 0.001 for diameter stenosis and F (1, 104) = 6.21, P = 0.014 for lesion length] and ALWSS [F (1, 104) = 66.10, P = 0.001 for diameter stenosis and F (1, 104) = 4.23, P = 0.047 for lesion length].

CONCLUSION

Our findings demonstrate that although all lesion characteristics correlate with abnormal shear stress, only stenosis severity and lesion length are independent predictors of pathogenic physiological processes.

Magnetohydrodynamic blood flow in patients with coronary artery disease

OBJECTIVES

We aim to investigate the effect of a magnetic field with varying intensities on haemodynamic perturbations in a cohort of patients with coronary artery disease.

METHODS

Transient computational fluid dynamics (CFD) simulations were performed in three-dimensional (3D) models of coronary arteries reconstructed from 3D quantitative coronary angiography. The effect of magnetic field on wall shear stress (WSS) derived parameters including maximum wall shear stress (MWSS) and size of regions with low wall shear stress (ALWSS) as well as length of flow recirculation zones were determined.

RESULTS

The results showed a substantial reduction in MWSS, ALWSS and length of flow recirculation zones in the presence of magnetic field, in particular for coronaries with moderate to severe stenoses. When the whole cohort examined, time-averaged wall shear stress (TAWSS), ALWSS and the length of flow recirculation zones in the absence of magnetic field were approximately 1.71, 4.69 and 8.46 times greater than those in the presence of magnetic field, respectively.

CONCLUSION

Our findings imply that an externally applied magnetic field can improve haemodynamic perturbations in human coronary arteries.

Unusual Presentation of Spontaneous Coronary Artery Dissection in an Older Male

Spontaneous coronary artery dissection (SCAD) is a variant of acute coronary syndrome (ACS) that is poorly understood. SCAD has been linked to fibromuscular dysplasia (FMD), connective tissue disease (CTD), pregnancy and hormonal imbalance, systemic inflammatory conditions (e.g. IBD, vasculitis), and coronary artery vasospasm rather than traditional cardiac risk factors. Symptomology generally accompanying SCAD is indistinguishable from ACS making the timely recognition and diagnosis vital for prompt treatment. Management of SCAD is not well defined given the absence of guidelines; conservative therapy with or without invasive intervention is assessed on a case-by-case basis. In this article, we report the case of a 62-year-old male, who presented with chest pain and dyspnea on exertion and was found to have an elevated troponin-I level and corresponding electrocardiogram (EKG) findings, subsequently diagnosed with a non-ST elevation myocardial infarction (NSTEMI). Coronary angiography revealed a distal right coronary artery (RCA) dissection, which was confirmed later with intravascular ultrasound (IVUS). The patient then underwent percutaneous coronary intervention (PCI) followed by stenting of the distal RCA and was discharged on optimal medical therapy. Herein, we report a case of SCAD in an otherwise healthy male with chest pain at rest and with mild exertion without conventional cardiac risk factors.

Development of a Computational Fluid Dynamics Model for Myocardial Bridging

Computational fluid dynamics (CFD) modeling of myocardial bridging (MB) remains challenging due to its dynamic and phasic nature. This study aims to develop a patient-specific CFD model of MB. There were two parts to this study. The first part consisted of developing an in silico model of the left anterior descending (LAD) coronary artery of a patient with MB. In this regard, a moving-boundary CFD algorithm was developed to simulate the patient-specific muscle compression caused by MB. A second simulation was also performed with the bridge artificially removed to determine the hemodynamics in the same vessel in the absence of MB. The second part of the study consisted of hemodynamic analysis of three patients with mild and moderate and severe MB in their LAD by means of the developed in silico model in the first part. The average shear stress in the proximal and bridge segments for model with MB were significantly different from those for model without MB (proximal segment: 0.32 ± 0.14 Pa (with MB) versus 0.97 ± 0.39 Pa (without MB), P < 0.0001 — bridge segment: 2.60 ± 0.94 Pa (with MB) versus 1.50 ± 0.64 Pa (without MB), P < 0.0001). When all three patients were evaluated, increasing the degree of vessel compression shear stress in the proximal segment decreased, whereas the shear stress in the bridge segment increased. The presence of MB resulted in hemodynamic abnormalities in the proximal segment, whereas segments within the bridge exhibited hemodynamic patterns which tend to discourage atheroma development.

The relationship between segmental wall shear stress and lipid core plaque derived from near-infrared spectroscopy

BACKGROUND AND AIMS

Wall shear stress (WSS) has an important role in the natural history of coronary atherosclerosis. The aim of this study is to investigate the relationship between WSS and the lipid content of atherosclerotic plaques as assessed by near-infrared spectroscopy (NIRS).

METHODS

We performed serial NIRS and intravascular ultrasound (IVUS) upon Doppler coronary flow guidewire of coronary plaques at baseline and after 12-18 months in 28 patients with <30% angiographic stenosis, who presented with coronary artery disease. Segmental WSS, plaque burden and NIRS-derived lipid rich plaque (LRP) were evaluated at both time-points in 482 consecutive 2-mm coronary segments.

RESULTS

Segments with LRP at baseline (n = 106) had a higher average WSS (1.4 ± 0.6 N/m²), compared to those without LRP (n = 376) (1.2 ± 0.6 N/m², p<0.001). In segments without baseline LRP, WSS was higher in those who subsequently developed new LRP (n = 35) than those who did not (n = 341) (1.4 ± 0.8 vs. 1.1 ± 0.6 N/m², p=0.002). Conversely, in segments with baseline LRP, WSS was lower in those who had regression of lipid content (n = 41) than those who did not (n = 65) (1.2 ± 0.4 vs. 1.6 ± 0.7 N/m², p=0.007). Segments with the highest tertile of WSS displayed greater progression of LCBI irrespective of baseline lipid content (p<0.001). Multivariate analysis revealed that baseline WSS (p=0.017), PAV (p<0.001) and LCBI (p<0.001) were all independent predictors of change in LCBI over time.

CONCLUSIONS

Coronary segments with high WSS associate with progression of lipid content over time, which may indicate transformation to a more vulnerable phenotype.

Local coronary wall eccentricity and endothelial function are closely related in patients with atherosclerotic coronary artery disease

BACKGROUND

Coronary endothelial function (CEF) in patients with coronary artery disease (CAD) varies among coronary segments in a given patient. Because both coronary vessel wall eccentricity and coronary endothelial dysfunction are predictors of adverse outcomes, we hypothesized that local coronary endothelial dysfunction is associated with local coronary artery eccentricity.

METHODS

We used 3 T coronary CMR to measure CEF as changes in coronary cross-sectional area (CSA) and coronary blood flow (CBF) during isometric handgrip exercise (IHE), a known endothelial-dependent stressor, in 29 patients with known CAD and 16 healthy subjects. Black-blood MRI quantified mean coronary wall thickness (CWT) and coronary eccentricity index (EI) and CEF was determined in the same segments.

RESULTS

IHE-induced changes in CSA and CBF in healthy subjects (10.6 ± 6.6% and 38.3 ± 29%, respectively) were greater than in CAD patients 1.3 ± 7.7% and 6.5 ± 19.6%, respectively, p < 0.001 vs. healthy for both measures), as expected. Mean CWT and EI in healthy subjects (1.1 ± 0.3 mm 1.9 ± 0.5, respectively) were less than those in CAD patients (1.6 ± 0.4 mm, p < 0.0001; and 2.6 ± 0.6, p = 0.006 vs. healthy). In CAD patients, we observed a significant inverse relationship between stress-induced %CSA change and both EI (r = -0.60, p = 0.0002), and CWT (r = -0.54, p = 0.001). Coronary EI was independently and significantly related to %CSA change with IHE even after controlling for mean CWT (adjusted r = -0.69, p = 0.0001). For every unit increase in EI, coronary CSA during IHE is expected to change by -6.7 ± 9.4% (95% confidence interval: -10.3 to -3.0, p = 0.001).

CONCLUSION

There is a significant inverse and independent relationship between coronary endothelial macrovascular function and the degree of local coronary wall eccentricity in CAD patients. Thus anatomic and physiologic indicators of high-risk coronary vascular pathology are closely related. The noninvasive identification of coronary eccentricity and its relationship with underlying coronary endothelial function, a marker of vascular health, may be useful in identifying high-risk patients and culprit lesions.

Hemodynamics of the string phenomenon in the internal thoracic artery grafted to the left anterior descending artery with moderate stenosis

PURPOSE

The internal thoracic artery is the choice of graft for coronary artery bypass grafting due to the excellent long-term patency. However internal thoracic artery graft failures still occur due to diffuse narrowing, known as the string phenomenon. Studies suggest that the string phenomenon is caused by competitive flow when the coronary stenosis is not serious, but the hemodynamics of the string phenomenon are still unclear. The purpose of this study is to clarify the hemodynamic characteristics of the string phenomenon.

MATERIALS

A patient-specific 3-dimensional model of the aortic arch and coronary arteries was reconstructed. A moderate stenosis was applied to the left anterior descending artery. The internal thoracic artery was used to bypass the stenosis. Two further 3D models were built to study the hemodynamics of the string phenomenon.

METHODS

A numerical study was performed by coupling the 3D artery model with 0-dimensional lumped parameter model of the cardiovascular system.

RESULTS

The graft flow, native coronary flow, wall shear stress and oscillatory shear index were calculated and illustrated. Inverse flow and high oscillatory shear index appeared on the internal thoracic artery graft when the stenosis was moderate.

CONCLUSION

High oscillatory shear index might be the major hemodynamic characteristic of the string phenomenon in internal thoracic artery graft. The inverse graft flow and the difference in graft flow caused by clamping the stenosis can be used to evaluate the probability of observing the string phenomenon.

Endothelial dysfunction: its clinical value and methods of assessment

Endothelial dysfunction (ED) is a systemic disorder characterized by reduced production of nitric oxide. This pathologic condition, which impairs vascular homeostasis, leads to the loss of protective properties of endothelial cells and is related to the pathogenesis of cardiovascular diseases. ED may affect every vascular bed, accounting for several clinical implications, particularly when the coronary bed is affected. Although the reliability of ED as a cardiovascular disease surrogate is still debated, many methods for its assessment have been proposed. In this review, we underline the clinical value of ED in the cardiovascular field and summarize the principal methods currently available for its assessment.