Coronary calcification represents a challenge in the treatment of coronary artery disease by stent placement. It negatively affects stent expansion and has been related to future adverse cardiac ...events. Intravascular ultrasound (IVUS) is known for its high sensitivity in detecting coronary calcification. At present, automated quantification of calcium as detected by IVUS is not available. For this reason, we developed and validated an optimized framework for accurate automated detection and quantification of calcified plaque in coronary atherosclerosis as seen by IVUS. Calcified lesions were detected by training a supported vector classifier per IVUS A-line on manually annotated IVUS images, followed by post-processing using regional information. We applied our framework to 35 IVUS pullbacks from each of the three commonly used IVUS systems. Cross-validation accuracy for each system was >0.9, and the testing accuracy was 0.87, 0.89 and 0.89 for the three systems. Using the detection result, we propose an IVUS calcium score, based on the fraction of calcium-positive A-lines in a pullback segment, to quantify the extent of calcified plaque. The high accuracy of the proposed classifier suggests that it may provide a robust and accurate tool to assess the presence and amount of coronary calcification and, thus, may play a role in image-guided coronary interventions.
To date, it is not known if 16-20-mm extracardiac conduits are outgrown during somatic growth from childhood to adolescence. This study aims to determine total cavopulmonary connection (TCPC) ...haemodynamics in adolescent Fontan patients at rest and during simulated exercise and to assess the relationship between conduit size and haemodynamics.
Patient-specific, magnetic resonance imaging-based computational fluid dynamic models of the TCPC were performed in 51 extracardiac Fontan patients with 16-20-mm conduits. Power loss, pressure gradient and normalized resistance were quantified in rest and during simulated exercise. The cross-sectional area (CSA) (mean and minimum) of the vessels of the TCPC was determined and normalized for flow rate (mm2/l/min). Peak (predicted) oxygen uptake was assessed.
The median age was 16.2 years (Q1-Q3 14.0-18.2). The normalized mean conduit CSA was 35-73% smaller compared to the inferior and superior vena cava, hepatic veins and left/right pulmonary artery (all P < 0.001). The median TCPC pressure gradient was 0.7 mmHg (Q1-Q3 0.5-0.8) and 2.0 (Q1-Q3 1.4-2.6) during rest and simulated exercise, respectively. A moderate-strong inverse non-linear relationship was present between normalized mean conduit CSA and TCPC haemodynamics in rest and exercise. TCPC pressure gradients of ≥1.0 at rest and ≥3.0 mmHg during simulated exercise were observed in patients with a conduit CSA ≤ 45 mm2/l/min and favourable haemodynamics (<1 mmHg during both rest and exercise) in conduits ≥125 mm2/l/min. Normalized TCPC resistance correlated with (predicted) peak oxygen uptake.
Extracardiac conduits of 16-20 mm have become relatively undersized in most adolescent Fontan patients leading to suboptimal haemodynamics.
The process of restenosis after a stenting procedure is related to local biomechanical environment. Arterial wall stresses caused by the interaction of the stent with the vascular wall and possibly ...stress induced stent strut fracture are two important parameters. The knowledge of these parameters after stent deployment in a patient derived 3D reconstruction of a diseased coronary artery might give insights in the understanding of the process of restenosis.
3D reconstruction of a mildly stenosed coronary artery was carried out based on a combination of biplane angiography and intravascular ultrasound. Finite element method computations were performed to simulate the deployment of a stent inside the reconstructed coronary artery model at inflation pressure of 1.0 MPa. Strut thickness of the stent was varied to investigate stresses in the stent and the vessel wall.
Deformed configurations, pressure-lumen area relationship and stress distribution in the arterial wall and stent struts were studied. The simulations show how the stent pushes the arterial wall towards the outside allowing the expansion of the occluded artery. Higher stresses in the arterial wall are present behind the stent struts and in regions where the arterial wall was thin. Values of 200 MPa for the peak stresses in the stent strut were detected near the connecting parts between the stent struts, and they were only just below the fatigue stress. Decreasing strut thickness might reduce arterial damage without increasing stresses in the struts significantly.
The method presented in this paper can be used to predict stresses in the stent struts and the vessel wall, and thus evaluate whether a specific stent design is optimal for a specific patient.
Aortic wall shear stress (WSS) is a known predictor of ascending aortic growth in patients with a bicuspid aortic valve (BAV). The aim of this study was to study regional WSS and changes over time in ...BAV patients.
BAV patients and age-matched healthy controls underwent 4D flow CMR. Regional, peak systolic ascending aortic WSS, aortic valve function, aortic stiffness measures and aortic dimensions were assessed. In BAV patients, 4D flow CMR was repeated after three years follow-up and both at baseline and follow-up computed tomography angiography (CTA) was acquired. Aortic growth (volume increase of ≥5%) was measured on CTA. Regional WSS differences within patients’ aorta and WSS changes over time were analysed using linear mixed-effect models and were associated with clinical parameters.
Thirty BAV patients (aged 34 years IQR 25-41) were included in the follow-up analysis. Additionally, another 16 BAV patients and 32 healthy controls (aged 33 years IQR 28-48) were included for other regional analyses. Magnitude, axial, and circumferential WSS increased over time (all p<0.001) irrespective of aortic growth. The percentage of regions exposed to a magnitude WSS >95th percentile of healthy controls increased from 21% (baseline 506/2400 regions) to 31% (follow-up 734/2400 regions) (p<0.001). WSS angle, a measure of helicity near the aortic wall, decreased during follow-up. Magnitude WSS changes over time were associated with systolic blood pressure, peak aortic valve velocity, aortic valve regurgitation fraction, aortic stiffness indexes, and normalized flow displacement (all p<0.05).
An increase of regional WSS over time was observed in BAV patients, irrespective of aortic growth. The increasing WSSs comprising a larger area of the aorta warrants further research to investigate the possible predictive value for aortic dissection.
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Abstract Wall shear stress (WSS), a parameter associated with endothelial function, is calculated by computational fluid dynamics (CFD) or phase-contrast (PC) MRI measurements. Although CFD is common ...in WSS (WSSCFD ) calculations, PC-MRI-based WSS (WSSMRI ) is more favorable in population studies; since it is straightforward and less time consuming. However, it is not clear if WSSMRI and WSSCFD show similar associations with vascular pathology. Our aim was to test the associations between wall thickness (WT) of the carotid arteries and WSSMRI and WSSCFD . The subjects ( n =14) with an asymptomatic carotid plaque who underwent MRI scans two times within 4 years of time were selected from the Rotterdam Study. We compared WSSCFD and WSSMRI at baseline and follow-up. Baseline WSSMRI and WSSCFD values were divided into 3 categories representing low, medium and high WSS tertiles. WT of each tertile was compared by a one-way ANOVA test. The WSSMRI and WSSCFD were 0.50±0.13 Pa and 0.73±0.25 Pa at baseline. Although WSSMRI was underestimated, a significant regression was found between WSSMRI and WSSCFD ( r2 =0.71). No significant difference was found between baseline and follow-up WSS by CFD and MRI-based calculations. The WT at baseline was 1.36±0.16 mm and did not change over time. The WT was 1.55±0.21 mm in low, 1.33±0.20 mm in medium and 1.21±0.21 mm in the high WSSMRI tertiles. Similarly, the WT was 1.49±0.21 mm in low, 1.33±0.20 mm in medium and 1.26±0.21 mm in high WSSCFD tertiles. We found that WSSMRI and WSSCFD were inversely related with WT. WSSMRI and WSSCFD patterns were similar although MRI-based calculations underestimated WSS.
Abstract
Atherosclerotic plaques prone to rupture may cause acute myocardial infarction (MI) but can also heal without causing an event. Certain common histopathological features, including ...inflammation, a thin fibrous cap, positive remodelling, a large necrotic core, microcalcification, and plaque haemorrhage are commonly found in plaques causing an acute event. Recent advances in imaging techniques have made it possible to detect not only luminal stenosis and overall coronary atherosclerosis burden but also to identify such adverse plaque characteristics. However, the predictive value of identifying individual adverse atherosclerotic plaques for future events has remained poor. In this Position Paper, the relationship between vulnerable plaque imaging and MI is addressed, mainly for non-invasive assessments but also for invasive imaging of adverse plaques in patients undergoing invasive coronary angiography. Dynamic changes in atherosclerotic plaque development and composition may indicate that an adverse plaque phenotype should be considered at the patient level rather than for individual plaques. Imaging of adverse plaque burden throughout the coronary vascular tree, in combination with biomarkers and biomechanical parameters, therefore holds promise for identifying subjects at increased risk of MI and for guiding medical and invasive treatment.
Exercise intolerance is common in total cavopulmonary connection (TCPC) patients. It has been suggested that power loss (Ploss) inside the TCPC plays a role in reduced exercise performance. Our ...objective is to establish the role of Ploss inside the TCPC during increased flow, simulating exercise in a patient-specific way.
Cardiac MRI (CMR) was used to obtain flow rates from the caval veins during rest and increased flow, simulating exercise with dobutamine. A 3D reconstruction of the TCPC was created using CMR data. Computational fluid dynamics (CFD) simulations were performed to calculate Ploss inside the TCPC structure for rest and stress conditions. To reflect the flow distribution during exercise, a condition where inferior caval vein (IVC) flow was increased twofold compared with rest was added. 29 TCPC patients (15 intra-atrial lateral tunnel (ILT) and 14 extracardiac conduit (ECC)) were included.
Mean Ploss at rest was 1.36 ± 0.94 (ILT) and 3.20 ± 1.26 (ECC) mW/m(2) (p<0.001), 2.84 ±1.95 (ILT) and 8.41 ± 3.77 (ECC) mW/m(2) (p<0.001) during dobutamine and 5.21 ± 3.50 (ILT) and 15.28 ± 8.30 (ECC) mW/m(2) (p=0.001) with twofold IVC flow. The correlation between cardiac index and Ploss was exponential (ILT: R(2)=0.811, p<0.001; ECC: R(2)=0.690, p<0.001).
Ploss inside the TCPC structure is limited but increases with simulated exercise. This relates to the anatomy of TCPC and the surgical technique used. In all flow conditions, ILT patients have lower Ploss than ECC patients. We did not find a relationship between Ploss and exercise capacity.
Coronary atherosclerosis is a leading cause of illness and death in Western World and its mechanisms are still non completely understood. Several animal models have been used to 1) study coronary ...atherosclerosis natural history and 2) propose predictive tools for this disease, that is asymptomatic for a long time, aiming for a direct translation of their findings to human coronary arteries. Among them, swine models are largely used due to the observed anatomical and pathophysiological similarities to humans. However, a direct comparison between swine and human models in terms of coronary hemodynamics, known to influence atherosclerotic onset/development, is still lacking. In this context, we performed a detailed comparative analysis between swine- and human-specific computational hemodynamic models of coronary arteries. The analysis involved several near-wall and intravascular flow descriptors, previously emerged as markers of coronary atherosclerosis initiation/progression, as well as anatomical features. To do that, non-culprit coronary arteries (18 right–RCA, 18 left anterior descending–LAD, 13 left circumflex–LCX coronary artery) from patients presenting with acute coronary syndrome were imaged by intravascular ultrasound and coronary computed tomography angiography. Similarly, the three main coronary arteries of ten adult mini-pigs were also imaged (10 RCA, 10 LAD, 10 LCX). The geometries of the imaged coronary arteries were reconstructed (49 human, 30 swine), and computational fluid dynamic simulations were performed by imposing individualized boundary conditions. Overall, no relevant differences in 1) wall shear stress-based quantities, 2) intravascular hemodynamics (in terms of helical flow features), and 3) anatomical features emerged between human- and swine-specific models. The findings of this study strongly support the use of swine-specific computational models to study and characterize the hemodynamic features linked to coronary atherosclerosis, sustaining the reliability of their translation to human vascular disease.
Abstract Background Heterogeneity in plaque composition in human coronary artery bifurcations is associated with blood flow induced shear stress. Shear stress is generally determined by combing 3D ...lumen data and computational fluid dynamics (CFD). We investigated two new procedures to generate 3D lumen reconstructions of coronary artery bifurcations for shear stress computations. Methods We imaged 10 patients with multislice computer tomography (MSCT) and intravascular ultrasound (IVUS). The 3D reconstruction of the main branch was based on the fusion of MSCT and IVUS. The proximal part of side branch was reconstructed using IVUS data or MSCT data, resulting in two different reconstructions of the bifurcation region. The distal part of the side branch was based on MSCT data alone. The reconstructed lumen was combined with CFD to determine the shear stress. Low and high shear stress regions were defined and shear stress patterns in the bifurcation regions were investigated. Results The 3D coronary bifurcations were successfully generated with both reconstruction procedures. The geometrical features of the bifurcation region for the two reconstruction procedures did not reveal appreciable differences. The shear stress maps showed a qualitative agreement, and the low and high shear stress regions were similar in size and average shear stress values were identical. The low and high shear stress regions showed an overlap of approximately 75%. Conclusion Reconstruction of the side branch with MSCT data alone is an adequate technique to study shear stress and wall thickness in the bifurcation region. The reconstruction procedure can be applied to further investigate the effect of shear stress on atherosclerosis in coronary bifurcations.
Congenital heart disease is the most common birth defect and functionally univentricular heart defects represent the most severe end of this spectrum. The Fontan circulation provides an unique ...solution for single ventricle patients, by connecting both caval veins directly to the pulmonary arteries. As a result, the pulmonary circulation in Fontan palliated patients is characterized by a passive, low-energy circulation that depends on increased systemic venous pressure to drive blood toward the lungs. The absence of a subpulmonary ventricle led to the widely believed concept that respiration, by sucking blood to the pulmonary circulation during inspiration, is of great importance as a driving force for antegrade blood flow in Fontan patients. However, recent studies show that respiration influences pulsatility, but has a limited effect on net forward flow in the Fontan circulation. Importantly, since MRI examination is recommended every 2 years in Fontan patients, clinicians should be aware that most conventional MRI flow sequences do not capture the pulsatility of the blood flow as a result of the respiration. In this review, the unique flow dynamics influenced by the cardiac and respiratory cycle at multiple locations within the Fontan circulation is discussed. The impact of (not) incorporating respiration in different MRI flow sequences on the interpretation of clinical flow parameters will be covered. Finally, the influence of incorporating respiration in advanced computational fluid dynamic modeling will be outlined.
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