Hemodynamic Metrics Research Articles

Assessment of structural and hemodynamic performance of vascular stents modelled as periodic lattices

This work considers vascular stents with tubular geometry assumed to follow a periodic arrangement of repeating unit cells. Structural and hemodynamic metrics are presented to assess alternative stent geometries, each defined by the topology of the unit cell. Structural metrics include foreshortening, elastic recoil and radial stiffness, whereas hemodynamic performance is described by a wall shear stress index quantifying the impact of in-stent restenosis. A representative volume element (RVE) modelling approach is used, and results are compared to those obtained from full simulations of entire stents. We demonstrate that the RVE approach can be used to quantify the impact of the topology of the repeating unit on the structural and hemodynamic properties of a stent, and thus support clinicians in making proper choices among alternative stent geometries.

Corrigendum.

McElroy M and Keshmiri A, Impact of using conventional inlet/outlet boundary conditions on haemodynamic metrics in a subject-specific rabbit aorta, Proc IMechE, Part H: Journal of Engineering in Medicine, first published on March 25, 2017, DOI: 10.1177/0954411917699237 Following OnlineFirst publication of the article, the authors informed SAGE of an error in the transient velocity inlet profile which had been defined inaccurately due to a human error in the interpretation of clinical data in the literature. As a result of this error in boundary conditions, some of the results of transient flow computations were incorrect. A watermarked version of the first publication of the article (as first published on March 25, 2017) is attached for reference in the PDF version of this corrigendum. The authors have revised and corrected their article. The revised version of the article has been accepted following peer review and replaces the article first published on March 25, 2017. Date received: 8 August 2017; accepted: 30 November 2017 (Revised version) Date received: 29 March 2016; accepted: 21 February 2017 (Original version) The correct and citable version of the article is accessible at the following DOI: 10.1177/0954411917699237.

Abstract TP79: Significant Correlations between Risk Factors for Rupture of Cerebral Aneurysms and Hemodynamic Factors by Using Computational Flow Dynamic (CFD) Analysis and Multivariate Analysis

Background and purpose: Although it is thought that hemodynamic factors are involved in cerebral aneurysm rupture, details are unknown. Using multivariate analysis and computational flow dynamic (CFD) analysis, we investigated here correlations between well-known aneurysm rupture risk factors and hemodynamic factors. Methods: Patient-specific inflow velocities and arterial geometries of 86 cerebral aneurysms (43 Anterior Communicating artery and 43 MCA aneurysms) were acquired from patients who consented to participate in the multi-institutional prospective clinical study, CFD ABO Study. Pulsatile blood flow was simulated using ANSYS-CFX, based on the Navier-Stokes equations for incompressible fluid. Multivariate regression analysis was performed to find independent predictors for wall shear stress (WSS) magnitude-based metrics (WSS, NWSS) and WSS disturbance-based metrics (OSI, NtransWSS) on the CFD modelling to predict potential factors, including maximum diameter, site, sex, age, history of hypertension and smoking. Results: The associations between maximum diameter and hemodynamic metrics were all significant [WSS: regression coefficient (RC), -0.65, 95%CI, -1.1 to -0.18; NWSS: RC, -0.96, 95%CI, -1.6 to -0.36; OSI: RC, 0.0032, 95%CI, 0.0018 to 0.0046; NtransWSS: RC, 0.013, 95%CI, 0.0075 to 0.018], while relations between site and WSS, NWSS, and NtransWSS, but not OSI, were significant (WSS: RC, -2.1, 95%CI, -3.1 to -0.10; NWSS: RC, -2.9, 95%CI, -4.1 to -1.6; NtransWSS: RC, 0.013, 95%CI, 0.0015 to 0.024). Among aneurysm maximum diameter, surface area, volume, and diameter-ratio between parent artery and aneurysm, diameter-ratio was the strongest correlation with all hemodynamic metrics (WSS: RC, -1.2, 95%CI, -2.2 to -0.23; NWSS: RC, -1.9, 95%CI, -3.1 to -0.64; OSI: RC, 0.0052, 95%CI, 0.0022 to 0.0082; NtransWSS: RC, 0.022, 95%CI, 0.011 to 0.034). Conclusions: The data suggest that a difference in rupture rate according to aneurysm site and size are hemodynamically dependent; lower WSS and increased disturbed flow may be associated with aneurysm rupture. Since diameter-ratio is most correlated with these hemodynamic factors, this index may be a good indicator for hemodynamic factors.

The role of dynamic contrast-enhanced MRI analysis of perfusion changes in hepatocellular carcinoma

Background Dynamic contrast-enhanced (DCE)-MRI functional imaging is primarily focused on quantitative evaluation of tumoral perfusion and permeability, thus enabling an insight into the pathophysiology of tissue and serving as early noninvasive biologic markers of tumorigenesis. Aim The aim was to evaluate the functional role of DCE-MRI analysis of perfusion changes in hepatocellular carcinoma (HCC). Patients and methods A total of 43 patients with liver cirrhosis having 65 HCCs all underwent 3 T multiphase DCE-MRI assessment. Maximum relative enhancement, area under curve, wash-in ratio, wash-out ratio, time to arrival, and time to peak semiquantitative measurements were analytically compared between the hepatocellular carcinogenic lesions and the adjacent lesion-free liver cirrhosis. Results Comparison of different perfusion metrics across hepatocellular carcinogenic lesions and adjacent lesion-free liver cirrhosis revealed exceling statistical significance. Diagnostic accuracies were highest when using wash-out ratio (86.2%) to detect HCC from background cirrhosis, whereas they were lowest using area under the curve (67.7%). Implementing wash-in ratio (81.9%), as a first-pass perfusion metric, surpassed its counterpart, maximum relative enhancement (73.4%), in diagnostic reliability. Regarding the timing of flow dynamics, time to arrival (84.1%) was more important than time to peak (78.1%) as a diagnostic indicator of hepatocarcinogenesis. Conclusion Multiphase DCE-MRI perfusion analyses provide quantitative hemodynamic metrics that promise potential usefulness as noninvasive biomarkers in the detection of HCC.

Using a Novel In Vitro Fontan Model and Condition-Specific Real-Time MRI Data to Examine Hemodynamic Effects of Respiration and Exercise.

Several studies exist modeling the Fontan connection to understand its hemodynamic ties to patient outcomes (Chopski in: Experimental and Computational Assessment of Mechanical Circulatory Assistance of a Patient-Specific Fontan Vessel Configuration. Dissertation, 2013; Khiabani et al. in J Biomech 45:2376-2381, 2012; Taylor and Figueroa in Annu Rev Biomed 11:109-134, 2009; Vukicevic et al. in ASAIO J 59:253-260, 2013). The most patient-accurate of these studies include flexible, patient-specific total cavopulmonary connections. This study improves Fontan hemodynamic modeling by validating Fontan model flexibility against a patient-specific bulk compliance value, and employing real-time phase contrast magnetic resonance flow data. The improved model was employed to acquire velocity field information under breath-held, free-breathing, and exercise conditions to investigate the effect of these conditions on clinically important Fontan hemodynamic metrics including power loss and viscous dissipation rate. The velocity data, obtained by stereoscopic particle image velocimetry, was visualized for qualitative three-dimensional flow field comparisons between the conditions. Key hemodynamic metrics were calculated from the velocity data and used to quantitatively compare the flow conditions. The data shows a multi-factorial and extremely patient-specific nature to Fontan hemodynamics.

Valve mediated hemodynamics and their association with distal ascending aortic diameter in bicuspid aortic valve subjects.

Valve mediated hemodynamics have been postulated to contribute to pathology of the ascending aorta (AAo). The objective of this study is to assess the association of aortic valve morphology and hemodynamics with downstream AAo size in subjects with bicuspid aortic valve (BAV) disease. Four-dimensional flow MRI at 1.5 or 3 Tesla was used to evaluate the hemodynamics in the proximal AAo of 52 subjects: size-matched controls with tricuspid aortic valves (n = 24, mid ascending aorta [MAA] diameter = 38.0 ± 4.9 mm) and BAV patients with aortic dilatation (n = 14 right and left coronary leaflet fusion [RL]-BAV, MAA diameter = 38.1 ± 5.3 mm; n = 14 right and noncoronary leaflet fusion [RN]-BAV, MAA diameter = 36.5 ± 6.6 mm). A validated semi-automated technique was used to evaluate hemodynamic metrics (flow angle, flow displacement, and jet quadrant) and valve morphology (orifice circularity) for all subjects. Regression analysis of these metrics to AAo diameter was performed. RN-BAV subjects displayed a stronger correlation between hemodynamic metrics in the proximal AAo with diameter in the distal AAo compared with size-matched tricuspid aortic valve (TAV) controls and RL-BAV subjects. The distal AAo diameter was found to be strongly correlated to the upstream flow displacement (R2adjusted = 0.75) and flow angle (R2adjusted = 0.66) measured at the sino-tubular junction (STJ). Orifice circularity was also strongly correlated (R2adjusted = 0.53) to the distal AAo diameter in RN-BAV subjects. For TAV controls and RL-BAV subjects, correlations were weaker (R2adjusted < 0.2). Hemodynamics in the STJ were strongly correlated to the distal AAo diameter for the RN-BAV subjects. Hemodynamic metrics were more strongly correlated to the downstream aortic size when compared with valve morphology metrics. 3 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;47:246-254.

Impact of Using Conventional Inlet/Outlet Boundary Conditions on Haemodynamic Metrics in a Subject-Specific Rabbit Aorta.

Computational fluid dynamics is a tool capable of accurately measuring metrics currently used to predict the behaviour of cardiovascular diseases. This study quantifies the impact various commonly used inlet and outlet boundary conditions have on various shear rate-based haemodynamic metrics currently used for predicting the localisation of cardiovascular diseases. Simulations are conducted on an accurately represented rabbit aorta configuration and comparison has been made against available in vivo data. The boundary conditions studied include two different inlet profiles, three outlet boundary conditions, and steady-state versus pulsatile flow cases. Large variations were found in the results, particularly when using different outlet boundary conditions, and the discrepancies were evaluated both quantitatively and qualitatively. The results clearly highlight the importance of the type of boundary condition used when simulating complex cardiovascular models. By restricting the attention to the flow within the aorta and the intercostal branches, the results suggest that prescribing transient simulation and fully developed flow at the inlet are not required. Furthermore, assuming the widely accepted low wall shear stress theory of Caro, it was found that Murray's law-based outlet boundary condition returns the most physiologically accurate results when compared to in vivo data.

Multi-Modality Imaging Enables Detailed Hemodynamic Simulations in Dissecting Aneurysms in Mice.

A multi-modality imaging-based modeling approach was used to study complex unsteady hemodynamics and lesion growth in a dissecting abdominal aortic aneurysm model. We combined in vivo ultrasound (geometry and flow) and in vitro optical coherence tomography(OCT) (geometry) to obtain the high resolution needed to construct detailed hemodynamic simulations over large portions of the murine vasculature, which include fine geometric complexities. We illustrate this approach for a spectrum of dissecting abdominal aortic aneurysms induced in male apolipoprotein E-null mice by high-dose angiotensin II infusion. In vivo morphological and hemodynamic data provide information on volumetric lesion growth and changes in blood flow dynamics, respectively, occurring from the day of initial aortic expansion. We validated the associated computational models by comparing results on time-varying outlet flows and vortical structures within the lesions. Three out of four lesions exhibited abrupt formation of thrombus, though different in size. We determined that a lesion without thrombus formed with a thickened vessel wall, which was resolvable by OCT and histology. We attribute differences in final sizes and compositions of these lesions to the different computed flow and vortical structures we obtained in our mouse-specific fluid dynamic models. Differences in morphology and hemodynamics play crucial roles in determining the evolution of dissecting abdominal aortic aneurysms. Coupled high resolution in vivo and in vitro imaging approaches provide much-improved geometric models for hemodynamic simulations. Our imaging-based computational findings suggest a link between perturbations in hemodynamic metrics and aneurysmal disease heterogeneity.

Abstract 13294: Valve Mediated Hemodynamics and Their Association With Ascending Aortic Diameter in Bicuspid Aortic Valve

Introduction: Bicuspid aortic valve (BAV) is the most common congenital heart defect, affecting 1-2% of the US population. Valve-mediated hemodynamics have been postulated to contribute to the cause and progression of ascending aorta (AAo) disease. Hypothesis: Aortic valve morphology and hemodynamics affect distal AAo diameter in subjects with BAV disease. Methods: Four-dimensional flow MRI was used to evaluate the hemodynamics in the proximal AAo of 52 subjects: size-matched controls with tricuspid aortic valves (n = 24) and BAV patients with aortic dilatation (n = 14 right and left coronary cusp fusion (RL-BAV); n = 14 right and non-coronary cusp fusion (RN-BAV)). A semi-automated technique was used to systematically quantify hemodynamic metrics (flow angle, flow displacement, and jet quadrant) and valve morphology (orifice circularity) for all subjects, as illustrated in the figure. A regression analysis was conducted to develop a relationship between upstream hemodynamics and distal AAo diameter. Results: RN-BAV subjects displayed a stronger correlation between hemodynamic metrics in the proximal AAo with diameter in the distal AAo when compared to size-matched TAV controls and RL-BAV subjects. The distal AAo diameter was found to be strongly correlated to the flow displacement (R 2 adjusted = 0.75) and flow angle (R 2 adjusted = 0.66) measured at the sino-tubular junction (STJ) in RN-BAV subjects. Orifice circularity was also strongly correlated (R 2 adjusted = 0.53) to the proximal AAo diameter in RN-BAV subjects. Conclusions: The findings in this work demonstrate that the hemodynamics in the STJ are significantly correlated to the distal AAo diameter in RN-BAV subjects. The hemodynamic metrics demonstrated more statistical significance than valve morphology when considering correlations to distal aortic size. These results could be used to design efficient imaging protocols for better prognosis of BAV-related aortopathy.

Simulations of morphotype-dependent hemodynamics in non-dilated bicuspid aortic valve aortas

Bicuspid aortic valves (BAVs) generate flow abnormalities that may promote aortopathy. While positive helix fraction (PHF) index, flow angle (θ), flow displacement (d) and wall shear stress (WSS) exhibit abnormalities in dilated BAV aortas, it is unclear whether those anomalies stem from the abnormal valve anatomy or the dilated aorta. Therefore, the objective of this study was to quantify the early impact of different BAV morphotypes on aorta hemodynamics prior to dilation. Fluid-structure interaction models were designed to quantify standard peak-systolic flow metrics and temporal WSS characteristics in a realistic non-dilated aorta connected to functional tricuspid aortic valve (TAV) and type-I BAVs. While BAVs generated increased helicity (PHF>0.68) in the middle ascending aorta (AA), larger systolic flow skewness (θ>11.2°) and displacement (d>6.8mm) relative to the TAV (PHF=0.51; θ<5.5°; d<3.3mm), no distinct pattern was observed between morphotypes. In contrast, WSS magnitude and directionality abnormalities were BAV morphotype- and site-dependent. Type-I BAVs subjected the AA convexity to peak-systolic WSS overloads (up to 1014% difference vs. TAV). While all BAVs increased WSS unidirectionality on the proximal AA relative to the TAV, the most significant abnormality was achieved by the BAV with left-right-coronary cusp fusion on the wall convexity (up to 0.26 decrease in oscillatory shear index vs. TAV). The results indicate the existence of strong hemodynamic abnormalities in non-dilated type-I BAV AAs, their colocalization with sites vulnerable to dilation and the superior specificity of WSS metrics over global hemodynamic metrics to the valve anatomy.

Can time-averaged flow boundary conditions be used to meet the clinical timeline for Fontan surgical planning?

Cardiovascular simulations have great potential as a clinical tool for planning and evaluating patient-specific treatment strategies for those suffering from congenital heart diseases, specifically Fontan patients. However, several bottlenecks have delayed wider deployment of the simulations for clinical use; the main obstacle is simulation cost. Currently, time-averaged clinical flow measurements are utilized as numerical boundary conditions (BCs) in order to reduce the computational power and time needed to offer surgical planning within a clinical time frame. Nevertheless, pulsatile blood flow is observed in vivo, and its significant impact on numerical simulations has been demonstrated. Therefore, it is imperative to carry out a comprehensive study analyzing the sensitivity of using time-averaged BCs. In this study, sensitivity is evaluated based on the discrepancies between hemodynamic metrics calculated using time-averaged and pulsatile BCs; smaller discrepancies indicate less sensitivity.The current study incorporates a comparison between 3D patient-specific CFD simulations using both the time-averaged and pulsatile BCs for 101 Fontan patients. The sensitivity analysis involves two clinically important hemodynamic metrics: hepatic flow distribution (HFD) and indexed power loss (iPL). Paired demographic group comparisons revealed that HFD sensitivity is significantly different between single and bilateral superior vena cava cohorts but no other demographic discrepancies were observed for HFD or iPL. Multivariate regression analyses show that the best predictors for sensitivity involve flow pulsatilities, time-averaged flow rates, and geometric characteristics of the Fontan connection. These predictors provide patient-specific guidelines to determine the effectiveness of analyzing patient-specific surgical options with time-averaged BCs within a clinical time frame.

A comparison of hemodynamic metrics and intraluminal thrombus burden in a common iliac artery aneurysm

Aneurysms of the common iliac artery (CIAA) are typically found in association with an abdominal aortic aneurysm (AAA). Isolated CIAAs, in the absence of an AAA, are uncommon. Similar to AAAs, CIAA may develop intraluminal thrombus (ILT). As isolated CIAAs have a contralateral common iliac artery for comparison, they provide an opportunity to study the hemodynamic mechanisms behind ILT formation. In this study, we compared a large isolated CIAA and the contralateral iliac artery using computational fluid dynamics to determine if hemodynamic metrics correlate with the location of ILT. We performed a comprehensive computational fluid dynamics study and investigated the residence time of platelets and monocytes, velocity fields, time-averaged wall shear stress, oscillatory shear index, and endothelial cell activation potential. We then correlated these data to ILT burden determined with computed tomography. We found that high cell residence times, low time-averaged wall shear stress, high oscillatory shear index, and high endothelial cell activation potential all correlate with regions of ILT development. Our results show agreement with previous hypotheses of thrombus formation in AAA and provide insights into the computational hemodynamics of iliac artery aneurysms.

Elimination of Transcoarctation Pressure Gradients Has No Impact on Left Ventricular Function or Aortic Shear Stress After Intervention in Patients With Mild Coarctation

This study sought to investigate the impact of transcatheter intervention on left ventricular function and aortic hemodynamics in patients with mild coarctation of the aorta (COA). The optimal method and timing of transcatheter intervention for COA remains unclear, especially whenthe severity of COA is mild (peak-to-peak transcoarctation pressure gradient<20 mmHg). Debate rages regarding the risk/benefit ratio of intervention versus long-term effects of persistent minimal gradient in this heterogeneous population with differing blood pressures, ventricular function, and peripheral perfusion. We developed a unique computational fluid dynamics and lumped parameter modeling framework based on patient-specific hemodynamic input parameters and validated it against patient-specific clinical outcomes (before and after intervention). We used clinically measured hemodynamic metrics and imaging of the aorta and the left ventricle in 34 patients with mild COA to make these correlations. Despite dramatic reduction in the transcoarctation pressure gradient (catheter and Doppler echocardiography pressure gradients reduced by 75% and 47.3%, respectively), there was only modest effect on aortic flow and no significant impact on aortic shear stress (the maximum time-averaged wall shear stress in descending aorta was reduced 5.1%). In no patient did transcatheter intervention improve left ventricular function (e.g., stroke work and normalized stroke work were reduced by only 4.48% and 3.9%, respectively). Transcatheter intervention that successfully relieves mild COA pressure gradients does not translate to decreased myocardial strain. The effects of the intervention were determined to the greatest degree by ventricular-vascular coupling hemodynamics and provide a novel valuable mechanism to evaluate patients with COA that may influence clinicalpractice.

The hemodynamic effects of acute aortic regurgitation into a stiffened left ventricle resulting from chronic aortic stenosis.

Acute aortic regurgitation (AR) post-chronic aortic stenosis is a prevalent phenomenon occurring in patients who undergo transcatheter aortic valve replacement (TAVR) surgery. The objective of this work was to characterize the effects of left ventricular diastolic stiffness (LVDS) and AR severity on LV performance. Three LVDS models were inserted into a physiological left heart simulator. AR severity was parametrically varied through four levels (ranging from trace to moderate) and compared with a competent aortic valve. Hemodynamic metrics such as average diastolic pressures (DP) and reduction in transmitral flow were measured. AR index was calculated as a function of AR severity and LVDS, and the work required to make up for lost volume due to AR was estimated. In the presence of trace AR, higher LVDS had up to a threefold reduction in transmitral flow (13% compared with 3.5%) and a significant increase in DP (2-fold). The AR index ranged from ∼42 to 16 (no AR to moderate AR), with stiffer LVs having lower values. To compensate for lost volume due to AR, the low, medium, and high LVDS models were found to require 5.1, 5.5, and 6.6 times more work, respectively. This work shows that the LVDS has a significant effect on the LV performance in the presence of AR. Therefore, the LVDS of potential TAVR patients should be assessed to gain an initial indication of their ability to tolerate post-procedural AR.

Abstract WP88: Hemodynamic Localizations in Anterior Communicating Artery Aneurysms in Comparison With Middle Cerebral Artery Aneurysms With Computational Fluid Dynamics Analysis

Introduction: In a series of reports using an animal model of experimentally induced cerebral aneurysms (CAs), we have proposed that an increase in wall shear stress (WSS)-related hemodynamics initiates CA development. Although several studies tried to clarify detailed hemodynamic stress in human CAs with computational fluid dynamics (CFD), the results so far are controversial. Thus, we started the multi-institutional prospective clinical trial to examine hemodynamics-related factors for CA development, enlargement, and rupture with CFD, named CFD ABO Study. We have proposed “normalized transverse WSS” (NtransWSS); a newly modified indicator based on transWSS for multi-directional disturbed flow, and indicated significant importance of WSS-associated disturbed flow in CA formation. We show here the interim report of the trial. Hypothesis: Unlike MCA aneurysms, anterior communicating artery (Acom) aneurysms usually have inlet flow from both sides of internal carotid arteries, which may cause more complicated hemodynamic circumstances, contributing to higher rupture rate of Acom aneurysms. In order to clarify this hypothesis, we elucidated differences in hemodynamics between Acom and MCA aneurysms. Methods: Three-dimensional CT angiographic images of human CAs and patient-specific flow velocities as inlet boundary conditions were used for CFD analysis. Results and Conclusions: In Acom aneurysms, WSS was lower over the entire aneurysm than neighboring arteries (p=0.02), but higher at neck of the CA (p=0.02). WSS gradient was higher at the neck (p=0.02). NtransWSS and OSI were higher over the entire aneurysm (p=0.02) and at the neck (p=0.02 and 0.04, respectively). Although distributions of some hemodynamic metrics in MCA aneurysms were statistically similar in Acom aneurysms, OSI at the neck was not significantly higher. In addition, WSS over the entire aneurysms of Acom was much lower as compared with MCA aneurysms (p=0.03). At the neck of Acom aneurysms compared with MCA aneurysms, NtransWSS and OSI were higher while WSS was lower (not significant). High WSS under disturbed flow may be involved in CA development, and low WSS with turbulences in rupture. Markedly lower WSS in Acom aneurysms may be associated with higher rupture rate in this site.

Hemodynamic Testing of Patient-Specific Mitral Valves Using a Pulse Duplicator: A Clinical Application of Three-Dimensional Printing.

To evaluate the feasibility of obtaining hemodynamic metrics of echocardiographically derived 3-dimensional printed mitral valve models deployed in a pulse-duplicator chamber. Exploratory study. Tertiary-care university hospital. Percutaneous MitraClip procedure patient. Three-dimensional R-wave gated, full-volume transesophageal echocardiography images were obtained after deployment of the MitraClip device. A high-quality diastolic frame of the mitral valve was segmented using Mimics Innovation Suite and merged with a flange. The data were exported as a stereolithography (.stl) file, and a rigid 3-dimensional model was printed using a MakerBot Replicator 2 printer. A flexible silicone cast then was created and deployed in the pulse-duplicator chamber filled with a blood-mimicking fluid. The authors were able to obtain continuous-wave Doppler tracings of the valve inflow with a transesophageal echocardiography transducer. They also were able to generate diastolic ventricular and atrial pressure tracings. Pressure half-time and mitral valve area were computed from these measurements. This pulse duplicator shows promising applications in hemodynamic testing of patient-specific anatomy. Future modifications to the system may allow for visualization and data collection of gradients across the aortic valve.

The Role of Wall Shear Stress in the Assessment of Right Ventricle Hydraulic Workload

Pulmonary hypertension (PH) is a devastating disease affecting approximately 15-50 people per million, with a higher incidence in women. PH mortality is mostly attributed to right ventricle (RV) failure, which results from RV hypotrophy due to an overburdened hydraulic workload. The objective of this study is to correlate wall shear stress (WSS) with hemodynamic metrics that are generally accepted as clinical indicators of RV workload and are well correlated with disease outcome. Retrospective right heart catheterization data for 20 PH patients were analyzed to derive pulmonary vascular resistance (PVR), arterial compliance (C), and an index of wave reflections (Γ). Patient-specific contrast-enhanced computed tomography chest images were used to reconstruct the individual pulmonary arterial trees up to the seventh generation. Computational fluid dynamics analyses simulating blood flow at peak systole were conducted for each vascular model to calculate WSS distributions on the endothelial surface of the pulmonary arteries. WSS was found to be decreased proportionally with elevated PVR and reduced C. Spatially averaged WSS (SAWSS) was positively correlated with PVR (R (2) = 0.66), C (R (2) = 0.73), and Γ (R (2) = 0.5) and also showed promising preliminary correlations with RV geometric characteristics. Evaluating WSS at random cross sections in the proximal vasculature (main, right, and left pulmonary arteries), the type of data that can be acquired from phase-contrast magnetic resonance imaging, did not reveal the same correlations. In conclusion, we found that WSS has the potential to be a viable and clinically useful noninvasive metric of PH disease progression and RV health. Future work should be focused on evaluating whether SAWSS has prognostic value in the management of PH and whether it can be used as a rapid reactivity assessment tool, which would aid in selection of appropriate therapies.

Numerical investigations of the haemodynamic changes associated with stent malapposition in an idealised coronary artery

The deployment of a coronary stent near complex lesions can sometimes lead to incomplete stent apposition (ISA), an undesirable side effect of coronary stent implantation. Three-dimensional computational fluid dynamics (CFD) calculations are performed on simplified stent models (with either square or circular cross-section struts) inside an idealised coronary artery to analyse the effect of different levels of ISA to the change in haemodynamics inside the artery. The clinical significance of ISA is reported using haemodynamic metrics like wall shear stress (WSS) and wall shear stress gradient (WSSG). A coronary stent with square cross-sectional strut shows different levels of reverse flow for malapposition distance (MD) between 0mm and 0.12mm. Chaotic blood flow is usually observed at late diastole and early systole for MD=0mm and 0.12mm but are suppressed for MD=0.06mm. The struts with circular cross section delay the flow chaotic process as compared to square cross-sectional struts at the same MD and also reduce the level of fluctuations found in the flow field. However, further increase in MD can lead to chaotic flow not only at late diastole and early systole, but it also leads to chaotic flow at the end of systole. In all cases, WSS increases above the threshold value (0.5Pa) as MD increases due to the diminishing reverse flow near the artery wall. Increasing MD also results in an elevated WSSG as flow becomes more chaotic, except for square struts at MD=0.06mm.

Accurate Assessment of Aortic Stenosis

Aortic valve (AV) stenosis is one of the most common valvular diseases and is the third most common cardiovascular disease in developed countries. It occurs in ≈2.8% of patients ≥75 years of age and can occur because of degenerative calcification and congenital valvular defects such as bicuspid AVs or rheumatic disease.1–3 Calcific aortic stenosis (AS) is associated with increased leaflet stiffness and a narrowed AV orifice, resulting in increased pressure gradients across the valve. The presence of a bicuspid AV significantly increases the risk of AS.4 The natural history of AS is a prolonged asymptomatic period, with progressive reduction of the AV orifice area due to sclerosis initially, culminating in calcific AS. This is accompanied by a corresponding increase in the transaortic pressure gradient (Δ P ) and myocardial pressure overload. Through the preload reserve, the left ventricle (LV) compensates for the increased workload until the sarcomeres stretch to their maximum diastolic length. Once the preload reserve is exhausted, increases in afterload are accompanied by a reduction in stroke volume (SV), resulting in afterload mismatch. Ultimately, this causes LV hypertrophy, associated with an enlargement of cardiac myocytes and increased LV wall thickness.5 Initial diagnosis of AS typically occurs during routine physical examination with the presence of a heart murmur, click, or other abnormal sounds, but undiagnosed patients may experience the onset of severe symptoms such as angina, syncope, and heart failure. Without intervention, patient mortality typically occurs within 5 years of the onset of symptoms.6–11 Multiple studies and reviews have focused on the clinical aspects of this disease, including disease progression, markers of disease severity, treatment guidelines, and outcomes.1–3,6,12–16 Very few reviews have focused on the hemodynamic principles underlying AS and on comparing data obtained across different …

The effect of levosimendan combined with 20% lipid emulsion treatment on survival from bupivacaine induced toxicity in experiment.

Recent reports demonstrated that levosimendan improved post-resuscitation myocardial function in rat and pig models. Rabbits were randomized into 4 groups as 12 rabbits in each group. Bupivacaine 10 mg/kg was injected as an intravenous bolus to all groups. Basic life support was performed by mechanical ventilation and manual external chest compressions. After 1 min, animals in the group 1 received 1.5 ml/ kg saline 0.9% solution, and animals in the groups 2 and 4 received 5 ml/kg 20% lipid emulsion for 1 min through the ear vein followed by continuous infusion at 0.25 ml/kg/min. Three additional boluses of 1.5 ml/ kg lipid emulsion were repeated at 5-min intervals. The group 3 received fluid resuscitation plus levosimendan (3 µg/kg/min) 1 min after asystole and the group 4 received both levosimendan and lipid emulsion treatment. Return of spontaneous circulation and hemodynamic metrics were obtained in 20 minutes. The number of rabbits that survived after cardiac resuscitation was lower in the Groups 1 (0%) and 3 (33.3%) than in the Group 4 (91.7%) with a statistically significant difference (p < 0.001). The number of rabbits that survived resuscitation was higher in the Group 4 than in the Group 2 (66.7%), though not with a statistically significant difference (p = 0.317). The median duration of cardiac arrest in the Group 4 was significantly shorter than that in the other three groups (p < 0.001). In this rabbit model of bupivacaine-induced cardiac arrest, resuscitation with combined iv lipid emulsion and levosimendan was more efficacious than lipid alone (Tab. 3, Ref. 24).