Computational analysis of aortic haemodynamics in the presence of ascending aortic aneurysm

BACKGROUND: The usefulness of numerical modelling of a patient’s cardiovascular system is growing in clinical treatment. Understanding blood flow mechanics can be crucial in identifying connections between haemodynamic factors and aortic wall pathologies. OBJECTIVE: This work investigates the haemodynamic parameters of an ascending aorta and ascending aortic aneurysm in humans. METHODS: Two aortic models were constructed from medical images using the SimVascular software. FEM blood flow modelling of cardiac cycle was performed using CFD and CMM-FSI at different vascular wall parameters. RESULTS: The results showed that highest blood velocity was 1.18 m/s in aorta with the aneurysm and 1.9 m/s in healthy aorta model. The largest displacements ware in the aorta with the aneurysm (0.73 mm). In the aorta with the aneurysm, time averaged WSS values throughout the artery range from 0 Pa to 1 Pa. In the healthy aorta, distribution of WSS values changes from 0.3 Pa to 0.6 Pa. CONCLUSIONS: In the case of an ascending aortic aneurysm, the maximum blood velocity was found to be 1.6 times lower than in the healthy aorta. The aneurysm-based model demonstrates a 45% greater wall displacement, while the oscillatory shear index decreased by 30% compared to healthy aortic results.

Analysis of Morphological-Hemodynamic Risk Factors for Aneurysm Rupture Including a Newly Introduced Total Volume Ratio

The purpose of this study was to evaluate morphological and hemodynamic factors, including the newly developed total volume ratio (TVR), in evaluating rupture risk of cerebral aneurysms using ≥7 mm sized aneurysms. Twenty-three aneurysms (11 unruptured and 12 ruptured) ≥ 7 mm were analyzed from 3-dimensional rotational cerebral angiography and computational fluid dynamics (CFD). Ten morphological and eleven hemodynamic factors of the aneurysms were qualitatively and quantitatively compared. Correlation analysis between morphological and hemodynamic factors was performed, and the relationship among the hemodynamic factors was analyzed. Morphological factors (ostium diameter, ostium area, aspect ratio, and bottleneck ratio) and hemodynamic factors (TVR, minimal wall shear stress of aneurysms, time-averaged wall shear stress of aneurysms, oscillatory shear index, relative residence time, low wall shear stress area, and ratio of low wall stress area) were statistically different between ruptured and unruptured aneurysms (p < 0.05). By simple regression analysis, the morphological factor aspect ratio and the hemodynamic factor TVR were significantly correlated (r2 = 0.602, p = 0.001). Ruptured aneurysms had complex and unstable flow. In ≥7 mm ruptured aneurysms, high aspect ratio, bottleneck ratio, complex flow, unstable flow, low TVR, wall shear stress at aneurysm, high oscillatory shear index, relative resistance time, low wall shear stress area, and ratio of low wall stress area were significant in determining the risk of aneurysm rupture.

Patient-Specific Computational Fluid Dynamics Reveal Localized Flow Patterns Predictive of Post–Left Ventricular Assist Device Aortic Incompetence

Background: Progressive aortic valve disease has remained a persistent cause of concern in patients with left ventricular assist devices. Aortic incompetence (AI) is a known predictor of both mortality and readmissions in this patient population and remains a challenging clinical problem. Methods: Ten left ventricular assist device patients with de novo aortic regurgitation and 19 control left ventricular assist device patients were identified. Three-dimensional models of patients’ aortas were created from their computed tomography scans, following which large-scale patient-specific computational fluid dynamics simulations were performed with physiologically accurate boundary conditions using the SimVascular flow solver. Results: The spatial distributions of time-averaged wall shear stress and oscillatory shear index show no significant differences in the aortic root in patients with and without AI (mean difference, 0.67 dyne/cm 2 [95% CI, −0.51 to 1.85]; P =0.23). Oscillatory shear index was also not significantly different between both groups of patients (mean difference, 0.03 [95% CI, −0.07 to 0.019]; P =0.22). The localized wall shear stress on the leaflet tips was significantly higher in the AI group than the non-AI group (1.62 versus 1.35 dyne/cm 2 ; mean difference [95% CI, 0.15–0.39]; P <0.001), whereas oscillatory shear index was not significantly different between both groups (95% CI, −0.009 to 0.001; P =0.17). Conclusions: Computational fluid dynamics serves a unique role in studying the hemodynamic features in left ventricular assist device patients where 4-dimensional magnetic resonance imaging remains unfeasible. Contrary to the widely accepted notions of highly disturbed flow, in this study, we demonstrate that the aortic root is a region of relatively stagnant flow. We further identified localized hemodynamic features in the aortic root that challenge our understanding of how AI develops in this patient population.

Simulation analysis of aneurysm embolization surgery: Hemorheology of aneurysms with different embolization rates (CTA)

BACKGROUND: Embolization degree acts as an important factor affecting recurrence of aneurysm. OBJECTIVE: To analyze the role of hemodynamics parameters of different degrees of embolization in the occurrence, development and post-treatment of aneurysms, and to determine the specific factors causing the occurrence and recurrence of aneurysms after hemodynamics treatment. Our study provides a theoretical basis for the prevention and treatment of aneurysms. METHODS: Computed Tomography Angiography (CTA) data of a patient with cerebral aneurysm were used to model 0%, 24%, 52%, 84% and 100% of endovascular embolization, respectively. The time average wall shear stress, time average wall shear stress, oscillatory shear index, hemodynamics formation index and relative retentive time were used to analyze the changes of hemodynamics indexes in different embolic models. RESULTS: With the increase of embolic rate, the values of time average wall shear stress, time average wall shear stress grade and aneurysm index formation gradually increased, and the values of relative retention time gradually decreased. Oscillatory shear index was higher in patients with incomplete embolization and decreased in patients with complete embolization. CONCLUSIONS: As the degree of embolization increased, the blood flow tended to stabilize, reducing the risk of cerebral aneurysm rupture, and finding that the wall of the vessel junction was susceptible to injury.

Non-Newtonian Blood Modeling in Intracranial Aneurysm Hemodynamics: Impact On the WSS and OSI Metrics for Ruptured and Unruptured Cases

When simulating blood flow in intracranial aneurysms, the Newtonian model seems to be ubiquitous. However, analyzing the results from the few studies on this subject, the doubt remains on whether it is necessary to use non-Newtonian models in wall shear stress (WSS) simulations of cerebral vascular flows. Another open question related to this topic is whether different rheology models would influence the flow parameters for ruptured and unruptured cases, especially because ruptured aneurysms normally have morphological features that could trigger non-Newtonian phenomena in the blood flow due to low shear rates. The objective of this study is to investigate such flows. By using Computational Fluid Dynamics (CFD) in an open-source framework, we simulated an equal number of ruptured and unruptured patient-specific aneurysms to assess the influence of the blood modeling on the main hemodynamic variables associated with aneurysm formation, growth, and rupture. Results for wall shear stress and oscillatory shear index and their metrics were obtained using Casson and Carreau-Yasuda non-Newtonian models and were compared with those obtained using the Newtonian model. We found that the wall shear stress at peak systole is overestimated by more than 50% by using the non-Newtonian models, but its metrics based on time and surface averaged values remain unaffected. On the other hand, the surface-averaged oscillatory shear index (OSI) is underestimated by more than 40% by the non-Newtonian models. In addition, all differences were consistent among all aneurysms cases irrespective of their rupture status.

Numerical insights into the determinants of stent performance for the management of aneurysm with a visceral vessel attached

Purpose: As the factors affecting the efficacy of the bare-metal stent in the treatment of aneurysm with a visceral vessel attached were not fully understood, we aimed to discuss the effects of different characteristics of the stent on the hemodynamics and flexibility in the treatment of the aneurysm. Methods: Single-layer (with different strut widths) and multi-layer (with a different number of struts) stent models divided into three porosity groups, with porosities of 72.3, 60.5, and 52.4%, were modeled for a comparison of their hemodynamic isolation and flexibility performance via computational fluid dynamics and finite element methods. Results: The velocity and timeaveraged wall shear stress decreased more noticeably with multi-layer stent interventions. A higher oscillatory shear index and relative residence time occurred at the aneurysmal sac wall after multi-layer stents were employed. Time-averaged wall shear stress on the aneurysmal wall decreased with an increase in the number of struts or a decrease in pore size, but oscillatory shear index and relative residence time increased as the number of struts increased or the pore size decreased. Besides, all stents affect the branch patency slightly. In the bending test, when the porosity exceeded 60.5%, multi-layer stents were more flexible. Conclusion: The number of struts or pore size of stent dominated the isolation in the management of the aneurysm and affected the flexibility significantly when the porosity was below 60.5%. These findings may contribute to the special design of the stent in the treatment of such types of aneurysms.

Computational fluid dynamics of internal mammary artery–left anterior descending artery anastomoses

OBJECTIVES The aim of this study was to elucidate the remodelling of the internal mammary artery (IMA)–left anterior descending artery anastomosis and compare 2 different anastomosis techniques (end-to-side versus side-to-side) using computational fluid dynamics. METHODS This study included 9 patients. Computed tomography (CT) angiography was performed immediately after coronary artery bypass grafting (CABG) and at 3–6 months later. The computational fluid dynamics models were made using the CT data. The pulsatile 3-dimensional blood flow was achieved with the finite volume method to evaluate the postoperative morphological and haemodynamic changes at the anastomosis in each patient. Flow velocity distribution, wall shear stress (WSS) and its fluctuation oscillatory shear index were measured. RESULTS No early or mid-term graft occlusion was observed in the study series. In the side-to-side anastomosis, pouch formation at the distal end of IMA caused a vortex flow with low WSS immediately after CABG. However, at 3–6 months after surgery, this pouch disappeared. As a result, the laminar straight flow with uniform WSS distribution was achieved inside the anastomosis. In the end-to-side anastomosis, the anastomosis shape was remodelled, resulting in a laminar flow pattern with uniform WSS distribution. A patchy high oscillatory shear index was detected at the IMA wall on the top of anastomosis in either anastomosis techniques immediately after the surgery, but it disappeared at 3–6 months after surgery. CONCLUSIONS Regardless of the anastomosis technique used, a successful remodelling of the IMA–left anterior descending artery anastomosis shape was achieved a few months after surgery, resulting in a straightforward flow streamline, with uniform WSS distribution and minimal oscillatory shear index.

High Spatial Endothelial Shear Stress Gradient Independently Predicts Site of Acute Coronary Plaque Rupture and Erosion

Aims To investigate local haemodynamics in the setting of acute coronary plaque rupture and erosion. Methods and Results Intracoronary optical coherence tomography performed in 37 patients with acute coronary syndromes caused by plaque rupture (n = 19) or plaque erosion (n = 18) was used for 3D reconstruction and computational fluid dynamic simulation. Endothelial shear stress (ESS), spatial ESS gradient (ESSG), and oscillatory shear index (OSI) were compared between plaque rupture and erosion through mixed-effects logistic regression. Lipid, calcium, macrophages, layered plaque, and cholesterol crystals were also analysed. By multivariable analysis, only high ESSG (odds ratio [OR] 5.29, 95% confidence interval [CI] 2.57-10.89, p &lt; 0.001), lipid (OR 12.98, 95% CI 6.57-25.67 p &lt; 0.001), and layered plaque (OR 3.17, 95% CI 1.82-5.50, p &lt; 0.001) were independently associated with plaque rupture. High ESSG (OR 13.28, 95% CI 6.88-25.64, p &lt; 0.001), ESS (OR 2.70, 95% CI 1.34-5.42, p = 0.005) and OSI (OR 2.18, 95% CI 1.33-3.54, p = 0.002) independently associated with plaque erosion. ESSG was higher at rupture sites than erosion sites (median (interquartile range): 5.78 (2.47, 21.15) versus 2.62 (1.44, 6.18) Pa/mm, p = 0.009), OSI was higher at erosion sites than rupture sites (1.04x10−2 (2.3x10−3, 4.74x10−2) versus 1.29x10−3 (9.39x10−5, 3.0x10−2), p &lt; 0.001), but ESS was similar (p = 0.29). Conclusions High ESSG is independently associated with plaque rupture while high ESSG, ESS, and OSI associate with plaque erosion. While ESSG is higher at rupture sites than erosion sites, OSI is higher at erosion sites and ESS was similar. These results suggest that ESSG and OSI may play critical roles in acute plaque rupture and erosion, respectively. Translational Perspective Plaque rupture and erosion are distinct pathological and clinical entities with possibly different optimal treatments. This study demonstrates that high endothelial shear stress gradient is independently associated with site of both rupture and erosion, and is significantly higher in rupture. High oscillatory shear index is independently associated with the site of erosion only, and is higher in erosion than rupture. Larger studies are necessary to determine whether these indices may detect and distinguish plaque rupture and erosion in a clinical setting or to assess overall risk for acute coronary syndromes.

A Simple Flow Classification Parameter Can Discriminate Rupture Status in Intracranial Aneurysms

BACKGROUND A simple dimensionless aneurysm number ($An$), which depends on geometry and flow pulsatility, was previously shown to distinguish the flow mode in intracranial aneurysms (IA): vortex mode with a dynamic vortex formation/evolution if $An &gt; 1$, and cavity mode with a steady shear layer if $An &lt; 1$. OBJECTIVE To hypothesize that $An\ &gt; \ 1$ can distinguish rupture status because vortex mode is associated with high oscillatory shear index, which, in turn, is statistically associated with rupture. METHODS The above hypothesis is tested on a retrospective, consecutively collected database of 204 patient-specific IAs. The first 119 cases are assigned to training and the remainder to testing dataset. $An$ is calculated based on the pulsatility index (PI) approximated either from the literature or solving an optimization problem (denoted as$\ \widehat {PI}$). Student's t-test and logistic regression (LR) are used for hypothesis testing and data fitting, respectively. RESULTS $An$ can significantly discriminate ruptured and unruptured status with 95% confidence level (P &lt; .0001). $An$ (using PI) and $\widehat {An}$ (using $\widehat {PI}$) significantly predict the ruptured IAs (for training dataset $An\!:\ $AUC = 0.85, $\widehat {An}\!:\ $AUC = 0.90, and for testing dataset $An\!:\ $sensitivity = 94%, specificity = 33%, $\widehat {An}\!:\ $sensitivity = 93.1%, specificity = 52.85%). CONCLUSION $An &gt; 1$ predicts ruptured status. Unlike traditional hemodynamic parameters such as wall shear stress and oscillatory shear index, $An$ has a physical threshold of one (does not depend on statistical analysis) and does not require time-consuming flow simulations. Therefore, $An$ is a simple, practical discriminator of IA rupture status.