Hemodynamic Effects of Multiple Overlapping Uncovered Stents on Aortic Dissection: Surgical Strategies and Implications for False Lumen Thrombosis

Biomechanical mechanisms behind the distal false lumen enlargement after TEVAR for type b aortic dissections: A computational one-way fluid-structure interaction study

Distal false lumen (FL) expansion is a common complication after thoracic endovascular aortic repair (TEVAR) of type-B aortic dissection (TBAD). FL expansion is likely to cause post dissection aortic aneurysm (PDAA). At present, the biomechanical mechanism leading to the expansion of the FL is not clear, resulting in difficulties in its prevention and treatment. This paper presents a patient-specific one-way fluid-structure interaction (FSI) method for post-TEVAR TBAD patients. This method was then employed to predict the hemodynamic parameters and wall stress in five unstable and five stable patients post-TEVAR. Simulation results were employed to identify the characteristic mechanical parameters for the FL expansion, and to propose a possible mechanism behind FL expansion involving the relationship between the aortic morphology and the characteristic parameters. The pressure difference between false and true lumen, and the average wall stress of FL are recognized as the characteristic parameters for FL expansion, which effectively differentiate the two groups. The threshold value of wall stress between the two groups is about 75 kPa. Abnormally high luminal pressure difference and wall stress in the unstable group were attributed to their anatomical features, such as: enlarged FL, compressed TL, elevated thrombus ratio in FL, and significantly larger tear size. In conclusion, post-TEVAR expansion of the FL is correlated to high luminal pressure difference and elevated FL wall stress, which might be caused by the morphological features of the aorta.

Mechanisms of aortic dissection: From pathological changes to experimental and in silico models

Aortic dissection continues to be responsible for significant morbidity and mortality, although recent advances in medical data assimilation and in experimental and in silico models have improved our understanding of the initiation and progression of the accumulation of blood within the aortic wall. Hence, there remains a pressing necessity for innovative and enhanced models to more accurately characterize the associated pathological changes. Early on, experimental models were employed to uncover mechanisms in aortic dissection, such as hemodynamic changes and alterations in wall microstructure, and to assess the efficacy of medical implants. While experimental models were once the only option available, more recently they are also being used to validate in silico models. Based on an improved understanding of the deteriorated microstructure of the aortic wall, numerous multiscale material models have been proposed in recent decades to study the state of stress in dissected aortas, including the changes associated with damage and failure. Furthermore, when integrated with accessible patient-derived medical data, in silico models prove to be an invaluable tool for identifying correlations between hemodynamics, wall stresses, or thrombus formation in the deteriorated aortic wall. They are also advantageous for model-guided design of medical implants with the aim of evaluating the deployment and migration of implants in patients. Nonetheless, the utility of in silico models depends largely on patient-derived medical data, such as chosen boundary conditions or tissue properties. In this review article, our objective is to provide a thorough summary of medical data elucidating the pathological alterations associated with this disease. Concurrently, we aim to assess experimental models, as well as multiscale material and patient data-informed in silico models, that investigate various aspects of aortic dissection. In conclusion, we present a discourse on future perspectives, encompassing aspects of disease modeling, numerical challenges, and clinical applications, with a particular focus on aortic dissection. The aspiration is to inspire future studies, deepen our comprehension of the disease, and ultimately shape clinical care and treatment decisions.

Computational fluid dynamics modelling of hemodynamics in aortic aneurysm and dissection: a review

Hemodynamic analysis based on computational fluid dynamics (CFD) modelling is expected to improve risk stratification for patients with aortic aneurysms and dissections. However, the parameter settings in CFD simulations involve considerable variability and uncertainty. Additionally, the exact relationship between hemodynamic features and disease progression remains unclear. These challenges limit the clinical application of aortic hemodynamic models. This review presents a detailed overview of the workflow for CFD-based aortic hemodynamic analysis, with a focus on recent advancements in the field. We also conducted a systematic review of 27 studies with large sample sizes (n > 5) that examine the hemodynamic characteristics of aortic aneurysms and dissections. Some studies identified consistent relationships between hemodynamic features and disease progression, reinforcing the potential for clinical application of aortic hemodynamic models. However, limitations such as small sample sizes and oversimplified patient-specific models remain. These findings emphasize the need for larger, more detailed studies to refine CFD modelling strategies, strengthen the connection between hemodynamics and diseases, and ultimately facilitate the clinical use of aortic hemodynamic models in disease management.

Analysis of the effect of platelet function and different doses of ticagrelor after flow diverter treatment of intracranial aneurysms

Ticagrelor has become the standard drug for the treatment of intracranial aneurysms (IAs) with flow diverters (FDs), but the dosage has not been standardized. The effect of platelet function on clinical and imaging prognosis remains unclear. This study aimed to show the effects of different doses of ticagrelor and platelet aggregation function on the clinical and imaging prognosis after FDs treatment of aneurysms. Patients with IAs and underwent FDs stenting were recruited between July 2019 and June 2023. Logistic regression was performed to assess the predictors of incomplete occlusion and in-stent stenosis (ISS). Linear regression analysis, scatter plot and violin diagram were used to investigate the predictors of maximum platelet aggregation rate induced by ADP (ADP-MPA). The study included 156 patients with 206 aneurysms. There was no significant difference in clinical prognosis and aneurysm occlusion rates between the standard-dose group (ticagrelor, 90 mg/bid) and the low-dose group (ticagrelor, 45 mg/bid). Multivariable analysis identified the ADP-MPA ≥ ADP-MPA (median) (24.2%) (p = 0.037) as an independent risk factor for incomplete occlusion of aneurysms. In addition, higher ADP-MPA (p = 0.045) was an independent risk factor for ISS. Uric acid level (p = 0.019) was negatively associated with ADP-MPA, whereas age (p = 0.031) and body mass index (BMI) (p = 0.042) were positively associated with ADP-MPA. The differences of clinical prognosis and aneurysm occlusion rates between the standard-dose group and the low-dose group were not significant for the treatment of aneurysms with FDs. Higher ADP-MPA predicted higher rates of incomplete occlusion and in-stent stenosis. Uric acid level was negatively associated with ADP-MPA, whereas age and BMI were positively associated with ADP-MPA.

Hemodynamic study of blood flow in the aorta during the interventional robot treatment using fluid-structure interaction

An interventional robot is a means for vascular diagnosis and treatment, and it can perform dredging, releasing drug and operating. Normal hemodynamic indicators are a prerequisite for the application of interventional robots. The current hemodynamic research is limited to the absence of interventional devices or interventional devices in fixed positions. Considering the coupling effect of blood, vessels and robots, based on the bi-directional fluid-structure interaction, using the computational fluid dynamics and particle image velocimetry methods, combined with the sliding and moving mesh technologies, we theoretically and experimentally study the hemodynamic indicators such as blood flow lines, blood pressure, equivalent stress, deformation and wall shear stress of blood vessels when the robot precesses, rotates or does not intervene in the pulsating blood flow. The results show that the intervention of the robot increase the blood flow rate, blood pressure, equivalent stress and deformation of the vessels by 76.4%, 55.4%, 76.5%, and 346%, respectively. The operating mode of the robot during low-speed operation has little impact on the hemodynamic indicators. Using the methyl silicone oil as the experimental fluid, the elastic silicone pipe as the experimental pipe, and the intervention robot having a bioplastic outer shell, the velocity of the fluid around the robot is measured on the developed experimental device for fluid flow field in a pulsating flow when the robot runs. The experimental results are similar to the numerical results. Our work provides an important reference for the hemodynamic study and optimization of the mobile interventional devices.

Influence of MRI-based boundary conditions on type B aortic dissection simulations in false lumen with or without abdominal aorta involvement

Most computational hemodynamic studies of aortic dissections rely on idealized or general boundary conditions. However, numerical simulations that ignore the characteristics of the abdominal branch arteries may not be conducive to accurately observing the hemodynamic changes below the branch arteries. In the present study, two men (M-I and M-II) with type B aortic dissection (TBAD) underwent arterial-phase computed tomography angiography and four-dimensional flow magnetic resonance imaging (MRI) before and after thoracic endovascular aortic repair (TEVAR). The finite element method was used to simulate the computational fluid dynamic parameters of TBAD [false lumen (FL) with or without visceral artery involvement] under MRI-specific and three idealized boundary conditions in one cardiac cycle. Compared to the results of zero pressure and outflow boundary conditions, the simulations with MRI boundary conditions were closer to the initial MRI data. The pressure difference between true lumen and FL after TEVAR under the other three boundary conditions was lower than that of the MRI-specific results. The results of the outflow boundary conditions could not characterize the effect of the increased wall pressure near the left renal artery caused by the impact of Tear-1, which raised concerns about the distal organ and limb perfused by FL. After TEVAR, the flow velocity and wall pressure in the FL and the distribution areas of high time average wall shear stress and oscillating shear index were reduced. The difference between the calculation results for different boundary conditions was lower in M-II, wherein FL did not involve the abdominal aorta branches than in M-I. The boundary conditions of the abdominal branch arteries from MRI data might be valuable in elucidating the hemodynamic changes of the descending aorta in TBAD patients before and after treatment, especially those with FL involving the branch arteries.