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Atrial fibrillation (AF) can alter intra-cardiac flow and cardiac output that subsequently affects aortic flow circulation. These changes may become more significant where they occur concomitantly with ageing. Aortic ageing is accompanied with morphological changes such as dilation, lengthening, and arch unfolding. While the recognition of AF mechanism has been the subject of numerous studies, less focus has been devoted to the aortic circulation during the AF and there is a lack of such investigation at different ages. The current work aims to address the present gap. First, we analyse aortic flow distribution in three configurations, which attribute to young, middle and old people, using geometries constructed via clinical data. We then introduce two transient inlet flow conditions representative of key AF-associated defects. Results demonstrate that both AF and ageing negatively affect flow circulation. The main consequence of concomitant occurrence is enhancement of endothelial cell activation potential (ECAP) throughout the vascular domain, mainly at aortic arch and descending thoracic aorta, which is consistent with some clinical observations. The outcome of the current study suggests that AF exacerbates the vascular defects occurred due to the ageing, which increases the possibility of cardiovascular diseases per se. Supplementary Information The online version contains supplementary material available at (10.1007/s10439-021-02744-9).

Atrial fibrillation (AF) is the most common type of arrhythmia, which undermines cardiac function. Atrial fibrillation is a multi-facet malady and it may occur as a result of other diseases or it may trigger other problems. One of the main complications of AF is stroke due to the possibility of clot formation inside the atrium. However, the possibility of stroke occurrence due to the AF and the location from which an embolus dispatches are subject of debate. Another hypothesis about the embolus formation during AF is thrombus formation in aorta and carotid arteries, embolus detachment and its movement. To investigate the possibility of the latter postulation, the current work suggests a parametric study to quantify the sensitivity of aortic flow to four common AF traits including lack of atrial kick, atrial remodelling, left ventricle systolic dysfunction, and high frequency fibrillation. The simulation was carried out by coupling several in-house codes and ANSYS-CFX module. The results reveal that AF traits lower flow rate at left ventricular outflow tract, which in general lowers blood perfusion to systemic, cerebral and coronary circulations. Consequently, it leads to endothelial cell activation potential (ECAP) increase and variation of flow structure that both suggest predisposed areas to atherogenesis and thrombus formation in different regions in ascending aorta, aortic arch and descending thoracic aorta. Electronic supplementary material The online version of this article (10.1007/s10439-020-02448-6) contains supplementary material, which is available to authorized users.

Congenital heart disease (CHD) is the most common birth defect globally and coarctation of the aorta (CoA) is one of the commoner CHD conditions, affecting around 1/1800 live births. CoA is considered a CHD of critical severity. Unfortunately, the prognosis for a child born in a low and lower-middle income country (LLMICs) with CoA is far worse than in a high-income country. Reduced diagnostic and interventional capacities of specialists in these regions lead to delayed diagnosis and treatment, which in turn lead to more cases presenting at an advanced stage. Computational fluid dynamics (CFD) is an important tool in this context since it can provide additional diagnostic data in the form of hemodynamic parameters. It also provides an in silico framework, both to test potential procedures and to assess the risk of further complications arising post-repair. Although this concept is already in practice in high income countries, the clinical infrastructure in LLMICs can be sparse, and access to advanced imaging modalities such as phase contrast magnetic resonance imaging (PC-MRI) is limited, if not impossible. In this study, a pipeline was developed in conjunction with clinicians at the Red Cross War Memorial Children’s Hospital, Cape Town and was applied to perform a patient-specific CFD study of CoA. The pipeline uses data acquired from CT angiography and Doppler transthoracic echocardiography (both much more clinically available than MRI in LLMICs), while segmentation is conducted via SimVascular and simulation is realized using OpenFOAM. The reduction in cost through use of open-source software and the use of broadly available imaging modalities makes the methodology clinically feasible and repeatable within resource-constrained environments. The project identifies the key role of Doppler echocardiography, despite its disadvantages, as an intrinsic component of the pipeline if it is to be used routinely in LLMICs.

Abdominal Aortic Aneurysm (AAA) is one of the main cardiovascular diseases, which threats human’s health while it appears, develops and in crucial cases ruptures and leads to hemorrhage. In the current work, we aim to investigate numerically the transient blood flow in a patient-specific AAA model, while effects of wall compliance is considered by employing the fluid-structure interaction method. The AAA model is reconstructed from acquired CT angiographic data of a patient diagnosed with AAA and an intraluminal thrombus (ILT). For the comparison purposes two different material models, i.e. isotropic and anisotropic are considered. Additionally, to have a better estimation, wall thickness variability is compared with simpler uniform wall thickness model. In this study Navier-Stokes equations along with elastodynamics equation are coupled through Arbitrary Lagrangian-Eulerian formulation method and solved numerically. Findings demonstrate that the isotropic material model with uniform wall thickness significantly underestimates wall stresses as compared to the anisotropic material model with variable wall thickness. Indeed, results emphasize that considering vessel wall as an anisotropic, heterogeneous (variable thickness) structure estimates much higher wall stresses comparing with isotropic, uniform thickness model. Therefore, given realistic vessel wall structure and the fact that the anisotropic, variable wall thickness model predicts higher wall stresses, it could be a more reliable model to give an accurate estimation to physicians to diagnose the stage of a disease and choosing an appropriate therapeutic procedure.

Over the past few decades, different therapeutic methods for the treatment of intracranial aneurysms have been developed. During recent years, novel standalone intrasaccular Woven EndoBridge (WEB) technique has paved the way for efficient therapy and reduced some deficiencies in prior procedures. Blood hemodynamics plays a crucial role in occurrence and perpetuating of aneurysm; therefore, understanding of relevant parameters can lead to a better treatment and evolution of design. Objectively, this paper has established the first mathematical framework to explore hemodynamic parameters for WEB-treated saccular aneurysms by employing Computational Fluid Dynamics (CFD). Two ideal models of artery — one is suffered by a bifurcation aneurysm at Basilar Artery (BA) and another Posterior Cerebral Artery (PCA) aneurysm — are selected. Simulations are performed for an untreated and three WEB-treated aneurysms by Dual Layer (DL), Single Layer (SL) and Single Layer Sphere (SLS) WEBs. Results demonstrate that, generally, the WEB reduces flow intrusion and circulation inside the aneurysm sac, which leads to lowering WSS; however, the infiltrated flow to the WEB causes slight increase in intrasaccular pressure. Moreover, the numerical results show that the WEB DL reduces velocity and WSS, and elevates pressure inside the sac more than the WEBs SL and SLS. Among the explored WEB models (DL, SL and SLS), by assuming thorough binding at the aneurysm neck, the WEB DL demonstrates much efficient performance in flow diversion from the aneurysm, while despite the different structure of WEBs SL and SLS, they perform similarly.