• Atrial Fibrillation
• Computational Analysis
• Computational Fluid Dynamic simulations
• Hemodynamics
• Left Atrial Appendage
• Left Atrium
• Parametric Design
• Thrombus Formation

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia, affecting more than 33 million people worldwide. It is a complex heart disease, which causes a disorder in the heart's electrical system and can lead to serious complications; in fact, is related to the risk of stroke and ischemic attacks, which are caused, in 90% of cases, by thrombi that form in the left atrial appendage (LAA), a muscular sac that protrudes from the left atrium (LA). The external appearance of the LAA is that of a finger-shaped, tubular, long, narrow and curved, slightly flattened structure, which internally has a usually well-defined oval orifice, called ostium. The appearance of the appendage varies significantly in shape, size and orientation, compared to the adjacent heart structures, and it may have different lobes, or protrusions of the main body, in a variable number according to the specific patient. Recent studies have shown that LAA can be classified into four main morphologies: "chicken wing", "cactus", "windsock" and "cauliflower".
The aim of this thesis project is to perform a computational analysis of the parametric left atrial appendage, to study the risk of thrombus formation. For the definition of the working domain, an idealized and simplified parametric CAD geometry was designed with the CAD software Solidworks; the model consists of the entire LA, including pulmonary veins and mitral orifice, and LAA. The model created guarantees the ability to modify multiple parameters of the geometry and, therefore, to develop a one-by-one influence analysis of all the parameters involved; the goal, in the end, was precisely to highlight the parameters that most influence hemodynamics, analyzing the impact of changing a single parameter at a time. The parameters of the appendage that have been modified include the length and size of the distal part, the angle between the distal and proximal parts, the number and position of secondary lobes. The variation of these parameters has given rise to 5 different models, resembling the different LAA morphological classes, according to the current clinical classification. Moreover, as an additional parameter influencing the hemodynamics of the appendage, also the size of the main LA chamber was changed.
After having built the geometry, all the models were meshed with the ANSA pre-processor program; a volume mesh with tetrahedral and hexahedral elements was created.
A CFD study was conducted to evaluate the trend of blood fluid dynamic through the atrium and appendage, especially looking at the fluid velocity. The analysis was done with Ansys Fluent under transient conditions. Regarding the boundary conditions, the pulmonary veins were chosen as the outlet with a constant pressure. A velocity profile from literature was imposed at the mitral valve as inlet condition; both condition of sinus rhythm (SR) and AF were simulated. The fluid was considered Newtonian and incompressible. For all the CFD analysis, the velocity results were analysed.
To complete the project, a standalone structural analysis of the atrium and appendage wall was carried out, with the Ansys Mechanical software. As for the characteristics of the material, it was defined as a linear elastic material according to the physiological properties of the heart wall. A further feature has been added: the material is defined as orthotropic with respect to temperature and a coefficient of thermal expansion has been chosen; a Thermal condition was applied to simulate the movement of the wall, imposing a thermal gradient. The computational results were analysed in terms of wall displacements and strains during the cardiac cycle, both at the level of the atrium and LAA; the volume variation of the atrium and appendage and the shape variation of the orifice were also evaluated.
In conclusion, the aim of this thesis was to highlight the effect of the atrium and LAA parameters variation on the blood flow pattern and to analyse the effect that the movement of the heart wall produces during the cardiac cycle. This was done with the final scope of developing a tool capable of analysing, qualitatively and quantitatively, the parameters that have the greatest influence on thrombus formation and, therefore, provide an additional tool for protecting the health of patients most at risk.