# Computational Flow Dynamic Analysis in Left Atrial Appendage Thrombus Formation Risk: A Review
## 1 Introduction  
The left atrial appendage (LAA), originating from the left atrium during fetal development, is described as a long, tubular, hooked structure with variations in size, shape, and volume [1]. The morphology of the LAA is highly diverse from patient to patient and is typically divided into four distinct types based on the structure it evokes: \"Chicken wing\" is the most frequent morphology (48%), followed by \"Cactus\" (30%), \"Windsock\" (19%), and \"Cauliflower\" (3%) [2]. Nevertheless, the classification is frequently open to misinterpretation and is reliant on the imaging plane. The volume size of LAA also varies significantly with the morphology [3]. Due to the LAA's characteristics mentioned above, its effect on left atrial (LA) flow is difficult to evaluate. Literature reveals that LAA is the most prevalent region for thrombus formation, increasing the risk of stroke in patients with atrial fibrillation (AF) [4; 5; 6]. AF is an electrophysiological pathology with irregular atrial beats, affecting between 1% and 2% of the general population, approximately 8% of people over 80 years old [7; 8]. It has been identified as the principal cause of thromboembolic events, such as stroke and vascular dementia [9]. Consequently, there is an urgent need for more effective strategies for identifying and preventing thromboembolic events in AF patients [10]. AF can result in electrical,structural, and contractile remodeling [11; 12; 13]. Atrial expansion, LA dysfunction, and inadequate atrial contraction result in thrombus development, especially in the LAA [11; 12; 13]. Furthermore, blood stagnation frequently occurs in the LAA since the blood flow velocity drops dramatically [1; 6; 13]. Consequently, LAA has received interest as a therapeutic target for preventing thrombosis, particularly in AF patients. Several therapies are currently available to prevent thrombus formation: (i) oral anticoagulation (i.e., warfarin and direct oral anticoagulants) [14; 15; 16]; (ii) LAA surgical exclusion [17]; and (iii) LAA percutaneous occlusion [18; 19]. However, all of these options have drawbacks that restrict their practice and effectiveness, such as the possibility of hemorrhagic consequences in the case of anticoagulation therapy [14; 15; 16] and the risks associated with invasive and transcatheter procedures (for example, vascular injury, air-embolic events, and peri-device leaks) [17] for surgical and percutaneous treatments, respectively [18; 19]. Although numerous treatments have been proven to reduce the risk of thrombotic events, research has shown a significant residual risk [1; 13; 20; 21]. Due to the diverse morphological factors, such as shape, size, and LAA volume, the reported approaches may fail. In addition, researchers have recognized hemodynamic parameters such as velocity, vorticity, and shear stress as thrombosis predictors [22; 23]. Blood flow within the left atrium has currently been evaluated using several methodologies. Transesophageal echocardiography (TEE) can measure the speed at which the LAA empties. However, in clinical practice, TEE cannot accurately measure other hemodynamic parameters, especially in the thrombus regions, since it can either incorrectly label muscles as thrombi or misidentify thrombi hidden in one of the lobes [24; 25]. Consequently, an improved strategy must be developed. In clinical research, 4D magnetic resonance imaging (MRI) is a cutting-edge technology that provides more information about 3D blood flow during the cardiac cycle. However, resolution limitations make it difficult to obtain blood flow parameters precisely. In addition, scan times are relatively long [26; 27]. Nowadays, computational modeling can provide a detailed knowledge of the mechanisms and effects of AF [28; 29]. Personalized computer models can enable the modeling of fibrosis, atrial fiber orientation, and wall thickness heterogeneity's influences on AF within realistic geometry and tissue properties [30; 31].