The role of patient specific morphology and contractility of the left atrial appendage on the thromboembolic risk in atrial fibrillation

The vast majority of thrombi that cause ischemic complications in atrial fibrillation originate in the left atrial appendage. The left atrial appendage is an anatomical structure that starts from the left atrium, characterized by a wide morphological variability between individuals. This work analyses simulated hemodynamic for different patient-specific models of the left atrial appendage, using computational fluid-structure interaction studies, modelling the effect of changes in contractility and shape resulting from atrial fibrillation. Three operating conditions were analysed: sinus rhythm, acute atrial fibrillation, and chronic atrial fibrillation. These were simulated on four patient-specific left atrial appendage morphologies, each associated with one of the major morphological variants identified by the common classification: chicken wing, cactus, windsock, and cauliflower. The active contractility of the wall muscle was calibrated on the basis of clinical assessments of the filling and emptying volumes and boundary conditions were imposed on the fluid to replicate physiological and pathological atrial pressures, typical of the different operating conditions. The volume of the left atrial appendage and the shear strain rates were analysed over time and space for the different models. Globally, under conditions of atrial fibrillation, all models were found to be well aligned in terms of shear rate values and expected risk level. Regions of low shear velocity, typically associated with an increased risk of clot, appeared to be promoted by sudden turns and focused on the trabeculae and lobes. These become substantially more pronounced and extensive with atrial fibrillation, especially in acute conditions. This work clarifies the role of active and passive contraction on healthy hemodynamic in the left atrial appendage, analysing the changes produced by atrial fibrillation that produce hemodynamic conditions that promote clot formation. The study indicates that the local topological features of the left atrial appendage are more directly associated with the onset of risk than the global form of the appendage, suggesting that more effective classification criteria should be identified.