Thromboembolism in the left atrial appendage under atrial fibrillation and after sinus rhythm restoration: a computational study

The impact of recovered atrial dynamics on pre-existing thrombi within the left atrial appendage (LAA) remains a poorly understood phenomenon, despite its potential clinical implications during spontaneous or induced restoration of sinus rhythm (SR) in patients with atrial fibrillation (AF). While computational studies have investigated thrombus formation during AF, none have examined the fate of established thrombi following SR restoration. This work addresses that gap by modelling thrombus formation and embolisation in the LAA under AF and after the return to normal rhythm. A meshless particle-based thrombus model was employed to simulate the formation of clots in a patient specific LAA, under AF conditions, and then analyse haemodynamic changes and thrombus behaviour under persistent AF and recovered SR. Results show that SR restoration profoundly modifies thrombus growth and erosion compared with AF. The resumption of atrial contractility increases local shear strain rate, especially in the proximity of anatomical features such as knees and trabeculae, driving progressive thrombi erosion and detachment from secondary lobes. These processes are amplified during the atrial systolic phase, when mechanical forces promote thrombus detachment. Conversely, if AF persists, the associated reduction in blood wash-out and shear stresses promote thrombus growth. Clots located in regions of higher stagnation remain stable under both restored SR and persistent AF. By providing the first direct computational comparison of thrombus behaviour in AF and after SR restoration, this work offers novel insights with potential to inform personalised therapeutic strategies.