Numerical analysis of hemodynamic changes in the left atrium due to atrial fibrillation

Atrial fibrillation (AF) disrupts movement of the left atrium (LA) and worsens the vital prognosis by causing thromboembolism. Ultrasound Doppler measurement, phase-contrast magnetic resonance imaging (PC MRI), as well as computational fluid dynamics (CFD) have revealed hemodynamic changes in the LA due to AF, such as stagnation of blood flow in the left atrial appendage (LAA). However, quantitative evaluation of the hemodynamics during AF has not been conducted, and the effects of important AF characteristics, such as a lack of active contraction of the LA (atrial kick) in late diastole and the occurrence of high-frequency fibrillation (>400 bpm) of the atrial wall, on blood flow field and concomitant hemodynamic stresses have not been completely understood. In this study, the effects of the above-mentioned two characteristic phenomena of AF on blood flow and hemodynamic parameters were quantitatively investigated. Based on MRI of a healthy volunteer heart, one healthy LA model and two AF models (one without atrial kick, and one without atrial kick and with high-frequency fibrillation) were constructed to perform hemodynamic analysis, and the computational results were compared. The results revealed that each characteristic phenomenon of AF influenced hemodynamics. Especially, atrial wall movement by high-frequency fibrillation had a large impact on the stagnation of blood flow. The relative residence time (RRT), which is an indicator of stagnation of blood flow, increased in the upper part of the LAA during AF. This result implies that there is a local thrombus-prone site in LAA when AF occurs.