Intra-left Atrial Flow Changes During the Start of Atrial Fibrillation

In the present study, our aim was to visualise the changes in the left atrial flow during atrial fibrillation (AF)using numerical simulations and an animal experiment. A geometric model of the left atrium (LA) was constructed based on MR images obtained into a computational model created using tetrahedral mesh. A flow simulation was performed using FLUENT. To simulate AF, we added low-amplitude and high-frequency contractions to the sinus rhythm (SR) mode, and subtractedactive contractions while the mitral valve was opening. In a goat model, the intra-left atrial flow was directly visualised with microbubble contrast agents using echocardiography under general anesthesia. The LA was electrically fibrillated during 9 V direct current stimulation of the left atrial wall. SR was recovered soon after the stimulation was terminated. The results of the computer simulation showed that, a small rotational flow present during ventricular diastole disappeared in the AF model. A large number of eddies were evident along the superior left pulmonary vein. During ventricular systole, although a vortex was formed, the density of the streamlines was lower than that observed in the SR model. In the animal experiment, the flow was obscured by local eddies when AF occurred. Some microbubbles remained at the junction of the left atrial body and pulmonary vein. Compared with the SR, the atrial vortices became obscured by an increased number of local eddies along the superior left pulmonary vein when AF was present, after which the intra-left atrial flow became congested.