Analyses of intra-left atrial vortex and flow dynamics from pulmonary veins to left ventricle using phase-resolved three-dimensional cine contrast Magnetic Resonance Imaging (4D-Flow MRI)

Background: The blood flow from pulmonary veins (PVs) to left ventricle (LV) through left atrium (LA) changes under various conditions, and affects global cardiac function and thrombogenesis. We aimed to clarify the velocity vectors in LA and the blood particles movement from PVs to LV using 4D-Flow MRI. Methods: Thirty two patients with and without organic heart diseases (59±14 years, mean±SD) underwent 4D-Flow with routine MRI and echocardiography. We set a plane traversing each exit of PV, and the velocity vectors in LA were post-processed to delineate streamline images (Fig. A). The percentage of blood particles that reached LV (%LV particles) was also analyzed during a cardiac cycle (Fig. B: initial phase and Fig. C: last phase). Results: (1) The streamline images revealed intra-LA vortex formation in 20 patients but did not in 12 patients. All the vortices showed characteristic counter-clockwise flow patterns in the cranial view. (2) The LV end-diastolic and end-systolic volume, and the LA volume were less in patients with vortex than in those without vortex (104±34 vs. 155±67 ml, 46±28 vs. 88±59 ml, and 41±19 vs. 75±31 ml, p<0.01, respectively). (3) The %LV particles in patients with vortex was higher than that in patients without vortex (14% vs. 2%, medians, p<0.01). The %LV particles from right PVs was also higher than that from left PVs in patients with vortex (22% vs. 5%, p<0.01), whereas it did not differ in patients without vortex (2% vs. 0%, p=ns). ![Figure][1] Conclusions: 4D-Flow MRI can visualize the intra-LA vortex formation and flow dynamics from PVs to LV. The vortex formation may be dependent on the LV and LA volume, and may affect the flow dynamic from PVs to LV. The blood flow from left PVs seems to be more stagnant within LA than that from right PVs. [1]: pending:yes