Characteristics of intra-left atrial flow dynamics and factors affecting formation of the vortex flow – analysis with phase-resolved 3-dimensional cine phase contrast magnetic resonance imaging.

Background: The intra-left atrial (LA) blood flow from pulmonary veins (PVs) to the left ventricle (LV) changes under various conditions and might affect global cardiac function. By using phase-resolved 3-dimensional cine phase contrast magnetic resonance imaging (4D-Flow), the intra-LA vortex formation was visualized and the factors affecting the intra-LA flow dynamics were examined.

Methods And Results: Thirty-two patients with or without organic heart diseases underwent 4D-Flow and transthoracic echocardiography. The intra-LA velocity vectors from each PV were post-processed to delineate streamline and pathline images. The vector images revealed intra-LA vortex formation in 20 of 32 patients. All the vortices developed during the late systolic and early diastolic phases and were directed counter-clockwise when viewed from the subjects' cranial side. The flow vectors from the right PVs lengthened predominantly toward the mitral valves and partly toward the LA appendage, whereas those from the left PVs directed rightward along the posterior wall and joined the vortex. Patients with vortex had less organic heart diseases, smaller LV and LA volume, and greater peak flow velocity and volume mainly in the left PVs, although the flow directions from each PV or PV areas did not differ.

Conclusions: 4D-Flow can clearly visualize the intra-LA vortex formation and analyze its characteristic features. The vortex formation might depend on LV and LA volume and on flow velocity and volume from PVs.