Poster T12 - 3-D Flow Visualization of Vortex Formation in the Left Ventricle

Introduction: Left Ventricular assist device (LVAD) redirects blood flow from the apex of the left ventricle (LV) into the ascending aorta, introducing flow patterns linked to thrombosis and areas of stagnation. Flow in the native heart is characterized by the formation of a large diastolic vortex in the LV assisting in blood circulation to minimize kinetic energy losses and cardiac work. Our previous studies found that heart failure in patients results in early decay of vortex circulation and decreased vortex strength but were limited to a single 2-D imaging plane, resulting in a velocity field that featured two counter-rotating vortices that were cross-sections of the vortex ring. By switching to a 3-D imaging plane, the vortex structure and geometry can be further characterized and extracted to compute vortex properties including circulation, kinetic energy and size. Therefore, the aim of this study was to quantitatively evaluate the 3-D velocity field and visualize vortex formation in the LV using a cardiac mock circulatory loop.

Materials and

Methods: A mock circulatory loop consisting of a silicone left ventricle, HeartMate 2 LVAD and Tygon tubing. Two bioprosthetic valves are placed in the mitral and aortic position. Flow and pressure sensors were placed on the vessels and aorta and measured at 200Hz using LabChart software. Three-dimensional velocity in the left ventricle was measured with particle image velocimetry (PIV). 63-micron fluorescent particles were injected into the circulatory loop and imaged with the LaVision Mini-shaker camera and an LED light for 3 sec periods. LaVision DaVis PIV software processing algorithms Shake-the-box and Tomo-PIV were used to track the particles as they entered the left ventricle.
Both LVAD speeds, 9000rpm and 10000rpm, were tested with the presence of a cardiac simulator. For the 2 conditions studied, mean aortic pressure was maintained at 80 mmHg to mimic patient conditions. The velocity field shows the intact vortex ring in 3-D, which can be isolated using the Q-criterion as a measure of the excessive rotation rate and strain rate using Matlab. The threshold Qth was determined to be 1, with points indexed at Q>Qth characterized as belonging to a vortex. A workflow was designed to first identify and extract the time-varying vortex, and then further characterize the vortex property waveforms.

Results, Conclusions, and Discussions: Vortex rings between the 2 LVAD conditions were observed to be larger with the higher LVAD speed of 10000rpm during late diastole when compared to the 9000rpm speed. All LVAD speeds tested produced coherent vortex structures. However, a comparison of the isosurfaces for these conditions show that the vortex ring grows more asymmetric as speed increases. The results of these studies suggest that increased LVAD support may assist with vortex formation. The vortex ring stores momentum and conserves energy during normal LV flow. Therefore, a strengthened vortex structure may aid in this conservation of energy and overall cardiac output. When patients have heart failure with weakened pulsatility, their vortex ring becomes less efficient and the heart muscle has to overcompensate to maintain the same activity level. Over time, this demand taxes the heart and initiates pathological remodeling, leading to a decline in health and potential heart failure.

Acknowledgements (Optional):