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Description
Left ventricular assist devices (LVADs) are mechanical pumps that are surgically attached to the heart and aorta. Clinical studies have demonstrated that LVADs improve patient health and quality of life, and dramatically reduce the mortality of cardiac failure patients. During periods of high LVAD support, blood flow occurs entirely through the LVAD, the aortic valve is continuously closed, and the heart operates in series with the pump. With sufficient intrinsic contraction, the heart and the LVAD operate in parallel. Both of these conditions alter the characteristic flow pattern in the left ventricle. In the presence of implanted medical devices: stagnation areas and other abnormal flow patterns are associated with thrombosis. A quantitative understanding of flow field patterns in the left ventricle of LVAD patients will advance the model as well as surgical integration of these devices' next generation towards thrombus prevention. Previous studies of normal healthy hearts have observed a large diastolic vortex that channels the transit of blood towards the aortic valve. This vortex is attenuated in cardiac dysfunction and heart failure patients. Our in vitro cardiac simulator studies have shown that the addition of a continuous flow LVAD modifies the normal intraventricular flow pattern by increasing the extent of the stagnation regions and disrupting the formation of the healthy diastolic vortex. In this study, we are validating these findings with clinical measurement. The ventricular 2D real time resolved velocity field in LVAD patients is measured before and after LVAD implantation using novel ultrasound flow imaging modalities and engineering analysis. The effect of these flow patterns on patient status are assessed by correlating the properties of the LV vortices and stagnation regions with clinical observations of thrombus from echocardiography or explanted heart pathology. Our result show an agreement with previous in vitro studies, vortex formation is dramatically altered by the LVAD, which results in low flow velocities and high blood residence time near the outflow tract. Vortex circulation and kinetic energy reflect an overall improvement in function with the LVAD, but also provide further evidence that LVAD introduces an additional risk for thrombus formation. Ventricular velocity field measurements, which provide a quantitative basis for thrombi diagnosing, vortex properties, and blood residence time can be served as thrombosis indicated markers. By understanding the LV fluid dynamics during LVAD supports, researchers will able to generate new models to estimate thrombus extent and location.
