the incidence of thrombosis for LVAD patients
PRESENTING AUTHOR FULL NAME: Fanette Chassagne
INSTITUTION: Department of Mechanical Engineering and Division of Cardiology, University of Washington, Seattle, WA, USA
ADDITIONAL AUTHORS NAMES, AS TO BE PUBLISHED: Marissa Miramontes, Venkat Keshav Chivukula, Jennifer Beckman, Claudius Mahr, Alberto Aliseda
BACKGROUND/PURPOSE: Over the past decade, the use of Left Assist Ventricular Device for patients with advanced heart failure has increased. Despite advances in LVAD design, thromboembolic events remain the primary cause of mortality and morbidity. The objective of this study is to assess how the hemodynamics in a Left Ventricle (LV) implanted with a LVAD depend on LVAD speed and patient blood pressure, and how certain combinations of patient/LVAD conditions could increase the risk of thromboembolic events.
METHOD: Particle Image Velocimetry (PIV) measurements are performed in a patient-specific LV phantom implanted with a commercially-available LVAD. A blood-mimicking fluid, which index of refraction is matched to the silicone phantom, is used in the LV for varying preload and afterload conditions, as well as varying LVAD speeds. Measurements during a pulsatile cycle where the LVAD speed is decreased and then increased are also analyzed to understand the impact of full ventricle hemodynamics versus intra-pump hemodynamics.
RESULTS: The measured velocity fields in the LV show stagnation and recirculation that predisposes to the formation of intraventricular thrombus. These stagnation zones are located in the region between the apex and the LVAD inflow cannula, and close to the aortic valve, which remains closed in all these experiments. Preload tended to modify the distribution of the stagnation and recirculation zones, leading to increased mixing in the LV. However, the variation of the LVAD speed (during the pump pulsatility cycle) is shown to have limited effect on ventricular mixing, for a constant pre-load and peripheral resistance. As the flowrate through the pump depends on afterload, increasing pump speed while keeping the peripheral resistance constant, with limited capacitance in the system as corresponds to heart failure patients, leads to an increase in Mean Arterial Pressure, and consequently a reduction in flowrate compared to the nominal increase from the increased pump speed.
CONCLUSION: The flow patterns observed in this study help explain the incidence of thrombosis for LVAD patients, even if implanted with third generation pumps.