S22 - Pump speed modulation encourages aortic root flow in the LVAD-assisted heart

Introduction: : Aortic valve opening (AVO) during LVAD support has been associated with reduced complications, e.g. thrombosis. Pump Speed Modulation (PSM) consists of a brief drop in LVAD speed which lowers the transvalvular pressure and allows flow to pass through the aortic valve, washing the aortic root. The purpose of this study was to directly measure the ability of PSM to produce AVO and flow in a mock circulatory loop (MCL).

Materials and

Methods: : Transparent versions of a patient derived aorta with a 60° outflow graft were 3D-printed and attached to a soft silicone rubber ventricle with bioprosthetic heart valves in the mitral and aortic positions as shown in Figure 1. The LVAD was inserted through the apical sleeve until it was flush with the LV apical border and secured with zip ties. The assembly was immersed in a water-filled tank attached to a Windkessel model of the systemic circulation and filled with a viscosity-matched blood analog of 40% glycerol and water. Pressure and flow were measured in several locations for various PSM conditions. A video camera recorded valve motion during the studies. AVO area and duration were determined from image analysis of the recorded video. Three-dimensional particle image velocimetry (PIV) was used to visualize the LV flow field. 60-m fluorescent particles were added to the solution and imaged with the LaVision Mini-shaker camera and LED light source for 10s sec periods at 650 Hz. Tomographic analysis yielded the time-resolved velocity field for each condition.

Results, Conclusions, and Discussions:: The MCL heartbeat (68 bpm) combined with the LVAD produced a QLVAD of 5.4 L/min and PAo of 75.1 mmHg at the baseline LVAD speed which resulted in no AVO. When the speed was reduced, the valve opened once for a duration of 0.04 ± 0.01s to a maximum of 11.21 ± 1.84 mm2 which permitted 18 ml of flow through the aortic valve. For a PSM cycle of 3s at baseline speed and 1s at low speed, the valve opened once every 4-5 cycles. This sequence was repeated with each speed modulation cycle, resulting in a net AV flow of 0.3 ± 0.04 L/min. The 3D PIV field confirms flow through the aortic valve during the low LVAD speed as shown in Figure 2. At baseline speed, the aortic root exhibits low velocity or stasis, which predisposes thrombus risk. When the LVAD speed is reduced during PSM (red boxes) the valve opens and flow passes through the valve and into the aortic root. Our findings demonstrate that AVO can be achieved using PSM, with a cycle of 3 seconds at baseline speed and 1 second of reduced speed which enables regular AV flow, thereby improving washout and reducing stagnation in the aortic root.

Acknowledgements and/or References (Optional):: The authors gratefully acknowledge funding support from Evaheart, Inc. for this study.