The Impact of Pump Speed and Blood Pressure Optimization on Severe Aortic Valve Insufficiency with Left Ventricular Assist Device: A Mock Loop Study

Abstract

It is cumbersome to medically optimize the RPM setup and afterload adjustment for patients with significant aortic valve insufficiency (AI) with left ventricular assist device (LVAD). Limited amount of information is available regarding the optimal RPM setting or afterload adjustment without adverse effect on the degree of AI. All measurements were performed using a mock circulatory system with a dilated silicone LV model attached to a HeartMateII LVAD (Abbott Labs). Baseline condition was established with 17% ejection fraction, 62 bpm heart rate, LVAD set at 8,800rpm pump flow and 90 mmHg systemic aortic pressure, followed by testing at 8,800 and 9,200 rpm, and two systemic aortic pressure conditions (90 and 80 mmHg at 8,800 rpm). Severe AI was created with a small 3-D printed stent which was nonobstructive to forward flow but prevented the leaflets from fully closing. LVAD, aortic valve and systemic flow were recorded in each situation. Q ratio was calculated with LVAD flow/systemic flow, which represented an efficiency of LVAD flow contribution to the systemic flow. With the constant circuit afterload at 90mmHg, an RPM increase from 8,800 RPM to 9,200 resulted in systemic flow increase by 21% (2.27 to 2.74 L/min) with a 16% increase in LVAD flow (3.09 to 3.58 L/min), similar aortic valve flow (-0.82 to -0.84 L/min) and improvement in Q ratio (1.36 to 1.31). The regurgitant flow was similar in 8,800 vs. 9,200 (-0.86 vs. -0.83 L/min) in the severe AI setting. With the constant RPM at 8,800, an afterload reduction by 10 mmHg resulted in an increase of the systemic flow by 28% (2.27 to 2.91 L/min) with a LVAD flow increase of 14% (3.09 to 3.52 L/min), aortic valve flow increase of 23% (-0.82 to -0.61 L/min) and improvement in Q ratio (1.36 to 1.21). The alteration in the regurgitant flow was minimal between 90mmHg vs. 80mmHg afterload (-0.86 to -0.81 L/min). Both RPM increase and afterload reduction increased systemic flow and LVAD flow with improved Q ratio. The regurgitant flow stayed constant either with RPM increase or afterload reduction with the fixed regurgitant valve area. This mock-loop study suggests that both afterload reduction and RPM increase should improve systemic flow without increasing the degree of AI after LVAD implant.