Aortic Insufficiency during LVAD Support: A Mock Loop Study

Abstract

Purpose Aortic valve (AoV) insufficiency (AI) is a serious complication in more than 20% of Left Ventricle Assist Device (LVAD) patients within 12 months of LVAD implantation. Normal AoV have developed AI following long-term LVAD support,which has been associated with a significant reduction in LVAD patient survival. During LVAD support, the AoV pressure difference is increased, which reduces systolic opening and worsens regurgitant flow through an incompetent valve. The goal of this study was to measure the effect of LVAD support on intraventricular flow during AI. Methods The velocity field was measured in the midplane of a dilated silicone LV model attached to a rotary LVAD (Abbott Labs, Chicago IL) in a mock circulatory loop. A Pre-LVAD without AI condition (BL) of 20% ejection fraction was established, followed by testing at three LVAD speeds. AI was created with a small 3-D printed stent which was nonobstructive to forward flow but prevented the leaflets from fully closing. LV and aortic pressure, and LVAD and distal aortic flow, were recorded. Results At the Pre-LVAD BL condition, the mean aortic pressure was 63 mmHg and the cardiac output was 2.3 L/min; AI maintained a similar pressure but reduced flow to 1.8 L/min producing a 32% regurgitant fraction (mild-moderate AI). At an LVAD speed of 6400rpm, total systemic flow was 4.3 L/min and 3.1 L/min for BL and AI, respectively, and LVAD flow was 4.2 and 3.6 L/min, producing a 45% regurgitant fraction (moderate-severe AI). The reduction of systemic flow was accompanied by higher LVAD flow, confirming that a regurgitant loop was present. Net forward flow through AoV during BL decreased progressively by 23%, 12% and 0.5% for 4800, 5400, and 6400rpm respectively. AI reduced forward flow and increased backward flow, such that net forward flow was 0.5%, -14%, and -17% at 4800, 5400 and 6400rpm. The AI vena contracta width increased from 2.3 to 3.4 mm as LVAD speed increased. Conclusion Overall, the results showed that an initially mild level of AI worsened with LVAD support prior to any remodeling, simply due to the altered biomechanics of the AoV. These findings provide a foundation for new strategies that can restore AoV biomechanics and reduce the impact of AI on patients with LVAD support.