Significance of Aortic Valve Insufficiency with Left Ventricular Assist Device: Duration and Regurgitant Flow in a Mock Loop Study

Abstract

In patients with left ventricular assist device (LVAD), aortic valve insufficiency (AI) could occur in longer period during the cardiac cycle, throughout the diastolic and part of the isovolumetric phases. As the result, the current echocardiographic evaluation of AI grade may underestimate the degree of AI in LVAD patients, especially those with significant AI. In this study, we investigated the differences in AI duration and regurgitant volume before and during LVAD supports (Off and On LVAD) using a mock circulatory loop. All measurements were performed using a mock circulatory system with a dilated silicone LV model attached to a HeartMate II LVAD (Abbott Lab), and pressure and flow measured in the LV, LVAD, and aorta. Baseline condition was established as no LVAD condition (Off LVAD setting) which has 17% ejection fraction, 62 bpm heart rate and 65 mmHg systemic pressure. LVAD condition (On LVAD setting) at 8,800 rpm with same ejection fraction, heart rate and systemic resistance (90 mmHg systemic pressure) was established, followed by testing at three AI severity conditions. AI severity was defined as mild, moderate, or severe based on effective regurgitant orifice area. AI conditions were created with small 3-D printed stents, which were nonobstructive to forward flow, but prevented the leaflets from fully closing. AI durations and regurgitant volumes were determined from the calculated backward flow through the aortic valve. With the constant systemic resistance in the On LVAD setting at 8,800 rpm, duration of AI increased by 8.3 % (75 to 83.3%) with mild AI, 5.6% (77.8 to 83.3%) with moderate AI, and 5.6% (77.8 to 83.3%) with severe AI compared to the Off LVAD setting. With the constant systemic resistance in the On LVAD setting at 8,800 rpm, regurgitant volume of AI increased by 0.11 L/min (0.12 to 0.23 L/min, 92%) in mild AI, 0.03 L/min (0.53 to 0.56 L/min, 5.7%) in moderate AI and 0.08L/min (0.78 to 0.86 L/min, 10.3%) with severe AI compared to the Off LVAD setting. This mock loop study demonstrated that AI duration was longer and regurgitant volume through the aortic valve was greater during LVAD support compared to same AI degree before LVAD. This suggests that clinical burden of AI may be underestimated in patients with LVAD.