Effect of Timings of the Lavare Cycle on the Ventricular Washout in an In Vitro Flow Visualization Setup

Abstract

Left ventricular assist devices inherently alter the intraventricular flow field and create areas of blood stasis with potential thrombus formation. The Lavare cycle of the Medtronic Heart-Ware HVAD was designed to improve ventricular washout. This study aims to evaluate its effects on ventricular washout in a pulsatile in vitro setting with a focus on the timing of pump speed changes. Ventricular flow fields were obtained via particle image velocimetry in two modes: With constant left ventricular assist devices speed and with the Lavare cycle applied. The start of the Lavare cycle was shifted over an entire cardiac cycle, and ventricular washout was evaluated based on velocity fields, kinetic energy, and normalized pulsatility of flow fields. The ventricular flow fields showed dependence on the timing of the Lavare cycle and interaction between speed changes and the cardiac phase. Higher apical velocity was observed for speed decreases at the late E wave and for increases at mid systole by 29% (P = 0.002) and 61% (P < 0.001), respectively. Mean apical kinetic energy for these phases also increased by 21% (P = 0.0013) and 46% (P < 0.001). The Lavare cycle generally promotes higher apical washout and can specifically generate further improved washout if speed steps are applied at the correct timing on the cardiac cycle.

In Vitro Investigation of the Effect of the Timing of Left Ventricular Assist Device Speed Modulation on Intraventricular Flow Patterns

“…Additionally, lower stagnation is observed when the MV jet does not directly enter the cannula but rather expands and promotes flow along the LV walls. A similar flow topology has also been observed in previous studies using 2D echo color Doppler velocimetry in vivo , 25 ex vivo , 23 in vitro , 17,27 and in silico . 34 Consequently, optimizing LVAD speed to the patient, allowing the MV jet to fill the LV, is crucial to reduce high stagnation areas.…”

“…Despite studying different speed modulation cycles (0.35 s here for the HeartMate 3, vs . 3 s for the previous HVAD study), the present and previous 23 studies both suggest that the synchronization of LVAD speed modulation with remaining LV contractility, varying over time and requiring a closed-loop feedback control, via ECG or pressure sensors, would greatly improve LV/LVAD washout characteristics.…”

“…22,27,28 Studies have focused on the effect of the 3 s HVAD speed modulation 17,24 and its timing on LV flow patterns. 23 Since these speed modulations are not synchronized with the patient’s LV contraction, 29 an in vitro study showed that the electrocardiogram (ECG) timing of the 3 s Lavare cycle influences LVAD flowrate and flow patterns. 23 However, no study has assessed the effect on LV flow patterns of the timing of the 0.35 s Heartmate 3 speed modulation.…”

Use of 3D anatomical models in mock circulatory loops for cardiac medical device testing

“…11,25,36,38,45,54,63,64,[67][68][69][70]73 In these cases, ventricular blood flow was simulated either as a generic sinusoidal waveform or using pulsatile pumps that could change the stroke volume, heart rate and systolediastole ratio. More sophisticated MCLs considered either part 12,[16][17][18][19]22,23,[30][31][32][33][34][35]46,48,52,60,61,65,66,74 or all the cardiovascular system 13,14,29,39,40,49,50,53,75 by including compliance chambers and variable resistances or, in few cases, by simulating it computationally.…”

“…Given the transparency of the 3D model, the same set‐up was also used to study the flow in the ventricular chamber with particle image velocimetry (PIV). Wong et al 33 and Khienwad et al 34 developed similar MCLs to investigate respectively the vortex formation in a dilated ventricle connected to a HeartMate III (Abbott, USA) and the flow pattern during Lavare cycle in a dilated ventricle connected to an HVAD (Medtronic, USA) with a PIV system.…”