The effect of timing of the LVAD speed modulation on intraventricular flow patterns. An in-vitro PIV study.

In the past decades, LVADs have become a common therapy for advanced heart failure patients. Despite a lower incidence of in-pump thrombosis, stroke remains the main complication. We hypothesize that the intraventricular flow patterns modified by the LVAD lead to stagnation, platelet activation and thrombogenecity. Pulsatility modes, periodically modulating the LVAD speed, aim to break down stagnation areas in the pump and the left ventricle (LV). However, their effect on flow patterns and risk of stroke is still under investigation. This study investigates the effect on flow patterns of the synchronicity of the pulsatility mode with the LV contraction cycle. 3C-2D velocity fields were obtained from PIV measurements performed in an LV silicone model implanted with an LVAD.  Different delays between the onset of the modulation and peak systole were experimented. This speed modulation showed a strong effect on LVAD flow rate, with lower minimums when the modulation happened during LV relaxation. In this condition, an increased stagnation was also observed from the velocity fields. These results show that the effect of the speed modulation is strongly dependent on native LV contractility, highlighting the need for physiological and LVAD parameters joint optimization to reduce thrombosis.