We evaluated mean, peak, and instantaneous pressure gradients across the outflow conduit in a pulsatile mock circulation loop which incorporated Heartware HVADs for left ventricular (LV) and right ventricular (RV) support. Steady-state 50 Hz measurements of left ventricular assist device (LVAD) flow (Q) and pressures within the proximal and distal outflow conduit were obtained at varying pump speed, LV contractility, hematocrit (HCT), heart rate (HR), and conduit diameter and length. Experiments were conducted using polyvinyl chloride (PVC) tubing and results confirmed in HVAD Gelweave conduit. Conduit diameter was negatively and nonlinearly associated with mean and peak gradient in both the PVC and HVAD conduits. There were no significant differences between the PVC and HVAD conduits in terms of mean Q, systolic dQdt, mean conduit gradient, or peak gradient. Across the 10 mm HVAD conduit, mean gradient correlated linearly with mean Q, systolic dQdt, HCT, and conduit length (r2 = 0.91), whereas peak gradient correlated with mean Q, systolic dQdt, and conduit length (r2 = 0.93). A nonlinear model to determine instantaneous gradient was highly predictive (r2 = 0.83) across a range of pump and circulatory conditions. In summary, hemodynamically significant pressure gradients are observed across the LVAD outflow conduit under physiologic conditions, which may result in diminished pump flow.
From the *St Vincent’s Hospital, Sydney, New South Wales, Australia
†University of New South Wales, Sydney, New South Wales, Australia
‡Victor Chang Cardiac Research Institute, Sydney, New South Wales, Australia.
Submitted for consideration September 2018; accepted for publication in revised form January 2019.
Disclosure: The authors have no conflicts of interest to report.
Christopher S. Hayward has received research funds from Medtronic HeartWare Inc. unrelated to the current study. This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.
Correspondence: Christopher S. Hayward, Cardiology Department, St Vincent’s Hospital, 390 Victoria Street, Darlinghurst, NSW, 2010 Australia. Email: firstname.lastname@example.org.