In Vivo Assessment of a Rotary Left Ventricular Assist Device‐induced Artificial Pulse in the Proximal and Distal Aorta

Abstract

The increasing clinical use of rotary left ventricular assist devices (LVADs) suggests that chronic attenuation of arterial pulse pressure has no clinically significant detrimental effects. However, it remains possible that modulating LVAD rotor speed to produce an artificial pulse may be of temporary or occasional benefit. We sought to evaluate a pulse produced by a continuous-flow, centrifugal pump in an ovine thoracic and abdominal aorta. Both ventricles of an adult sheep were resected to eliminate all native cardiac contributions to pulsatility, each replaced by a continuous-flow Thoratec HeartMate III blood pump (Burlington, MA, USA). An LVAD-induced pulsatile flow was achieved by sharply alternating the speed of the magnetically levitated rotor of the left pump between 1,500 rpm (artificial diastole) and 5,500 rpm (artificial systole) at a rate of 60 bpm at a "systolic" interval of 30%. A catheter was advanced from the ascending aorta to the iliac bifurcation via the ventricular assist device outflow graft for pressure measurement and data acquisition. The mean LVAD-induced pulse pressures were 34, 29, 27, and 26 mm Hg in the ascending, thoracic, and abdominal aorta, and the iliac bifurcation, respectively. The maximum rate of pressure rise (deltap/deltat) was between 189 and 238 mm Hg/s, approaching that of the native pulse, although the energy equivalent pressure did not exceed the mean arterial pressure. The HeartMate III's relatively stiff speed control, low rotor mass, and robust magnetic rotor suspension result in a responsive system, enabling very rapid speed changes that can be used to simulate physiologic pulse pressure and deltap/deltat.

Design Rationale and Preclinical Evaluation of the HeartMate 3 Left Ventricular Assist System for Hemocompatibility

“…The large gaps enable the sharp speed changes employed by the HM3 artificial pulse. 17,18 By alternating the speed every 2 seconds, changing blood flow within the LVAD precludes the organization of recirculation and stasis zones. The role pulsatility plays in von Willebrand factor degradation leads to a hypothesis that gastrointestinal bleeding, hemorrhagic stroke, and epistaxis may be reduced by reducing effects on blood proteins and reducing platelet activation, although clinical experience will be required to substantiate that.…”

High-frequency operation of a pulsatile VAD – a simulation study

“…The importance of a pulsatile blood flow is also reflected in attempts to augment pulsatility on tVADs by varying the pump speed for the newer generation of VADs such as the HeartMate III (St. Jude Medical, Inc., St. Paul, MN, USA). Several groups have published studies about speed modulation for tVADs currently available and in development [5,9,23], as well as algorithms designed to restore some form of pulsatile flow [16].…”

Numerical Optimal Control of Turbo Dynamic Ventricular Assist Devices

“…A number of approaches for realizing a speed modulation of tVADs has been analyzed earlier. A square-wave speed profile was applied by Bearnson et al [11] and Bourque et al [12] to increase arterial pulse pressure, where the speed profile was not synchronized to the cardiac cycle. Different types of speed profiles, synchronized to the natural cardiac cycle, have been applied in silico and in vitro to analyze their influence on perfusion, pulse pressure and ventricular unloading [13][14][15][16][17][18].…”