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, U.S.A.). An LVAD-induced pulsatile flow was achieved by sharply alternating the speed of the magnetically levitated rotor of the left pump between 1500 rpm (artificial diastole) and 5500 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 (δp/δt) 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 δp/δt.