Interaction of a Transapical Miniaturized Ventricular Assist Device With the Left Ventricle: Hemodynamic Evaluation and Visualization in an Isolated Heart Setup

Abstract

New left ventricular assist devices (LVADs) offer both important advantages and potential hazards. VAD development requires better and expeditious ways to identify these advantages and hazards. We validated in an isolated working heart the hemodynamic performance of an intraventricular LVAD and investigated how its outflow cannula interacted with the aortic valve. Hearts from six pigs were explanted and connected to an isolated working heart setup. A miniaturized LVAD was implanted within the left ventricle (tMVAD, HeartWare Inc., Miami Lakes, FL, USA). In four experiments blood was used to investigate hemodynamics under various loading conditions. In two experiments crystalloid perfusate was used, allowing visualization of the outflow cannula within the aortic valve. In all hearts the transapical miniaturized ventricular assist device (tMVAD) implantation was successful. In the blood experiments hemodynamics similar to those observed clinically were achieved. Pump speeds ranged from 9 to 22 krpm with a maximum of 7.6 L/min against a pressure difference between ventricle and aorta of ∼50 mm Hg. With crystalloid perfusate, central positioning of the outflow cannula in the aortic root was observed during full and partial support. With decreasing aortic pressures the cannula tended to drift toward the aortic root wall. The tMVAD could unload the ventricle similarly to LVADs under conventional cannulation. Aortic pressure influenced central positioning of the outflow cannula in the aortic root. The isolated heart is a simple, accessible evaluation platform unaffected by complex reactions within a whole, living animal. This platform allowed detection and visualization of potential hazards.

Ventricular Flow Field Visualization During Mechanical Circulatory Support in the Assisted Isolated Beating Heart

“…The apparent low velocities further substantiate the connection between no aortic valve opening and prevalence of thromboembolic events, 8,13,36,37,46 which was also demonstrated in other experimental and simulation studies. 33,43,45,52 To prevent thrombus formation in these regions, LVAD research has focused on periodic or synchronous pump speed changes 21,29,32,52,55 to promote aortic valve opening and minimize potential stagnation areas within the ventricle and the pump. 21,29,32,55 However, the required amplitude, frequency, and clinical applicability of these speed changes to ensure proper washout in the LVOT remains unknown.…”

Dynamic measurement of centering forces on transvalvular cannulas

“…Additional aspects like the movement of the cannula because of systolic ejection, cannula movement caused by the cardiac contraction, or aortic motion as well as effects of connected pumps to the cannula (eg, Impella) were not measured in this setup. However, for a specific transvalvular VAD the dynamic interaction and the pressures necessary to center the transvalvular cannula were investigated previously in an isolated heart setup . Therefore it might be important to measure the forces for specific configurations and devices separately.…”

“…However, below physiologic low aortic pressures (~25 mmHg), the cannula touched the wall and the force applied by the cusps was not sufficient to allow centering with this device. 28 The forces acting on the aortic cusps and transvalvular devices are unknown and might affect the design of new pumps or cannulas that allow centering caused by small forces. The aim of this work was to investigate the dynamic interaction of cannulas with functional aortic valves by measuring quantitative forces that act on transvalvular cannulas.…”

“…However, for a specific transvalvular VAD the dynamic interaction and the pressures necessary to center the transvalvular cannula were investigated previously in an isolated heart setup. 28 Therefore it might be important to measure the forces for specific configurations and devices separately.…”

“…In this configuration, when the aortic valve closed, the aortic cusps pushed the cannula toward the aortic center at physiologic aortic pressures. However, below physiologic low aortic pressures (~25 mmHg), the cannula touched the wall and the force applied by the cusps was not sufficient to allow centering with this device …”