Left Ventricular Assist Device Flow Pattern Analysis Using Computational Fluid Dynamics at the Time of Invasive Hemodynamic Ramp Study: Using Patient-Specific Data to Optimize the Ramp Study

Abstract

<h3>Purpose</h3> Invasive hemodynamic ramp studies have been shown to decrease the rates of left ventricular assist device (LVAD) complications however hemocompatibility related adverse events (HRAE) still remain unacceptably high. Computational fluid dynamics (CFD) allows for a more thorough analysis of shear rate (SR) and shear stress (SS) which influences endothelial function and thrombotic potential. <h3>Methods</h3> An invasive hemodynamic ramp study was performed on a patient with a HeartMate 3 (HM3). An anatomical model of the patient was reconstructed from computed tomography (CT) images, and the LVAD outflow cannula was used as the inflow boundary. The LVAD flow was calculated separately using a lumped-parameter-model (LPM) of the circulation. Ventricular volumes were reconstructed from CT and the patient's hemodynamic tracings. The contribution of flow from the HM3 was implemented in the LPM via published H-Q curves. CFD simulations were then carried out over the entire clinical operating condition of the HM3 from 4600 to 6400 RPM. SS and SR were quantified in the outflow cannula, ascending aorta, aortic arch and cerebral circulation. <h3>Results</h3> As speed was increased from 4600 to 5500, and then to 6400 RPM, blood volume exposed to a SR greater than 500 s⁻¹ increased, respectively, by 1.46 fold and 2.18 fold (2.00 to 2.93 to 4.37 cm³). Increase of SS in the cannula was 1.37 fold and 1.74 fold (1.88 to 2.56 to 3.26 Pa), in the ascending aorta was 1.44 fold and 1.92 fold (0.60 to 0.86 to 1.14 Pa), and in the aortic arch and cerebral circulation was 1.40 fold and 1.88 fold (0.46 to 0.65 to 0.87 Pa). <h3>Conclusion</h3> Hemodynamic optimization during ramp studies needs to be balanced with increased rates of SS and SR that occur with incremental speed increases. CFD when applied to a ramp study can provide additive patient-specific information that may further mitigate HRAE.