Description
Left ventricular assist device (LVAD) pump thrombus (PT) is a serious complication that often requires LVAD pump exchange surgery. When clots form in the LVAD, they often grow slowly over time, eventually occluding the LVAD inflow, a progression that is difficult to detect with current treatment standards. Most patients with thrombus will have difficulty with LVAD unloading, indicating a clot has formed. However, by that point, the thrombus is usually too large to treat with increased anticoagulant therapy and a pump exchange must be performed. Pump replacement can be avoided if thrombus formation is detected early and treated. Recently, multiple parameters have been identified as sensitive indices, including the S/D ratio. Our goal in this study was to assess these indices in the detection of PT using an experimental model with matched flow conditions in a mock circulatory loop. Experimental studies were performed with a silicone model of the LV with dilated cardiomyopathy and the HeartMate II LVAD. A particle image velocimetry system captured an image sequence of a 2-D velocity field of the LV midplane. A range of LVAD speeds were tested from 8-11krpm at baseline and during PT. PT was simulated with disks centered over the rotor inflow housing, reducing the orifice area between 17-76%. Localized velocity was calculated for regions of interest (ROI) at the entrance of the inflow cannula (IC) and the mitral valve outflow. LVAD to total flow ratio decreased as PT increased, determining an increase in outflow through the aortic valve opening. Comparable to clinical data, the ROI analysis revealed diastolic (D) decreasing and systolic (S) remaining constant at the LVAD IC with an increase of PT, producing an increase in the S/D ratio. Overall, PT increased resistance to LVAD inflow that increases with LVAD speed. The hemodynamics revealed a higher amount of aortic valve opening as PT obstruction reached 40%. The difference in S/D ratio between baseline and PT suggested a ratio of less than 10% to be small thrombus, a 10 - 25% ratio to be medium thrombi, and any S/D ratio over 25% to be large PT.
