Optimization of Flow Dynamics During the HeartWare HVAD to HeartMate 3 Exchange: A Computational Study Assessing Differential Surgical Techniques

Abstract

<h3>Purpose</h3> With the discontinuation of the HeartWare HVAD, patients who experience a device complication will require exchange to another pump. The HeartMate 3 (HM3) is now the only commercially available LVAD in the United States. The optimal surgical configuration for connecting the 10 mm HVAD outflow graft to the 14 mm HM3 outflow graft has yet to be defined. <h3>Methods</h3> A lumped-parameter computational fluid dynamic (CFD) model of the circulatory system, including HQ curves of the HM3 was created. The model was coupled with 3D CFD model, in which outflow cannula flow served as the boundary conditions for blood flow simulations in the aorta. In total, 4 variations of the outflow cannula were tested: 1) Anastomosis near the pump (long 10 mm); 2) Anastomosis near the aorta (long 14 mm); 3) Anastomosis 5 cm from the aorta (mid transition); 4) The entire cannula 14 mm (complete exchange). The flow patterns were characterized based on the results of 3D CFD simulations. <h3>Results</h3> Maximum velocity was highest in the configurations with longer sections of 10 mm graft (long 10 mm, 4.20 m/s; long 14 mm, 4.12 m/s, mid transition, 4.18 m/s; complete exchange, 2.27 m/s). This resulted in a 176% larger blood volume exposed to very high shear rate (SR) >5000 s⁻¹ for the long 10 mm vs the long 14 mm configuration (0.59 ml vs 0.21 ml) and a 805% increase compared to the complete exchange (0.065 ml). There was a 21% increase in right coronary flow (0.29 ml/s vs 0.24 ml/s) and a 22% increase in left coronary flow (1.41 ml/s vs 1.16 ml/s) with the long 10 mm compared to the 14 mm configuration. When the long 10 mm cannula was compared against complete exchange, the flow increase was 26% (0.29 ml/s vs 0.23 ml/s) for right coronary and 62% (1.41 ml/s vs 0.87 ml/s) for left coronary. <h3>Conclusion</h3> When planning for a HVAD to HM3 exchange, the location of the anastomosis and relative length of the 10 and 14 mm grafts has important implications related to shear rate and coronary blood flow which should be accounted for during surgery.