Numerical model of full cardiac cycle hemodynamics in Syncardia total artificial heart. G., M., W.C., C., S., P., M., H., M.J., S., & D., B. Volume San Antonio, TX, USA, October 22-25, 2014.
abstract   bibtex   

Introduction: The total artificial heart (TAH) (SynCardia Inc. Tucson, AZ) is the only such device approved by the Food and Drug Administration (FDA) for both bridge-to-transplant and as destination therapy under Humanitarian Use Device (HUD) for patients with congestive heart failure. A smaller 50 cc TAH has been designed for small adults and pediatric and smaller patients that cannot receive the original 70 cc TAH. The aim of this study was to evaluate the flow regime in the 50 cc TAH and to estimate its thrombogenic potential relative to larger and smaller TAH devices.

Materials and Methods: Three TAH models simulating transient blood flow, deforming diaphragm, and two moving valves, are introduced. The rigid body motion of the valves is coupled with the flow solution. The dynamic mesh during the systole and before the diastole is depicted (Fig. 1 first row). A multiphase model with injected platelet particles is employed to calculate their trajectories. The shear stress accumulation in the three models are calculated along these trajectories and their probability density functions, representing their 'thrombogenic footprint', are compared.

Results and Discussion: The calculated flow regime successfully captures the mitral regurgitation and the flows that open and close the aortic valve. The left column shows the systolic configuration with fully opened aortic valve (marked in blue) and fully closed mitral valve (marked in green). The mitral regurgitation and the strong aortic flow can be clearly seen. The right column presents a transition phase between the systole and the diastole. At this stage, the diaphragm pumps the blood into the chamber causing closing and opening of the aortic and mitral valves, respectively. Physiological velocity magnitudes are found in all three models, with higher velocities and increased stress accumulation (SA) in the smaller devices (third row). Median SA of 3.41, 2.19 and 1.12 dyne•s/cm2, are found in the 37.7, 50 and 66.6 cc TAHs, respectively. The probability for SA of more than 10 dyne•s/cm2 is lower than 1% in the three TAHs with a slightly higher probability for elevated stresses in smaller TAHs. The probability for SA larger than Hellums criterion (35 dyne•s/cm2) is smaller than 0.012%.

Conclusions: There is a mild trend of increased probability that platelets in smaller devices will be exposed to elevated stresses because of the combined effect of higher pumping frequency and smaller dimensions. These elevated stresses may translate into a mild increase in platelet activation, although this may be mitigated by the lower cardiac output (CO) that the smaller devices may produce.

Acknowledgements: This study was funded by grants from the National Institute of Health: NIBIB Quantum Award: Implementation Phase II U01 EB012487-0 (D.B.). The software was provided by ANSYS Academic Partnership with Stony Brook University.

image

Figure 1. The 50 cc TAH model during systole and before diastole. Representative cross sections of the mesh and velocity vectors are shown in the first and second rows, respectively. PDF of the stress accumulation of the three TAHs with different sizes is shown in third row.

@proceedings{n14,
  cpaper				   = {1},
  Title                    = {{Numerical model of full cardiac cycle hemodynamics in Syncardia total artificial heart}},
  Author                   = {Marom G. and Chiu W.C. and Prabhakar S. and Horner M. and Slepian M.J. and Bluestein D.},
  Booktitle				   = {BMES Annual Meeting 2014 (BMES2014)},
  address 				   = {San Antonio, TX, USA}, 
  month					   = {October 22-25}, 
  Year                     = {2014}, 

  Abstract				   = {
														<p>Introduction: The total artificial heart (TAH) (SynCardia Inc. Tucson, AZ) is the only such device approved by the Food and Drug Administration (FDA) for both bridge-to-transplant and as destination therapy under Humanitarian Use Device (HUD) for patients with congestive heart failure. A smaller 50 cc TAH has been designed for small adults and pediatric and smaller patients that cannot receive the original 70 cc TAH. The aim of this study was to evaluate the flow regime in the 50 cc TAH and to estimate its thrombogenic potential relative to larger and smaller TAH devices.</p>
														<p>Materials and Methods: Three TAH models simulating transient blood flow, deforming diaphragm, and two moving valves, are introduced. The rigid body motion of the valves is coupled with the flow solution. The dynamic mesh during the systole and before the diastole is depicted (Fig. 1 first row). A multiphase model with injected platelet particles is employed to calculate their trajectories. The shear stress accumulation in the three models are calculated along these trajectories and their probability density functions, representing their 'thrombogenic footprint', are compared.</p>
														<p>Results and Discussion: The calculated flow regime successfully captures the mitral regurgitation and the flows that open and close the aortic valve. The left column shows the systolic configuration with fully opened aortic valve (marked in blue) and fully closed mitral valve (marked in green). The mitral regurgitation and the strong aortic flow can be clearly seen. The right column presents a transition phase between the systole and the diastole. At this stage, the diaphragm pumps the blood into the chamber causing closing and opening of the aortic and mitral valves, respectively. Physiological velocity magnitudes are found in all three models, with higher velocities and increased stress accumulation (SA) in the smaller devices (third row). Median SA of 3.41, 2.19 and 1.12 dyne•s/cm2, are found in the 37.7, 50 and 66.6 cc TAHs, respectively. The probability for SA of more than 10 dyne•s/cm2 is lower than 1% in the three TAHs with a slightly higher probability for elevated stresses in smaller TAHs. The probability for SA larger than Hellums criterion (35 dyne•s/cm2) is smaller than 0.012%.</p>
														<p>Conclusions: There is a mild trend of increased probability that platelets in smaller devices will be exposed to elevated stresses because of the combined effect of higher pumping frequency and smaller dimensions. These elevated stresses may translate into a mild increase in platelet activation, although this may be mitigated by the lower cardiac output (CO) that the smaller devices may produce.</p>
														<p>Acknowledgements: This study was funded by grants from the National Institute of Health: NIBIB Quantum Award: Implementation Phase II U01 EB012487-0 (D.B.). The software was provided by ANSYS Academic Partnership with Stony Brook University.</p>
														
														<img alt="image" src="pages/BMES14-TAH.png"  class="img-responsive">
														<p>Figure 1. The 50 cc TAH model during systole and before diastole. Representative cross sections of the mesh and velocity vectors are shown in the first and second rows, respectively. PDF of the stress accumulation of the three TAHs with different sizes is shown in third row.</p>
							}												
}
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