A correlative study of fluid mechanics and evidence of thrombus formation within the Penn State 50 cc V-2 left ventricular assist device

Open Access
Author:
Topper, Stephen Robert
Area of Honors:
Bioengineering
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Keefe B Manning, Thesis Supervisor
  • Peter J Butler, Honors Advisor
  • Steven Deutsch, Faculty Reader
Keywords:
  • ventricular assist device
  • thrombosis
  • fluid dynamics
  • pulsatile
  • wall shear
  • surface evaluation
  • particle image velocimetry
Abstract:
Ventricular assist devices (VADs) are important alternatives for patients with insufficient cardiac function due to congestive heart failure. With limited donors, heart transplants are often not available. As an alternative to heart replacement, VADs are bridge-to-recovery or life prolonging devices. Clinically, thrombus formation may occur both within the pump and at the cannula junctions and may embolize leading to strokes. Here, we correlate the velocity and shear fluid dynamics obtained from particle image velocimetry (PIV) in a pulsatile VAD against regions on the sac surface within an explanted VAD from a bovine study with particular attention to low shear areas and platelet and fibrin deposition. The bovine study was conducted at the Penn State Hershey Medical Center where a model of the 50 cc Penn State V-2 VAD was implanted and maintained at a constant beat rate of 75 beats per minute (bpm). At the conclusion of the study, the device was explanted and the sac surface was analyzed using scanning electron microscopy (SEM) and, after immunofluorescent labeling for platelets and fibrin, confocal microscopy. Areas were examined based on PIV measurements, with special attention to low shear regions where platelet and fibrin deposition are most likely to occur. To mimic physiological conditions in vitro, a mock circulatory loop was used with a blood analog that matched blood’s viscoelastic behavior. Under normal physiologic pressures and for a heart rate of 75 bpm as in the in vivo study, PIV data was acquired and shear maps were produced. Data collected within the outlet port in a direction normal to the front wall of the VAD shows that areas experience shear rates less than 500 s-1. Shear rates below this value indicate insufficient washing along the device walls and increase the likelihood of platelet and fibrin deposition. This is quantified by the thrombus susceptibility potential, a calculation to correlate low shear with deposition. Computational fluid dynamics confirms the microscopy and PIV data and together, these studies provide information about VADs that will improve their design and increase their clinical effectiveness.