Christopher A Siedlecki

Gerson Rosenberg

Keefe B Manning

Michael A Navitsky

Stephen R Topper

Steven Deutsch

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Copyright © 2012 by ASME 1 
INTRODUCTION 
 An estimated 82.6 million American adults live with one or more 
forms of cardiovascular disease and in past years, it was the cause of 
over 55% of all deaths in the United States, more than any other type 
of major disease [1]. With a limited number of available donors, heart 
transplants are seldom an option. As a result, ventricular assist devices 
(VADs) have become a viable alternative to immediate transplant. 
Today, VADs are widely used as bridge-to-recovery, bridge-to-
transplant and destination therapy devices. Despite past improvements 
in VAD design, a major complication that continues to arise is 
thrombus formation within the pump.  
 Thrombus formation within VADs is both a fluid mechanics and 
a biomaterials phenomenon. Previous work by Hubbell and McIntire 
have shown that thrombus formation is shear dependent and that 
thrombus formation on polyurethane is more likely in areas 
experiencing shear rates below 500 s-1 [2]. In previous left ventricular 
assist device (LVAD) models, Hochareon et al. measured low shear in 
PIV studies that corresponded to areas where macroscopic thrombi 
were found in vivo [3]. While improvements in LVAD design have 
largely eliminated macroscopic thrombi, precursors to thrombus 
formation, such as platelets and fibrin, can lead to eventual thrombus 
formation. The objective of this study is to correlate and quantify areas 
of similar low shear within a pulsatile V-2 LVAD found in vitro with 
evidence of platelet and fibrin deposition on blood sacs from animal 
studies.  
 
METHODS AND MATERIALS 
   The fluid mechanics within an acrylic model of a Penn State 50cc 
V-2 LVAD were analyzed using particle image velocimetry. Flow of a 
viscoelastic blood analog was visualized along the front and bottom of 
the device. Dual-pulsed Nd:YAG lasers (New Wave Research Inc, 
Fremont, CA) illuminate 10 µm diameter glass particles as a 
synchronized high speed digital CCD camera (TSI, Inc., Shoreview, 
MN) acquired images, allowing the tracking of particle displacement 
over time during systole and diastole. With InsightTM software and 
post-processing, shear maps were produced for areas on the front and 
bottom surfaces of the device throughout the entire cardiac cycle. A 
beat rate of 75 beats per minute (bpm) was used for this study and data 
was acquired from both the front and bottom surfaces as indicated in 
Figure 1a.  
 
 
 
 
 
 
 
 
 
 
          (a)           (b) 
 
Figure 1.  (a) Regions of the sac removed from the bottom for 
microscopic evaluation. (b) Front view of the V-2 LVAD 
indicating planes where PIV data was collected.   
 
 A microscopic surface evaluation, similar to that conducted by 
Yamanaka et al. [5], was then conducted on the polyurethane blood 
sac lining a V-2 LVAD explanted after a 30-day bovine study at the 
Hershey Medical Center. Throughout the study, the device was 
maintained at a constant beat rate of 75 bpm. At the end of the study, 
the device was explanted and areas identified as thrombus-prone 
 
A CORRELATIVE STUDY OF FLUID MECHANICS AND EVIDENCE OF THROMBUS 
FORMATION WITHIN THE PENN STATE 50 CC LEFT VENTRICULAR ASSIST DEVICE 
 
Stephen R. Topper,
1
 Michael A. Navitsky,
1
 Christopher A. Siedlecki,
1,2
  
Steven Deutsch,
1
 Gerson Rosenberg,
1,2
 Keefe B. Manning
1
 
 
1 Department of Bioengineering 
The Pennsylvania State University 
University Park, PA, USA 
 
2 Division of Artifical Organs 
1Department of Bioengine ring 
The Pennsylvania State University 
University Park, PA, USA 
34.24 mm 26.9 mm 
2Division of Artificial Organs 
The Penn State Hershey Medical Center 
Hershey, PA, USA 
Proceedings of the ASME 2012 Summer Bioengineering Conference 
SBC2012 
June 20-23, 2012, Fajardo, Puerto Rico 
SBC2012-80576
Downloaded From: https://proceedings.asmedigitalcollection.asme.org on 07/01/2019 Terms of Use: http://www.asme.org/about-asme/terms-of-use
Copyright © 2012 by ASME 2 
regions along the front and bottom surfaces were examined for 
evidence of platelet and fibrin deposition. Samples approximately 
5mm by 10mm were removed from the sac at locations corresponding 
to areas examined with PIV and then were further divided into four 
sub-sections. Two sub-sections were labeled with primary antibodies 
specific to surface proteins found on platelets and fibrin. After 
treatment with fluorescent secondary antibodies, samples were imaged 
using an Olympus FV1000 confocal microscope at a magnification of 
600x. The remaining sub-samples were dehydrated using an alcohol 
dehydration series, placed in a critical point dryer, sputter coated with 
gold/palladium and examined using a JEOL 5400 scanning electron 
microscope (SEM) at a magnification of 500x.  
 
RESULTS AND DISCUSSION  
 The current inlet valve orientation produces a substantial jet that 
allows for high shear due to washing along the bottom wall, 
particularly on the inlet side [4].  This inlet jet is seen below in Figure 
2a. As a result, the shear rates observed in those areas of the pump 
tend to be higher throughout diastole. More specifically, the shear 
rates at the intersections of the 5mm parallel plane and the 26.9 mm 
and 34.24 mm normal planes (Figure 1b) are over the 500 s-1 threshold 
(Figure 2b).  
 
 
(a) 
 
 
(b) 
 
Figure 2.  (a) Flow visualization of the inlet jet during diastole. (b) 
Shear rates at each normal plane along the 5 mm parallel plane 
during diastole. 
 
 The outlet side of the pump tends to experience lower shears 
because of jet detachment near the extreme bottom of the pump and 
subsequent recirculation in the center of the pump as the cycle 
progresses to systole (Figure 2a). On the same 5 mm parallel plane but 
at intersections with the 42.5 mm and 50.8 mm normal planes, the 
shear rate remains below 250 s-1 (Figure 2b).  
 Correspondingly, microscopic surface evaluation supports the 
hypothesis that more deposition occurs in areas of low shear. In high 
shear areas near the inlet, low fluorescence activity confirms little 
platelet and fibrin deposition (Figure 3a). However, the bottom surface 
on the outlet side shows substantially more evidence of platelet and 
fibrin deposition. In many randomly selected areas, fibrin clots (red) 
with occasionally embedded platelets (green) were found on the sac 
surface (Figure 3b). This demonstrates that this area of the device 
remains a concern. 
 
  
 
 
 
 
 
 
 
 
 
 
 
 (a)                 (b) 
 
Figure 3.  (a) An image acquired at the 19.5 mm normal plane and 
5 mm parallel plane intersection. (b) An image acquired at the 
50.8 mm normal plane and 5 mm parallel plane intersection.  
 
 
CONCLUSIONS 
 The study of thrombus formation is multidisciplinary and 
complicated. The research to date has led to vast improvements in 
thrombosis from both fluid mechanics and material evaluation 
perspectives. This data and previous data indicate a strong correlation 
between regions of low shear and evidence of thrombosis such as 
platelet and fibrin deposition. In order to continue the progression 
towards clinical success of these devices, computational fluid 
dynamics may lead to models that serve as strong thrombosis 
predictors.  
 
ACKNOWLEDGEMENT 
 Supported by NIH NHLBI HL60276. 
  
REFERENCES 
[1] Véronique, R. L., et al., 2011, ―AHA Statistical Update, Heart 
Disease and Stroke Statistics—2011 Update,‖ Circulation, 123, pp. 
18–209. 
[2] Hubbell J. A., McIntire L. V., 1986, ―Visualization and Analysis of 
Mural Thrombogenesis on Collagen, Polyurethane and Nylon,‖ 
Biomaterials, 7, pp. 354–363. 
[3] Hochareon, P., et al., 2004, ―Correlation of In Vivo Clot Deposition 
With the Flow Characteristics in the 50 cc Penn State Artificial Heart: 
A Preliminary Study,‖ ASAIO J., 50, pp. 537–542.   
[4] Kreider, J., et al., 2006, ―The 50cc Penn State LVAD: a Parametric 
Study of Valve Orientation Flow Dynamics,‖ ASAIO J., 52, pp. 123–
131. 
[5] Yamanaka, H., et al., 2005, ―Multiscale Analysis of Surface 
Thrombosis In Vivo in a Left Ventricular Assist System,‖ ASAIO J., 
51(5), pp. 567-577.  
 
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A Correlative Study of Fluid Mechanics and Evidence of Thrombus Formation Within the Penn State 50 cc Left Ventricular Assist Device

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A Correlative Study of Fluid Mechanics and Evidence of Thrombus Formation Within the Penn State 50 cc Left Ventricular Assist Device

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