Pulsatile Flow Leads to Intimal Flap Motion and Flow Reversal in an In Vitro Model of Type B Aortic Dissection
- 431 Downloads
Understanding of the hemodynamics of Type B aortic dissection may improve outcomes by informing upon patient selection, device design, and deployment strategies. This project characterized changes to aortic hemodynamics as the result of dissection. We hypothesized that dissection would lead to elevated flow reversal and disrupted pulsatile flow patterns in the aorta that can be detected and quantified by non-invasive magnetic resonance imaging. Flexible, anatomic models of both normal aorta and dissected aorta, with a mobile intimal flap containing entry and exit tears, were perfused with a physiologic pulsatile waveform. Four-dimensional phase contrast magnetic resonance (4D PCMR) imaging was used to measure the hemodynamics. These images were processed to quantify pulsatile fluid velocities, flow rate, and flow reversal. Four-dimensional flow imaging in the dissected aorta revealed pockets of reverse flow and vortices primarily in the false lumen. The dissected aorta exhibited significantly greater flow reversal in the proximal-to-mid dissection as compared to normal (21.1 ± 3.8 vs. 1.98 ± 0.4%, p < 0.001). Pulsatility induced unsteady vortices and a pumping motion of the distal intimal flap corresponding to flow reversal. Summed true and false lumen flow rates in dissected models (4.0 ± 2.0 L/min) equaled normal flow rates (3.8 ± 0.1 L/min, p > 0.05), validated against external flow measurement. Pulsatile aortic hemodynamics in the presence of an anatomic, elastic dissection differed significantly from those of both steady flow through a dissection and pulsatile flow through a normal aorta. New hemodynamic features including flow reversal, large exit tear vortices, and pumping action of the mobile intimal flap, were observed. False lumen flow reversal would possess a time-averaged velocity close to stagnation, which may induce future thrombosis. Focal vortices may identify the location of tears that could be covered with a stent-graft. Future correlation of hemodynamics with outcomes may indicate which patients require earlier intervention.
Keywords4D PCMR Aortic dissection Flow model Hemodynamics Intimal flap motion
We would like to acknowledge funding for this work from Medtronic, Inc.
Conflicts of Interest
Joav Birjiniuk has received a graduate research assistantship from Medtronic, Inc. Lucas Timmins declares that he has no conflict of interest. Mark Young is an employee of Medtronic, Inc. John Oshinski declares that he has no conflict of interest. David Ku declares that he has no conflict of interest. Ravi Veeraswamy has received consulting fees from Medtronic, Inc.
This article does not contain any studies with human participants or animals performed by any of the authors.
This study was funded by Medtronic, Inc. The following authors have received benefits for personal or professional use from a commercial party (Medtronic, Inc.) related directly to the subject matter of this manuscript: graduate research assistantship (J.B.), employment and salary (M.Y.), and consulting fees (R.K.V).
Supplemental Video 1 Fluid flow reconstructed from PCMR data. Detail on right demonstrating diastolic vortex forming at exit tear (MP4 16570 kb)
Supplemental Video 2 Dye visualization of reversed false lumen flow and exit tear vortex formation in aortic dissection model (MOV 332517 kb)
- 6.“Characteristic Properties of Silicone Rubber Compounds.” Shin-Etsu Co. http://www.silicone.jp/e/catalog/pdf/rubber_e.pdf.
- 20.Ku, D. N., D. P. Giddens, C. K. Zarins, and S. Glagov. Pulsatile flow and atherosclerosis in the human carotid bifurcation. Positive correlation between plaque location and low oscillating shear stress. Arterioscler. Thromb. Vasc. Biol. 5(3):293–302, 1985.Google Scholar
- 30.Ranjan, V., Z. Xiao, and S. L. Diamond. Constitutive NOS expression in cultured endothelial cells is elevated by fluid shear stress. Am. J. Physiol. 269(2):H550–H555, 1995.Google Scholar
- 35.Sueyoshi, E., I. Sakamoto, K. Hayashi, T. Yamaguchi, and T. Imada. Growth rate of aortic diameter in patients with Type B aortic dissection during the chronic phase. Circulation 110(Supplemental II):II256–II261, 2004.Google Scholar