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Pulsatile Flow Leads to Intimal Flap Motion and Flow Reversal in an In Vitro Model of Type B Aortic Dissection

Abstract

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.

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Acknowledgments

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.

Ethical Approval

This article does not contain any studies with human participants or animals performed by any of the authors.

Funding

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).

Author information

Correspondence to Joav Birjiniuk.

Additional information

Associate Editors Francesco Migliavacca and Ajit P. Yoganathan oversaw the review of this article.

Electronic supplementary material

Below is the link to the electronic supplementary material.

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)

Supplemental Figure 1 Pump driver voltage (top), central aortic pressure (middle), and model outlet flow rate (bottom) traces demonstrating physiologic pumping (TIFF 439 kb)

Supplemental Figure 2 Transverse motion of the intimal flap at different points in the cardiac cycle. Note accentuated motion of the intimal flap at the level of the exit tear (arrow) during fluid deceleration (TIFF 2093 kb)

Supplemental Figure 3 Pathline visualizations in both normal and dissected aortae. Physiological, helical flows can be noted throughout the aortic arch in both models, with significant skewing of velocity profile towards true lumen in the dissected case. Note filling of distal true lumen with cessation of flow partway down the false lumen (TIFF 5918 kb)

Supplemental Figure 4 Luminal flow rates in normal (black) and dissected (colored) aorta. Slice locations on right correspond to slices designated on left (asterisks indicate significant difference from the Normal aorta at all slices, p < 0.05) (TIFF 1392 kb)

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)

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Birjiniuk, J., Timmins, L.H., Young, M. et al. Pulsatile Flow Leads to Intimal Flap Motion and Flow Reversal in an In Vitro Model of Type B Aortic Dissection. Cardiovasc Eng Tech 8, 378–389 (2017) doi:10.1007/s13239-017-0312-3

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Keywords

  • 4D PCMR
  • Aortic dissection
  • Flow model
  • Hemodynamics
  • Intimal flap motion