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      A Pilot Study Exploring the Mechanisms Involved in the Longitudinal Propagation of Acute Aortic Dissection through Computational Fluid Dynamic Analysis

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          Abstract

          Objective: This study sought to elucidate the underlying hemodynamic mechanisms involved in the longitudinal propagation of acute, type-B aortic dissections. Methods: Three-dimensional patient-specific aortic geometry was reconstructed from computed tomography images of 3 cases, followed by computational fluid dynamic analysis using finite-element analysis modeling. Three models were reconstructed; the normal-aortic model (from a healthy volunteer), the visceral-involvement model (from a patient whose visceral arteries were involved) and the progression model (from a patient whose visceral arteries were intact at admission). Wall pressure distribution was analyzed in all three models. Results: In the systolic phase of a cardiac cycle, the wall pressure dropped from the proximal to the distal aorta within the true lumen. This pressure gradient was observed in all three models. A milder pressure gradient was seen in the false lumen in the visceral-involvement model, whereas the pressure in the false lumen remained almost constant in the progression model. The dyssynchrony of the pressure gradients in the true and false lumens caused an imbalance in pressure between the two lumens. Conclusion: The interluminal pressure differential may be a contributing factor in the compression of the true lumen and the cleavage force of the aortic wall, leading to the longitudinal propagation of the dissection.

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          Most cited references6

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          Randomized comparison of strategies for type B aortic dissection: the INvestigation of STEnt Grafts in Aortic Dissection (INSTEAD) trial.

          Thoracic endovascular aortic repair (TEVAR) represents a novel concept for type B aortic dissection. Although life-saving in acute emergencies, outcomes and survival of TEVAR in stable dissection are unknown. One hundred forty patients in stable clinical condition at least 2 weeks after index dissection were randomly subjected to elective stent-graft placement in addition to optimal medical therapy (n=72) or to optimal medical therapy alone (n=68) with surveillance (arterial pressure according to World Health Organization guidelines < or =120/80 mm Hg). The primary end point was all-cause death at 2 years, whereas aorta-related death, progression (with need for conversion or additional endovascular or open surgery), and aortic remodeling were secondary end points. There was no difference in all-cause deaths, with a 2-year cumulative survival rate of 95.6+/-2.5% with optimal medical therapy versus 88.9+/-3.7% with TEVAR (P=0.15); the trial, however, turned out to be underpowered. Moreover, the aorta-related death rate was not different (P=0.44), and the risk for the combined end point of aorta-related death (rupture) and progression (including conversion or additional endovascular or open surgery) was similar (P=0.65). Three neurological adverse events occurred in the TEVAR group (1 paraplegia, 1 stroke, and 1 transient paraparesis), versus 1 case of paraparesis with medical treatment. Finally, aortic remodeling (with true-lumen recovery and thoracic false-lumen thrombosis) occurred in 91.3% of patients with TEVAR versus 19.4% of those who received medical treatment (P<0.001), which suggests ongoing aortic remodeling. In the first randomized study on elective stent-graft placement in survivors of uncomplicated type B aortic dissection, TEVAR failed to improve 2-year survival and adverse event rates despite favorable aortic remodeling.
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            Acute aortic dissection: epidemiology and outcomes.

            Little epidemiological information on acute aortic dissection (AAD) is available in the literature. The objective of the present study was to determine the incidence and mortality rates of AAD in the general population and to analyze its clinical features.
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              Investigation of pulsatile flowfield in healthy thoracic aorta models.

              Cardiovascular disease is the primary cause of morbidity and mortality in the western world. Complex hemodynamics plays a critical role in the development of aortic dissection and atherosclerosis, as well as many other diseases. Since fundamental fluid mechanics are important for the understanding of the blood flow in the cardiovascular circulatory system of the human body aspects, a joint experimental and numerical study was conducted in this study to determine the distributions of wall shear stress and pressure and oscillatory WSS index, and to examine their correlation with the aortic disorders, especially dissection. Experimentally, the Phase-Contrast Magnetic Resonance Imaging (PC-MRI) method was used to acquire the true geometry of a normal human thoracic aorta, which was readily converted into a transparent thoracic aorta model by the rapid prototyping (RP) technique. The thoracic aorta model was then used in the in vitro experiments and computations. Simulations were performed using the computational fluid dynamic (CFD) code ACE+((R)) to determine flow characteristics of the three-dimensional, pulsatile, incompressible, and Newtonian fluid in the thoracic aorta model. The unsteady boundary conditions at the inlet and the outlet of the aortic flow were specified from the measured flowrate and pressure results during in vitro experiments. For the code validation, the predicted axial velocity reasonably agrees with the PC-MRI experimental data in the oblique sagittal plane of the thoracic aorta model. The thorough analyses of the thoracic aorta flow, WSSs, WSS index (OSI), and wall pressures are presented. The predicted locations of the maxima of WSS and the wall pressure can be then correlated with that of the thoracic aorta dissection, and thereby may lead to a useful biological significance. The numerical results also suggest that the effects of low WSS and high OSI tend to cause wall thickening occurred along the inferior wall of the aortic arch and the anterior wall of the brachiocephalic artery, similar implication reported in a number of previous studies.
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                Author and article information

                Journal
                CRD
                Cardiology
                10.1159/issn.0008-6312
                Cardiology
                S. Karger AG
                0008-6312
                1421-9751
                2014
                May 2014
                24 April 2014
                : 128
                : 2
                : 220-225
                Affiliations
                aDivision of Vascular Surgery, Changhai Hospital, and bMilitary Institute of Vascular Disease, the First Affiliated Hospital of the Second Military Medical University, Shanghai, and cDepartment of Vascular Surgery, the Second Affiliated Hospital of Lanzhou University, Lanzhou, PR China; dDepartment of Radiology, University of Cambridge, Cambridge, UK
                Author notes
                *Qingsheng Lu, MD, Division of Vascular Surgery, Changhai Hospital, 168 Changhai Road, 200433 Shanghai (PR China), E-Mail luqs@xueguan.net, Zaiping Jing, MD, Military Institute of Vascular Disease, The First Affiliated Hospital of the Second Military Medical University, 168 Changhai Road, 200433 Shanghai (PR China)
                Article
                358041 Cardiology 2014;128:220-225
                10.1159/000358041
                24776380
                64f65bf6-ea6c-4882-8764-3c15a19507fd
                © 2014 S. Karger AG, Basel

                Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher. Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug. Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.

                History
                : 03 October 2013
                : 12 December 2013
                Page count
                Figures: 4, Tables: 2, Pages: 6
                Categories
                Original Research

                General medicine,Neurology,Cardiovascular Medicine,Internal medicine,Nephrology
                Propagation,Pressure,Aortic dissection,Hemodynamics

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