Aortic coarctation: Recent developments in experimental and computational methods to assess treatments for this simple condition

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Abstract

Coarctation of the aorta (CoA) is often considered a relatively simple disease, but long-term outcomes suggest otherwise as life expectancies are decades less than in the average population and substantial morbidity often exists. What follows is an expanded version of collective work conducted by the authors' and numerous collaborators that was presented at the 1st International Conference on Computational Simulation in Congenital Heart Disease pertaining to recent advances for CoA. The work begins by focusing on what is known about blood flow, pressure and indices of wall shear stress (WSS) in patients with normal vascular anatomy from both clinical imaging and the use of computational fluid dynamics (CFD) techniques. Hemodynamic alterations observed in CFD studies from untreated CoA patients and those undergoing surgical or interventional treatment are subsequently discussed. The impact of surgical approach, stent design and valve morphology are also presented for these patient populations. Finally, recent work from a representative experimental animal model of CoA that may offer insight into proposed mechanisms of long-term morbidity in CoA is presented.

Section snippets

What is normal anyway?

To fully characterize hemodynamic alterations associated with CoA, we must first understand related indices under normal conditions. Hemodynamic and vascular biomechanics in the thoracic aorta and its branches are complex, but particularly depend on several key factors that should be implemented when performing CFD modeling for CoA patients. Importantly, consideration of these factors allows for the replication of normal physiology and thoracic aortic anatomy and likely the greatest chance for

Do previous and current treatments restore normalcy?

Traditionally surgery by resection with end-to-end anastomosis has been the gold standard for repair of CoA. While CFD has been used extensively to study possible morbidity due to altered flow conditions in smaller blood vessels prone to atherosclerosis, the potentially deleterious effects of alterations in blood flow patterns in the human thoracic aorta have not been as widely studied.

Fig. 1 shows results from an ongoing investigation in which patient-specific CFD modeling was performed for

Local hemodynamics alterations after stenting for CoA

The invasive nature of surgical treatments combined with the shorter hospitalization, reduced pain and decreased cost of catheter-based therapies has led to stent implantation playing an increasing role in the treatment of CoA. Although currently there are no FDA-approved stents specifically designed for children, several stents are commonly used off-label with CoA patients and recent studies have documented some fundamental concerns regarding the use of these stents in a manner other than that

How does the aortic valve impact normal?

The prevalence of a bicuspid aortic valve (BAV) is ~ 2% in the general population [33], but 50–80% of patients diagnosed with CoA also have a BAV [[33], [34]]. This is particularly concerning as reports have documented a nine-fold increased risk of ascending aortic dissection with BAV [33]. Imaging studies using Doppler ultrasound [2] and 4D MRI flow measurements [35] have indicated BAV cause flow disturbances in the ascending aorta and progressive ascending aortic dilatation. Past studies have

In vivo rabbit model of CoA

Despite notable efforts underway for the projects summarized above, the precise cause of long-term morbidity for CoA patients is difficult to assess due to the small number of patients at any institution, and their heterogeneity. A modified rabbit coarctation model was therefore created to assess hemodynamic indices including blood flow, BP and WSS caused by CoA using a coupled imaging and CFD approach. The experimental MRI protocol mirrors the protocol that was used to obtain the human MRI

Summary

The examples discussed above show that computational simulation is currently being used to address many of the questions that persist related to treatment for CoA. Although larger studies are necessary, these recent results support the hypothesis of O'Rourke and Cartmill from nearly four decades ago. We anticipate that as the severity of hemodynamic and vascular biomechanics alterations continue to be elucidated through computational simulation, engineers and clinicians will be able to work

Acknowledgments

The insight, collaboration, guidance and technical assistance of C. Alberto Figueroa PhD in the Department of Mechanical Engineering and Cardiovascular Biomechanics Research Laboratory at Stanford University, Irene Vignon-Clementel PhD of INRIA, and Hyun Jin Kim PhD are gratefully acknowledged. The authors would also like to especially thank Margaret Samyn MD and Joe Cave MD, PhD in the Department of Pediatrics at the Children's Hospital and Medical College of Wisconsin, and Frandics Chan MD,

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