(174t) Analysis of Repaired Coarctation of the Aorta Using CFD Simulations

Coarctation of the aorta (CoA) is defined as a stenosis of the descending thoracic aorta (DAo)¹ which results in the narrowing of the aortic arch. Current clinical guidelines recommend intervention when there is significant aortic narrowing,² and when a significant pressure gradient is measured during cardiac catheterization. Patients with CoA remain at high risk due to complications including increased mortality, hypertension, stroke, and decreased exercise capacity.³ This condition effects approximately 6-8% of the population.⁴ The aortic arch plays a crucial role in the delivery of blood from the heart to the body. This project aims to model the flow through the aortic arch using computational fluid dynamics (CFD) to analyze the complex flow patterns and pressure gradients in patients pre and post CoA repair with the goal of providing insight to the flow patterns to better understand the effect of the repair, as well as contribute to future repair strategies. Multiple geometric measures following CoA repair are used to predict late complications, including abnormal arch diameter due to dilation or stenosis, and abnormal arch shape, both likely impacting flow patterns and resistance to flow. Aortic arch stenosis has been associated with changes in left ventricular (LV) function, late systemic hypertension, hypertensive response to exercise, and pathologic wave reflections. Aortic arches after CoA repair adopt specific arch shapes. Altered arch shape has been associated with late systemic hypertension, decreased LV function, increased LV end-diastolic volume, and increased LV mass. Altered arch shape has also been shown to affect wall shear stress patterns, an important cause of aortopathy in this population. Aortic stenosis, dilation, and abnormal curvature all impact flow characteristics after CoA repair. CFD can be used to understand the flow and pressure patterns in geometries of patients with CoA by accurately modeling the patients aortic arch for velocity gradients, pressure gradients and flow fields to understand how the geometry, and repairs to the geometry effect patients. The arch contains four outlets, three of which distribute oxygenated blood to the upper half of our body, while the fourth delivers to the lower body. If left untreated, serious heart conditions can arise later in life due to the hindrance in blood flow to both the upper and lower extremities. Today, surgical techniques include extended end-to-end anastomosis which involves removing the constricted part of the aorta. Depending on the size of the constricted area, the ends of the artery can be reconnected simply by stitches or inserting a graft. Earlier techniques involve aortoplasty, which uses synthetic materials such as balloons or stents to reinforce the artery wall.

CFD is a branch of mechanics that creates simulations for a variety of applications. CFD can be used to understand the flow and pressure patterns in geometries of patients with CoA by accurately modeling the aortic arch for velocity gradients, pressure gradients, and flow fields to fully understand how the geometry and repairs to the geometry effect patients. CFD is a useful tool in medical applications and can be used to study the flow patterns within the human body. In this project specifically, CFD is used to predict the flow behavior in patients who experienced surgical repair due to CoA. We compare the flow within repaired arches to those with normal geometries to enable comparative analysis. Under an IRB (Internal Review Board) approved study, clinical data was supplied by the University of Rochester Medical Center. This data included aortic arch anatomy in MRI and CT scan format, along with flow data, and heart rates from cardiac MRI studies, as well as blood pressures from outpatient visits. Velocity streamlines, cross sections, pressure, and wall shear contours within each arch were studied. All simulations were conducted with normal blood parameters for density and viscosity and governed using the Continuity and Navier-Stokes equations.

Three different flow models were compared: SST k-omega, k-epsilon and laminar. Results indicate that the SST k-omega produced the most accurate residuals for most patients, with a reasonable time of convergence of 2-3 hours. The efficiency of convergence corresponds to a smooth model and properly designed mesh. In contrast to the k-epsilon model, the SST k-omega model consistently converged in trials when the k-epsilon model did not. The SST k-omega and laminar model simulation results were similar, but additional parameters in the SST k-omega model resulted in more accurate near-wall simulations. In addition, Reynolds number calculations concluded that flow within the arch is turbulent, furthering our conclusion with the use of the SST k-omega flow model.

After examination of flow properties for twelve patients, those with CoA displayed more interrupted velocity streamlines, and greater pressure gradients near the third head vessel on the arch. Continued CFD modeling of aortic arches will provide assistance to medical professionals with an in-depth review of the blood flow before and after surgery. This information will enable surgeons to determine whether the current surgical procedure is efficient in recovering natural blood flow in operated patients, leading to better CoA surgical practices in the future.

References

• Jonas R. Comprehensive Surgical Management of Congenital Heart Disease. 2nd ed. CRC Press; 2014.
• Stout KK, Daniels CJ, Aboulhosn JA, et al. 2018 AHA/ACC Guideline for the Management of Adults With Congenital Heart Disease: Executive Summary: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines. Circulation. 2019;139(14).
• Kempny A, Dimopoulos K, Uebing A, et al. Reference values for exercise limitations among adults with congenital heart disease. Relation to activities of daily life--single center experience and review of published data. European Heart Journal. 2012;33(11):1386-1396.
• Doshi, Arpan R, and Sathish Chikkabyrappa. “Coarctation of Aorta in Children.” Cureus 10,12 e3690. 2018.