Hemodynamic Evaluation of Aortic Coarctation Treatment using MRI Data

Background: Aortic coarctation (CoA) accounts for approximately 10% of congenital heart diseases. CoA causing high pressure gradient can be successfully treated. Long-term results, however, revealed decreased life expectancy associated with abnormal hemodynamics. To understand better CoA treatment, patient-specific computational fluid dynamics (CFD) models were created to simulate pre- and post-treatment hemodynamics with a focus on pressure gradient. Methods: Flow simulations using CFD program FLUENT using non-newtonian blood model and k-w turbulence model were performed in three CoA cases (case 1: 40 years old (yo), female, 88% stenosis; case 2: 23 yo, female, 47% stenosis; case 3: 29 yo, female, 62% stenosis) that were reconstructed from MRI data using software ZIB-Amira. 4D MRI flow data were used to simulate peak systole flow (case 1: 260 ml/s, Re=1580; case 2: 350 ml/s, Re=3800; case 3: 350 ml/s, Re=6700). The peak systole pressure drop is the major parameter used in the clinical practice for the treatment decision. All three cases were treated by stents. Angiography data were used to reconstruct post-treatment geometries. Two inlet flow conditions were investigated: plug inlet velocity profile and in vivo velocity profile obtained by MRI. 4D MRI flow data were analyzed using software MEVISFlow. Results: The swirl flow generated by left ventricle and the aortic valve reduces recirculation zone behind the stenosis and shift the flow towards the inner wall of the aortic arch thus reducing the pressure drop. All three cases revealed lower pressure drop with the MRI based inlet flow profiles (Pre-treatment: plug profile - dPcase1=49.2 mmHg, dPcase2=17.4 mmHg, dPcase3=14.8 mmHg vs. MRI based profile - dPcase1=45.3 mmHg, dPcase2=13.2 mmHg, dPcase3=13.0 mmHg). Stent treatment of CoA reduced pressure drop in all three cases. The pressure drop reduction due to treatment was also better with the MRI based inlet flow profile (Post-treatment: plug profile - dPcase1=9.0 mmHg, dPcase2=10.1 mmHg, dPcase3=5.9 mmHg vs. MRI based profile - dPcase1=3.3 mmHg, dPcase2=6.1 mmHg, dPcase3=3.1 mmHg). Conclusion: In vivo velocity profile at the inlet of the aorta including secondary flow features (swirl) generated by the left ventricle and the aortic valve affects both: the estimation of the pressure drop caused by the aortic coarctation and the effect of the treatment. We conclude that the use of the in vivo velocity profile as can be assessed by a 4D MRI flow data is important for both: the correct in silico estimation of the pressure drop due to the aortic coarctation that is important for the treatment decision and for the estimation of the hemodynamic impact of a treatment