Impact of Residual Intimal Flap Displacement Post-TEVAR on TBAD Haemodynamics in Compliant, Patient-specific CFD Simulations Informed by MRI

We propose a novel formulation of a moving boundary method to account for the motion of the intimal flap (IF) in a TBAD post-thoracic endovascular aortic repair using patient-specific compliant computational fluid dynamics simulations. The simulations were informed by non-invasive 4D flow MRI sequences. Predicted flow waveforms, aortic wall, and IF displacements were validated against in vivo 4D flow MRI and cine-MRI data. The patient-specific simulation showed that at peak systole, the dynamic interplay between high IF displacement and high transmural pressures promoted true lumen compression and false lumen expansion, whilst luminal patterns were reversed at the deceleration phase. High vorticity and swirling flow patterns were observed throughout the cardiac cycle at the primary entry tear, the descending aorta and proximal to the visceral aortic branches, correlating with high relative residence time, which could indicate an increased localised risk of aortic growth proximal to the IF. A rigid IF simulation revealed significant discrepancies in haemodynamic metrics, highlighting the potential mispredictions when using a rigid wall assumption to assess disease progression. Simulations assuming a more compliant IF highlighted potential increased risks of visceral branches malperfusion and localised aortic wall degeneration. The study underscores the necessity of patient-specific compliant IF simulations for accurate TBAD haemodynamic assessments. These insights can improve disease understanding and inform future treatment strategies.