Hemodynamic simulation of aortic remodeling after thoracic endovascular aortic repair

  Background  The remodeling of true lumen and false lumen of abdominal residual dissection after thoracic endovascular aortic repair (TEVAR) is not good in some cases. How to accurately predict the trend of aortic remodeling in the early stage after TEVAR and how to perform secondary intervention for cases with poor prediction are urgent problems in clinic.

  Objective  To investigate the effectiveness of early hemodynamic parameters in predicting the trend of aortic remodeling after thoracic endovascular aortic repair (TEVAR) and the effect of sealing the infrarenal residual tears on aortic remodeling.

  Methods  Two patients with type B aortic dissection (AD) who were treated with TEVAR in the department of vascular and endovascular surgery, the First Medical Center of Chinese PLA General Hospital in 2016 were enrolled. Case 1 was a male patient aged 32 years, and case 2 was a male patient aged 47 years. Based on the data of computed tomography angiography before TEVAR and during follow-up within 2 years after surgery, two groups of individual geometric models were constructed and the 3-dimensional morphological parameters were calculated. Computational fluid dynamic (CFD) simulation was used to calculate hemodynamic parameters before surgery and at 3 months after surgery and predict the trend of aortic remodeling, which was compared with follow-up outcomes. Two modified models were obtained by sealing the residual tears of infrarenal abdominal aorta on the real model at 3 months after TEVAR to simulate the procedure of secondary intervention and calculate the changes of corresponding parameters.

  Results  After surgery, both patients had an increase in the total volume of the true lumen (TL) and a reduction in the volumes of the false lumen (FL), with significant enlargement of the regions where the pressure difference between the TL and the FL was greater than zero, and the distal movement distance of the first balance position of the pressure difference accounted for 3.46% and 3.77% of the total length of AD, respectively. The rate of blood shunting into the FL decreased from 19.9% to 7.22% in case 1 and from 17.3% to 2.45% in case 2 after TEVAR, and jet blood flow was observed in the region of residual tears of the renal artery. These parameters indicated that both patients could achieve good overall outcome and remodeling of the FL after surgery, but the FL around the tears of the renal artery might not completely disappear. These predicted outcomes were consistent with those of mid- and long-term follow-up. Further quantification of the volumes of the TL and the FL at subsequent follow-up time points showed that in case 1, the volume of the TL decreased from 148.3 cm³ to 142.8 cm³ from 3 to 18 months after TEVAR, while in case 2, the volume of the TL of the abdominal segment increased slightly from 7.9 cm³ to 8.5 cm³ from 3 to 24 months after TEVAR. This phenomenon suggested unsatisfactory remodeling of the TL in the distal aorta in both cases. Two modified models were designed to solve this problem, and the calculation of parameters showed that the pressure of the TL was greater than that of the FL in the whole residual dissection of the two modified models, with a significant increase in the relative residence time of the FL. These results indicated that the modified models could obtain a better remodeling effect of the TL and the FL of the abdominal segment.

  Conclusion  Hemodynamic parameters based on CFD simulation may effectively predict the mid- and long-term trend of aortic remodeling in the early stage (about 3 months) after TEVAR, and early sealing of infrarenal residual tears (about half a year after TEVAR) may achieve better remodeling of abdominal residual dissection, especially in cases with high compression of the distal TL.