Computational investigation of interaction between stent graft and aorta in retrograde type A dissection after thoracic endovascular aortic repair for type B aortic dissection

Objective: Retrograde type A dissection (RTAD) after thoracic endovascular aortic repair (TEVAR) has been a major drawback of endovascular treatment. To our knowledge, no studies have evaluated aortic injuries caused by stent grafts (SGs). Therefore, the aim of this study was to evaluate and to quantify the SG-aorta interaction and to analyze the risk factors for injury through computational simulation. Methods: The aortic geometry was extracted from an RTAD case. Five SG models were assembled based on Valiant and Talent (Medtronic Vascular, Santa Rosa, Calif) SGs, and modifications were made to the original SG design by adding and removing the connecting bar. TEVAR simulations were performed seven times for each SG model with 0% and 15% oversizing ratio (OSR), and the maximum aortic stress (MAS) was calculated and compared within the groups. Results: In all TEVAR models, MAS was seen at the proximal bare stent (PBS). The PBS in the Valiant and Talent SGs generated higher stress toward the aortic wall than other SG parts did. MAS was significantly higher for the 15% OSR (0.54 +/- 0.07 MPa) than for the 0% OSR (1.32 +/- 0.74 MPa) in 172.5- mm Valiant models. MAS was significantly higher in the Talent with connecting bar SG model (0.73 +/- 0.24 MPa) than in the Talent without connecting bar SG model (0.51 +/- 0.11 MPa). MAS was significantly higher in the Valiant with connecting bar SG model (0.82 +/- 0.29 MPa) than in the Valiant without connecting bar SG model (0.54 +/- 0.07 MPa). MAS was not significantly different in models with 172.5- mm and 140-mm Valiant SG implantations with 0% OSR (0.54 +/- 0.07 MPa vs 0.60 +/- 0.12 MPa) and 15% OSR (1.32 +/- 0.74 MPa vs 1.12 +/- 0.33 MPa). Conclusions: The characteristic MAS distribution remained at the location where the apexes of the PBS interacted with the aortic wall at its greater curve. Both higher OSR and the presence of a connecting bar can significantly increase the MAS after SG implantation. Moreover, the chronic MAS at the PBS area may injure the aortic wall, causing RTAD. (J Vasc Surg 2018;68:14S-21S.) Clinical Relevance: After endovascular aortic repair, the stent graft (SG) generates stress toward the aorta and may injure the aortic wall, causing retrograde type A dissection. However, the stress cannot be measured in vivo. In our patient-specific computational models, we simulated SG implantation and quantified the maximum aortic stress (MAS) and found a characteristic MAS distribution. The MAS was seen at the proximal bare stent in Valiant and Talent models and was significantly higher in higher oversizing ratio models and in SG with connecting bar models. The understanding of biomechanical behavior of SG-induced aortic injury will allow SG design to evolve.