Thoracobifemoral Bypass Exhibits Hemodynamic Superiority Compared With Axillobifemoral Bypass For Infrarenal Aortic Occlusion

Introduction: Thoracobifemoral bypass (TFB) is a historically proven durable bypass option for patients with proximal aortoiliac occlusive disease and infrarenal aortic occlusion (IRAO). However, this operation is rarely done secondary to increased morbidity and difficulty of a thoracoabdominal exposure. This patient population is often relegated to an axillobifemoral bypass (AxFB) which has comparatively inferior bypass patency rates. In this study we sought to quantify the hemodynamic superiority of TFB compared with AxFB. Methods: Two patients who underwent a TFB and AxFB were used for this analysis. Their postoperative CT scans were segmented to build patient-specific 3D models that captured the flow lumens of their bypass grafts and infrarenal aortic pathology. We then performed computational fluid dynamic (CFD) simulations with a cardiac cycle inlet velocity and compared the average velocity at specified sites within the grafts. CFD models for both the TFB and the AxFB patients are shown in figure 1a-b. Results: In the AxFB model, there was a hemodynamically significant velocity drop across the proximal anastomosis. Additionally we found that there was a 75% velocity reduction over the length of the graft, regardless of the proximal inflow drop across the anastomosis. Conversely the inflow velocities were preserved in the proximal portion of the TFB graft. These velocities increased as we progressed to the distal anastomosis, suggesting a preservation of flow across a smaller caliber graft. Conclusion: Our models show TFB to be a hemodynamically superior choice over AxFB based on greater velocity degradation seen in our AxFB model. We conclude that in patients who are fit to undergo a thoracoabdominal exposure, TFB be considered over AxFB in cases of IRAO where infrarenal aortobifemoral bypass is not anatomically feasible. Figure 1a-b: CFD models of a TFB (a) and an AxFB (b). The color scale represents relatively higher (red) and lower (blue) velocities in m/s.