Bridging Stent-Graft Pullout Force Analysis

Abstract

To assess the pullout force (POF) of bridging stent-grafts used in thoracoabdominal stent-grafts and iliac bifurcated grafts. In an experimental setup, the POFs of Viabahn or Fluency with or without a Zilver stent were measured when deployed into the renal and celiac branches of a Zenith thoracoabdominal cuff-bearing branched stent-graft. The POFs of the Atrium i-Cast, Viabahn, Fluency, and Fluency+Zilver were measured when deployed into an iliac bifurcated graft with a short side-branch for the internal iliac artery. At least 10 trials were performed for each stent in air at room temperature. The median POF (IQR; absolute range) required to dislodge each bridging stent-graft from the 6-mm renal branch was 1.89 N (0.47 N; 1.65-2.5) for the 7-mm Viabahn, 1.17 N (0.39 N; 0.68-1.57 N) for the 7-mm Fluency, and 2.08 N (0.49 N; 1.59-2.62 N) for the 7-mm Fluency with a supporting 8-mm Zilver stent (p<0.001). For the 8-mm celiac branch, the POFs were 2.79 N (0.82 N; 2.31-4.16 N), 1.74 N (0.18 N; 1.51-1.91 N), and 2.73 N (0.94 N; 1.9-3.61 N) for the 9-mm Viabahn, 9-mm Fluency, and 9-mm Fluency with a 10-mm Zilver stent, respectively (p<0.001). For the 8-mm internal iliac branch, the POFs were 3.53 N (0.85 N; 2.55-4.72 N) for the 9-mm i-Cast, 3.82 N (0.41 N; 3.29-4.45 N) for the 9-mm Viabahn, 2.32 N (0.23 N; 1.63-2.64 N) for the 9-mm Fluency, and 2.61 N (0.71 N; 1.65-3.63 N) for the 9-mm Fluency with a 10-mm Zilver stent (p<0.001). There is a small but significant difference in pullout forces among various bridging stent-grafts. As pullout forces may be one factor contributing to type III endoleaks in complex endovascular repairs involving fenestrated and branched stent-grafts, further study is warranted to compare these grafts clinically to determine if they perform differently. According to this study, the theoretical advantages associated with the Viabahn stent-graft make it a strong choice for minimizing branch dislocations.