First insights into the role of wall shear stress in the development of a distal stent graft induced new entry through computational fluid dynamics simulations

Abstract

Background: Distal stent graft induced new entry (dSINE) is an emerging complication after frozen elephant trunk (FET) procedure. The aim of this computational fluid dynamics (CFD) study was to investigate the role of wall shear stress (WSS) after the development of dSINE based on hemodynamic changes.

Methods: Aortic diameter and WSS of five patients who developed a dSINE after FET procedure were retrospectively analyzed before and after the occurrence of dSINE. Patient-specific 3-dimentional surface models of the aortic lumen were reconstructed from computed tomography angiographic datasets (pre dSINE: n=5, dSINE: n=5) to perform steady-state CFD simulations with laminar blood flow and zero pressure outlet conditions. WSS was calculated at the level of the stent graft (SG), the landing zone of the SG and at a location further distal to the SG, as well as on the outer and inner curvature of the aorta from SG center to its distal end.

Results: Post dSINE occurrence, median WSS increased significantly from 0.87 [interquartile range (IQR): 0.83-1.03] to 1.55 (IQR: 1.09-2.70) Pa, (P=0.043) within the SG and from 1.22 (IQR: 0.81-1.44) to 1.76 (IQR: 1.55-3.60) Pa, (P=0.043) at the landing zone of the SG. A non-significant increase from 1.22 (IQR: 0.59-3.50) to 2.58 (IQR: 1.16-3.78) Pa, (P=0.686) further downstream was observed. WSS at the outer curvature of the SG was significantly higher compared to WSS at the inner curvature for dSINE.

Conclusions: Adverse hemodynamic conditions in the form of elevated WSS consist inside and at the distal end of the SG as well as at the outer curvature of the aorta, which may contribute to weakening of the aortic wall. These new findings emphasize the relevance and potential of WSS in dSINE for additional adverse events, such as aortic rupture. Further prospective studies are warranted to explore if the combination of clinical parameters with WSS might be useful to decide which patients require an urgent reintervention in terms of a SG extension.

Keywords: Wall shear stress (WSS); aortic dissection; computational fluid dynamics simulation; distal stent graft induced new entry (dSINE); frozen elephant trunk (FET).

Figure 1

Aortic and TL diameters were measured at the level of the stented segment (L1), at the landing zone (L2) and 2 cm further distally to the SG ending (L3) (A). WSS was assessed at the same locations (B). TL, true lumen; SG, stent graft; WSS, wall shear stress.

Figure 2

Streamlines visualize the blood flow patterns in the aorta. Streamlines were colored by the magnitude of the fluid velocity. Red represents high flow, blue represents low flow velocity.

Figure 3

WSS is presented for each patient prior (A) and after the development of dSINE (B) (arrows show the distal end of the FET). WSS was significantly elevated after the development of dSINE (B) within the SG and at its distal end. In patient No. 1, 3 and 5 a localized WSS increase was apparent at the landing zone of the SG and/or distally (A). In patient No. 4 WSS post-dSINE was increased in the whole aorta. The streamlines, in Figure 2 show, that flow with elevated velocity passes close to the anterior wall, thereby causing the higher WSS at that wall. WSS, wall shear stress; dSINE, distal stent graft induced new entry; FET, frozen elephant trunk; SG, stent graft.

Figure 4

Maximal aortic diameters of each patient are presented at the level of the stented segment (L1) (A), at the distal end of the SG (L2) (B) and 2 cm further distally to the SG ending (L3) (C). Median aortic diameter increased at all locations, reaching statistical significance at L2. dSINE, distal stent graft induced new entry; SG, stent graft.