PURPOSE

To use computational simulations to compare the hemodynamic characteristics of a classic bifurcated stent-graft to an equally long endograft design with "dog bone"-shaped limbs (DB), which have large diameter proximal and distal ends and significant narrowing at the midsection to accommodate aneurysms with an extremely narrow bifurcation.

MATERIALS AND METHODS

A 3-dimensional model was constructed using commercially available validated software. Inlet and outlet diameters were 28 and 14 mm, respectively. The total length of both models was kept constant to 180 mm, but the main body of the DB model was 20 mm shorter than the bifurcated endograft. The iliac limbs of the DB model had a 9-mm stenosis over a 30-mm segmental length in the midsection. Flow was quantified by time-averaged wall shear stress, oscillatory shear index (OSI), and relative residence time (RRT). The displacement forces in newtons (N) and maximum wall shear stress (WSS) in pascals (Pa) were compared during a cardiac cycle at 3 segments (main body, bifurcation, and iliac limbs) of both models with computational fluid dynamics analysis.

RESULTS

The DB accommodation was associated with higher forces at the main body (range 3.15-4.9 Ν) compared with the classic configuration (1.56-2.34 N). On the contrary, the forces at the bifurcation (3.81-5.98 vs 3.76-5.54 N) and at the iliac limbs (0.34-0.85 vs 0.49-0.74 N) were comparable for both models. Accordingly, maximum WSS was detected at the iliac sites for both models throughout the cardiac cycle. The highest values were detected at peak systole and equaled 26.6 and 12 Pa for the DB and bifurcated configurations, respectively. The narrow segments in the DB model displayed high stress values but low OSI and very low RRT.

CONCLUSION

The DB accommodation seems to correlate with higher displacement forces at the main body and higher stresses at the iliac limbs. Consequently, regular imaging follow-up of the DB design deems necessary to delineate its mid- and long-term clinical performance.