Influence of thoracic endovascular aortic repair on true lumen helical morphology for Stanford type B dissections

Objective: Thoracic endovascular aortic repair (TEVAR) can change the morphology of the flow lumen in aortic dissections, which may affect aortic hemodynamics and function. This study characterizes how the helical morphology of the true lumen in type B aortic dissections is altered by TEVAR. Methods: Patients with type B aortic dissection who underwent computed tomography angiography before and after TEVAR were retrospectively reviewed. Images were used to construct three-dimensional stereolithographic surface models of the true lumen and whole aorta using custom software. Stereolithographic models were segmented and co-registered to determine helical morphology of the true lumen with respect to the whole aorta. The true lumen region covered by the endograft was defined based on fiducial markers before and after TEVAR. The helical angle, average helical twist, peak helical twist, and cross-sectional eccentricity, area, and circumference were quantified in this region for pre- and post-TEVAR geometries. Results: Sixteen patients (61.3 ± 8.0 years; 12.5% female) were treated successfully for type B dissection (5 acute and 11 chronic) with TEVAR and scans before and after TEVAR were retrospectively obtained (follow-up interval 52 ± 91 days). From before to after TEVAR, the true lumen helical angle (–70.0 ± 71.1 to –64.9 ± 75.4°; P =.782), average helical twist (–4.1 ± 4.0 to –3.7 ± 3.8°/cm; P =.674), and peak helical twist (–13.2 ± 15.2 to –15.4 ± 14.2°/cm; P =.629) did not change. However, the true lumen helical radius (1.4 ± 0.5 to 1.0 ± 0.6 cm; P <.05) and eccentricity (0.9 ± 0.1 to 0.7 ± 0.1; P <.05) decreased, and the cross-sectional area (3.0 ± 1.1 to 5.0 ± 2.0 cm²; P <.05) and circumference (7.1 ± 1.0 to 8.0 ± 1.4 cm; P <.05) increased significantly from before to after TEVAR. The distinct bimodal distribution of chiral and achiral native dissections disappeared after TEVAR, and subgroup analyses showed that the true lumen circumference of acute dissections increased with TEVAR, although it did not for chronic dissections. Conclusions: The unchanged helical angle and average and peak helical twists as a result of TEVAR suggest that the angular positions of the true lumen are constrained and that the endografts were helically conformable in the angular direction. The decrease of helical radius indicated a straightening of the corkscrew shape of the true lumen, and in combination with more circular and expanded lumen cross-sections, TEVAR produced luminal morphology that theoretically allows for lower flow resistance through the endografted portion. The impact of TEVAR on dissection flow lumen morphology and the interaction between endografts and aortic tissue can provide insight for improving device design, implantation technique, and long-term clinical outcomes.