Blood flow helical pattern in type III arch configuration as a potential risk factor for type B aortic dissection

OBJECTIVES: Abnormal helical flow (HF) in the aortic arch has been proposed as a causative factor for aortic dilatation and aortic dissections (ADs). Patients with type B AD present a high prevalence of type III arch configuration, which comprises recognized anatomic AD risk factors. Our aim was to assess whether the type III arch configures a consistent secondary HF pattern. METHODS: We employed computational fluid dynamics to compare HF features associated with type I-III arches. The intra-aortic blood flow pattern was regionally assessed through the Modified Arch Landing Areas Nomenclature (MALAN) for planning endovascular aortic repair. Aortic flow pathlines were extracted from the systolic aortic velocity field and objectively characterized through intrinsic shape indices of absolute curvature vertical bar kappa vertical bar and absolute torsion vertical bar tau vertical bar. Absolute local normalized helicity was computed and mapped on aortic flow pathlines. RESULTS: The tendency of aortic flow pathlines to bend and rotate exacerbated in the isthmus of type III arch (MALAN 3/III), where the highest vertical bar kappa vertical bar values (P < 0.0001) were paralleled by the lowest vertical bar tau vertical bar values (P = 0.010), demonstrating the persistence of a high rotational HF heavily insisting on 3/III. In 3/III area, local normalized helicity was higher than both 3/I and 3/II (P = 0.053). CONCLUSIONS: Type III arch configuration is associated with a specific, consistent and abnormal secondary HF pattern, which may account for its high prevalence in patients with type B AD.