Aortic Valve Phenotype Shapes Helical Flow in the Ascending Aorta: Insights from 4D Flow MRI

PURPOSE: Helical flow in the ascending aorta (AAo) is recognized as beneficial to cardiovascular physiology. Previous in vivo studies of bicuspid aortic valve (BAV) disease have mainly relied on qualitative assessments or surrogate measures of helical flow, hampering its use as potential hemodynamic biomarker. Here, we leveraged a rigorous fluid mechanical framework for helical flow structures to (i) determine how aortic valve (AV) phenotype-tricuspid (TAV) versus bicuspid-influences AAo helical flow and (ii) identify its principal anatomical and hemodynamic determinants. METHODS: 4D flow MRI data from sixty subjects (41 TAV, 19 BAV) were analyzed. Helicity-derived quantities were computed to quantify the intensity and topology of AAo helical flow. Conventional hemodynamic and anatomical parameters were also extracted and their association with helicity-based quantities was explored. RESULTS: Compared with TAV subjects, BAV patients exhibited lower helicity intensity and reduced predisposition to form coherent helical flow patterns. In TAV, helical flow topology was primarily influenced by flow pulsatility and vessel anatomy, whereas in BAV, eccentric systolic jets promoted the arrangement of blood flow into helical structures without enhancing helicity intensity. Helical flow topology emerged as highly sensitive to AV phenotype, with its discriminative power augmented by conventional anatomical or hemodynamic parameters. CONCLUSION: AV phenotype critically shapes helical flow in AAo through phenotype-specific anatomical and hemodynamic determinants. The eccentric jet associated with BAV disrupts helicity intensity, potentially diminishing the protective role of helical flow. Integrating conventional hemodynamic and anatomical parameters with helical flow topology yields a robust, in vivo measurable morpho-hemodynamic signature of BAV, offering diagnostic and prognostic potential.