With the advancement of disease, necrotic core is less often located at low WSS regions, but exposed to high WSS, which is probably the result of lumen narrowing. Necrotic core in contact with the lumen was most frequently exposed to high WSS.

Funding Acknowledgements Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): The Dutch Heart Foundation Background Patients with bicuspid aortic valve (BAV) have altered flow velocity patterns with different wall shear stress (WSS) distributions in the ascending aorta compared to patients with tricuspid aortic valves. These WSS distributions are associated with aortic dilatation in cross sectional studies, however, longitudinal data demonstrating a potential causative role is missing. Purpose The aim of this study was to assess the differences in WSS distributions between BAV patients and healthy subjects and to determine the predictive value of WSS for aortic growth in patients with a BAV. Methods Forty patients with a BAV and 32 healthy matched subjects were prospectively studied by 4D-flow cardiovascular magnetic resonance (CMR). Peak velocity, pulse wave velocity, aortic distensibility, peak systolic WSS (magnitude), the different WSS components (axial and circumferential), and WSS angle were assessed in the proximal ascending aorta. WSS angle was defined as the angle between the WSSmagnitude and WSSaxial component. In the BAV patients, aortic volumetric growth over three years was determined in the proximal ascending aorta (first 5cm) based on CT angiography. Multivariate linear regression analysis was used to identify independent predictors of aortic volumetric growth. Results Of the BAV patients, 21 (53%) had a left-right fusion pattern and eight patients had Turner syndrome. WSSaxial was significantly lower in BAV patients compared to healthy subjects (p = 0.008) and WSScircumferential and WSS angle were significantly higher (both p < 0.001, see Figure). WSSmagnitude, pulse wave velocity, and aorta distensibility were not statistically significant different. WSSmagnitude (0.69 N/m² [0.51-0.81] vs 1.08 N/m² [0.89-1.24], p = 0.005), WSSaxial (0.50 N/m² [0.39-0.61] vs 0.72 N/m²  [0.54-0.94], p = 0.015) and WSScircumferential (0.34 N/m² [0.32-0.46] vs 0.64 N/m² [0.47-0.81], p = 0.008) were significantly lower in BAV Turner patients compared to BAV non-Turner patients, while WSS angle (40° [34-41] vs 40° [32-48], p = 0.607) was not statistically significant different. During a follow-up of three years, there was a significant growth of the proximal ascending aorta in the BAV patients (1.2 cm3 [-0.2-2.5], p = 0.001). In multivariate analysis corrected for baseline aortic volume and diastolic blood pressure, WSS angle was the only independent predictor for proximal aortic volume growth (β=0.108, p = 0.030). Conclusions Increased WSScircumferential and especially WSS angle are present in patients with BAV. WSS angle was the only independent predictor of aortic growth. These findings highlight the potential role of  WSS measurements in patients with BAV to stratify patients at risk for aortic dilation.

Funding Acknowledgements Type of funding sources: Foundation. Main funding source(s): Stichting Hartekind en Thorax Foundation Background Optimal timing of pulmonary valve replacement (PVR) in Tetralogy of Fallot (TOF) patients remains challenging. Wall stress is considered to be a possible early marker of right ventricular (RV) dysfunction. With patient-specific computational models, wall stress can be determined regionally and with high accuracy, especially in complex shaped ventricles such as in TOF patients. We aimed to 1) develop patient-specific computational models to assess RV diastolic wall stresses and 2) investigate the association of wall stresses and their change over time with functional parameters in TOF patients. Methods Repaired TOF patients with at least moderate pulmonary regurgitation (PR) and prior to PVR were included. MRI-based patient-specific computational ventricular models were created (figure). The ventricular geometry was created by stacking endo- and epicardial contours traced on short axis SSFP cine images. Pressure in the right ventricle was estimated from echocardiography. Mid-diastolic wall stress in the RV free wall was analysed globally and regionally (basal, mid, apical, anterior, lateral and posterior) at two time points. RV ejection fraction (RVEF), NT-proBNP and exercise tests (% maximum predicted workload) were used as outcomes for RV function. Associations between wall stresses and outcomes were investigated using linear mixed models adjusted for follow-up duration. Results Five males and five females were included with an age at baseline of 24 (IQR 16-28) years and RV end-diastolic volume of 140 (IQR 127-144) ml/m2. The period between the two time points was 7.0 (IQR 5.8-7.3) years. Global wall stress of the RV free wall combining both time points was 5.8 kPa (IQR 5.2-7.2). There was no statistical difference between baseline and follow-up global wall stress. The mean wall stresses in the mid region was 1.69 kPa (p < 0.01) higher than in the basal region and was 1.05 kPa (p = 0.03) higher than in the apical region cross-sectionally. The wall stress also increased more in the mid region compared to basal and apical region, corrected for duration of follow-up. Patients with more severe PR at baseline demonstrated a higher increase of global wall stress over time (p = 0.02), especially in lateral free wall. Higher global free wall stresses were cross-sectionally independently associated with lower RVEF, adjusted for LVEF and RVEDV (β=-1.29 % RVEF per kPa increase in wall stress, p = 0.01). This association was most prominent in the anterior, basal and mid part. No statistically significant association was found between wall stress, NT-proBNP, and exercise capacity. Conclusions This study generated a novel MRI-based method to calculate wall stress in geometrically complex ventricles. Wall stress associated negatively with RVEF in patients with TOF and PR. This promising tool for RV wall stress analysis can be used in future larger studies to validate these preliminary findings and to assess the predictive value of wall stress in TOF. Abstract Figure.