Quantification of hemodynamic wall shear stress in patients with bicuspid aortic valve using phase-contrast MRI

Bicuspid aortic valve (BAV) is often concomitant with aortic dilatation, aneurysm, and dissection. This valve lesion and its complications may affect positional and temporal wall shear stress (WSS), a parameter reported to regulate transcriptional events in vascular remodeling. Thus, this pilot study seeks to determine if the WSS in the ascending aorta (AAo) of BAV patients differs from control patients. Phase-contrast magnetic resonance imaging (PC-MRI) was used to perform flow analysis at the level of the AAo in 15 BAV and 15 control patients. Measurement of the aorta dimensions, flow rates, regurgitant fraction (RF), flow reversal ratio (FRR), temporal and spatial WSS, and shear range indices (SRI) were performed. The BAV and control group showed a significant difference between the circumferentially averaged WSS (p=0.03) and positional WSS at systole (minimum p<0.001). Regressions found that SRI (r=0.77, p<0.001), RF (r=0.68, p<0.001), and WSS at systole (r=0.66, p<0.001) were correlated to AAo size. The spatial distribution and magnitude of systolic WSS in BAV patients (-6.7+/-4.3 dynes/cm2) differed significantly from control patients (-11.5+/-6.6 dynes/cm2, p=0.03). The SRI metric, a measure of shear symmetry along the lumen circumference, was also significantly different (p=0.006) and indicated a heterogenic pattern of dilatation in the BAV patients.