Thoracic aorta 3D hemodynamics in pediatric and young adult patients with bicuspid aortic valve

Bicuspid aortic valve (BAV) is the most commonly diagnosed congenital heart defect with a prevalence ranging from 0.5 to 2% of the population1 and is often coincident with other congenital cardiovascular diseases, particularly left-sided obstructive lesions such as coarctation of the aorta.2 Pediatric BAV patients are known to have larger aortic dimensions than children with trileaflet valves, and are prone to progressive ascending aorta (AAo) dilatation.3 As these patients progress into adulthood, they are at increased risk for aortic dissection as a result of the disease4; however, the risk of primary cardiac events in childhood is minimal.5 Nonetheless, when diagnosed at an early age, BAV patients may require surgical intervention to normalize valve function and alter thoracic aorta anatomy in hopes of reducing long term risk.6 Time-resolved, three dimensional (3D) phase contrast (4D flow) MRI is increasingly used to study the role of cardiovascular hemodynamics in BAV.7 Recent studies in adult patients have shown that congenitally abnormal valves are associated with altered ascending aortic blood flow including high velocity outflow jet patterns and deranged helix and vortex type flow.8-12 Moreover, coarctation of the aorta can also result in varied hemodynamics in both the ascending and descending aorta in BAV patients.13 These hemodynamic alterations can result in changes in aortic wall shear stress (WSS) which have been shown to promote endothelial cell dysfunction and may ultimately lead to vascular remodeling.14 Elevated AAo WSS resulting from high velocity, asymmetric outflow jets in BAV patients has been hypothesized to play a role in progressive aortic dilatation in this cohort. Recent studies have demonstrated that adults with BAV have systematically higher and more asymmetric WSS relative to age and aortic size matched controls,9-11,15,16 and recent work by van Ooij et al using 4D flow MRI demonstrated increased volumetric WSS in the ascending aorta of adult BAV patients with aortic valve stenosis.17 Other hemodynamic parameters such as peak velocity, flow jet angle,18 and outflow eccentricity (flow displacement)19 have also been used in an attempt to quantify the impact of valvular heart disease on aortic hemodynamics. In the pediatric population, 4D flow MRI assessment has generally been described in small studies or case reports that have focused on patients with complex congenital heart or vascular defects or on postsurgical hemodynamics such as Fontan circulation.20-23 Truong et al recently used 2D phase contrast of the right pulmonary artery to measure WSS in children with pulmonary artery hypertension.24 However, the impact of BAV on changes in blood flow and the association with age and aortic size is poorly understood. In this pilot study, our aim was to describe the influence of BAV on thoracic aorta hemodynamic parameters in a group of pediatric and young adult patients using 4D flow MRI.