Regional Wall Shear Stress and Ascending Aorta Dilation in BAV

Quick Takes

  • Patients with bicuspid aortic valve (BAV) are at risk of progressive ascending aorta (AAo) dilation potentially attributable to an intrinsic abnormality of the AAo wall (bicuspid aortopathy) and/or hemodynamic abnormalities caused by the BAV resulting in alterations of the aortic wall.
  • This retrospective study used serial four-dimensional flow CMR, and found an association between larger areas of elevated wall shear stress in the AAo and in the entire aorta with higher rates of progressive AAo dilation; adding support that hemodynamics plays a role in AAo dilation.
  • Ideally, prospective studies should be used to confirm the findings and to help inform clinical recommendations for the identification of patients with BAV who may be at increased risk of progressive AAo dilation and its clinical complications.

Study Questions:

What is the role of wall shear stress (WSS) in ascending aorta (AAo) progressive dilation among people with bicuspid aortic valve (BAV)?

Methods:

A cohort of 72 patients with BAV (aged 45 ± 12 years) who underwent cardiac magnetic resonance (CMR) for surveillance of aortic dilation at baseline and ≥5 years of follow-up were retrospectively identified. Four-dimensional flow CMR analysis included the calculation of WSS heat maps to compare regional WSS in individual patients with population averages of healthy age- and sex-matched subjects (database of 136 controls). The relative areas of the AAo and aorta (in %) exposed to elevated WSS (outside the 95% confidence interval [CI] of healthy population averages) were quantified.

Results:

At a median follow-up duration of 6.0 years, the mean AAo growth rate was 0.24 ± 0.20 mm/yr. The fraction of the AAo exposed to elevated WSS at baseline was increased among patients with higher growth rates (>0.24 mm/yr, n = 32) compared with those with growth rates <0.24 mm/yr (19.9% [IQR, 10.2%-25.5%] vs. 5.7% [IQR, 1.5%-21.3%]; p = 0.008). Larger areas of elevated WSS in the AAo and entire aorta were associated with higher rates of AAo dilation >0.24 mm/yr (odds ratio, 1.51; 95% CI, 1.05-2.17; p = 0.026 and odds ratio, 1.70; 95% CI, 1.01-3.15; p = 0.046, respectively).

Conclusions:

Among patients with BAV, the area of elevated AAo WSS assessed by four-dimensional flow CMR identified higher rates of aortic dilation and thus might determine which patients require closer follow-up.

Perspective:

People with BAV are known to be at risk for AAo dilation and its associated complications. Potential explanations include a proposed theory of a primary bicuspid aortopathy, with the assumption of an abnormal aortic wall matrix that is susceptible to dilation; and a hemodynamic hypothesis, postulating that abnormal flow mediated by the BAV results in aortic wall alterations. Previous studies have variably associated valve morphology, valve function, and ascending aorta morphology with AAo dilation; and specific risk factors for progressive AAo dilation have not been definitively established. This retrospective study found an association between larger areas of elevated WSS in the AAo and in the entire aorta using four-dimensional flow CMR with higher rates of AAo dilation, adding support that hemodynamics plays a role in progressive AAo dilation. The study was relatively small, CMR techniques were not consistent throughout the follow-up interval, the retrospective study design could have introduced bias, and aortic dilation is taken as a surrogate for clinical complications. Ideally, prospective studies should be used to confirm the findings and to help inform clinical recommendations for the identification of patients with BAV who may be at increased risk of progressive AAo dilation and its clinical complications.

Keywords: Aortic Valve Stenosis, Bicuspid Aortic Valve Disease, Diagnostic Imaging, Dilatation, Heart Defects, Congenital, Heart Valve Diseases, Hemodynamics, Magnetic Resonance Spectroscopy, Risk Factors, Vascular Diseases


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