Abstract
Objectives: Clinical management decisions surrounding ascending aorta (AAo) dilation in bicuspid aortic valve (BAV) disease benefit from personalized predictive tools. 4D-flow MRI may provide patient-specific markers reflective of BAV-associated aortopathy. This study aims to explore novel 4D-flow MRI parametric voxel-by-voxel forward flow, reverse flow, kinetic energy and stasis in BAV disease. We hypothesize that novel parametric voxel-by-voxel markers will be associated with aortic dilation and referral for surgery and can enhance our understanding of BAV hemodynamics beyond standard metrics. Methods: A total of 96 subjects (73 BAV patients, 23 healthy controls) underwent MRI scan. Healthy controls had no known cardiovascular disease. Patients were clinically referred for AAo dilation assessment. Indexed diameters were obtained by dividing the aortic diameter by the patient’s body surface area. Patients were followed for the occurrence of aortic surgery. 4D-flow analysis was performed by a single observer in five regions: left ventricular outflow tract (LVOT), AAo, arch, proximal descending aorta (PDAo), and distal descending aorta (DDAo). In each region peak velocity, kinetic energy (KE), forward flow (FF), reverse flow (RF), and stasis were measured on a voxel-by-voxel basis. T-tests (or non-parametric equivalent) compared flow parameters between cohorts. Univariate and multivariate analyses explored associations between diameter and parametric voxel-by-voxel parameters. Results: Compared to controls, BAV patients showed reduced stasis (p < 0.01) and increased RF and FF (p < 0.01) throughout the aorta, and KE remained similar. In the AAo, indexed diameter correlated with age (R = 0.326, p = 0.01), FF (R = −0.648, p < 0.001), RF (R = −0.441, p < 0.001), and stasis (R = −0.288, p < 0.05). In multivariate analysis, FF showed a significant inverse association with AAo indexed diameter, independent of age. During a median 179 ± 180 days of follow-up, 23 patients (32%) required aortic surgery. Compared to patients not requiring surgery, they showed increased KE and peak velocity in the proximal aorta (p < 0.01), accompanied by increased RF and reduced stasis throughout the entire aorta (p < 0.01). Conclusion: Novel voxel-by-voxel reverse flow and stasis were altered in BAV patients and are associated with aortic dilation and surgical treatment.
Highlights
Bicuspid aortic valve (BAV) is considered the most common congenital valvular malformation with an overall prevalence in the general population of 0.5–2% (Siu and Silversides, 2010)
Patients were excluded for the following reasons: history of prior myocardial infarction or known non-ischemic cardiomyopathy, complex congenital heart disease, MRI-coded moderate-severe mitral insufficiency, or a left ventricle ejection fraction (LVEF) < 50%
Patients with type 2 or un-identified valve phenotype were not included in statistical analyses due to the small sample size
Summary
Bicuspid aortic valve (BAV) is considered the most common congenital valvular malformation with an overall prevalence in the general population of 0.5–2% (Siu and Silversides, 2010). There is still variability in the clinical management guidelines (Baumgartner et al, 2017; Borger et al, 2018) for BAV aortopathy and strategies among cardiovascular surgeons vary substantially (Verma et al, 2013). This may be related to current recommendations relying on binary thresholds of ascending aorta (AAo) diameter to guide timing of proximal aortic aneurysm surgery, though these are recognized as poor predictors of acute aortic events (Pape et al, 2007). Much emphasis has been placed on identifying alternative, patient-specific markers of BAV aortopathy that may provide improved characterization for this patient population
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