Evaluation of Aortic Stiffness as a Prognostic Indicator of Aortic Dilatation in Patients With Bicuspid Aortic Valve (BAV) by Multimodal Imaging (MRI, Echocardiography and Ultrafast Ultrasound Imaging)

Background Bicuspid Aortic Valve (BAV) is the most common congenital heart defect with prevalence around 1 to 2% of the general population . It is defined by the presence of two functional cusps with less than three parallel zones of apposition between the cusps. This different valve's morphology is associated with a spectrum of valvular (aortic stenosis and insufficiency) and aortic complications (aneurysm and dissection). Indeed, the valvular abnormality is associated with changes in the aortic arch with an increase in the incidence of ascending aortic aneurysm unrelated to valvular functional impairment. The mechanisms responsible for aortic involvement are still incompletely understood but combine, in varying proportions, a constitutional fragility (linked to a common embryological origin of the aortic valve and the aortic arch) and to the haemodynamic modifications, generated by the specific morphology of BAV .

Current risk prediction of aneurysm development is currently performed only with the ascending aortic diameter, associated with history of aortic coarctation and familial history of dissection. Moreover, aortic dilatation may occur after aortic valve replacement alone, necessitating a second intervention, with a higher surgical risk. Improvement of the aortopathy evaluation is therefore a major stake in the evaluation of the BAV patient.

Studies of the biomechanical properties of the BAV aortic wall converge towards an increase in arterial stiffness as well as in other elastopathies such as Marfan's disease. Thus, measurements of aortic distensibility in trans-thoracic echocardiography (TTE) or MRI, or the measurement of the Pulse Wave Velocity (PWV) are significantly different case of BAV compared to the general population. However, no prospective study has demonstrated the prognostic role of these morphological biomarkers in the prediction of aortic dilation.

From a biomechanical point of view, the vessel's rupture appears when the mechanical stress applied to the wall exceeds the material resistance properties. The aortic resistance evaluation requires the use of different imaging modalities which propose the measurement of stiffness parameters. Circumferential stiffness (with TTE or MRI) can be evaluated by measuring the distensibility. In addition, longitudinal stiffness can be evaluated by measuring the local PWV.

We aim at better defining the vascular involvement of BAV patients by determining the prognostic role of functional parameters as non-invasive predictive factors for aortic dilation.