The emerging roles of cardiovascular magnetic resonance imaging in transcatheter aortic valve implantation (TAVI)

Multimodality imaging in bicuspid aortic valve

Bicuspid aortic valve (BAV) patients are at increased risk of valve dysfunction and ascending aorta aneurysm. Imaging techniques are essential to establish diagnosis, identify complications and indicate surgical treatment. Transthoracic echocardiography (TTE) is the imaging technique of choice to diagnose BAV, valve morphotype and valvular dysfunction in clinical practice. However, it can be less precise in assessing the aortic root and proximal ascending aorta, and visualization of the mid-distal ascending aorta and the arch may be difficult in some adults where cardiac magnetic resonance (CMR) and computed tomography, using multiplanar reconstructions, are better at assessing aortic diameters. Although valvular dysfunction is very variable, almost half of the patients have more than mild aortic valve disease. TTE is the most effective and accurate test for evaluating the severity of valvular dysfunction and guiding appropriate management decisions. Aorta dilation is a common finding in patients with BAV. The pattern of aortic dimensions has been categorized in three aortic phenotypes: no-dilation phenotype, ascending aorta phenotype and root phenotype. Controversial data exist regarding the relationship between BAV morphology and aorta dilation phenotype. The assessment of aortic stiffness (measuring distensibility or the velocity of propagation of flow) has raised special interest in order to predict progressive aorta dilation. However, current data indicates that BAV aortas do not show altered stiffness compared to those associated with a tricuspid valve with a similar aorta size. Moreover, novel 4D-flow CMR sequences have been crucial in the evaluation of abnormal ascending aorta flow, showing that flow in the aorta of BAV patients is asymmetric and includes the formation of large vortices. Such flow abnormalities are thought to produce changes in wall shear stress which has been associated with extracellular matrix dysregulation. The key points to understand familial screening and the recommendations for establishing the follow-up and therapeutic management of BAV patients are exposed in the review. The main objective of this article is to review the advantages and limitations of the imaging techniques in the diagnosis and management of BAV and the best strategies in the use of multimodality imaging.