Bicuspid Aortic Valve Phenotype and Aortopathy: Nomenclature and Role of Aortic Hemodynamics

We read with great interest the recently published paper by Kang et al. (1) regarding the importance of bicuspid aortic valve (BAV) phenotypic classification and its association with valvular dysfunction and aortopathy. The findings provide new and valuable data regarding risk stratification of BAV patients according to leaflet morphology. Of particular interest is the potential utility of this information, combined with knowledge of family history and hemodynamics (2), to provide a better understanding of patient prognosis.

Unfortunately, in the context of the existing literature, the authors chose unconventional nomenclature to stratify BAV phenotypes. In the paper, the term BAV-RL designates valves with free leaflets in the lateral position rather than the more common practice of describing fusion of the right and left coronary leaflets (3–5). Although somewhat arbitrary, this terminology contradicts the classification scheme adapted from one of the key references (3) and produces yet another naming scheme. The question of what constitutes a BAV-RL is sure to cause confusion amongst the community and in future research efforts where nomenclature swapping propagates and goes unnoticed. This highlights a growing need for a uniform classification scheme, similar to that proposed by Sievers et al. (4).

Furthermore, the discussion of aortic hemodynamic changes as a potential link between valve morphology and development of aortopathy is somewhat incomplete. Although we strongly agree that BAVs alter aortic hemodynamics, as has recently been shown by us and others, the assertion that left-handed helical flow exists in the BAV phenotype with free leaflets in the lateral position is unproven, with a single-center report in the literature.

Our experience is that the orientation of the flow helix is predominantly right-handed. We and others have shown that the incomplete opening of the BAV results in an abnormal flow jet dependent on the position of a conjoint leaflet. In the case of lateral leaflet fusion, the conjoint leaflet can cause a flow jet to reflect off of the inner arch curvature and impinge on the greater arch at a more downstream position, thereby causing helical flow with right-handed orientation (5). In addition, the authors did not address recent developments that have shown that magnetic resonance imaging can be used to directly quantify the impact of aortic valve disease on the aortic wall by means of metrics such as segmental wall shear stress (5). In this context, aortic wall shear stress is altered regardless of the orientation of helix flow and may be a more fundamental parameter to investigate for abnormal aortic remodeling.

In essence, we believe that the data of Kang et al. (1) are an important step toward understanding the role genetics and mechanotransduction may play in BAV-mediated aortopathy. We agree that advanced imaging techniques offer promising diagnostic imaging tools. However, a consistent description of the subtle variations in valve morphology, as well as newly developed in vivo metrics of hemodynamic changes associated with aortic valve disease, should not be overlooked: without a uniform classification scheme, we run the risk of confounding future efforts.