Multiple aortopathy phenotypes with bicuspid aortic valve: the importance of terminology and definition criteria

Abstract

We read with interest the paper by Jackson et al. [1] reporting the absence of association between valve morphology and ascending aorta configuration in 300 bicuspid aortic valve (BAV) patients referred for surgery. Although previous studies had already addressed the phenotypic heterogeneity of BAV aortopathy [2, 3], the authors were the first to use trans-oesophageal echocardiography and surgical inspection respectively for aorta and BAV morphology definition throughout. Although the surgical referral may have constituted a limit, as it precluded earlier stage dilatations from being analysed, it allowed for commendable consistency of diagnostic methods. However, the paper from Stockholm [1] raises concerns with regard to the terminology and definitions employed. The authors distinguished ‘N’, ‘A’ and ‘E’ morphologies of the aorta, citing Schaefer et al. [3] as the source for this nomenclature; however, they used it quite differently. In particular, the ‘A’ term, instead of indicating ascending tract dilatation with normal sinuses, surgically treatable by supracoronary replacement [2–4], stood for dilatation with sino-tubular diameter smaller than the sinus diameter ‘regardless of position, that is, aortic root or ascending aorta’ [1]. While the Schaefer’s ‘E’ form consisted of sinus effacement [3], corresponding to the ‘root phenotype’ previously defined by us [2], Jackson et al. described it as a dilatation with the sino-tubular junction exceeding the sinuses: a diffuse enlargement of the entire ascending aorta, according to the mean diameters reported [1]. This is not only a terminological matter, as classifications should have a surgical rationale and pathogenetic relevance. Defining an aortic aneurysm as ‘root phenotype’ implies that a Bentall or valve-sparing procedure is required to treat it, rather than supracoronary replacement [2, 4]: the proportion of Jackson’s type ‘A’ dilatations requiring root procedures was imponderable. Root versus ascending phenotype distinction may also have a pathogenetic meaning [2], with root type being more likely subtended by some genetic defect, as confirmed by a recent study disclosing signs of subclinical aortopathy in first-degree relatives of BAV probands with root phenotype aorta [5]. Indeed, Jackson’s starting assumption that a correlation between cusp configuration and aortic phenotype would have suggested a causal role of haemodynamics may be simplistic. Even a haemodynamically triggered dilatation could later progress independently of flow-related factors [6], thus the clinical importance of the pathogenetic question might be actually overrated. The phenotypic heterogeneity of BAV aortopathy probably suggests that genetic and haemodynamic causative factors may coexist and combine in variable ways [2]. Identifying methods to discriminate, in the individual patient, the respective contributions of either pathogenetic factor is the real challenge that the research on BAV aortopathy must face. To quantify the haemodynamic component, i.e. the degree of flow derangement even in echocardiographically normofunctional BAVs, we have recently identified and validated a magnetic resonance imaging parameter, namely the cusp opening angle (A. Della Corte, et al. J Thorac Cardiovasc Surg, in press; doi:10.1016/j.jtcvs.2011.10.014). In order to be able to transfer the implications of BAV aortopathy heterogeneity into our clinical practice, we need to speak a common language, that is, terminology and classification criteria should be strictly codified.