Whether the dilatation of proximal aorta in patients with bicuspid aortic valve is secondary to hemodynamic effects related to the abnormal aortic valve or a primary manifestation of the genetic disorder remains controversial. We discuss in this paper the recent data on the BAV function and transvalvular flow patterns in relation with the dilatation type of the proximal aorta. Different morphological forms of bicuspid aortic valve in relation with the specific transvalvular blood flow patterns are focus of the first paragraph of this paper. In the second part of this paper we present the pathogenetic insight into the different clinically observed phenotypes of bicuspid aortic valve disease (i.e., association of proximal aortic shapes with the specific cusp fusion patterns), based on the data from recent rheological studies. 1. Introduction It is widely accepted that bicuspid aortic valve (BAV) is a very heterogeneous disease and that the different phenotypes of BAV-associated aortopathy may be caused by unique pathogenetic mechanisms [1, 2]. In persons with BAV, the dimensions of the proximal aorta are significantly larger than those in persons with tricuspid aortic valve, even in the absence of significant valvular hemodynamic disturbance [3]. Whether the dilatation of proximal aorta in patients with BAV is secondary to hemodynamic effects related to the abnormal aortic valve or a primary manifestation of the genetic disorder remains controversial. The clarification of this phenomenon is not simply theoretical in nature, since this may significantly affect the surgical approach to the dilated ascending aorta in patients presenting with BAV disease. The prevailing theory of BAV-associated aortopathy will undoubtedly tailor the surgical treatment of this common clinical entity. Moreover, specific BAV phenotypes may require different therapeutic approaches and would support an individual treatment strategy of BAV disease. In the face of the growing body of evidence on BAV function, we found it important to address the issue of systolic transvalvular flow through the BAV. Indeed, this is one of the crucial points which may resolve the controversy regarding the pathogenesis of BAV-associated aortopathy. We discuss in this paper the recent data on the BAV function and transvalvular flow patterns in relation with the dilatation type of the proximal aorta. These rheological studies are supportive of hemodynamic origin of the distinct BAV phenotypes and will be discussed in details in the following paragraphs. 2. BAV Morphology and Transvalvular Flow The
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