Aortic replacement in the setting of bicuspid aortic valve: how big? How much?

Despite more than a decade of intense investigation, controversy persists regarding appropriate triggers for aortic replacement in the setting of bicuspid aortic valve. The difficulty is that the data are inescapably imperfect. Although we can count individuals with bicuspid valve who suffer dissection, we have an insufficient understanding of the true denominator of individuals at risk to calculate the probability of dissection for an individual patient. In addition, our own decision-making process is subject to "denominator neglect" or focus on the fact of the occurrence of the event rather than on the risk of the occurrence. Furthermore, the data are inherently incomplete given the asymmetric nature of outcomes information. Specifically, although we can see those who did or did not dissect among the patients not undergoing surgery, the converse is not true; the tragedy of prophylactic surgery is that one cannot distinguish those who have benefited through prevention of dissection from those who paid the price of surgery but in whom dissection would never have occurred. Finally, we have data for only some of the critical determinants of dissection. Structural failure occurs when stresses exceed strengths. Aortic diameter gives us some insight into stress but we have little information on the material strength of the aorta. Early indications that patients undergoing aortic valve replacement for bicuspid valve had a significant risk of aortic dissection were followed by laboratory data showing histologic, biochemical, and mechanical abnormalities supporting an aggressive approach to resection; however, more recent clinical studies call this into question.