level of the tubular portion of the ascending aorta and 20% at the level of the sinuses [ie, root]). Indeed, other studies have demonstrated that a bicuspid aortic valve is associated with a dilated aorta, regardless of the presence or absence of hemodynamically significant valve dysfunction. 8 Cystic medial degeneration has been found to be the underlying cause of the aortic dilatation associated with a bicuspid aortic valve. In one study, 75% of those with a bicuspid aortic valve undergoing aortic valve replacement surgery had biopsy-proven cystic medial necrosis of the ascending aorta, compared with only 14% of those with tricuspid aortic valves undergoing similar surgery. 9 Inadequate production of fibrillin-1 during embryogenesis may result in both the bicuspid aortic valve and a weakened aortic wall. 10 Fedak et al11 examined ascending aortic specimens from those with bicuspid aortic valves and tricuspid aortic valves undergoing cardiac surgery. They found that patients with bicuspid aortic valves had significantly less fibrillin-1 than did patients with tricuspid aortic valves, and the reduction in fibrillin-1 was independent of patient age or aortic valve function. Interestingly, samples of the pulmonary arteries of the same subjects showed a similar reduction in fibrillin-1 content among those with bicuspid aortic valves. This might account for why some patients with a bicuspid valve having undergone the Ross procedure develop late dilatation of the pulmonary autograft (see later sections). Additionally, in a recent study of patients with ascending thoracic aortic aneurysms, Schmid et al12 found that compared with tricuspid aortic valve controls, the aortic aneurysm tissue of those with a bicuspid aortic valve demonstrated more lymphocyte infiltration and smooth muscle cell apoptosis. This suggests that the walls of aneurysms associated with bicuspid aortic valves may be weaker than more “typical” aneurysms.

Because half of those with a bicuspid valve have aortic dilatation, cardiologists should routinely image the ascending aorta in all bicuspid aortic valve patients. In many cases, this can be accomplished with echocardiography. However, whereas the aortic root is easily visualized in most transthoracic echocardiograms, in many cases the midportion of the ascending aorta is not. Consequently, if an ascending aortic diameter is not reported on an echocardiogram, one cannot safely assume that it was visualized and found to be normal in diameter. One might review the images to specifically examine the ascending aorta, but if it was not adequately visualized, one should instead obtain a computed tomography (CT) scan or magnetic resonance imaging (MRI) study to determine aortic diameter.