Comparative Histology of Aortic Dilatation Associated With Bileaflet Versus Trileaflet Aortic Valves

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A more aggressive posture toward resection of the dilated aorta has been advocated when associated with bicuspid aortic valve (BAV), based on the notion that aortic material properties are weaker in this setting despite scant data to support or refute this position. The hypothesis that histologic abnormality reflects aortic wall strength was tested by comparing aortas from patients with BAV and trileaflet aortic valve. Resected aortas associated with BAV (n = 60) and trileaflet aortic valve (n = 24) were compared with normal diameter aortas from patients undergoing cardiac transplantation (n = 16) by five histologic criteria: elastic fiber loss (graded 0-4), smooth muscle cell loss (graded 0-4), medial proteoglycan accumulation (graded 0-3), medial fibrosis (graded 0-3), and atherosclerosis (graded 0-3). Patients with known connective tissue disorders, systemic inflammatory conditions, dissection, or prior heart surgery were excluded. Patients with BAV were a decade younger and more often had functional stenosis. The extent of elastic fiber loss, smooth muscle cell loss, medial fibrosis, and atherosclerosis was more severe in trileaflet aortic valve than BAV when considered across all diameters and when stratified to those between 4 and 5 cm. More severe histologic abnormalities associated with trileaflet aortic valve compared with BAV, especially when stratified by diameter, do not support a more aggressive approach to surgical intervention for dilatation associated with BAV. Indeed, if based on histologic diagnosis alone, our findings are suggestive that the converse might be true. Additionally, the lack of correlation between aortic diameter and histologic abnormality in the setting of BAV highlights the inadequacy of diameter alone as a criterion for aortic resection.