Proximal aortic aneurysms: correlation of maximum aortic diameter and aortic wall thickness

The goal of therapy of proximal aortic aneurysms is to prevent an aortic catastrophe, e.g. acute dissection or rupture. The decision to intervene is currently based on maximum aortic diameter complemented by known risk factors like bicuspid aortic valve, positive family history or rapid growth rate. When applying Laplace's law, wall tension is determined by pressure × radius divided by aortic wall thickness. Because current imaging modalities lack precision, wall thickness is currently neglected. The purpose of our study was therefore to correlate maximum aortic diameter with aortic wall thickness and known indices for adverse aortic events.

Aortic samples from 292 patients were collected during cardiac surgery, of whom 158 presented with a bicuspid aortic valve and 134, with a tricuspid aortic valve. Aortic specimens were obtained during the operation and stored in 4% formaldehyde. Histological staining and analysis were performed to determine the thickness of the aortic wall.

Patients were 62 ± 13 years old at the time of the operation; 77% were men. The mean aortic dimensions were 44 mm, 41 mm and 51 mm at the aortic root, sinotubular junction and ascending aorta, respectively. Aortic valve stenosis was the most frequent (49%) valvular dysfunction, followed by aortic valve regurgitation (33%) and combined dysfunction (10%). The maximum aortic diameter at the ascending level did not correlate with the thickness of the media (R = 0.07) or the intima (R = 0.28) at the convex sample site. There was also no correlation of the ascending aortic diameter with age (R = -0.18) or body surface area (R = 0.07). The thickness of the intima (r = 0.31) and the media (R = 0.035) did not correlate with the Svensson index of aortic risk. Similarly, there was a low (R = 0.29) or absent (R = -0.04) correlation between the aortic size index and the intima or media thickness, respectively. There was a similar relationship of median thickness of the intima in the 4 aortic height index risk categories (P < 0.001).

Aortic diameter and conventional indices of aortic risk do not correlate with aortic wall thickness. Other indices may be required in order to identify patients at high risk for aortic complications.