Collagen fibre changes in the ascending aorta for patients with an altered aortic valve

The aorta is a flexible type of artery that provides systemic circulation. It can be structurally changed if congenital abnormalities of bicuspid aortic valves (BAVs), altered tricuspid aortic valves (TAVs), age-related changes or hypertension are present. Deposits of inflammatory and fat cells, as well as morphological alternations of collagen fibres in the aortic wall layers (tunica intima, tunica media, tunica adventitia) can cause dissection, aneurysms, or stenosis. Aim. To evaluate collagen fibre changes in the ascending aorta of both patients with altered aortic valves (AVs) and controls.
We used surgical material from 28 patients with altered AVs and autopsies from 13 individuals defined as controls. Tissue samples were stained using Sirius Red and Masson’s trichrome methods. Light microscopy was used to estimate the relative thickness, fragmentation, and organization of collagen bundles. The statistical analysis was performed using SPSS v27. The Kruskal-Wallis test was performed to detect statistically significant differences between groups. Correlations between the parameters were determined using Spearman’s rho test. The organization of collagen fibres in the tunica intima differed statistically significantly (H=11.15, p=0.004) when three groups were compared. More organized collagen fibres were observed in controls (mode=1) compared to patients with TAVs (mode=2) and BAVs (mode=2). Also, the relative density of collagen fibres in the tunica adventitia differed statistically significantly in all groups (H= 28.07, p<0.001). The relative density of collagen fibres in the tunica adventitia in the BAVs group (mode=2) was less dense than in controls (mode=3) or TAVs group (mode=3). A significant correlation was found in tunica intima between the fragmentation and organization of collagen bundles (controls, p<0.001, BAVs group, p=0.009, TAVs group, p<0.001). A significant correlation was found between the relative density and fragmentation of bundles in tunica media (BAVs group, p=0.027, TAVs group, p=0.02). In addition, tunica adventitia showed that there was a correlation between the relative density of collagen bundles and fat cell deposits (controls, p=0.01, BAVs group, p=0.002). Controls showed a more organized tunica intima layer than the other groups, which may indicate that patients with altered BAVs and TAVs had disrupted hemodynamics that directly affected the tunica intima. The BAVs group had less dense tunica adventitia, which could be due to fat cell deposits, which were more common in this group. Correlations indicate that more fragmented collagen fibres tend to be more disorganized, which can happen because of their rupture.