Impact of aortic and pulmonary artery wall histology on radicular dilatation during the Ross procedure.

Objective: In our study, we aim to explore the structural differences between the aortic root and the pulmonary artery to better understand the process of pulmonary autograft dilatation during the Ross procedure.

Materials And Methods: We studied twenty human fetuses (aged 14-36 weeks of gestation) and four adults (one female and three males, aged 30-45 years, mean age = 37 ± 16 years). Samples of aortic root and pulmonary artery were obtained through dissection. Histological examinations, including hematoxylin-eosin, Masson's trichrome, and orcein staining, as well as immunohistochemical technique with caldesmon staining, were performed. Microscopic counting was conducted to assess the number of elastic laminae and smooth muscle cells in each arterial wall. Statistical analyses were performed using R software. Means and standard deviations were used to present central tendencies and data dispersion for elastic laminae and smooth muscle.

Results: Significant histological differences were observed between the aortic root and pulmonary artery in both adults and fetuses. In fetuses, no difference was found between the two vessels in terms of elastic laminae (p = 0.26) and smooth muscle cells (p = 0.69). However, in adults, significant differences were found for elastic laminae (p < 0.001) and smooth muscle cells (p < 0.001) between the aorta and pulmonary artery.

Conclusions: The microscopic vascular structure impacts the mechanical properties of the pulmonary autograft wall and explains its observed dilatation remote from the Ross procedure due to wall stresses related to systemic pressure.