POST ENDOVASCULAR STENT REPAIR OF DESCENDING AORTA: SIDE EFFECTS AND DEVELOPMENT OF ANEURYSM IN THE ASCENDING AORTA

Abstract

Thoracic aortic aneurysms are an indolent but catastrophic process. The purpose of this study was to evaluate changes in the wall mechanics in the ascending aorta proximal to where the endovascular stent graft is placed. Secondary purpose was to investigate the growth of the ascending segment after endovascular placement of a stent in the descending aorta. Patient’s population: From December 2005 to December 2013, 16 patients (14 males and 3 females, aged of 60 ± 10 years) with descending thoracic aortic lesions subjects. Patients were monitored prior to surgery and between 2 to 24 months after the surgery with repeated contrast-enhanced multislice Computed Tomography (CT). Geometry Reconstruction: A 3D model of the thoracic aorta was obtained from CT images using the segmentation features of the image processing software ScanIP (Simpleware Ltd., Exeter, UK). The maximum diameter was manually evaluated directly from CT images by using the existing measuring tool in Scan IP. Non-linear isotropic constitutive descriptions of the wall as proposed previously were used for the FE analysis. The mean arterial blood pressure of 100 mmHg (13.33 kPa) was prescribed, and the nodal degrees of freedom of the distal ends of supra-aortic vessels, the descending aorta and the proximal aortic sinus were fixed in all directions. No contact with the surrounding organs was considered. The stress field was evaluated and the Maximum Wall Stress of the Ascending aorta (MWSA) was computed. The maximum principal Cauchy stress distribution obtained for one representative preoperative model is plotted in Figure 1. Stress and a diameter increase was observed in the postoperative analysis. In details, for the postoperative representative model the MWSA increased from 200 kPa to 212 kPa, while the ascending aorta diameter increased from 32 mm to 33.2 mm with an average growth rate of 0.2 mm/months. Additionally, not only the magnitude of MWSA was increased in the postoperative model but also the location changed over time. The tissue response to implantation of an endovascular device involves a complex interplay among device design, materials, and deployment technique. Our data underlines the sensitivity of the ascending aorta to endovascular grafting of the descending aorta. The maximum diameter growth was about 0.36 mm/months in our cohort. As an immediate consequence of diameter increase and geometrical changes of the ascending aorta, the stress distribution changes and the maximum stress rise post stent-graft in the descending aorta.