Thoracic endovascular stent grafting inhibits aortic growth: an experimental study

OBJECTIVE: Dilatation of the aorta at the landing zone site may be exaggerated by the radial force of stent grafts potentially limiting long-term results of endovascular therapy. We evaluated growth patterns and morphology of the thoracic aorta in young piglets after thoracic stent-graft placement. METHODS: Eight domestic piglets (37+/-2 kg) had an endovascular stent graft placed in the proximal descending thoracic aorta using retroperitoneal access. At implantation, the stent was oversized by 10%. Aortic size was documented after thoracotomy by intraoperative measurement and angiography. Subsequently the piglets were grown to adult size (181+/-42 kg). At explantation 6-15 months later, CT scan and surgical evaluation for endoleaks, defined as perigraft flow, was performed. Histopathological assessment of the explanted aorta was performed in stented and non-stented segments and compared to five normal porcine aortas. RESULTS: No endoleak (perigraft flow) or stent migration occurred even in 230kg pigs. The stent grafts expanded to full size, but there was no further growth in the stented area. The aortic diameter increased significantly by 32+/-9% 1cm proximal to the stents (p=0.0012) and by 45+/-13% 1cm distal to the stents (p=0.0033). The stented area grew less than the proximal (p=0.0011) and distal aorta (p<0.0001). In all pigs, the distal aorta was larger than the proximal overstented segment. Histology of the stented aorta showed significant thickening of the intima (p=0.018) and media (p=0.006) with neointimal formation and segmental fibrosis of the inner 1/3 of the media with loss of smooth muscle cells and compression of the elastic fibers but normal architecture in the outer 2/3 of the media. CONCLUSIONS: Endovascular stent grafting may inhibit growth of the nonatherosclerotic normal aorta and lead to intimal hyperplasia and focal fibrosis in the inner media part adjacent to the stent. Stent-graft interaction with aortic tissue over time is important and should receive more detailed evaluation. Testing this interaction in an animal model of nonatherosclerotic dilative aortic disease could be of great interest.