Experimental Modifications to a Canine Infrarenal Aortic Aneurysm Model for the Validation of Endovascular Stent-Grafts: An Exploratory Study

Abstract

The intraluminal elastase perfusion model has been proven to be potentially effective in producing abdominal aortic aneurysms (AAA) in rodents, yet has produced unpredictable results in larger animals. The purpose of this study was to explore different variations to an existing elastase perfusion model in the dog in the hopes of producing a consistent AAA for endovascular graft validation. The elastase perfusion canine model was modified as follows: (1) inflation of a balloon catheter in the infrarenal aorta (IA) of 3 dogs following elastase perfusion with doses of 2800 U for 40 min; (2) perfusion of the IA of 5 dogs with various elastase doses ranging from 2800 U to 8400 U for 2 h; and (3) perfusion of the IA of 2 dogs with elastase and collagenase for 2 h. The dogs were sacrificed at 4, 7, and 29 weeks. Prior to sacrifice, the treated aortic segments were either examined in vivo by x-ray angiography or by ultrasonography to measure aneurysmal dilation. The aortas were examined macroscopically postmortem to assess the luminal surface characteristics, and under light microscopy and scanning electron microscopy to reveal any pathological injuries induced by the various treatments on the aortic wall. Perfusion of the aorta with 2800 U elastase for 40 min followed by balloon catheter inflation either immediately or 3 weeks after perfusion produced no dilation. Perfusion for 2 h with either elastase alone or in combination with collagenase showed an increased aortic diameter averaging 65.6 ± 20.80/0, with an irregular dilation of the aortic wall. Histological examination revealed partially digested elastic network of the intima, media, and adventitia, as well as a reduction in the number of smooth muscle cells. An intimal hyperplasic reaction was observed in some of the dogs. Located sparingly within the intima were extravasated erythrocytes associated with recent hemorrhages, intramural thrombi in reorganization, and occasional necrotic lesions. The various modifications brought to the elastase perfusion model failed to produced an aneurysmal dilation with enough expansion to make it a reliable model for endovascular graft validation.