Concepts for optimizing stent graft treatment of abdominal aortic aneurysms based on results of animal experiments

Abstract

In the endoluminal therapy of abdominal aortic aneurysms, a short proximal aneurysm neck, endoleaks and the large size and stiffness of the introducer systems are responsible for many of the complications and sub-optimal outcomes. The purposes of the present review article is to to suggest strategies to minimize these complications based on the results of experimental studies in animals. After implanting various types of stents across the renal artery origins, the functional and morphological changes in the kidneys and renal vessels were studied by various authors. In order to prevent progressive widening of the proximal aneurysmal neck and graft dislocation, Sonesson et al. performed a laparoscopic banding around the proximal neck in pigs. To study the effects of endoleaks, Marty, Schurink and Pitton carried out pressure measurements in experimental aneurysms with and without endoleaks. Sakaguchi und Pavcnik developed the "Twin-tube endografts" (TTEG) and the "Bifurcated drum occluder endografts" (BDOEG) and tested them in dogs. Up to 3 months after suprarenal stent placement, Chavan et al. detected no significant fall in the mean inulin clearance in sheep (140 +/- 46 ml/min before, 137 +/- 58 ml/min after). Nasim et al. and Malina et al. reported similar observations with respect to renal function. Suprarenal fixation may result in isolated thrombotic occlusions of the renal arteries and microinfarcts in the kidneys. Mean aortic diameters at the level of banding were significantly smaller in the animals with aortic banding as opposed to those in the control group without banding (8 mm vs 11 mm, p = 0.004). The banding caused a secure proximal fixation of the stent-graft. Persistent endoleaks resulted in significantly higher intraaneurysmal pressures. Although the TTEG and the BDOEG stent-grafts required smaller sheaths, occlusions were observed in 8% (TTEG) and 60% (BDOEG) of the graft limbs. Supra-renal fixation of the stent-graft does not significantly affect renal function. Depending partly on the stent-graft-Design, isolated microinfarcts in the kidneys or thrombotic occlusions of the renal arteries may occur. A laparoscopic banding of the aorta at the proximal neck after graft implantation could prevent widening of the proximal neck and graft dislocation with the passage of time. To reduce the incidence of endoleaks, embolization of large branches, particularly those arising from aneurysms without mural thrombus is advisable. Due to the relatively high rate of occlusion of the graft limbs, the TTEG and the BDOEG stent-graft designs still require refinement. A rational application of the results of these animal experimental studies in clinical practice could markedly improve the long-term results of endoluminal stent grafting of abdominal aortic aneurysms.