Concepts to optimize stent-grafting of abdominal aortic aneurysms based onresults of experimental studies

Purpose. In the endoluminal therapy of abdominal aortic aneurysms, a short proximal aneurysm neck, endoleaks and the large size and stiffness of the i ntroducer systems are responsible for many of the complications and sub-opt imal outcomes. The purpose of the present review article is to to suggest s trategies to minimize these complications based on the results of experimen tal studies in animals. Material and methods. After implanting various types of stents across the r enal artery origins,the functional and morphological changes in the kidneys and renal vessels were studied by various authors. In order to prevent pro gressive widening of the proximal aneurysmal neck and graft dislocation, So nesson 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 endol eaks. Sakaguchi und Pavcnik developed the "Twin-tube endografts" (TTEG) and the "Bifurcated drum occluder endografts" (BDOEG) and tested them in dogs. Results. Up to 3 months after suprarenal stent placement, Chavan et al. det ected 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. re ported similar observations with respect to renal function. Suprarenal fixa tion may result in isolated thrombotic occlusions of the renal arteries and microinfarcts in the kidneys. Mean aortic diameters at the level of bandin g 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 e ndoleaks resulted in significantly higher intraaneurysmal pressures. Althou gh the TTEG and the BDOEG stent-grafts required smaller sheaths, occlusions were observed in 8% (TTEG) and 60% (BDOEG) of the graft limbs. Discussion. 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 arterie s may occur. A laparoscopic banding of the aorta at the proximal neck after graft implantation could prevent widening of the proximal neck and graft d islocation with the passage of time. To reduce the incidence of endoleaks, embolization of large branches, particularly those arising from aneurysms w ithout mural thrombus is advisable. Due to the relatively high rate of occl usion of the graft limbs,the TTEG and the BDOEG stent-graft designs still r equire refinement. A rational application of the results of these animal ex perimental studies in clinical practice could markedly improve the long-ter m results of endoluminal stent grafting of abdominal aortic aneurysms.