HEMODYNAMICS OF ABDOMINAL AORTIC ANEURYSM AND ITS CLINICAL RELEVANCE IN PATIENTS WITH INFRARENAL STENT-GRAFT IMPLANTATION

摘要

In 2008 the overall rate of death attributable to cardiovascular disease, or CVD, is 244.8 per 100,000. On the basis of these mortality rate data, one American dies due to CVD on an average of every 39 seconds. Of these deaths, abdominal aortic aneurysm (AAA) accounts for 11,079 [1]. Although an estimate of the total economic burden of AAA is not available, the average cost per discharge for a ruptured AAA exceeded $93,000 in 2003 [2]. Generally, an abdominal aortic aneurysm (AAA) is an irreversible focal dilation of an artery to 1.5 times its normal diameter [3]. AAAs are characterized by the destruction of elastin and collagen in the media and adventitia, smooth muscle cell loss with thinning of the medial wall, infiltration of lymphocytes and macrophages, and neovascularization [4, 5]. The most common treatment for AAA is endovascular aneurysm repair (EVAR) by implanting a stent-graft (SG) to the affected segment for shielding the aneurysm wall from the blood pressure, eliminating blood circulation in the aneurysm intra-sac, and thus prevent wall rupture [6]. Traditionally bare metal stents were used in these surgeries but with high failure rate due to restenosis and thrombosis. Alternatively, drug-eluting stents (DES) were introduced as a remedy but still, the safety of DES needs to be re-examined as DES have been implicated in higher rates of late stent thrombosis (LST) [7]. The causes of majority of SG failures include seepage of blood into the cavity (endoleak), SG migration, and SG fatigue and fracture. Among these causes, endoleak is recognized as the main problem associated with SG, and is used as an endpoint in clinical trials [8]. Endoleak is defined as a blood flow external to the stent-graft and inside the aneurysm sac [9], and can be identified in as high as 52% of patients after EVAR. The existence of endoleak raises concerns of possible aneurysm enlargement and rupture. [10]. A classification system has evolved in which endoleak is organized into five categories [11], and they are highly correlated with peak flow pressure and stress concentrated locally along the interface between SG and aneurysm sac. It has been evidenced that early detection of the locations of endoleak will reduce the risk of SG failure. Therefore, the aim of this study is to quantify hemodynamics in AAA patients after SG implantation to elucidate the effect of flow-induced mechanical forces on the appearance of endoleak, for better endoleak management in clinics and to assist new SG designs.