1. H OW S ECURE IS THE D ISTAL S EALING Z ONE OF D IFFERENT E NDOVASCULAR L IMB E XTENSIONS IN AN E XPERIMENTAL P ORCINE M ODEL? Shah S 1, Jones S 1,2, Williams RL 1 1 Institute of Ageing and Chronic Disease, University of Liverpool, Liverpool 2 Liverpool Vascular and Endovascular Service, RLBUHT, Liverpool I NTRODUCTION A IMS AND O BJECTIVES M ETHODS C ONCLUSION R EFERENCES The advent of endovascular stent-grafts (ESG) has revolutionised the management of AAA. Despite the indisputable benefits of endovascular aneurysmal repair (EVAR) as compared to open surgical repair, there remains the need for life long surveillance to identify early signs of stent-graft failure. One important sign is migration which may lead to endoleak, kinking, occlusion and possible late rupture 1. Several factors contribute towards in vivo stent-graft migration. Research has shown that hypertension, smoking, aneurysmal anatomy and size of ESG may all play a role 2. Other studies have shown the importance of stent-graft oversizing and vessel angulation. Most importantly, however, are the in-situ haemodynamic forces that exert a 'drag' force on the ESG to provoke migration. This force is counteracted by the device’s fixation force. Thus, as the drag force exceeds the fixation force, the ESG begins to migrate 2. The aim of this experiment is to determine the distal fixation force of different Zenith® iliac stent-graft limbs in a porcine aorta. This data will help to identify ESGs at risk of failure in patients. Three types of ESG limb were tested: the Zenith Low Profile® (ZALL), Zenith Flex® (TFLE) and Zenith Spiral-Z® (ZSLE) (Cook Medical). Figure 1 illustrates the experimental setup: ‒in vivo physiological conditions were replicated: aortas were stretched by 10% in length and pressurised to 100mmHg using warmed 0.9% saline (at 37°C). ‒ESGs were coated in porcine gelatine prior to testing. ‒A customised deployment mechanism was used to deliver the ESG. ‒ESGs were oversized by 10%. ‒A tensile tester (50N load cell) was used to cause displacement of the ESG at a rate of 50mm/min. 1.Mohan IV, Harris PL, Van Marrewijk CJ, Laheij RJ, How TV. Factors and forces influencing stent-graft migration after endovascular aortic aneurysm repair. Journal of endovascular therapy : an official journal of the International Society of Endovascular Specialists. 2002;9(6):748-55. 2.Sinha Roy A, Westt K, Rontala RS, Greenberg RK, Banerjee RK. In vitro measurement and calculation of drag force on iliac limb stentgraft in a compliant arterial wall model. Molecular & cellular biomechanics : MCB. 2007;4(4):211-26. R ESULTS The ZALL ESG has a significantly lower fixation force compared to other types of ESG; particularly the ZSLE. Further research is warranted to determine whether this has implications regarding the use of ZALL ESGs in patients. Table 1 - Adjusted Peak Force* (APF) Data for Tested ESGs 16mm ZSLE 16mm TFLE 20mm ZSLE 20mm ZALL Experiments4663 Average APF (N)2.512.321.910.70 SD APF (N)0.450.560.260.32 *Adjusted Peak Force is defined as the peak force where initial migration of the ESG occurs. SD = Standard Deviation. Figure 2 shows the average load for each ESG. Whilst both ZSLE stents and the TFLE stent are shown to have comparable loads, the ZALL stent has a significantly lower fixation force at respective displacements. The primary peak (where migration can be seen to occur) is also much lower in the ZALL ESG. The Mann-Whitney U test was used to compare ESGs. Figure 3 and Table 1 demonstrate further evidence of differences between ZALL and other ESGs. The average APF for the ZALL ESG is almost 3 times lower comparatively. There was no significant difference in APF between the 16mm ZSLE and 16mm TFLE ESG (p=0.548). There was a significant difference between the 20mm ZSLE and 20mm ZALL ESG (p=0.036). Such differences in fixation force may be explained by the ZALL’s nitinol frame and thinner polyester graft material; the other ESGs have a stainless steel frame.