W.M.P.F. Bosman

The Proximal Fixation Strength of Modern EVAR Grafts in a Short Aneurysm Neck. An In Vitro Study

OBJECTIVES The study aims to measure the strength of the proximal fixation of endografts in short and long necks. DESIGN Three types of endografts were compared: Gore Excluder, Vascutek Anaconda and Medtronic Endurant. MATERIALS AND METHODS The proximal part of the stent grafts was inserted in bovine arteries and the graft was then attached to a tensile testing machine. The force to obtain dislodgement (DF) from the aorta was recorded for each graft at proximal seal lengths of 10 and 15 mm. RESULTS The median DF (interquartile range, IQR) for the Excluder, the Anaconda and the Endurant with a seal length of 15 mm was: 11.8 (10.5-12.0) N, 20.8 (18.0-30.1) N and 10.7 (10.4-11.3) N. With the shorter proximal seal of 10mm, DF was, respectively: 6.0 (4.5-6.6) N, 17.0 (11.2-36.6) N and 6.4 (6.1-12.0) N. CONCLUSIONS The proximal fixation of the Anaconda is superior to the Excluder and the Endurant at short necks of 10 and 15 mm in an experimental set-up. There is a statistically significant decrease of proximal fixation for the Excluder stent graft, when decreasing the length of the proximal neck from 15 to 10 mm.

Aortic Customize: An In Vivo Feasibility Study of a Percutaneous Technique for the Repair of Aortic Aneurysms Using Injectable Elastomer

OBJECTIVE This study aimed to test a percutaneous technique for aneurysm-sac filling by means of in situ polymerisation in an in vivo model. DESIGN Aortic Customize is a new endovascular treatment concept for aortic aneurysms: a non-cross-linked liquid elastomer is injected to fill the aneurysm sac around a balloon-catheter. With this method, a compliant elastomer mould with a patent lumen is created. MATERIAL The formulation used in the experiments consisted of a two-component addition-cure liquid-silicone formulation, based on vinyl-terminated polydimethylsiloxane (PDMS). METHODS The concept of aneurysm-sac filling was tested in vivo in porcine experiments (n = 3). RESULTS In vivo porcine experiments with the sac-filling application showed successful exclusion of the created aneurysms with patent lumens and absence of endoleaks. The aneurysms were excluded successfully in the in vivo model, injecting elastomer through a 7-French catheter, filling up the entire aneurysm sac. CONCLUSIONS These in vivo experiments demonstrate that the principle of aneurysm-sac filling by means of in situ curing is feasible, excluding the aneurysm and creating a new lumen. Further long-term animal experiments must be done prior to consideration of clinical application.

Aortic customize: a new alternative endovascular approach to aortic aneurysm repair using injectable biocompatible elastomer. An in vitro study.

PURPOSE Aortic Customize is a new concept for endovascular aortic aneurysm repair in which a non polymerized elastomer is injected to fill the aneurysm sac around a balloon catheter. The aim of this in vitro study was to investigate the extent of aneurysm wall stress reduction by the presence of a noncompliant elastomer cuff. METHODS A thin-walled latex aneurysm (inner radius sac 18 mm, inner radius neck 8 mm), equipped with 12 tantalum markers, was attached to an in vitro circulation model. Fluoroscopic roentgenographic stereo photogrammetric analysis (FRSA) was used to measure marker movement during six cardiac cycles. The radius of three circles drawn through the markers was measured before and after sac filling. Wall movement was measured at different systemic pressures. Wall stress was calculated from the measured radius (sigma = pr/2t). RESULTS The calculated wall stress was 7.5-15.6 N/cm(2) before sac filling and was diminished to 0.43-1.1 N/cm(2) after sac filling. Before sac filling, there was a clear increase (P < .001) in radius of the proximal (range, 7.9%-33.5%), middle (range, 3.3%-25.2%), and distal (range, 10.5%-184.3%) rings with increasing systemic pressure. After sac filling with the elastomer, there remained a small, significant (P < .001) increase in the radius of the circles (ranges: 6.8%-8.8%; 0.7%-1.1%; 5.3%-6.7%). The sac filling reduced the extent of radius increase. The treated aneurysm withstood systemic pressures up to 220/140 mm Hg without noticeable wall movement. After the sac filling, there was no pulsation visible in the aneurysm wall. CONCLUSIONS Filling the aneurysm sac of a simplified in vitro latex model with a biocompatible elastomer leads to successful exclusion of the aneurysm sac from the circulation. Wall movement and calculated wall stress are diminished noticeably by the injection of biocompatible elastomer.

Effect of Stent-Graft Compliance on Endotension after EVAR

Purpose: To investigate whether, and to which extent, the type of graft has influence on the pressure in the aneurysm sac. Methods: The study consisted of a dynamic and a static experiment. In the dynamic experiment, a latex aneurysm was inserted into an in-vitro circulation model, with variable (80–180 mmHg) systemic systolic pressure and a pulse pressure of 40 mmHg. Seven types of devices were used to exclude the aneurysm: a latex reference graft, 3 stentless grafts made of different fabrics, and 3 different types of commercially produced stented grafts used for endovascular aneurysm repair (EVAR). The systolic and diastolic intra-aneurysm pressures (IAP) were measured, along with the pulse pressure. The mean IAP and pulse pressures were compared for each category of graft (stented/stentless) and for each graft. In the static experiments, the compliance of each graft and the latex aneurysm were determined by measuring the change in volume necessary to obtain a change in pressure. Furthermore, the IAP with each graft was measured in a nonpulsatile situation under systolic pressures varying between 60 and 140 mmHg. Results: The experiments showed that, with increasing systemic pressures, there was a small pressure (<5 mmHg) increase in the aneurysm, but there was no significant difference among grafts in the dynamic or the static experiments (p=0.12 and p=0.17, respectively). With the 3 stented EVAR grafts, there was less pressure transmission than with the 3 stentless grafts, but this difference was not significant (p>0.05). Conclusion: This in-vitro study demonstrated that there is a clinically irrelevant pressure transmission through the graft wall and no significant difference in the pressure transmission between stented and stentless grafts.

The effect of injectable biocompatible elastomer (PDMS) on the strength of the proximal fixation of endovascular aneurysm repair grafts: An in vitro study

PURPOSE One of the major concerns in the long-term success of endovascular aneurysm repair (EVAR) is stent graft migration, which can cause type I endoleak and even aneurysm rupture. Fixation depends on the mechanical forces between the graft and both the aortic neck and the blood flow. Therefore, there are anatomical restrictions for EVAR, such as short and angulated necks. To improve the fixation of EVAR grafts, elastomer (PDMS) can be injected in the aneurysm sac. The support given by the elastomer might prevent dislocation and migration of the graft. The aim of this study was to measure the influence of an injectable biocompatible elastomer on the fixation strength of different EVAR grafts in an in vitro model. METHODS The proximal part of three different stent grafts was inserted in a bovine artery with an attached latex aneurysm. The graft was connected to a tensile testing machine, applying force to the proximal fixation, while the artery with the aneurysm was fixated to the setup. The force to obtain graft dislodgement (DF) from the aorta was recorded in Newtons (N). Three different proximal seal lengths (5, 10, and 15 mm) were evaluated. The experiments were repeated after the space between the graft and the latex aneurysm was filled with the elastomer. Independent sample ttests were used for the comparison between the DF before and after elastomer treatment for each seal length. RESULTS The mean DF (mean +/- SD) of all grafts without elastomer sac filling for a proximal seal length of 5, 10, and 15 mm were respectively, 4.4 +/- 3.1 N, 12.2 +/- 10.6 N, and 15.1 +/- 6.9 N. After elastomer sac filling, the dislodgement forces increased significantly (P < .001) to 20.9 +/- 3.8 N, 31.8 +/- 9.8 N, and 36.0 +/- 14.1 N, respectively. CONCLUSIONS The present study shows that aneurysm sac filling may have a role as an adjuvant procedure to the present EVAR technique. The strength of the proximal fixation of three different stent grafts increases significantly in this in vitro setting. Further in vivo research must be done to see if this could facilitate the treatment of aneurysms with short infrarenal necks.

Thrombogenicity of a New Injectable Biocompatible Elastomer for Aneurysm Exclusion, Compared to Expanded Polytetrafluoroethylene in a Human Ex Vivo Model

OBJECTIVES Customized aortic repair (CAR) is a new concept for endovascular aortic aneurysm repair in which a non-polymerised elastomer is injected to fill the aneurysm sac around a balloon catheter. Amongst other variables, the thrombogenicity of the elastomer should be tested, before further clinical experiments can take place. The aim of this human ex vivo study was to measure the thrombogenicity of the elastomer and to compare it to expanded polytetrafluoroethylene (ePTFE). DESIGN AND MATERIALS In a validated ex vivo model, non-anticoagulated blood was drawn from the antecubital veins of 10 healthy donors with a 19-gauge needle. It was drawn through elastomer tubes and through ePTFE Gore-Tex vascular grafts, both 60 cm long and with an inner diameter of 3 mm. METHODS Fibrinopeptide A (FPA) and P-selectin expression was measured in blood samples, collected at the end of the grafts. After the experiments, the deposition of platelets and fibrin onto the grafts was visualised by scanning electron microscopy. RESULTS For these graft types, a progressive increase in FPA production was observed in time. No significant difference was observed between the elastomer and ePTFE grafts (p > 0.05). No increase in P-selectin expression, and thereby no platelet activation, was observed in the perfusate of either grafts (p > 0.05). By scanning electron microscopy, numerous platelet aggregates were observed on the ePTFE grafts, whereas just a few adhered platelets and no aggregates were observed in the elastomer grafts. CONCLUSIONS The elastomer in its current formulation has a low thrombogenicity, comparable to ePTFE, making it an ideal substance for endovascular aneurysm sac filling. Further research should clarify the feasibility of CAR in vivo.

Treatment of types II-IV endoleaks by injecting biocompatible elastomer (PDMS) in the aneurysm sac: an in vitro study.

Purpose To investigate if an elastomer [polydimethylsiloxane (PDMS)] can be used to effectively treat endoleaks after endovascular aneurysm repair. Methods A latex aneurysm (36-mm inner diameter sac, 15-mm inner diameter neck) was attached to an in vitro circulation model. The aneurysm was excluded from the circulation by placing an unstented polyester graft. Endoleak types II–IV were created using different setups. While the circulation setup running, the aneurysm was filled with contrast medium and then the biocompatible PDMS elastomer was injected to exclude the endoleaks and the perigraft area. The sac was considered full when all contrast was pushed out of the sac and the elastomer flowed into the proximal efferent lumbar artery. Treatment was successful when the aneurysm was free of endoleak after control angiography. Results The endoleaks were created successfully in the latex aneurysm models, with contrast present in the sac before “treatment.” After elastomer sac filling, all endoleaks were successfully excluded on angiography; there was no leakage of contrast outside the graft lumen in any of the setups. With the type III endoleak, the disruption in the graft material was sealed by the elastomer, while the entire porous graft was encased in elastomer in the type IV endoleak setup. There was no elastomer within the graft lumen in either case. Conclusions This concept of filling the aneurysm sac with PDMS may lead to a percutaneous treatment for endoleaks. While the results of this study show that PDMS may be used to treat endoleaks in vitro, further tests are required to determine if this approach is suitable in vivo.

Influence of aneurysm wall stiffness and the presence of intraluminal thrombus on the wall movement of an aneurysm - an in vitro study.

The purpose of this in vitro study was to investigate the influence of aneurysm wall stiffness and of the presence of intraluminal thrombus (ILT) on aneurysm wall movement. Three latex aneurysms were used with different wall stiffness. The aneurysms, equipped with 20 tantalum markers, were attached to an in vitro circulation model. Fluoroscopic roentgenographic stereo photogrammetric analysis was used to measure marker movement during six cardiac cycles at three different systemic pressures. To investigate the influence of ILT on wall movement, we repeated the same experiment with one of the aneurysms. The aneurysm sac was then filled with one of two E-moduli differing thrombus analogues (Novalyse 8 and 20) or with perfusate as a control. It was noted that the amplitude of the wall movement (mm) increased significantly (P < 0.05) as the compliance of the wall increased. The mean amplitude of the wall movement decreased (P < 0.05) as the stiffness (E-modulus) of the ILT increased. In conclusion, ILT has a ‘cushioning effect’. Wall movement (and theoretically wall stress) diminishes when the stiffness of the ILT increases. Compliance of the aneurysm wall influences wall movement. When the stiffness of the wall increases, the wall movement diminishes.