Reduced pulsatile wall motion of abdominal aortic aneurysms after endovascular repair

Numerical investigation of the effects of blood rheology and wall elasticity in abdominal aortic aneurysm under pulsatile flow conditions

BACKGROUND

Previous studies on aneurysm modeling have focused on the blood rheology and vessel elasticity separately. The combined effects of blood shear thinning properties and wall elasticity need to be revealed.

OBJECTIVE

To provide insights on how pulsatile hemodynamics vary with blood rheology and vessel elasticity for a developed abdominal aortic aneurysm (AAA).

METHOD

An Arbitrary Lagrangian-Eulerian fluid-solid interaction method is adopted with the Newtonian and the shear thinning Carreau constitutive models for the fluid with the linearly elastic and the hyperelastic Yeoh models for the vessel. Finite element based numerical solver is used to simulate the blood flow in the AAA.

RESULTS

Newtonian model overestimates the velocity values compared to the Carreau model and the difference in the velocity field increases as the shear rate decreases at the instances of the cardiac cycle. The rigid walled simulations display higher deviations in the velocity and wall shear stress with the fluid rheology. The risk indicators show that Newtonian assumption combined with the linearly elastic model may overlook degeneration risk of arterial tissue.

CONCLUSIONS

Newtonian assumption for the blood as well as modelling the arterial wall as linearly elastic lead to significant differences in oscillatory hemodynamic properties with respect to the use of Carreau fluid together with hyperelastic vessel model, even in large vessel aneurysms.

Type III and Type IV Endoleak: Toward a Complete Definition of Blood Flow in the Sac after Endoluminal AAA Repair

In this document the authors continue to refine their seminal categorization of endoleak, a major complication of endovascular aneurysm repair. In addition to type I (related to the graft device itself) and type II (retrograde flow from collateral branches) endoleak, they propose two new categories: endoleak due to fabric tears, graft disconnection, or disintegration would be classified type III, and flow through the graft presumed to be associated with graft wall “porosity” would be categorized as type IV endoleak.

Endovascular AAA Repair: Prevention of Side Branch Endoleaks with Thrombogenic Sponge

Purpose:

To report a technique that might decrease the incidence of lumbar artery endoleaks following endovascular repair (EVR) of abdominal aortic aneurysms (AAAs).

Methods:

Ninety-three patients (86 males, median age 72 years, range 56 to 88) undergoing EVR with the aortomonoiliac technique were entered into a study to detect and then occlude patent side branches before completion of the endografting procedure. Prior to deploying the iliac occluder, an aneurysmogram was performed to detect patent aortic side branches. If these side branches were found, an absorbable gelatin sponge was inserted into the aneurysm sac via the occluder introducer sheath. The patients were followed with contrast-enhanced spiral computed tomography (CT) at 1 week and 3, 6, and 12 months to detect the presence of endoleaks.

Results:

Forty-eight (52%) patients demonstrated patent side branches that were occluded by the insertion of gelatin sponges into the aneurysm sac. The remaining 45 patients without evidence of side branch flow were untreated. Ten (10.7%) patients died in the perioperative period, and 15 (16.1%) primary endoleaks (13 proximal, 2 distal) were detected. This left 68 (73.1%) patients for follow-up, 33 (48.5%) of whom had patent branch vessels treated with the thrombogenic sponge. The median follow-up was 4 months (range 1 to 17), during which time no side branch endoleak was detected on surveillance CT scans in any of the 68 patients, which included all patients treated with the thrombogenic sponge technique and those in whom no patent side branches had been identified.

Conclusions:

We have demonstrated a safe and reliable method of preventing lumbar artery endoleaks following endovascular AAA repair.

Endotension: An Explanation for Continued AAA Growth after Successful Endoluminal Repair

Purpose:

To present and analyze several cases that illustrate persistent sac pressurization following endovascular abdominal aortic aneurysm (AAA) repair.

Methods and Results:

Four patients with successful endovascular AAA exclusion presented in follow-up with an expanding aneurysm. Two had initial sac diameter decrease, but by 18 and 24 months, respectively, the AAA had enlarged and become pulsatile. There was no endoleak evident, but the proximal attachment stents had migrated distally in both cases. One patient developed endoleak with aneurysm expansion at 6 months; contained rupture occurred at 12 months. The last case had slowly evolving aneurysm expansion over 36 months but no endoleak. All endografts were removed and successfully replaced with conventional grafts. Intrasac thrombus was implicated as the means of pressure transmission that precipitated AAA expansion in these cases.

Conclusions:

Excluded AAAs can increase in size owing to persistent or recurrent pressurization (endotension) of the sac even when there is no evidence of endoleak. One proposed mechanism is pressure transmission via thrombus that lines the attachment site. Endotension may also represent an indiscernible, very low flow endoleak that allows blood to clot at the source of leakage.

Noninvasive Estimation of Aneurysm Sac Pressurization Following Endovascular Aneurysm Repair Using M-Mode Ultrasonography to Evaluate Significance of Endoleaks: A Feasibility Study

PURPOSE

To establish the feasibility of indirectly estimating aneurysm sac pressurization from recordings of aortic pulsatile wall motion (PWM) using M-mode ultrasonography before and after endovascular aneurysm repair (EVAR).

METHODS

Twenty consecutive patients (mean age 72 years; 19 men) scheduled for EVAR in a single institution underwent M-mode ultrasonography 1 day before EVAR to record PWM of the abdominal aortic aneurysm wall during the cardiac cycle, along with simultaneous blood pressure measurements. The recording was repeated the first postoperative day. Pressure-strain elastic modulus (Ep) was calculated from the preoperative displacement and pressure data. This value and the postoperative PWM were used to inverse estimate pulse pressure in the abdominal aortic aneurysm sac post EVAR. Immediate pressure reduction post EVAR was compared between groups of endoleak vs no endoleak and expansion vs no expansion during 6-month follow-up.

RESULTS

Intraobserver variability of the method presented a mean value of 0.04 mm with a 1.2-mm coefficient of variation (95% limits of agreement -1.16 to 1.24 mm). PWM was significantly reduced postoperatively (1.2 vs 0.3 mm, p<0.001) as was pulse pressure exerted on the aneurysm sac (67 vs 16 mm Hg, p<0.001). The pressure reduction was similar between the endoleak vs no endoleak groups (79% vs 75%, p=0.65), but it was significantly greater in the no expansion group (79.5%) vs the group with aneurysm expansion (50%, p=0.008).

CONCLUSION

M-mode ultrasonography may provide a useful adjunct during EVAR surveillance to noninvasively estimate sac pressurization and identify aneurysms at risk of enlargement.

Isotropic 3D black blood MRI of abdominal aortic aneurysm wall and intraluminal thrombus

INTRODUCTION

The aortic wall and intraluminal thrombus (ILT) have been increasingly studied as potential markers of progressive disease with abdominal aortic aneurysms (AAAs). Our goal was to develop a high resolution, 3D black blood MR technique for AAA wall and ILT imaging within a clinically acceptable scan time.

METHODS

Twenty two patients with AAAs (maximal diameter 4.3±1.0cm), along with five healthy volunteers, were imaged at 3T with a 3D T1-weighted fast-spin-echo sequence using variable flip angle trains (SPACE) with a preparation pulse (DANTE) for suppressing blood signal. Volunteers and ten patients were also scanned with SPACE alone for comparison purposes. The signal to noise ratio (SNR) and the aortic wall/ILT to lumen contrast to noise ratio (CNR) were measured. Qualitative image scores (1-4 scale) assessing the inner lumen and outer wall boundaries of AAA were performed by two blinded reviewers. In patients with ILT, the ratio of ILT signal intensity (ILTSI) over psoas muscle SI (MuscleSI) was calculated, and the signal heterogeneity of ILT was quantified as standard deviation (SD) over the mean.

RESULTS

All subjects were imaged successfully with an average scan time of 7.8±0.7minutes. The DANTE preparation pulse for blood suppression substantially reduced flow artifacts in SPACE with lower lumen SNR (8.8 vs. 21.4, p<0.001) and improved the wall/ILT to lumen CNR (9.9 vs. 6.3, p<0.001) in patients. Qualitative assessment showed improved visualization of lumen boundaries (73% higher scores on average, p=0.01) and comparable visualization of outer wall boundary (p>0.05). ILT was present in ten patients, with relatively high signal and a wide SD (average ILTSI/MuscleSI 1.42±0.48 (range 0.75-2.11)) and with SD/mean of 27.7%±6.6% (range 19.6%-39.4%).

CONCLUSION

High resolution, 3D black blood MRI of AAAs can be achieved in a clinical accepted scan time with reduction of flow artifacts using the DANTE preparation pulse. Signal characteristics of ILT can be quantified and may be used for improved patient-specific risk stratification.

Multilayer flow modulator stent technology: a treatment revolution for US patients?

Thoracoabdominal aortic repair is a high-risk procedure in most experienced centers, not only because of anatomical complexity but also due to the fragility of the patients in whom these aneurysms occur. Such repairs are complex, time-consuming and impose a systemic injury upon the patients, regardless of whether the repair is performed by open surgery or via a fenestrated/branched technique. The substantive risks associated with such repairs include death, dialysis and paralysis. The multilayer flow modulator (MFM) is a disruptive technology which promises a minimally invasive reproducible treatment option, with clinical results demonstrating physiological modulation of the aortic sac with abolition of spinal injury. The mode of action of MFM forces us to completely rethink aneurysm pathogenesis and, consequently, it has been met with much cynicism. We aim to uncloak some of the mystery surrounding the MFM, clarify its mode of action and explore the truth behind its clinical effectiveness.

Review of postoperative CT and ultrasound for endovascular aneurysm repair using Talent stent graft: can we simplify the surveillance protocol and reduce the number of CT scans?

BACKGROUND

Simplifying a postoperative surveillance protocol for endovascular aneurysm repair (EVAR) requires quality control comparing computerized tomography (CT) and ultrasound (US) results of abdominal aortic aneurysm (AAA) diameter measurements and endoleaks.

PURPOSE

To test if US is comparable to CT, then assess a simplified follow-up with our conventional surveillance to assess patient safety.

MATERIAL AND METHODS

During 2001-2006, data on 56 patients treated with Talent stent graft were prospectively registered. Median follow-up was 41.5 months (range, 2-94 months), with CT, US, and plain film abdomen X-rays (PFA) at 1, 6, and 12 months, then yearly. Bland-Altman plot was used to assess the agreement between CT and US measuring the AAA diameters and mixed model by the time effect to assess the difference in diameter over time. Sensitivity and specificity for detection of endoleaks by US, with CT as 'gold standard' were calculated. A simplified surveillance protocol with US/PFA at 6 and 8 weeks, CT/US/PFA at 1 year, and yearly US/PFA thereafter, was evaluated. CT was carried out when poor visibility, endoleak detected, AAA diameter increase (≥5 mm) on US or migration (≥10 mm) on PFA. This regime was compared with our conventional follow-up protocol.

RESULTS

Diameter measurements on US appear comparable to CT with 91% specificity and 85% sensitivity for endoleaks detected by US. Using the simplified surveillance protocol no endoleaks, migrations, or endotension requiring treatment were overlooked. The simplified protocol generated 53 selective CT scans, avoiding approximately 144 CT scans. If further simplified by omitting the 1-year CT scan, one type II endoleak would be missed with a 1-year delay, eliminating a further 45 CT scans.

CONCLUSION

US appears comparable to CT in the follow-up of Talent stent grafts in our institution. The proposed simplified surveillance protocol seems safe and can lead to a significant reduction in the number of CT scans.

Agreement between computed tomography and ultrasound on abdominal aortic aneurysms and implications on clinical decisions

OBJECTIVES

The United Kingdom abdominal aortic aneurysm (AAA) screening programme refers aneurysms with ultrasound (US) diameters of ≥5.5 cm to vascular services for consideration of computed tomography (CT) and intervention. We investigated the discrepancy between US and CT, implications on clinical decisions and question at which stage CT be used.

DESIGN/METHODS

AAA USs over 5 years were retrospectively analysed. Patients included had aneurysms measuring ≥5 cm on US with subsequent CT within 2 months (n = 123). Based on maximum US diameters, 44 patients had aneurysms between 5 and 5.4 cm (group I) and 79 patients ≥5.5 cm (group II). Results were cross-referenced. Correlation and limits of agreement were calculated. Two radiologists re-measured 44 pairs of CT/US scans and the inter-observer bias in determining discrepancies between imaging modalities calculated.

RESULTS

Mean difference between imaging modalities was 0.21 cm (±0.39 cm, p < 0.001). Limits of agreement were -0.55 to 0.96 cm, exceeding clinical acceptability. Mean difference was higher and significant in group I (0.39 cm, p < 0.001) compared to group II (0.10 cm, p > 0.05). Seventy-percent of group I patients had CT scans revealing diameters of ≥5.5 cm. Inter-observer bias was not significant.

CONCLUSION

Significant differences between imaging modalities, more in US diameters of below 5.5 cm, exist. We recommend AAAs measuring ≥5 cm on US should undergo earlier referral to a vascular service and CT.

In vivo quantification of murine aortic cyclic strain, motion, and curvature: implications for abdominal aortic aneurysm growth

PURPOSE

To develop methods to quantify cyclic strain, motion, and curvature of the murine abdominal aorta in vivo.

MATERIALS AND METHODS

C57BL/6J and apoE(-/-) mice underwent three-dimensional (3D) time-of-flight MR angiography to position cardiac-gated 2D slices at four locations along the abdominal aorta where circumferential cyclic strain and lumen centroid motion were calculated. From the 3D data, a centerline through the aorta was created to quantify geometric curvature at 0.1-mm intervals. Medial elastin content was quantified with histology postmortem. The location and shape of abdominal aortic aneurysms (AAAs), created from angiotensin II infusion, were evaluated qualitatively.

RESULTS

Strain waveforms were similar at all locations and between groups. Centroid motion was significantly larger and more leftward above the renal vessels than below (P < 0.05). Maximum geometric curvature occurred slightly proximal to the right renal artery. Elastin content was similar around the circumference of the vessel. AAAs developed in the same location as the maximum curvature and grew in the same direction as vessel curvature and motion.

CONCLUSION

The methods presented provide temporally and spatially resolved data quantifying murine aortic motion and curvature in vivo. This noninvasive methodology will allow serial quantification of how these parameters influence the location and direction of AAA growth.

Fluid-structure interaction of a patient-specific abdominal aortic aneurysm treated with an endovascular stent-graft

Background

Abdominal aortic aneurysms (AAA) are local dilatations of the infrarenal aorta. If left untreated they may rupture and lead to death. One form of treatment is the minimally invasive insertion of a stent-graft into the aneurysm. Despite this effective treatment aneurysms may occasionally continue to expand and this may eventually result in post-operative rupture of the aneurysm. Fluid-structure interaction (FSI) is a particularly useful tool for investigating aneurysm biomechanics as both the wall stresses and fluid forces can be examined.

Methods

Pre-op, Post-op and Follow-up models were reconstructed from CT scans of a single patient and FSI simulations were performed on each model. The FSI approach involved coupling Abaqus and Fluent via a third-party software - MpCCI. Aneurysm wall stress and compliance were investigated as well as the drag force acting on the stent-graft.

Results

Aneurysm wall stress was reduced from 0.38 MPa before surgery to a value of 0.03 MPa after insertion of the stent-graft. Higher stresses were seen in the aneurysm neck and iliac legs post-operatively. The compliance of the aneurysm was also reduced post-operatively. The peak Post-op axial drag force was found to be 4.85 N. This increased to 6.37 N in the Follow-up model.

Conclusion

In a patient-specific case peak aneurysm wall stress was reduced by 92%. Such a reduction in aneurysm wall stress may lead to shrinkage of the aneurysm over time. Hence, post-operative stress patterns may help in determining the likelihood of aneurysm shrinkage post EVAR. Post-operative remodelling of the aneurysm may lead to increased drag forces.

Current state of dynamic imaging in endovascular aortic aneurysm repair

Dynamic imaging, in which the time dimension has a specific function in data (image) interpretation, is becoming increasingly important when contemplating endovascular aneurysm repair. Clinical parameters and complications, including proper sizing, successful aneurysm sac exclusion, optimal stent-graft design, endoleaks, graft migration, and stent fracture are beginning to be better understood through dynamic magnetic resonance, ultrasound, and dynamic computed tomography. The current practice using static 3-dimensional reconstructions for the planning and follow-up of aortic aneurysm endograft treatment will most likely evolve, and the use of dynamic aortic imaging will continue to increase. Validation of these imaging modalities in larger scale trials is needed.

Aneurysm pulsatility after endovascular exclusion--an experimental study using human aortic aneurysms

OBJECTIVE

To measure the pulsatility of human aneurysms before and after complete exclusion with an endograft.

METHOD

Five aortic aneurysms obtained during necropsy were submitted to pulsatile perfusion before and after implantation of a bifurcated endograft. The specimens were contained in a closed chamber filled with saline solution. A vertical tube attached to the chamber was used to measure volume dislocation in each systole. Mural thrombus was kept intact, and the space around the device was filled with human blood. After each experiment, the aneurysm was opened to check for the correct positioning and attachment of the device.

RESULTS

The level of the saline column oscillated during pulsation in each case, with respective amplitudes of 17, 16, 13, 7, and 25 cm before the endograft insertion. After the insertion, the amplitudes dropped to 13, 12, 9, 3.5, and 23 cm, respectively. The differences were not significant. During the post-experimental examination, all devices were found to be in position and well attached to the neck and iliacs. No endoleak was detected during perfusion or by visual inspection.

CONCLUSION

Pulsation of an endograft is transmitted to the aneurysm wall even in the absence of endoleak, and should not be interpreted as procedural failure.

Increased anterior abdominal aortic wall motion: possible role in aneurysm pathogenesis and design of endovascular devices

PURPOSE

To determine whether variations in aortic wall motion exist in mammalian species other than humans and to consider the potential implications of such variations.

METHODS

M-mode ultrasound was used to measure abdominal aortic wall motion in 4 animal species [mice (n=10), rats (n=8), rabbits (n=7), and pigs (n=5)], and humans (n=6). Anterior wall displacement, posterior wall displacement, and diastolic diameter were measured. The ratio of displacement to diameter and cyclic strain were calculated.

RESULTS

Body mass varied from 24.1+/-2.4 g (mouse) to 61.8+/-13.4 kg (human); aortic diameter varied from 0.53+/-0.07 mm (mouse) to 1.2+/-1 mm (human). Anterior wall displacement was 2.5 to 4.0 times greater than posterior among the species studied. The ratios of wall displacement to diastolic diameter were similar for the anterior (range 9.40%-11.80%) and posterior (range 2.49%-3.91%) walls among species. The ratio of anterior to posterior displacement (range 2.47-4.03) and aortic wall circumferential cyclic strain (range 12.1%-15.7%) were also similar. An allometric scaling exponent was experimentally derived relating anterior wall (0.377+/-0.032, R2=0.94) and posterior wall (0.378+/-0.037, R2=0.93) displacement to body mass.

CONCLUSION

Abdominal aortic wall dynamics are similar in animals and humans regardless of aortic size, wih more anterior than posterior wall motion. Wall displacement increases linearly with diameter, but allometrically with body mass. These data suggest increased dynamic strain of the anterior wall. Increased strain, corresponding to increased elastin fatigue, may help explain why human abdominal aortic aneurysms initially develop anteriorly. Aortic wall motion should be considered when developing endovascular devices, since asymmetric motion may affect device migration, fixation, and sealing.

Aneurysm Sac Pressure after EVAR: The Role of Endoleak

OBJECTIVE

The relation between endoleak and aneurysm sac pressure is not completely clear. This review evaluates the effect of endoleaks on aneurysm sac pressure and summarizes the present knowledge regarding aneurysm sac pressure after EVAR.

METHODS

A systematic search of literature was carried out using MEDLINE, EMBASE and Web of Science. Studies were included if aneurysm sac pressure measurements as well as systemic pressure measurements were performed during or after EVAR. Mean pressure indices (MPI), ratio mean aneurysm sac pressure to mean systemic pressure), in the absence of endoleaks and in the presence of different type of endoleaks were compared.

RESULTS

Stent-graft deployment does not seem to result in immediate reduction of aneurysm sac in the absence of an endoleak. Aneurysm sac pressure is elevated in the presence of an endoleak. However, the MPIs differ widely between studies both in the absence and presence of an endoleak.

CONCLUSION

MPI is not specific to the type of endoleak. This implies that the same type of endoleak does not necessarily pose the same MPI and by this the same hazard of aneurysm rupture, because the aneurysm sac pressure is directly related to the aneurysm wall stress.

Assessing the effectiveness of endografts: Clinical and experimental perspectives

The increasing use of endografts to treat abdominal aortic aneurysms has prompted the need for improved postoperative imaging and surveillance. Although patients benefit from decreased morbidity with endovascular repair compared with open abdominal aortic aneurysm repair, the long-term outcome of stent repair has yet to be fully determined. The persistence of endoleaks highlights the need for close follow-up, particularly because this may lead to aneurysm rupture, even after endograft repair. The current mainstay of assessing the healing of endografts is obtaining serial helical computed tomography angiography (CTA) to identify endoleaks, graft migration, thrombosis, and structural failure. CTA is not completely effective at identifying endoleaks and predicting aneurysm rupture, however. Other modalities have been studied to improve on current imaging methods, including three-dimensional CTA with volumetric analysis, contrast-enhanced duplex ultrasound imaging, cine magnetic resonance angiography, and explant analysis. In vitro and large-animal models of abdominal aortic aneurysm have also been developed to study the pathophysiology and treatment response of aneurysm exclusion. Thus, clinical and experimental models of endograft healing are attempting to define the optimal method of postoperative surveillance of endovascular repair.

Aortic compliance following EVAR and the influence of different endografts: determination using dynamic MRA

PURPOSE

To utilize dynamic magnetic resonance angiography (MRA) to characterize aortic stiffness (beta) and elastic modulus (Ep) as indexes of wall compliance during the cardiac cycle and determine any influence of different endograft designs or the presence of endoleaks on these indexes.

METHODS

Eleven consecutive patients (11 men; median age 74 years, range 63-78) with abdominal aortic aneurysm (AAA) selected for endovascular repair were scanned pre- and postoperatively. Aortic area and diameter changes during the cardiac cycle were determined using dynamic MRA at 4 levels: 3 cm above the renal arteries, between the renal arteries, 1 cm below the renal arteries, and at the level of maximum aneurysm sac diameter. Ep and beta were calculated. Data are presented as median (range); p<0.05 was considered significant.

RESULTS

Preoperatively, Ep and beta were significantly higher at the level of the aneurysm sac compared to all other levels (p<0.05). Following EVAR, stiffness increased at this level (p<0.05). After implantation, patients with an Excluder endograft demonstrated Ep and beta measurements at the aneurysm neck that were 94% and 60% higher, respectively, compared to those with a Talent (p<0.05) endograft. The presence of an endoleak had no effect on Ep or beta.

CONCLUSION

This study introduces the feasibility of dynamic MRA imaging-based calculations of aortic elastic modulus and stiffness. AAA patients demonstrate increased Ep and beta at the level of the aneurysm sac. EVAR results in increased aneurysm sac Ep and beta. Stent-graft design seems to alter Ep and beta within the aneurysm neck, which may have consequences for endograft durability. The presence of an endoleak does not seem to have an effect on Ep or beta.

Dynamic magnetic resonance angiography of the aneurysm neck: Conformational changes during the cardiac cycle with possible consequences for endograft sizing and future design

OBJECTIVE

Proper proximal fixation and stent-graft sealing within the aneurysm neck are critical for endovascular aneurysm repair (EVAR) durability. Computed tomography angiography (CTA) is the gold standard for preoperative sizing of endograft diameters, but the accuracy of these measurements is uncertain because they rely on static images of a dynamic process. The aortic configuration and diameter may change during the cardiac cycle. We studied these phenomena using dynamic electrocardiograph-triggered magnetic resonance angiography (MRA).

METHODS

Eleven consecutive EVAR patients were included. Dynamic MRA was used to perform preoperative and postoperative measurements. Changes were measured in transverse aortic sections 10 mm below the lowest renal artery (level A), at the level of the renal arteries (level B), and 3 cm above the lowest renal artery (level C). Data were analyzed using image segmentation software. Aortic area and diameter changes along 256 axes were determined.

RESULTS

Dynamic MRA demonstrated significant aortic area changes during the cardiac cycle before and after EVAR at all three measured levels. Pre-EVAR aortic area significantly increased per cardiac cycle: 8.4% at level A; 9.3% at level B; and 13.3% at level C (P < .001 for all levels). Post-EVAR aortic area increased 9.7% at level A, 9.6% at level B, and 15.8% at level C per cardiac cycle (P < .001 for all levels). Significant diameter changes during cardiac cycles were also observed at all three levels. Pre-EVAR mean diameter changed up to 8.9% (P < .001) compared with post-EVAR aortic changes of up to 11.5% (P < .001). EVAR had no effect on change in aortic area and diameter. Dynamic MRA also demonstrated that pulsatile aortic distension was not equal in all axes, but rather occurred as an asymmetrical expansion and contraction.

CONCLUSION

In patients with (atherosclerotic) aneurysm disease, the aortic dimensions at the level of and proximal to the aneurysm neck change during the cardiac cycle. This phenomenon is preserved after EVAR. Therefore, maximum diameter using dynamic MRA may not be similar to the maximum diameter with static CTA in all patients, and a standard regimen of 10% to 15% oversizing of an endograft based on static CTA images may be inadequate for some patients. Further studies using dynamic MRA to evaluate effects of different endografts are anticipated, with possible consequences for endograft designs.

Dynamic cine-CT angiography for the evaluation of the thoracic aorta; insight in dynamic changes with implications for thoracic endograft treatment

OBJECTIVE

Thoracic aneurysm preoperative imaging is performed using static techniques without consideration of normal aortic dynamics. Improved understanding of the native aortic environment into which thoracic endografts are placed may aid in device selection. It is unclear what comprises normal thoracic aortic pulsatility. We studied these phenomena dynamically using ECG-gated 64-slice CTA.

METHODS

Maximum diameter and area change per cardiac cycle was measured at surgically relevant anatomic thoracic landmarks in ten patients; 1.0 cm proximal and distal to the subclavian artery, 3.0 cm distal to the subclavian artery, and 3.0 cm proximal to the celiac trunk. Data was acquired using a novel ECG-gated dynamic 64-slice CT scanner during a single breath hold with a standard radiation dose and contrast load. Eight gated data sets, covering the cardiac cycle were reconstructed, perpendicular to the central lumen.

RESULTS

There is impressive change in both maximum diameter and area in the thoracic aorta during the cardiac cycle. Mean maximum diameter changes of greater than 10% are observed in the typical sealing zones of commercially available endografts corresponding to diameter increases of up to 5mm. Aortic area increases by over 5% per cardiac cycle.

CONCLUSIONS

ECG-gated dynamic CTA with standard radiation dose is feasible on a 64-slice scanner and provides insight into (patho) physiology of thoracic aortic conformational changes. Clinicians typically oversize thoracic endografts by 10%. With aortic pulsatility resulting in diameter changes of up to 17.8%, the potential exists for endograft undersizing, graft migration, intermittent type I endoleak, and poor patient outcome. Furthermore, aortic pulsatility is not evenly distributed, and non-circular stentgraft designs should be considered in the future since aortic distension in the aneurysm neck is not evenly distributed.

Age related changes of human aortic distensibility: evaluation with ECG-gated CT

Aortic distensibility is a parameter to grade vascular diseases and age-related effects because it is related to the elastic properties of the vessel wall. In this study vascular cross-sectional area changes have been determined using ECG-gated CT to analyse the age dependency of aortic distensibility. Distensibility measurements of the aorta were performed in 31 subjects (28 to 85 years). Time-resolved images were acquired either with a 4- or 16-detector row CT system using a modified CT angiography protocol. Cross-sectional area changes of the aorta were calculated by semiautomatic segmentation, and distensibility values were obtained using additional systemic blood pressure measurements. The aorta could be segmented successfully in all subjects. A decrease of aortic distensibility with age was found (r=0.50). Below (above) the renal arteries, the annual decrease was Delta D ( infrarenal ) =(-2.1+/-0.7).10(-7 )Pa(-1)a(-1), (D ( suprarenal ) Delta=(-3.5+/-1.1).10(-7 )Pa(-1)a(-1)). Differences between the ages, the youngest third and oldest third studied, were found to be significant (P( suprarenal )=0.003; P( infrarenal )=0.025). An age-dependent decrease of aortic wall elasticity can be determined in a modified routine CT angiography study.

AUSTRALIAN VASCULAR QUALITY OF LIFE INDEX (AUSVIQUOL): A PILOT STUDY OF A DISEASE-SPECIFIC QUALITY OF LIFE MEASURE

BACKGROUND

To develop and test a quality of life (QOL) index specific for patients with vascular disease and appropriate for patients with abdominal aortic aneurysm (AAA) in the clinical setting.

METHODS

The questions and domains of the Australian Vascular Quality of Life Index (AUSVIQUOL) were determined by examination of a prospective database for frequency of symptoms and an in-depth interview of a sample population. The validity of the AUSVIQUOL was tested by comparing it with the Medical Outcomes Short Form Health Survey (SF-36) in a study involving 60 patients who underwent endovascular AAA repair and 48 open AAA repair. A subpopulation of 22 patients representative of the two groups was then reassessed using the SF-36 and the AUSVIQUOL, to compare the reliability of the two indices.

RESULTS

Similar domains of the SF-36 and the AUSVIQUOL measured common QOL elements. The correlation between the two indices was moderate; the AUSVIQUOL measured additional disease-specific QOL factors. The AUSVIQUOL showed better reliability than the SF-36 in all domains and statistically better in the physical function domain (P < 0.05).

CONCLUSION

The AUSVIQUOL is an appropriate tool for the QOL assessment of patients with AAA in the clinical setting.

Pilot Study of Dynamic Cine CT Angiography for the Evaluation of Abdominal Aortic Aneurysms: Implications for Endograft Treatment

PURPOSE

To utilize 40-slice electrocardiographically (ECG)-gated cine computed tomographic angiography (CTA) to characterize normal aortic motion during the cardiac cycle at relevant anatomical landmarks in preoperative abdominal aortic aneurysm (AAA) patients.

METHODS

In 10 consecutive preoperative AAA patients (10 men; mean age 78.8 years, range 69-86), an ECG-gated CTA dataset was acquired on a 40-slice CT scanner using a standard radiation dose. CTA quality was graded and scan time was measured. Pulsatility measurements at multiple relevant anatomical levels were performed in the axial plane. Changes in aortic circumference were determined for both the aortic wall and the luminal diameter.

RESULTS

All 10 CT scans were of good quality. All patients could be scanned in 14 to 33 seconds (mean 21). At each anatomical level measured, there was a 2.2- to 3.4-mm increase in the aortic wall circumference per cardiac cycle. A similar increase was observed in luminal circumference, with a 2.4- to 3.6-mm increase per cycle.

CONCLUSION

This study introduces the concept of dynamic cine CTA imaging of aortic motion, providing insight into the pathophysiology of abdominal aortic and iliac pulsations. Patients with AAAs selected for EVAR demonstrate changes in aortic circumference with each cardiac cycle that may have consequences for endograft sizing and future design. The potential for graft migration, intermittent type I endoleak, and poor patient outcome following EVAR can be anticipated. Complex aortic dynamics deserve increased scrutiny in an effort to prevent potential complications.

Fluid-structure interaction effects on sac-blood pressure and wall stress in a stented aneurysm

An aneurysm is a local artery ballooning greater than 50% of its nominal diameter with a risk of sudden rupture. Minimally invasive repair can be achieved by inserting surgically a stent-graft, called an endovascular graft (EVG), which is either straight tubular curved tubular or bifurcating. However post-procedural complications may arise because of elevated stagnant blood pressure in the cavity, i.e., the sac formed by the EVG and the weakened aneurysm wall In order to investigate the underlying mechanisms leading to elevated sac-pressures and hence to potentially dangerous wall stress levels and aneurysm rupture, a transient 3-D stented abdominal aortic aneurysm model and a coupled fluid-structure interaction solver were employed. Simulation results indicate that, even without the presence of endoleaks (blood flowing into the cavity), elevated sac pressure can occur due to complex fluid-structure interactions between the luminal blood flow, EVG wall, intra-sac stagnant blood, including an intra-luminal thrombus, and the aneurysm wall. Nevertheless, the impact of sac-blood volume changes due to leakage on the sac pressure and aneurysm wall stress was analyzed as well. While blood flow conditions, EVG and aneurysm geometries as well as wall mechanical properties play important roles in both sac pressure and wall stress generation, it is always the maximum wall stress that is one of the most critical parameters in aneurysm rupture prediction. All simulation results are in agreement with experimental data and clinical observations.

Blood flow and structure interactions in a stented abdominal aortic aneurysm model

Since the introduction of endovascular techniques in the early 1990s for the treatment of abdominal aortic aneurysms (AAAs), the insertion of an endovascular graft (EVG) into the affected artery segment has been greatly successful for a certain group of AAA patients and is continuously evolving. However, although minimally invasive endovascular aneurysm repair (EVAR) is very attractive, post-operative complications may occur. Typically, they are the result of excessive fluid-structure interaction dynamics, possibly leading to EVG migration. Considering a 3D stented AAA, a coupled fluid flow and solid mechanics solver was employed to simulate and analyze the interactive dynamics, i.e., pulsatile blood flow in the EVG lumen, pressure levels in the stagnant blood filling the AAA cavity, as well as stresses and displacements in the EVG and AAA walls. The validated numerical results show that a securely placed EVG shields the diseased AAA wall from the pulsatile blood pressure and hence keeps the maximum wall stress 20 times below the wall stress value in the non-stented AAA. The sac pressure is reduced significantly but remains non-zero and transient, caused by the complex fluid-structure interactions between luminal blood flow, EVG wall, stagnant sac blood, and aneurysm wall. The time-varying drag force on the EVG exerted by physiological blood flow is unavoidable, where for patients with severe hypertension the risk of EVG migration is very high.

Infrarenal Abdominal Aortic Aneurysm Complicated by Persistent Endotension After Endovascular Repair: Report of a Case

Endoleak and endotension may prevent the successful exclusion of an aneurysm after endovascular aortic aneurysm repair (EVAR). The pressurization in the excluded aneurysm sac caused by endotension may lead to rupture of the aneurysm; however, the cause of endotension and its underlying mechanisms remain unclear. We report a case of infrarenal abdominal aortic aneurysm (AAA) complicated by persistent endotension after EVAR. Although no endoleaks were found on conventional double-phase computed tomographic scans, a thrombosed endoleak existed in the side branch and attachment site of the endograft. After treating the undetectable thrombosed endoleaks, physical examination revealed that the pressure of the excluded aneurysm had diminished, with shrinkage of the aneurysm. This case report suggests that a high-pressure undetectable type I or type II endoleak could be a major cause of endotension. Thus, postoperative evaluation of the attachment site of an endograft is important after EVAR.

Compliance of abdominal aortic aneurysms evaluated by tissue Doppler imaging: Correlation with aneurysm size

OBJECTIVES

Several studies have shown that an increase in abdominal aortic aneurysm (AAA) growth rate occurs when the diameter reaches 40 to 50 mm. AAA expansion is related to remodeling of the parietal extracellular matrix. The parietal mechanisms involved in this critical phase of sudden increase remain unexplained. Analysis of AAA wall movements and determination of AAA compliance may provide information about the constitution of the arterial wall. If a change in parietal wall motion somewhere between 40 and 50 mm could be shown, this would contribute to the understanding of the growth of AAA. Furthermore, it would provide a valuable additional parameter for AAA monitoring. This study had two aims: first, to evaluate the relationship between AAA compliance and maximum diameter using the tissue Doppler imaging system; and second, to test the hypothesis of a change in AAA behavior at around 45 mm in diameter.

METHODS

Fifty-six patients with AAA (mean diameter, 39 mm) were prospectively investigated using the tissue Doppler imaging system, which provides information concerning arterial wall motion. Maximum mean segmental dilation (MMSD), segmental compliance, pressure strain elastic modulus (Ep), and stiffness were determined and related to the maximum diameter of AAA. Results After natural log transformation of all variables, there was a significant positive linear relationship between maximum diameter and both MMSD (P < .001) and segmental compliance (P < .001) but not with Ep or stiffness (P = .37 and .22, respectively). MMSD and segmental compliance were significantly higher in AAA > or = 45 mm than in AAA < 45 mm (P < .0002 and <. 004, respectively). Ep and stiffness tended to decrease in larger AAAs, but this was not statistically significant (P < .43 and .24, respectively). Dispersion of Ep and stiffness values seemed to be wider among AAA < 45 mm compared with those > or = 45 mm.

CONCLUSION

Compliance parameters can easily be measured during routine AAA ultrasound monitoring using the tissue Doppler imaging system. The study showed an increase in MMSD and segmental compliance as well as a nonsignificant trend toward increased distensibility (decreased Ep and stiffness) with increased AAA diameter. A change in dispersion of AAA distensibility may appear around 45 mm in diameter, but a larger study will be needed to clarify this.

Transrenal fixation of aortic stent-grafts: current status and future directions

Aortic stent-graft repair has been widely used in clinical practice for more than a decade, achieving satisfactory results compared to open surgical techniques. Transrenal fixation of stent-grafts is designed to obtain secure fixation of the proximal end of the stent-graft to avoid graft migration and to prevent type I endoleak. Unlike infrarenal deployment of stent-grafts, transrenal fixation takes advantage of the relative stability of the suprarenal aorta as a landing zone for the uncovered struts of the proximal stent. These transostial wires have sparked concern about the patency of the renal arteries, interference with renal blood flow, and effects on renal function. Although short to midterm results with suprarenal stent-grafts have not shown significant changes in renal function, long-term effects of this technique are still not fully understood. This review will explore the current status of transrenal fixation of aortic stent-grafts, potential risks of stent struts relative to the renal ostium, alternative methods to preserve blood flow to the renal arteries, and future directions or developments in stent-graft design to prevent myointimal proliferation around the stent struts.

A canine model to study the significance and hemodynamics of type II endoleaks1

OBJECTIVE

The clinical significance of Type 2 endoleak after endovascular repair of abdominal aortic aneurysms (AAA) remains incompletely delineated. This study describes the development of a novel canine model that allows for continuous monitoring of intraaneurysmal pressure in the setting of Type 2 endoleak.

METHODS

Infrarenal AAA were created in 10 mongrel dogs by implanting a prosthetic aneurysm containing an intraluminal, solid-state, strain gauge pressure transducer which is able to measure pressures in both solid and liquid media. A segment of native aorta with two or more patent side branch vessels was reimplanted into the prosthetic aneurysm using a Carrel patch. Four animals had two lumbar vessels implanted; two had two lumbar vessels and the caudal mesenteric artery implanted, and four control animals had no vessels reimplanted. Retrograde flow in the aneurysmal side branches caused a Type 2 endoleak after the aneurysm was excluded from antegrade flow by deploying a stent graft. Both systemic and intra-sac pressures were measured daily for up to 90 days after endovascular exclusion and indexed to systemic pressure. Endoleak patency and flow were assessed with digital subtraction angiography, duplex ultrasound, and cine-magnetic resonance angiography (MRA). Histological characterization of the intraaneurysmal contents was performed.

RESULTS

Before endovascular exclusion, the systolic, mean arterial, and pulse pressure within the aneurysmal sac closely matched that of the systemic circulation (systolic, 0.96 +/- 0.22; mean, 0.94 +/- 0.21; pulse pressure, 0.97 +/- 0.22) (R value, 0.97). Endovascular exclusion in animals with no collateral side branch vessels resulted in no endoleak and significantly reduced intraaneurysmal pressure when compared to systemic pressure, with systolic, mean arterial, and pulse pressure 0.172 +/- 0.05, 0.137 +/- 0.05, and 0.098 +/- 0.02, respectively (P < 0.001). In animals with Type 2 endoleaks, the pressures were lower than systemic pressure, but statistically significant in their difference from the control group. The systolic pressure of those with Type 2 endoleaks was 0.702 +/- 0.048; mean arterial pressure was 0.784 +/- 0.028, and pulse pressure was 0.406 +/- 0.031 when indexed to systemic pressure (P < 0.001). Cine-MRA and Duplex ultrasound documented persistent patency of the Type 2 endoleaks throughout the study period in animals with multiple side branches.

CONCLUSION

Intraaneurysmal pressure in the setting of Type 2 endoleaks may be accurately determined using this canine model. Intraaneurysmal pressure is maintained at a significant level in the context of this retrograde collateral perfusion, suggesting that persistent Type 2 endoleaks are of clinical significance. This model may serve to allow further evaluation and characterization of Type 2 endoleaks.

Surveillance for endoleaks: How to detect all of them

Endovascular aneurysm repair has proven to be a valuable alternative to open repair in selected patients. This less invasive procedure, however, requires long-term surveillance for its own set of potential complications, including perigraft leakage, or endoleak. This article focuses on the detection of these leaks, first defining and classifying endoleaks and then describing various means of detecting them, including computed tomographic angiography, magnetic resonance angiography, color-flow duplex ultrasonography, and conventional angiography.

Pulsatile Wall Motion (PWM) Measurements after Endovascular Abdominal Aortic Aneurysm Exclusion are not Useful in the Classification of Endoleak

The pulsatile wall motion (PWM) of AAA is reduced after endovascular stent-graft placement. The purpose of this study was to identify whether PWM after endografting was useful in the classification of endoleak.

PATIENTS AND METHODS

162 patients treated with EVAR underwent pre- and post-operative PWM assessment with ultrasonography. Follow-up was 1-9 years. 111 patients had well-excluded aneurysms, three patients had enlarging aneurysms without any recognizable endoleak (endotension), 16 had type I, 31 had type II and 1 had type III endoleak.

RESULTS

The PWM was reduced from about 1mm pre-operatively to 0.24 mm post-operatively in well-excluded aneurysms. PWM remained stable during follow-up. Type I endoleak was associated with moderately reduced PWM (proximal endoleak 0.79 mm and distal 0.32 mm). PWM in patients with type II endoleak was higher (0.32 mm) post-operatively (p=0.002) compared to well-excluded aneurysms.

CONCLUSION

PWM is permanently reduced after endografting. The smallest reduction in PWM was in patients with type II endoleaks. However, the overlap between the groups does not allow reliable identification of patients having endoleak with PWM-measurements.

Direct intra-aneurysm sac pressure measurement using tip-pressure sensors: In vivo and in vitro evaluation

OBJECTIVE

Direct intra-aneurysm sac pressure measurement with percutaneous translumbar puncture is a new method for follow-up after endovascular aneurysm repair. The purpose of this study was to evaluate a tip-pressure sensor system for intra-aneurysm pressure measurement in an in vitro aneurysm model and in vivo in patients by studying intraobserver variability.

METHODS

We used 0.014-inch guide wire-mounted tip-pressure sensors. For the in vitro aneurysm model, saccular aneurysms filled with thrombus were inserted in a left-heart-driven aneurysm model. Pressure was measured simultaneously with guide wire pressure sensors in the lumen of the model and within the aneurysm thrombus. In vivo, intraobserver variability was evaluated with double percutaneous translumbar puncture of the abdominal aortic aneurysm (AAA) with pressure measurement in 15 patients (14 men, 1 woman; median age, 75 years [63-80 years]; median AAA diameter, 55 mm [47-80 mm]) at a median of 32 months (2-100 months) after endovascular aneurysm repair. Mean pressure index was calculated as the percentage of mean intraaneurysm pressure relative to simultaneous mean systemic pressure.

RESULTS

In vitro, the difference in pressure between the tip-sensor measurements and the pressure output of the aneurysm model was 2 mm Hg (1-4 mm Hg) when the output varied between 150/50 and 200/100 mm Hg (n = 90). Mean pressure in the lumen of the model and within the aneurysm thrombus differed by 1 mm Hg (-5-15 mm Hg (n = 10). In vivo, intraobserver variability of mean pressure index (Bland-Altman plot) was 0% (-7%-17%; n = 15%).

CONCLUSION

Direct intra-aneurysm sac pressure measurement with tip-pressure sensors mounted on 0.014-inch guide wires is a reliable and reproducible technique for measuring intra-AAA pressure both in vitro and in vivo.

Compliance of abdominal aortic aneurysms: evaluation of tissue Doppler imaging

Expansion of abdominal aortic aneurysms (AAA) is due to remodeling of the parietal extra-cellular matrix and may lead to rupture. This remodeling is reflected by compliance which may be an indicator of AAA behavior and thus useful for clinicians. Tissue Doppler Imaging (TDI) is an ultrasonographic modality which allows wall motion measurements along an arterial segment. It has previously been evaluated in normal aortas and was then evaluated in thirty-five patients with AAA. Mean values (+/-standard deviation) characterizing maximum diameter AAA compliance were dilation 809 mum (+/-465), strain 2.2% (+/-1), pressure strain elastic modulus 3.94 10(5) Pa [3.25; 4.8] and stiffness 28.8 [24; 34.5], last values being expressed as geometric mean [interquartile range]. They were in accordance with those previously obtained with other systems. Segmental parameter values were maximum mean segmental dilation 534 mum (+/-305) and segmental compliance 14.6 (+/-8.3) 10(-2) mum/Pa. Reproducibility was appropriate for clinical studies. The TDI system is simple and reliable for measurement of AAA compliance, and compliance can easily be recorded during routine ultrasound control.

Intra-aneurysm sac pressure measurements after endovascular aneurysm repair: differences between shrinking, unchanged, and expanding aneurysms with and without endoleaks

OBJECTIVE

Our objective was to study intra-aneurysm pressure after endovascular aneurysm repair (EVAR) in shrinking, unchanged, and expanding abdominal aortic aneurysms (AAAs) with and without endoleaks.

METHODS

Direct intra-aneurysm sac pressure measurement (DISP) by percutaneous translumbar puncture of the AAA under fluoroscopic guidance was performed 46 times during the follow-up of 37 patients (30 men; median age, 73 years [range, 58-82 years]; AAA diameter: median, 60 mm [range, 48-84 mm]). Three patients were included in two different groups because DISP was performed more than once with different indications. Tip-pressure sensors mounted on 0.014-inch guidewires were used for simultaneous measurement of systemic and AAA sac pressures. Mean pressure index (MPI) was calculated as the percentage of mean intra-aneurysm pressure relative to the simultaneous mean intra-aortic pressure.

RESULTS

Median MPI was 19% in shrinking (11 patients), 30% in unchanged (10 patients), and 59% in expanding (9 patients) aneurysms without endoleaks. Pulse pressure was also higher in expanding (10 mm Hg) compared with shrinking (2 mm Hg; P <.0001) AAAs. Four of the nine patients with expanding AAAs underwent five repeated DISPs later in the follow-up, and MPIs were consistently elevated. Seven of the 10 patients with unchanged AAAs without endoleaks underwent further computed tomography follow-up after DISP; 2 expanded (MPI, 47%-63%), 4 shrank (MPI, 21%-30%), and 1 remained unchanged (MPI, 14%). Type II endoleaks (6 patients, 7 DISPs) were associated with wide range of MPI (22%-92%). Successful endoleak embolization (n = 4) resulted in pressure reduction.

CONCLUSIONS

Intra-aneurysm sac pressure measurement is an important adjunctive for EVAR evaluation, possibly allowing early detection of failures. High pressure is associated with AAA expansion and low pressure with shrinkage. Type II endoleaks can be responsible for AAA pressurization, and successful embolization appears to result in pressure reduction.

Type II endoleak in porcine model of abdominal aortic aneurysm

PURPOSE

The purpose of this study was to develop a reliable in vivo porcine model of type II endoleak resulting from endovascular aortic aneurysm repair (EVAR), for the study and treatment of type II endoleak.

METHODS

Eight pigs underwent creation of an infrarenal aortic aneurysm, with a Dacron patch with preservation of lumbar branches. An indwelling pressure transducer was placed in the aneurysm sac. After 1 week the animals underwent EVAR with a custom-made Talent endograft. After another week the animals underwent laparoscopic lumbar artery ligation. Abdominal and pelvic computed tomography was performed after each procedure. Aneurysm sac pressure was measured in sedated and awake animals.

RESULTS

All eight animals underwent successful creation of an aortic aneurysm and EVAR resulting in exclusion of the aneurysm sac. After creation of the aneurysm the sac mean arterial pressure (MAP) was 72.5 +/- 6.1 mm Hg and the sac pulse pressure was 44.8 +/- 8.7 mm Hg. Postoperative computed tomography scans demonstrated a type II endoleak from the lumbar branches in all animals. While aneurysm sac MAP (56.5 +/- 7.9 mm Hg; P <.01) and pulse pressure (13.6 +/- 4.1 mm Hg; P <.01) decreased after EVAR, sac pulse pressure remained, with type II endoleak. All animals underwent laparoscopic lumbar artery ligation, which resulted in further reduction in the sac MAP (38.3 +/- 4.6 mm Hg; P <.02) and immediate absence of sac pulse pressure (0 mm Hg; P <.01). Necropsy confirmed the absence of collateral flow in the aneurysm sac, with fresh thrombus formation in all animals.

CONCLUSION

We present a reliable and clinically relevant in vivo large animal model of type II endoleak.

CLINICAL RELEVANCE

We set out to show that aortic aneurysm sac pressurization caused by lumbar arterial flow in the setting of type II endoleak can be reproduced in an in vivo porcine model of endovascular aortic aneurysm repair. Indeed, in this model the aneurysm sac pulse pressure was a sensitive indicator of type II endoleak, correlating well with findings at computed tomography, and lumbar artery ligation eliminated the endoleak, as demonstrated on computed tomography scans and sac pressure measurement. Therefore we believe this in vivo large animal model can be instrumental in the study of many aspects of the physiologic features of type II endoleak.