Endotension distribution and the role of thrombus following endovascular AAA exclusion

Contrast-Free Endovascular Aneurysm Repair Combined With Fibrin Sealant Filling for Treating Abdominal Aortic Aneurysm: Technical Note

INTRODUCTION

Endovascular aneurysm repair using iodinated contrast agents risks contrast-induced nephropathy, especially in high-risk patients. This technical note describes a contrast-free endovascular aneurysm repair (EVAR) protocol using preoperative imaging measurement and fibrin sealant (FS) filling.

TECHNIQUE

Preoperative imaging measurement and intraoperative guidewire manipulation facilitated anatomical identification without contrast. After endograft deployment, the aneurysm sac was filled with FS if endoleak was indicated by pressure fluctuations.

RESULT

Between 2017 and 2020, 6 high-risk patients underwent contrast-free EVAR with FS filling. Complete exclusion was achieved in all cases. Over follow-up, no endoleaks, deterioration in renal function, or other complications were observed.

CONCLUSION

Contrast-free EVAR with FS filling shows early feasibility as an alternative technique for contrast-induced nephropathy (CIN) high-risk patients, while larger studies with long-term monitoring are imperative to validate outcomes.

CLINICAL IMPACT

This study showcases a contrast-free EVAR technique with fibrin sealant filling for high-risk CIN patients. It offers a safer approach for those with renal challenges, reducing CIN risk. The technique's feasibility in a small cohort suggests its utility in treating AAA without iodinated contrast, crucial for patients with specific health risks. For clinicians, it introduces a method that decreases nephrotoxic risks, potentially changing practice for vulnerable patients.

Surgical Findings and Outcomes of Endotension following Endovascular Aneurysm Repair

BACKGROUND

Endotension is one of the detrimental complications after endovascular aneurysm repair (EVAR) and surgical management has been considered as standard of care. However, there is a paucity of data regarding the findings and outcomes of such surgical intervention. The aim of this study was to investigate intraoperative findings and outcomes of surgical treatment for endotension after EVAR.

METHODS

Between January 2005 and October 2018, of the 708 patients who underwent EVAR for aneurysm aortic aneurysm; 12 patients (mean age of 76.1; range 66-88) who underwent open repair for endotension were retrospectively analyzed. The anatomical characteristics of the aorta and surgical findings were reviewed. The rates of early and late procedural complications, and overall mortality were evaluated.

RESULTS

The median interval between the EVAR and surgical conversion was 45.9 months (range 17.1-46.9). Three of the twelve patients underwent emergency surgery due to aneurysm rupture. The median aneurysm sac size, the proximal neck diameter, and the proximal neck length before EVAR were 64 mm, 23.5 mm, and 30.5 mm, respectively, that changed before open repair to 93.5 mm (p = .02), 25 mm (p = .011), and 23 mm (p = .003), respectively. In four of the twelve patients, radiographically undetected endoleak was identified during surgery to be Type Ia, Ib, II, and III, respectively. The rates of early and late procedural complications, and overall mortality were 8.3%, 8.3% and 8.3%, respectively.

CONCLUSIONS

Patients with endotension have a risk of delayed endoleak and aneurysm rupture; secondary intervention should be performed in such cases to prevent fatal complications. Surgical treatment appears to be a curative treatment for endotension with favorable outcomes. In addition, the possibility of an undetected endoleak should be considered as a potential cause of endotension.

Endovascular Exclusion of Saphenous Vein Graft Aneurysms Complicating Abdominal Aortic Aneurysm Repair

A 64-year-old man was referred for vascular evaluation before renal transplantation for ischemic nephropathy. In the past he had undergone bilateral renal artery revascularizations using saphenous vein. At the time of transplant evaluation, he was found to have bilateral aneurysms of the saphenous veins used to bypass his renal artery stenoses. He underwent successful endovascular exclusion of the aneurysms with 2 endovascular AneuRx extension cuffs. This case highlights both the versatility of endovascular treatments as well as the importance of a comprehensive vascular examination.

Aneurysm sac shrinkage after endovascular treatment of the aorta: Beyond sac pressure and endoleaks

The isolation of the aneurysm sac from systemic pressure and its consequent shrinkage are considered criteria of success after endovascular repair (EVAR). However, the process of shrinkage does not solely depend on the intrasac pressure, the predictive role of which remains ambiguous. This brief review summarizes the additional pathophysiological mechanisms that regulate the biomechanical properties of the aneurysm wall and may interfere with the process of aneurysm sac shrinkage.

Significance of initial aortic aneurysm pressure sensor readings varies with aortic endograft design

BACKGROUND

The differences in implantable pressure sensor aneurysm sac readings were compared following endovascular aneurysm repair (EVAR) among three different stent grafts.

METHODS

From January 2006 to March 2009, 51 aortic stent grafts were implanted along with the Endosure sensor. Grafts used were Zenith, Talent, and Excluder. In the present retrospective study, pulse ratios were measured intraoperatively before and after aneurysm sac exclusion and in follow-up (within 30 days). Analysis of variance was used to determine significance.

RESULTS

The average aneurysm size that was repaired was 5.75 cm (range: 4-8.5 cm); 41 patients (80.4%) being male with an average age of 76.3 years (range: 58-90 years). Thirty-four grafts were Zenith, 9 were Talent, and 8 were Excluder. The average pre-aneurysm exclusion pulse ratios for the Zenith, Talent, and Excluder were 1.00, 1.08, and 0.95 (p = 0.18), respectively. The average post-aneurysm exclusion pulse ratios were 0.34, 0.67, and 0.35, respectively (p = 0.003). Pulse ratios at the time of follow-up (within 30 days) were 0.17, 0.22, and 0.11, respectively (p = 0.44). Nine of 51 (17.6%) patients had a reduction of pulse ratio of less than 30% after endograft implantation. Five of those 9 patients (55.5%) had the Talent endograft, although there was no angiographic evidence of endoleak.

CONCLUSIONS

The Talent graft has significantly higher pulse ratios following endograft implantation despite having no angiographic evidence of endoleak when compared to the Zenith and Excluder grafts. However, the pulse ratios decreased to levels similar to Zenith and Excluder within 30 days of endograft implantation. This suggests that the Talent endograft may have increased porosity initially. If pulse ratios do not appropriately decrease immediately after device implantation, further angiographic imaging may not be necessary if no obvious endoleak is seen.

Evaluation of pressure transmission and intra-aneurysmal contents after endovascular repair using the Trivascular Enovus expanded polytetrafluoroethylene stent graft in a canine model of abdominal aortic aneurysm

OBJECTIVE

Endotension has been defined as persistently increased pressure within the excluded sac of an abdominal aortic aneurysm (AAA) resulting in increasing aneurysm size after endovascular repair in the absence of endoleak. Devices that use expanded polytetrafluoroethylene (ePTFE) have been associated with the development of endotension and continued AAA enlargement. In this study, intra-aneurysmal pressure and aneurysm content were evaluated after endovascular repair with the Enovus ePTFE stent graft in a canine model.

METHODS

Prosthetic ePTFE aneurysms, each containing a solid-state, strain-gauge pressure transducer, were implanted in the infrarenal aorta of 13 mongrel dogs (25-35 kg). A second pressure transducer was inserted into the native aorta for systemic arterial pressure measurement. The stent graft was then deployed to exclude the aneurysm via distal aortic access. Comparison was made among three distinct stent grafts: the Trivascular Enovus (nonporous ePTFE; four animals), the original Gore Excluder (porous ePTFE; five animals), and the Medtronic AneuRx (Dacron; four animals). Daily systemic and intra-AAA pressures were measured for 4 weeks. Intra-aneurysmal pressures were indexed to simultaneously measured systemic pressures. After 4 weeks, the aorta, the prosthetic aneurysm, and its contents were harvested, photographed, and processed for histologic investigation with hematoxylin and eosin and Masson trichrome staining.

RESULTS

Within 24 hours after exclusion, the mean arterial pressure and pulse pressure within the AAA sac tapered to less than 20% of systemic pressure for all three stent graft types. Throughout the postoperative period, significantly lower indexed intra-aneurysmal pressures were present in the Enovus- and AneuRx-treated aneurysms as compared with those treated with the original Excluder stent graft (0.05 +/- 0.04, 0.16 +/- 0.06, and 0.06 +/- 0.03 for the Enovus, Excluder, and AneuRx, respectively). Histologic analysis of the Enovus-treated aneurysms demonstrated intraluminal content characterized almost entirely by erythrocytes and infrequent white blood cells without the fibrin organization-characteristics of acute or chronic thrombus. This contrasted with the content of the Excluder-treated aneurysms, which contained poorly organized fibrin deposition suggestive of acute thrombus, and of the AneuRx-treated aneurysms, which demonstrated mature, well-organized collagenous connective tissue.

CONCLUSIONS

Exclusion of the AAA with the Enovus stent graft resulted in nearly complete elimination of intra-aneurysmal pressure in this model. Histologic analysis of the aneurysm content further suggested complete exclusion, including elimination of circulating clotting factors and fibroblasts responsible for thrombus formation and reorganization. Ultimately, clinical evaluation will be necessary to demonstrate the effectiveness of this stent graft in preventing the development of endotension.

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.

Detecting endoleaks after endovascular AAA repair with a minimally invasive, implantable, telemetric pressure sensor: an in vitro study

A feasibility study on a completely digital telemetric pressure sensor (TPS) to detect endoleaks was performed in an in vitro model of an abdominal aortic aneurysm (AAA). An endovascular-stented AAA silicone model with different types (I-III) and sizes (3-11 French) of endoleaks was created and pulsatile pressure was applied with physiological flow and pressure rates [mean intraaortic pressure (IAP): 95-130 mmHg] and different degrees of thrombosis of the aneurysm sac. Aneurysm sac pressure (ASP) was measured with the TPS and with wired pressure sensors (WPS) as a reference. Statistical analysis included paired t-test, Pearson's correlation analysis and Bland-Altman plots. After opening an endoleak, the mean ASP increased significantly (P < 0.0001) from 15 to almost 95% of the mean IAP depending on endoleak type and size. ASP could be measured accurately with the TPS and the WPS. The telemetric and wired ASP increase showed a high Pearson's correlation coefficient (r) for a non-thrombosed (r = 0.97) and a thrombosed (r = 0.96) aneurysm sac. In an in vitro silicone model, the newly designed telemetric pressure sensor was able to detect the occurrence of an endoleak in a non-invasive way and might be a valuable device for follow-up of endovascular AAA repair.

Abdominal aortic aneurysm sac shrinkage after endovascular aneurysm repair: Correlation with chronic sac pressure measurement

OBJECTIVES

Abdominal aortic aneurysm (AAA) sac shrinkage after endovascular aneurysm repair (EVAR) is considered to be evidence of clinical success. Exclusion of the sac from systemic pressure is the likely cause of shrinkage. We report our continuing clinical experience with the use of a permanently implantable, ultrasound-activated remote pressure transducer to measure intrasac pressure and its correlation with changes in sac diameter over time.

METHODS

Over a 22-month period, 21 patients underwent EVAR of an infrarenal AAA with implantation of an ultrasound-activated remote pressure transducer fixed to the outside of the stent-graft and exposed to the excluded aortic sac. Intrasac pressures were measured directly with an intravascular catheter and by the remote sensor at the time of stent-graft deployment. Follow-up sac pressures were measured by remote sensor and compared with systemic arterial pressure at every follow-up visit. Mean follow-up was 11.4 +/- 5.0 months (range, 1 to 26 months). Twenty patients had follow-up of > or =6 months. Mean pressure index (MPI) was calculated as the ratio of mean sac pressure to mean systemic pressure.

RESULTS

Pressures could be obtained at all visits in 15 of the 21 patients. Fourteen of these 15 patients had follow-up of at least 6 months. Aneurysm sac shrinkage of >5 mm was seen in seven (50%) of these 14 patients. No aneurysm enlargement was observed in any patient. The MPI was significantly lower in patients with sac shrinkage at 6 months and at final follow-up.

CONCLUSIONS

Endovascular aneurysm repair results in marked reduction of sac pressure in most patients. Patients with aneurysm shrinkage after EVAR have significantly lower MPI; however, the absence of sac shrinkage does not imply persistent pressurization of the sac. Further clinical follow-up will delineate the role of long-term sac pressure monitoring in surveillance after EVAR.

Effect of intraluminal thrombus on pressure transmission in the abdominal aortic aneurysm

OBJECTIVE

To clarify the effect of intraluminal thrombus on pressure transmission.

METHODS

A saccular aneurysm was inserted into an artificial circulation system. Subsequently, the saccular aneurysm was filled with eight different human aortic aneurysm thrombus samples. Starch solution in an empty aneurysm was used as a control. A pressure sensor measured the pressure in the circulation, and a second piezoelectric sensor measured the pressure in the saccular aneurysm at 3, 2, and 1 cm from the endoluminal surface (23 locations). The influence of the elastic characteristics of the aneurysm wall on the extent of pressure reduction was evaluated by experiments performed with aneurysms made of rubber and paraffin.

RESULTS

The pressures measured in the empty aneurysm were identical to those measured in circulation (P > .05). The pressure measured in the thrombus was significantly lower than the pressure measured in the circulation (P < .05). The mean pressure ratio between the systolic thrombus pressure and systolic circulation pressure at 1, 2, and 3 cm was 0.90 +/- 0.09, 0.86 +/- 0.10, and 0.81 +/- 0.09, respectively. However, there was a clear correlation between the pressure in the circulation and in the thrombus (Pearson correlation coefficient: mean, r = 0.997; range, 0.975-0.999; P < .01). The change in circulatory pressure was followed by an almost identical change in thrombus pressure (regression coefficient: mean, beta = .997; range, .983-1.000; P < .01). In stiff aneurysms, the pressure reduction is less than in more compliant ones (P < .05).

CONCLUSIONS

In an in vitro model, pressure in the aneurysmal sac is reduced by fibrinous thrombus.

CLINICAL RELEVANCE

Endovascular aneurysm repair (EVAR) aims at reducing the pressure in the aneurysmal sac. Therefore, it seems attractive to use pressure monitoring in the aneurysmal sac as a follow-up after EVAR. This study contributes to the development of the rationale of pressure monitoring in the aneurysmal sac as a follow-up method after EVAR. The aneurysmal sac is filled with thrombus. To interpret pressure measurements in the thrombus, we have to learn about the effect of the thrombus on pressure transmission and on the pressure measurements themselves. Our study demonstrates that reduction of pressure occurs as it is transmitted through a human aortic thrombus.

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.

Treatment of type II endoleaks with a novel polyurethane thrombogenic foam: Induction of endoleak thrombosis and elimination of intra-aneurysmal pressure in the canine model

OBJECTIVE

The clinical significance and treatment of retrograde collateral arterial perfusion of abdominal aortic aneurysms after endovascular repair (type II endoleak) have not been completely characterized. A canine abdominal aortic aneurysm model of type II endoleak with an implanted pressure transducer was used to evaluate the use of polyurethane foam to induce thrombosis of type II endoleaks. The effect on endoleak patency, intra-aneurysmal pressure, and thrombus histology was studied.

METHODS

Prosthetic aneurysms with an intraluminal, solid-state, strain-gauge pressure transducer were created in the infrarenal aorta of 14 mongrel dogs. Aneurysm side-branch vessels were reimplanted into the prosthetic aneurysm of 10 animals by using a Carrel patch. Type II (retrograde) endoleaks were created by excluding the aneurysm from antegrade perfusion with an impermeable stent graft. Thrombosis of the type II endoleak was induced by implantation of polyurethane foam into the prosthetic aneurysm sac of four animals. Six animals with type II endoleaks were not treated. In four control animals, no collateral side branches were reimplanted, and therefore no endoleak was created. Intra-aneurysmal and systemic pressures were measured daily for 60 to 90 days after the implantation of the stent graft. Endoleak patency and flow were assessed during surgery and at the time of death by using angiographic imaging and duplex ultrasonography. Histologic analysis of the intra-aneurysmal thrombus was also performed.

RESULTS

Intra-aneurysmal pressure values are indexed to systemic pressure and are represented as a percentage of the simultaneously obtained systemic pressure, which has a value of 1.0. All six animals with untreated type II endoleaks maintained patency of the endoleak and side-branch arteries throughout the study period. Compared with control aneurysms that had no endoleak, animals with patent type II endoleaks exhibited significantly higher intra-aneurysmal pressurization (systolic pressure: patent type II endoleak, 0.702 +/- 0.283; control, 0.172 +/- 0.091; P < .001; mean pressure: endoleak, 0.784 +/- 0.229; control, 0.137 +/- 0.102; P < .001; pulse pressure: endoleak, 0.406 +/- 0.248; control, 0.098 +/- 0.077; P < .001; P < .001 for comparison for all groups by analysis of variance). Treatment of the type II endoleak with polyurethane foam induced thrombosis of the endoleak and feeding side-branch arteries in all four animals with type II endoleaks. This resulted in intra-aneurysmal pressures statistically indistinguishable from the controls (systolic pressure, 0.183 +/- 0.08; mean pressure, 0.142 +/- 0.09; pulse pressure, 0.054 +/- 0.04; not significant). Angiography and histology documented persistent patency up to the time of death (mean, 64 days) for untreated type II endoleaks and confirmed thrombosis of polyurethane foam-treated endoleaks in all cases.

CONCLUSIONS

Untreated type II endoleaks were associated with intra-aneurysmal pressures that were 70% to 80% of systemic pressure. Treatment with polyurethane foam resulted in a reduction of intra-aneurysmal pressure to a level that was indistinguishable from control aneurysms that had no endoleak.

CLINICAL RELEVANCE

Endovascular repair of abdominal aortic aneurysms is dependent on the successful exclusion of the aneurysm from arterial circulation. Type II endoleaks originate from retrograde flow into the aneurysm sac. This study demonstrates the use of polyurethane foam to induce thrombosis in a canine model of a type II endoleak, thereby reducing intra-aneurysmal pressure to levels similar to levels in animals without endoleaks. This approach may be a strategy for future treatment of type II endoleaks.

First experience in human beings with a permanently implantable intrasac pressure transducer for monitoring endovascular repair of abdominal aortic aneurysms

OBJECTIVES

Endovascular stent graft repair of abdominal aortic aneurysms (AAAs) prevents rupture by excluding the aneurysm sac from systemic arterial pressure. Current surveillance protocols after endovascular aneurysm repair (EVAR) follow secondary markers of sac pressurization, namely, endoleak and sac enlargement. We report the first clinical experience with the use of a permanently implantable, ultrasound-activated remote pressure transducer to measure intrasac pressure after EVAR.

METHODS

Over 7 months, 14 patients underwent EVAR of an infrarenal abdominal aortic aneurysm with implantation of an ultrasound-activated remote pressure transducer fixed to the outside of the stent graft and exposed to the excluded aortic sac. Twelve patients received modular bifurcated stent grafts, and 2 patients received aortouniiliac devices. Intrasac pressures were measured directly with an intravascular catheter and by the remote sensor at stent-graft deployment. Follow-up sac pressures were measured with a remote sensor and correlated with systemic arterial pressure at every follow-up visit. Mean follow-up was 2.6 +/-1.9 months.

RESULTS

Excellent concordance was found between catheter-derived and transducer-derived intrasac pressssure intraoperatively. Pulsatile waveforms were seen in all functioning transducers at each evaluation interval. One implant ceased to function at 2 months of follow-up. In 1 patient a type I endoleak was diagnosed on 1-month computed tomography (CT) scans; 3 type II endoleaks were observed. Those patients with complete exclusion of the aneurysm on CT scans had a significant difference in systemic and sac systolic pressures initially (P <.001) and at 1 month (P <.001). Initial sac diastolic pressures were higher than systemic diastolic pressures (P <.001). The ratio of systemic to sac systolic pressure increased over time in those patients with complete aneurysm exclusion ( P <.001). Four of 6 patients with no endoleak and greater than 1-month follow-up had diminution of sac systolic pressure to 40 mm Hg or less by 3 months.

CONCLUSION

This is the first report of a totally implantable chronic pressure transducer to monitor the results of EVAR in human beings. Aneurysm exclusion leads to gradual diminution of sac pressure over several months. Additional clinical follow-up will be necessary to determine whether aneurysm sac pressure monitoring can replace CT in the long-term surveillance of patients after EVAR.

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.

Distribution of sac pressure in an experimental aneurysm model after endovascular repair: the effect of endoleak types I and II

PURPOSE

To study in an experimental aneurysm model the differential distribution of strain/pressure (S/P) on the aneurysm wall before and after endograft exclusion and in the presence of individual type I and type II endoleaks.

METHODS

Two tapered elliptical Gore-Tex patches were sutured to an anterior and posterior longitudinal arteriotomy of an 8-mm Gore-Tex tube graft, thus creating a fusiform aneurysm. Two S/P transducers were placed at the proximal sac adjacent to the proximal neck, 2 at the site of the widest sac diameter, and 2 at the sac adjacent to the distal neck. The aneurysm, which was connected to a pulsatile pump system, was excluded using a 10-mm endograft. Type I and type II endoleaks were created and tested individually. S/P measurements were obtained at systemic systolic pressures (BP) of 80, 110, and 150 mmHg. Thrombosis of the sac contents was induced by injection of thrombin and calcium in the sac. Angiography was used to verify presence or absence of flow in the sac.

RESULTS

Aneurysm exclusion resulted in significant S/P reductions at all 3 BP levels versus prior to exclusion (p<0.05). Thrombus in the sac did not alter S/P in the excluded sac (p>0.05 for all 3 BP levels). In the presence of a proximal type I endoleak, S/P distribution was not uniform, and S/P at the proximal neck was close to S/P prior to exclusion (p>0.05 no graft versus type I endoleak for all 3 BP levels). This was also true in the presence of thrombus. With a type II endoleak, S/P was more evenly distributed and was not significantly elevated compared to the pressure without an endoleak (p>0.05, graft versus type II endoleak for all 3 BP levels). Thrombus had no effect on intrasac S/P with a type II endoleak. Intrasac S/P was significantly higher in the presence of a type I endoleak compared to a type II endoleak when BP=150 mmHg (p=0.008).

CONCLUSIONS

Endovascular exclusion of an aneurysm results in uniform S/P reduction in the aneurysm sac. Type I endoleak, but not type II endoleak, results in significantly higher S/P in an area of the sac adjacent to the proximal neck. Thrombus does not result in significantly different S/P distribution in the aneurysm sac.