Intra-aneurysmal pressure after incomplete endovascular exclusion

Impact of antithrombotic therapy on clinical outcomes in patients with type B acute aortic syndrome

Objective

Antithrombotic therapy has the potential to interfere with false lumen thrombosis. In type B acute aortic syndrome, the degree of false lumen thrombosis affects clinical outcomes. We aimed to explore the association of antithrombotic therapy with the prognosis of patients with type B acute aortic syndrome.

Methods

We reviewed 406 patients with type B acute aortic syndrome who were discharged alive with and without antithrombotic therapy. The primary outcome was aorta-related adverse events, defined as a composite of aorta-related death, aortic rupture, aortic repair, and progressive aortic dilation.

Results

Of the 406 patients, 64 (16%) were discharged with antithrombotic therapy and 342 (84%) were discharged without antithrombotic therapy. A total of 249 patients (61%) presented with intramural hematoma with complete thrombosis of the false lumen, and 157 patients (39%) presented with aortic dissection. During a median follow-up of 4.6 years, 32 patients (50%) in the antithrombotic group and 93 patients (27%) in the nonantithrombotic group had a primary outcome event. Cumulative incidence of aorta-related events at 1 and 3 years with death as the competing risk was higher in the antithrombotic group than in the nonantithrombotic group (19% ± 5% vs 9% ± 2% at 1 year and 40% ± 7% vs 17% ± 2% at 3 years, P < .001).

Conclusions

Antithrombotic therapy might be associated with an increased risk of aorta-related events in patients with type B acute aortic syndrome.

Is Partially Thrombosed False Lumen Really a Predictor for Adverse Events in Uncomplicated Type B Aortic Dissection: A Systematic Review and Meta-Analysis?

Objective:

This meta-analysis and systematic review investigated whether partial thrombosed false lumen was a predictor for adverse events in uncomplicated Type B aortic dissection (TBAD).

Methods:

We performed the current systematic review of the medical literature according to the 2009 Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. The Newcastle-Ottawa Scale was used to evaluate the quality of individual studies. Search terms based on the MEDLINE database included “type B aortic dissection,” “false lumen” and “thrombosis.” The primary outcomes included mortality, intervention, and aortic growth.

Results:

Six studies were included in this systematic review, with a total number of 692 patients, including 197 patency (28.5%), 214 partial thrombosis (30.9%), and 281 complete thrombosis (40.6%). Due to the insufficient data for quantitative analysis, we only conducted a scoping review for mortality and intervention. For aortic growth, we conducted a meta-analysis based on Standardized Mean Difference (SMD). The SMD of PT vs. P by random effect model was −0.05 (random effect model) [95% confidence interval (CI), −0.39 to 0.29]. The 95% CI crossed with the null line of 0, indicating no significant difference. The SMD was 0.37 (fixed effects model) (95% CI, 0.03–0.71) and 0.70 (fixed effects model) (95% CI, 0.37–1.04) for PT vs. CT, and P vs. CT, respectively.

Conclusions:

Current researches on partial thrombosis of TBAD are inconsistent. Partial thrombosis is not associated with a faster aortic growth rate. Until more solid evidence is available, we do not recommend partial thrombosis as a surgical indication or high-risk profile for TBAD.

Systematic Review Registration: Unique Identifier: CRD42019121912.

Endotension: twenty years of a controversial term

Use of the term endotension in the treatment of aortic aneurysm is currently controversial. Initially it was proposed to define the circumstance in which there is an enlargement of the aneurysm sac after endovascular repair without a demonstrable endoleak. The term was established with the aim of transmitting the possibility of causes other than pressure applying stress to the aneurysm wall. Twenty years have passed since the proposal of this terminology was published. The literature is reviewed with the purpose of providing an update on advances in the knowledge of the possible etiological mechanisms. The experimental studies call into question that causes other than pressure determine the increase of the aneurysm. On the basis of this review, the term `Sac Expansion Without Evident Leak´ (SEWEL) is proposed as a more accurate and precise denomination for what is aimed to be defined. Evidence suggests that the more likely mechanisms of persistent pressurization of the aneurysm sac are an unidentified endoleak (likely type I or low-flow Type II) or thrombus occluding wide and short channels that connects with the excluded aneurysm sac (at the attachment sites of the stent-graft or at the branch vessels orifices).

Flow density of computed tomography aortography for predicting early unfavorable aortic remodeling after TEVAR in type IIIb aortic dissection

OBJECTIVE

Patients diagnosed of DeBakey type III aortic dissection with partial thrombosis of false lumen (FL) have a higher mortality rate. However, IIIb dissections with full patent FL tend to exhibit a partially thrombosed FL quickly after thoracic endovascular aortic repair (TEVAR); thus, we investigated survival and aortic remodeling in this population.

METHODS

We reviewed computed tomography aortograms (CTAs) of 123 patients with TEVAR-treated IIIb aortic dissections from July 2006 to June 2015; contrast density of CTAs represented intraluminal flow. Patients were selected to fit in 2 groups of FL in term of FL contrast density: low flow (LF) group (non-opacification in the midway of FL) and high flow (HF) group (full patent FL).

RESULTS

Surgical mortality was 10.3% in the HF group and 4.5% in the LF group (n = 61; LF = 22; HF = 39). 3 patients in the HF group suffered from lethal aortic rupture in 10 days postoperatively. The HF group showed significant increase in maximal diameter, and had larger thoracic (+4.00 ± 2.68 vs -1.16 ± 3.42 mm, P < .001) aortic diameter expansion from preoperation to one week postoperation. Both groups exhibited significant favorable thoracic TL expansion and maximal aortic diameter shrinkage in postoperative one week to one year. However, HF group displayed less thoracic aortic FL regression (-70.9 ± 83.5 vs -113.9 ± 95.0 cm³, P = .1) and TL expansion (+14.5 ± 27.2 vs +36.8 ± 28.3 cm³, P = .008) when compared to LF group.

CONCLUSIONS

Preoperative HF in the FL has an unfavorable effect on thoracic aortic diameter in one week post-TEVAR. This might increase the risk of aortic rupture.

Management of Concealed Type IV Endoleak and Aortic Sac Hygroma by Prone ContrASt EnHancement Computed Tomography Angiography

BACKGROUND

Aortic sac hygroma and concealed endoleaks (EL) after endovascular aneurysm repair (EVAR) of abdominal aortic aneurysm needs particular attention with aggressive management as they are associated with rapid sac expansion and rupture risk. However, they can be erroneously reported as type IV or V EL with supine computed tomography (CT) scans, leading to delay in management. Therefore, we describe a novel diagnostic technique, 'Prone contrASt enHanced computed tomography Angiography' (PASHA), to document concealed EL METHODS: We present eight case descriptions with continuous sac expansion after primary EVAR. Management began with diagnosis using the PASHA imaging technique. PASHA is a multiphase CTA positional technique for increasing the accuracy of detecting EL after EVAR. Furthermore, the PASHA imaging technique also guides whether the open or endovascular intervention could be used effectively to manage the sac expansion. In synchrony with the PASHA technique, "EVAR GORE SalvAge FAbric Technique" (ARAFAT) was to salvage previous EVAR.

RESULTS

The PASHA technique diagnosed all cases of type IIIb EL, as it enhanced the degree of contrast infiltration into the aortic sac when microleaks were present. ARAFAT was effectively used in five elderly patients. Another three had an open conversion; two with double breasting of the aortic sac and one EVAR explantation.

CONCLUSIONS

The PASHA protocol helped classify and localize the concealed EL (type IV, V), which were not appropriately diagnosed by supine CT protocols. PASHA and ARAFAT were used as a fully functioning protocol to overcome apparent challenges in accurate diagnosis and subsequent concealed EL management in high-risk patients.

In Vitro Quantification of Gutter Formation and Chimney Graft Compression in Chimney EVAR Stent-Graft Configurations Using Electrocardiography-Gated Computed Tomography

Purpose: To assess the dynamic behavior of chimney grafts during the cardiac cycle. Methods: Three chimney endovascular aneurysm repair (EVAR) stent-graft configurations (Endurant and Advanta V12, Endurant and Viabahn, and Endurant and BeGraft) were placed in silicone aneurysm models and subjected to physiologic flow. Electrocardiography (ECG)-gated contrast-enhanced computed tomography was used to visualize geometric changes during the cardiac cycle. Endograft and chimney graft surface, gutter volume, chimney graft angulation over the center lumen line, and the D-ratio (the ratio between the lengths of the major and minor axes) were independently assessed by 2 observers at 10 time points in the cardiac cycle. Results: Both gutter volumes and chimney graft geometry changed significantly during the cardiac cycle in all 3 configurations (p<0.001). Gutters and endoleaks were observed in all configurations. The largest gutter volume (232.8 mm3) and change in volume (20.7 mm3) between systole and diastole were observed in the Endurant-Advanta configuration. These values were 2.7- and 3.0-fold higher, respectively, compared to the Endurant-Viabahn configuration and 1.7- and 1.6-fold higher as observed in the Endurant-BeGraft configuration. The Endurant-Viabahn configuration had the highest D-ratio (right, 1.26–1.35; left, 1.33–1.48), while the Endurant-BeGraft configuration had the lowest (right, 1.11–1.17; left, 1.08–1.15). Assessment of the interobserver variability showed a high correlation (intraclass correlation >0.935) between measurements. Conclusion: Gutter volumes and stent compression are dynamic phenomena that reshape during the cardiac cycle. Compelling differences were observed during the cardiac cycle in all configurations, with the self-expanding (Endurant–Viabahn) chimney EVAR configurations having smaller gutters and less variation in gutter volume during the cardiac cycle yet more stent compression without affecting the chimney graft surface.

Computed Tomography Imaging Features in Acute Uncomplicated Stanford Type-B Aortic Dissection Predict Late Adverse Events

BACKGROUND

Medical treatment of initially uncomplicated acute Stanford type-B aortic dissection is associated with a high rate of late adverse events. Identification of individuals who potentially benefit from preventive endografting is highly desirable.

METHODS AND RESULTS

The association of computed tomography imaging features with late adverse events was retrospectively assessed in 83 patients with acute uncomplicated Stanford type-B aortic dissection, followed over a median of 850 (interquartile range 247-1824) days. Adverse events were defined as fatal or nonfatal aortic rupture, rapid aortic growth (>10 mm/y), aneurysm formation (≥6 cm), organ or limb ischemia, or new uncontrollable hypertension or pain. Five significant predictors were identified using multivariable Cox regression analysis: connective tissue disease (hazard ratio [HR] 2.94, 95% confidence interval [CI]: 1.29-6.72; P=0.01), circumferential extent of false lumen in angular degrees (HR 1.03 per degree, 95% CI: 1.01-1.04, P=0.003), maximum aortic diameter (HR 1.10 per mm, 95% CI: 1.02-1.18, P=0.015), false lumen outflow (HR 0.999 per mL/min, 95% CI: 0.998-1.000; P=0.055), and number of intercostal arteries (HR 0.89 per n, 95% CI: 0.80-0.98; P=0.024). A prediction model was constructed to calculate patient specific risk at 1, 2, and 5 years and to stratify patients into high-, intermediate-, and low-risk groups. The model was internally validated by bootstrapping and showed good discriminatory ability with an optimism-corrected C statistic of 70.1%.

CONCLUSIONS

Computed tomography imaging-based morphological features combined into a prediction model may be able to identify patients at high risk for late adverse events after an initially uncomplicated type-B aortic dissection.

Influence of endoleak positions on the pressure shielding ability of stent-graft after endovascular aneurysm repair (EVAR) of abdominal aortic aneurysm (AAA)

Background

Abdominal aortic aneurysm (AAA) is a kind of dangerous aortic vascular disease, which is characterized by abdominal aorta partial enlargement. At present, endovascular aneurysm repair (EVAR) is one of the main treatments of abdominal aortic aneurysm. However for some patients after EVAR the aneurysm re-expanded and even ruptured, leading to poor postoperative effect. The stent-graft endoleak after EVAR was realized to influence the AAA in-sac pressure and contribute to the aneurysm re-enlargement.

Methods

In order to analyze the influence of endoleaks positions on the pressure shielding ability of stent-graft after EVAR, type I and type III endoleak models were reconstructed based on computed tomography (CT) scan images, and the hemodynamic environment in AAA was numerically simulated.

Results

When the endoleak was at the proximal position the pressure shielding ability will be obviously weakened. While, the pressure shielding ability was higher in the systole phase than that in diastole phase when the endoleak located at the middle or distal positions. Unfortunately, when the endoleak located at the proximal position, the pressure shielding ability would be relatively weak in the whole cardiac cycle.

Conclusions

The results revealed that the influence of endoleaks on pressure shielding ability of stent-graft was both location and time specific.

Early distal remodeling after elephant trunk repair of thoraco-abdominal aortic aneurysms

Hemodynamic alterations occur when the elephant trunk (ET) technique is adopted to treat extensive aortic aneurysms. In planning the 2nd stage operation to complete ET repair, surgeons must weigh an adequate recovery time after initial surgery against the risk of postoperative ET-related complications. The purpose of this study was to understand the mechanistic link between the flow alteration caused by the ET graft and the development of premature aortic rupture before the 2nd stage operation. Specifically, fluid-structure interaction (FSI) analysis was performed using the CT imaging data of aorta at different stages of ET repair, and then computational variables were compared to those observed in patients who underwent a prophylactic 2nd stage operation to complete aortic repair. Results show that intramural stress exerted near the distal ET anastomosis (IMS=37.5kPa) at the time of urgent intervention was comparable to that of the extensive aortic aneurysm (IMS=47.4kPa) at initial in-hospital admission, but was considerably higher than that occurring after the 1st stage procedure (IMS=3.5kPa). Pressure index suggested higher peri-graft pressurization than aortic lumen pressure during diastole, imparting an apparent risk of aortic dilatation. These critical hemodynamic and structural parameters are related to the impending rupture of descending aorta observed clinically and can thus guide prophylactic intervention and optimal timing for the 2nd stage operation of a ET technique.

Endotension is Influenced by Aneurysm Volume: Experimental Findings

Purpose:

To investigate in an in vitro model whether and to what extent pressure is influenced by aneurysm size.

Methods:

Latex aneurysms of 3 different volumes (24, 30, and 81 mL) were inserted into an in vitro circulation model. The systemic mean pressure (SPmean) was varied from 50 to 120 mmHg. The aneurysms were excluded using a woven polyethylene graft. Aneurysm sac mean pressure (ASPmean) was measured.

Results:

In the in vitro model, endovascular aneurysm repair created a closed chamber without endoleak but showed a relevant aneurysm sac pressure. At an SPmean of 80 mmHg, the ASPmean was 42.0 ± 0.6 mmHg in the 24-mL aneurysm, 40.5 ± 0.5 mmHg in the 30-mL model, and 19.3 ± 0.5 mmHg in the 81-mL aneurysm (p < 0.05). The ASPmean rose with increasing SPmean and was inversely dependent on the aneurysm volume.

Conclusions:

This in vitro model demonstrated that the sac mean pressure correlated to the systemic pressure and that a greater aneurysm volume reduced aneurysm sac pressure. These data highlight the need for further studies regarding endotension.

Flow-independent dynamics in aneurysms: intra-aneurysm pressure measurements following complete flow cessation in internal carotid artery aneurysms

PURPOSE

To determine if complete flow obliteration by covered stents reduces intra-aneurysm pressures in internal carotid artery (ICA) aneurysms.

METHODS

A single lumen microcatheter was placed into the aneurysm sac prior to covered stent deployment in 3 patients and connected to a pressure monitoring system. The intra-aneurysm pressure was continuously monitored, and readings were recorded prior to and immediately after stent deployment and at 5-minute intervals up to 20 minutes after stent placement. Complete occlusion of flow into the aneurysms was confirmed by carotid angiography.

RESULTS

There was no change in mean pressure within the aneurysm before and immediately after stent placement (80 mmHg) in any patient, nor was there a change in waveform of the intra-aneurysm pressure recording. The average of intra-aneurysm pressures among the 3 patients was higher (99 mmHg) at 10 and 15 minutes after stent placement. In 2 patients, the microcatheter was retracted into the parent arterial lumen; no difference in pressure was noted.

CONCLUSION

Our observations suggest no change in the pressures within the aneurysm after complete flow cessation (flow-independent). These findings may assist clinicians in better understanding aneurysm hemodynamics and rupture after covered stent deployment.

Potential risk factors of re-intervention after endovascular repair for type B aortic dissections

OBJECTIVES

To assess the potential risk factors of re-intervention after thoracic endovascular aortic repair (TEVAR).

BACKGROUND

TEVAR has been chosen as a less invasive alternative for Type B aortic dissections (TBADs); however, the potential risk factors of re-intervention remain unclear.

METHODS

A total of 252 TBADs patients initially treated with TEVAR between September 1998 and July 2012 were retrospectively reviewed. The indications for the initial TEVAR were 32 aorta enlargement (24 chronic), 71 malperfusion, 46 rupture (32 chronic), 67 refractory pain (54 chronic), and 44 refractory hypertension (38 chronic). The patients were stratified into single-intervention group and multi-intervention group.

RESULTS

The mean age was 54.1 years with 81.7% of male. We found the time from symptom onset to TEVAR was longer in multi-intervention group (17 vs. 112.5 days, P = 0.006). Higher proportions of chronic dissection and smoking occurred in multi-intervention group (53.9% vs. 79.2% and 43.9% vs. 70.8%, P = 0.018 and 0.012, respectively). The differences of oversizing, operation time, contrast medium dose, and blood loss between the groups were significant (13.8 ± 2.4% vs. 16.4 ± 2.9%, 92.5 vs. 196 minutes, 110 vs. 210 ml, 100 vs. 300 ml; P < 0.001, <0.001, =0.002, and =0.003, respectively). The mortality within 30 days was 2.4% and the rates of stoke, paraplegia and retrograde dissection were 3.6%, 5.6% and 0.8%, respectively. The most common reasons of re-intervention were endoleaks, new dissections and incomplete thrombosis of the false lumen.

CONCLUSIONS

we concluded that chronic phase, smoking and too big oversizing were potential risk factors of re-intervention.

Determination of coefficient of friction for self-expanding stent-grafts

Migration of stent-grafts (SGs) after endovascular aneurysm repair of abdominal aortic aneurysms is a serious complication that may require secondary intervention. Experimental, analytical, and computational studies have been carried out in the past to understand the factors responsible for migration. In an experimental setting, it can be very challenging to correctly capture and understand the interaction between a SG and an artery. Quantities such as coefficient of friction (COF) and contact pressures that characterize this interaction are difficult to measure using an experimental approach. This behavior can be investigated with good accuracy using finite element modeling. Although finite element models are able to incorporate frictional behavior of SGs, the absence of reliable values of coefficient of friction make these simulations unreliable. The aim of this paper is to demonstrate a method for determining the coefficients of friction of a self-expanding endovascular stent-graft. The methodology is demonstrated by considering three commercially available self-expanding SGs, labeled as A, B, and C. The SGs were compressed, expanded, and pulled out of polymeric cylinders of varying diameters and the pullout force was recorded in each case. The SG geometries were recreated using computer-aided design modeling and the entire experiment was simulated in ABAQUS 6.8/STANDARD. An optimization procedure was carried out for each SG oversize configuration to determine the COF that generated a frictional force corresponding to that measured in the experiment. The experimental pullout force and analytically determined COF for SGs A, B, and C were in the range of 6-9 N, 3-12 N, and 3-9 N and 0.08-0.16, 0.22-0.46, and 0.012-0.018, respectively. The computational model predicted COFs in the range of 0.00025-0.0055, 0.025-0.07, and 0.00025-0.006 for SGs A, B, and C, respectively. Our results suggest that for SGs A and B, which are exoskeleton based devices, the pullout forces increase upto a particular oversize beyond which they plateau, while pullout forces showed a continuous increase with oversize for SG C, which is an endoskeleton based device. The COF decreased with oversizing for both types of SGs. The proposed methodology will be useful for determining the COF between self-expanding stent-grafts from pullout tests on human arterial tissue.

Type II endoleaks: when is intervention indicated and what is the index of suspicion for types I or III?

One of the principal reasons for failure of endovascular aneurysm repair (EVAR) is the occurrence of endoleaks, which regardless of size or type can transmit systemic pressure to the aneurysm sac. There is little debate that type I endoleaks (poor proximal or distal sealing) are associated with continued risk of aneurysm rupture and require treatment. Similarly, with type III endoleak, there is agreement that the defect in the device needs to be addressed; however, what to do with type II endoleaks and their effect on long-term outcome are not so clear. Aneurysm sac change is a primary parameter for determining the presence of an endoleak and assessing its impact. While diameter measurement has been the most commonly used method for determining sac changes, volume measurement has now been proven superior for monitoring structural changes in the 3-dimensional sac. Determining the source of an endoleak and the direction of flow are necessary for proper classification; however, while computed tomographic angiography has high sensitivity and specificity for detecting endoleaks, it is limited in its ability to show the direction of flow. Contrast-enhanced duplex ultrasound, on the other hand, is better able to quantify flow and characterize endoleaks. Flow is evidence of pressure, and increasing intrasac pressure increases wall tension, thus inducing progressive aneurysm expansion until rupture. Hence, determining intrasac pressure is becoming a vital component of endoleak assessment. All endoleaks can create systemic pressure inside the aneurysm sac, and there are a variety of intrasac pressure transducers being evaluated to assess this effect. A clinical pathway for patients with suspected type II endoleaks is based on a combination of imaging and pressure measurements. Imaging alone requires at least two interval examinations to determine the trend, while pressure measurements give immediate reassurance or an indication to intervene. Although still under development, pressure measurement is destined for general use and will provide a scientific basis for the management of type II endoleaks.

Modelos animais de aneurisma de aorta

Os modelos experimentais em animais vêm sendo utilizados em cirurgia vascular há décadas. O desenvolvimento de novas técnicas para tratamento endovascular dos aneurismas requer a criação de bons modelos experimentais para testar esses dispositivos e estudar seu impacto sobre a progressão da doença. Este artigo tem por objetivo revisar os modelos de aneurisma arterial descritos atualmente. Entre os diversos modelos descritos, nenhum reúne todas as características de um modelo ideal de aneurisma. Os modelos em animais de grande porte são adequados para treino, estudo de alterações em parâmetros fisiológicos durante e após a liberação dos dispositivos e integração do mesmo à parede do vaso. Algumas desvantagens significantes incluem dificuldade do manejo, alto custo, difícil manutenção e regulamentações legais, dificultando a disponibilidade de diversas espécies animais. Modelos em animais menores, como os coelhos e camundongos, embora sejam menos caros e de fácil obtenção, não são adequados para estudos de técnicas endovasculares pelas pequenas dimensões de seus vasos. Nenhum modelo descrito até o momento consegue reproduzir todas as características dos aneurismas observados em humanos. Modelos disponíveis são descritos nesta revisão, e suas vantagens e desvantagens são discutidas.

Endotension following endovascular aneurysm repair

Abstract

Endovascular aneurysm repair (EVAR) is a new and minimally invasive alternative to open repair for patients with abdominal aortic aneurysm (AAA). Soon after its introduction in 1990, it was recognized that EVAR had potential and distinct advantages in the elective and emergency settings. However, long-term follow-up has shown enlargement of the AAA in a substantial percentage of patients who underwent EVAR with the original-permeability Excluder. Of interest is that sac expansion frequently occurs in the absence of endoleak, often referred to as endotension. The pathophysiology of endoleak is beginning to be elucidated and its management is ready to be established, while controversy still exists about the etiology and clinical consequences of endotension. Fortunately, the incidence of endotension is decreasing and it appears that AAA expansion after EVAR with the original Excluder can be arrested by endovascular relining with a low-permeability Excluder endoprosthesis. The aim of this brief review is to provide historical perspective and a good understanding of the etiology, diagnosis, and management of endotension.

Assessment of endoleak significance after endovascular repair of abdominal aortic aneurysms: A lumped parameter model

The outcome of endovascular repair of abdominal aortic aneurysms (AAAs) is greatly compromised by the possible occurrence of endoleak. Previously, the causes and effects of endoleak on a patient-specific basis have mainly been investigated in experimental studies. In order to both reconcile and physically substantiate the various experimental findings, a lumped parameter model of an incompletely excluded AAA was developed. After experimental validation, the model was applied to study the effects on the intrasac pressure of the degree of endoleak, the degree of stent-graft compliance, and the resistance of a possible outflow tract formed by a branching vessel. It is concluded that the presence of endoleak leads to elevated intrasac pressure, the mean of which is mainly governed by the outflow tract resistance, while the pulse pressure is governed by both the endoleak resistance and the stent-graft compliance. Based on the agreement of the current results with previous findings, it is further concluded that the lumped parameter modelling method provides a useful numerical tool for validating experimental endoleak studies.

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.

Fluid-Structure Interaction Analyses of Stented Abdominal Aortic Aneurysms

Rupture of abdominal aortic aneurysms (AAAs) alone is the thirteenth leading cause of death in the United States. Thus, reliable AAA-rupture risk prediction is an important advancement. If repair becomes necessary, the minimally invasive technique of inserting a stent-graft (SG), commonly referred to as endovascular aneurysm repair (EVAR), is a viable option in many cases. However, postoperative complications, such as endoleaks and/or SG migration, may occur. Computational fluid-structure interaction simulations provide physical insight into the hemodynamics coupled with multi-wall mechanics' function as an assessment tool for optimal SG placement and improved device design.

Partial thrombosis of the false lumen in patients with acute type B aortic dissection

BACKGROUND

Patency or thrombosis of the false lumen in type B acute aortic dissection has been found to predict outcomes. The prognostic implications of partial thrombosis of the false lumen have not yet been elucidated.

METHODS

We examined 201 patients with type B acute aortic dissection who were enrolled in the International Registry of Acute Aortic Dissection between 1996 and 2003 and who survived to hospital discharge. Kaplan-Meier mortality curves were stratified according to the status of the false lumen (patent, partial thrombosis, or complete thrombosis) as determined during the index hospitalization. Cox proportional-hazards analysis was performed to identify independent predictors of death.

RESULTS

During the index hospitalization, 114 patients (56.7%) had a patent false lumen, 68 patients (33.8%) had partial thrombosis of the false lumen, and 19 (9.5%) had complete thrombosis of the false lumen. The mean (+/-SD) 3-year mortality rate for patients with a patent false lumen was 13.7+/-7.1%, for those with partial thrombosis was 31.6+/-12.4%, and for those with complete thrombosis was 22.6+/-22.6% (median follow-up, 2.8 years; P=0.003 by the log-rank test). Independent predictors of postdischarge mortality were partial thrombosis of the false lumen (relative risk, 2.69; 95% confidence interval [CI], 1.45 to 4.98; P=0.002), a history of aortic aneurysm (relative risk, 2.05; 95% CI, 1.07 to 3.93; P=0.03), and a history of atherosclerosis (relative risk, 1.87; 95% CI, 1.01 to 3.47; P=0.05).

CONCLUSIONS

Mortality is high after discharge from the hospital among patients with type B acute aortic dissection. Partial thrombosis of the false lumen, as compared with complete patency, is a significant independent predictor of postdischarge mortality in these patients.

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.

Evaluation of the accuracy of a wireless pressure sensor in a canine model of retrograde-collateral (type II) endoleak and correlation with histologic analysis

BACKGROUND

The utility of intra-aneurysmal pressure determination is dependent on the ability to measure pressure in the presence of endoleak and thrombosis. In this study, the accuracy of a CardioMEMS wireless pressure sensor (CardioMEMS, Atlanta, Ga) transducer in the presence of thrombus associated with type II endoleak was measured.

METHODS

Type II endoleaks were created in four mongrel dogs by implanting four collateral arterial side branches (lumbar and caudal mesenteric arteries) as a Carrel patch onto a 3-cm prosthetic polytetrafluoroethylene abdominal aortic aneurysm (AAA). The aneurysm was excluded 2 weeks later from antegrade perfusion by a stent graft. The wireless pressure sensor was positioned in the AAA external to the stent graft. A Konigsberg intraluminal solid-state strain-gauge pressure transducer (Konigsberg Instruments, Pasadena, Calif) that is accurate in the presence of thrombus served as the control to determine AAA pressure. Both of the transducers were implanted on the luminal surface of the aneurysm, 180 degrees opposite from the Carrel patch and endoleak channel. Intra-aneurysmal pressure resulting from the type II endoleak was measured twice daily for 4 weeks using both transducers. A total of 56 pre-exclusion and 224 post-exclusion distinct pressure determinations were made. Intra-aneurysmal pressure was indexed to the systemic pressure that was simultaneously measured by a strain-gauge pressure transducer implanted in the native aorta. Histologic analysis of the aneurysm contents was performed with hematoxylin and eosin.

RESULTS

The intra-aneurysmal systolic, mean, and pulse pressures produced by the type II endoleak were significantly lower than systemic pressure in all animals and were < 60% of systemic pressure (P < .001). Close correlation between the wireless transducer and the control strain-gauge transducer was observed (R = 0.83, P < .001). Arteriography and Doppler ultrasound documented retrograde flow through the aneurysm side branches and persistent endoleak patency up to the time of euthanasia. Pathologic analysis demonstrated the endoleak channel to be patent and separated from the transducers by thrombus, which surrounded both transducers.

CONCLUSIONS

Intra-aneurysmal pressure generated by type II endoleaks may be accurately measured through thrombus using a wireless pressure sensor in the canine model. The wireless sensor has the potential for clinical applicability in diagnosing and characterizing type II endoleaks.

Embolization-driven Occlusion of the Abdominal Aortic Aneurysmal Sac as the Basis of Prevention of Endoleaks in a New Swine Model

OBJECTIVES

To assess the effect of a new polymer in embolization of endoleaks using an animal model.

METHODS

A modified aortic stent-graft was placed in 20 pigs. Embolization was performed at the time of graft insertion with non-cytotoxic n-butyl-2-cyanoacrylate-metacryloxysulpholane and lipiodol (0.2:0.8ratio, 2 ml). Angiography, scanning electron microscopy and immuno-histochemistry were obtained at day 0, 1 week and 3 months.

RESULTS

In control animals both type I and II endoleaks were demonstrated. In treated animals, neither type-I nor type-II endoleaks were observed and a fibro-proliferative response was demonstrated within the aneurysm thrombus.

CONCLUSIONS

Host vascular responses govern the fate of the excluded aneurysm. Embolization of the sac and feeding arteries with non-cytotoxic glue sealed all occlusions by stimulating a massive restenosis-like process.

Sac enlargement due to seroma after endovascular abdominal aortic aneurysm repair with the Endologix PowerLink device

A patient who had undergone endovascular repair of an abdominal aortic aneurysm with the Endologix PowerLink bifurcated system presented with delayed aortic aneurysm enlargement due to assumed endotension. He was treated with aortic sac evacuation and wrapping of the endograft. This is the first report of endotension and aneurysm sac enlargement after implantation of the PowerLink endograft.

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.

Computational analysis of type II endoleaks in a stented abdominal aortic aneurysm model

Insertion of a stent-graft into an aneurysm to form a new (synthetic) blood vessel and prevent the weakened artery wall from rupture is an attractive surgical intervention when compared to traditional open surgery. However, focusing on a stented abdominal aortic aneurysm (AAA), post-operative complications such as endoleaks may occur. An endoleak is the net influx of blood during the cardiac cycle into the cavity (or sac) formed by the stent-graft and the AAA wall. A natural endoleak source may stem from one or two secondary branches leading to and from the aneurysm, labeled types IIa and IIb endoleaks. Employing experimentally validated fluid-structure interaction solvers, the transient 3-D lumen and cavity blood flows, wall movements, pressure variations, maximum wall stresses and migration forces were computed for types IIa and IIb endoleaks. Simulation results indicate that the sac pressure caused by these endoleaks depends largely on the inlet branch pressure, where the branch inlet pressure increases, the sac pressure may reach the systemic level and AAA-rupture is possible. The maximum wall stress is typically located near the anterior-distal side in this model, while the maximum stent-graft stress occurs near the bifurcating point, in both cases, due to local stress concentrations. The time-varying leakage rate depends on the pressure difference between AAA sac and inlet branch. In contrast, the stent-graft migration force is reduced by type II endoleaks because it greatly depends on the pressure difference between the stent-graft and the aneurysm cavity.

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.

Type II lumbar endoleaks: Hemodynamic differentiation by contrast-enhanced ultrasound scanning and influence on aneurysm enlargement after endovascular aneurysm repair

OBJECTIVE

The objective of this study was to differentiate type II lumbar endoleaks on the basis of dynamic features identified by contrast-enhanced ultrasound scanning (CUS) and to evaluate the role of this differentiation in detecting abdominal aortic aneurysm (AAA) enlargement > or =1 mL/mo.

METHODS

Eighteen male patients (mean age, 71.8 years) with type II lumbar endoleak suspected at CUS underwent computed tomography angiography (CTA) and digital subtraction angiography (DSA). On CTA, AAA volumes and endoleak visualization and volume were assessed. At CUS, performed after a bolus of 1.5 to 2.4 mL of a second generation blood pool contrast agent, the following parameters were evaluated: presence of contrast material within the aneurysmal sac (endoleak), delay of endoleak detection (wash-in) and disappearance (washout) from the beginning of contrast injection, visualization of inflow and outflow vessels, and presence of cavity filling. Statistical analysis was performed regarding endoleak features at CUS, endoleak detection at CTA, and rate of AAA enlargement.

RESULTS

DSA confirmed all the endoleaks. Mean +/- standard deviation wash-in and washout times were 121.9 +/- 132.6 and 337.2 +/- 193.7 seconds, respectively; a significant relation was observed between these two parameters (P < .01, analysis of variance). By Youden plots, endoleaks were classified as hyperdynamic when wash-in was <100 seconds (n = 10, 55.5%) and/or washout was <520 seconds (n = 13, 72.2%). A slower washout was associated with nonvisualized outflow (66.7%) and/or inflow arteries (66.7%) ( P < .05). Eight endoleaks (44.4%) were missed at CTA; it occurred in hypodynamic endoleaks, absence of detectable inflow or outflow vessels, and absence of cavity filling at CUS (P < .05). Overall mean AAA volume increase rate was 1.1 +/- 1.7 mL/mo. By multiple logistic regression model, the washout time > or = 520 seconds was the only independent predictor of AAA volume increase > or = 1 mL/mo (8 patients, 44.4%).

CONCLUSION

Type II lumbar endoleaks show different hemodynamic features at CUS, which might influence the rate of aneurysm enlargement, addressing the need for treatment.

Intrasac pressure waveforms after endovascular aneurysm repair (EVAR) are a reliable marker of type I endoleaks, but not type II or combined types: an experimental study

PURPOSE

To ascertain the nature of the pressure wave transmitted through aneurysm thrombus and the changes produced after endovascular repair and the development of type I and II endoleaks.

METHODS

A 25 mm Talent endovascular graft was deployed in a latex model of an abdominal aortic aneurysm, which was incorporated in a pulsatile flow unit. The graft was surrounded by thrombus analogue to simulate conditions in vivo. Pressure waveforms in the sac were captured over 5s at 1000 Hz in these settings: (i) no endoleaks (baseline), after introduction of (ii) type I (iii) type II and (iv) combined type I and II endoleaks. The arterial blood pressure settings used were 140/100 and 130/90 mmHg, denoted the high and low settings, respectively. ANOVA in Minitab 13 was applied for statistical analysis.

RESULTS

Pulsatile waveforms were transmitted through the thrombus. Intrasac pressure after stent-grafting reduced to 110/107, 99/96 mmHg (p<0.001) (high, low settings, respectively). Introduction of a type I endoleak caused this to rise to 120/112, 115/107 mmHg (p<0.001, vs. baseline); after producing a type II endoleak these were 101/98, 91/88 mmHg (p<0.001, vs. baseline). A combined type I and II endoleak produced intrasac pressures identical to that of a type I endoleak.

CONCLUSIONS

Intrasac pressure waveforms following EVAR are easily defined following a type I endoleak. Waveforms obtained following type II endoleak simulation resemble the baseline waveform in an attenuated form. Intrasac pressures are, therefore, a reliable marker for type I, but not a type II endoleak. In the case of a combined endoleak, the type I endoleak waveform effectively masks that of the type II. Intrasac thrombus faithfully transmits intrasac pressures.

Characterization of retrograde collateral (type II) endoleak using a new canine model

OBJECTIVE

The clinical significance of retrograde collateral arterial perfusion of abdominal aortic aneurysms after endovascular repair (type II endoleak) has not been completely characterized. In this study a canine model was used to analyze intra-aneurysmal pressure, thrombus histologic characteristics, endoleak patency, and radiographic appearance of type II endoleaks originating from single and multiple aneurysm side branches.

METHODS

Prosthetic aneurysms with an intraluminal solid-state strain-gauge pressure transducer were created in the infrarenal aorta of 14 mongrel dogs. A single collateral side branch was reimplanted in 4 animals, multiple side branches were reimplanted in 6 animals, and no side branches were reimplanted in 4 control animals. Intra-aneurysmal and systemic pressure was measured for 60 to 90 days after creation of the type II endoleak. Endoleak patency and flow were assessed with duplex ultrasound scanning and cine-magnetic resonance angiography. Histologic analysis of the intra-aneurysmal thrombus was also performed.

RESULTS

Stent-graft exclusion reduced intra-aneurysmal pressure significantly in all animals, as compared with systemic pressure (P < .001). All intra-aneurysmal pressure values are indexed to the systemic pressure, and are represented as a percentage of the simultaneously obtained systemic pressure, which has a value of 1.0. Type II endoleaks originating from multiple side branches exhibited significantly increased intra-aneurysmal systolic pressure, mean pressure, and pulse pressure, as compared with endoleaks derived from either a single side branch (systolic pressure: multiple, 0.70 +/- 0.28 vs single, 0.50 +/- 0.19; P < .001; mean pressure: multiple, 0.78 +/- 0.23 vs single, 0.59 +/- 0.22, P < .001; pulse pressure: multiple, 0.41 +/- 0.25 vs single, 0.17 +/- 0.15, P < .001) or excluded control aneurysms that had no side branches and no endoleak (systolic pressure, 0.17 +/- 0.09; mean pressure, 0.14 +/- 0.10; pulse pressure, 0.098 +/- 0.08; P < .001). Cine-magnetic resonance angiograms and duplex ultrasound scans documented persistent patency of multiple branch endoleaks up to the time of euthanasia. In contrast, single side branch endoleaks thrombosed within 3 days (P < .001). Thrombus in the aneurysm sac in close proximity to the endoleak contained intact red blood cells and limited fibrin. Thrombus distant from the endoleak demonstrated extensive fibrin deposition and degraded red blood cells.

CONCLUSION

The canine model may be used to reliably measure intra-aneurysmal pressure in the presence of patent and thrombosed type II endoleaks. In this model 2 or more side branches are necessary to maintain persistent patency of type II endoleaks. These endoleaks are associated with significantly elevated intra-aneurysmal pressure, that is, 70% to 80% of systemic pressure. These results suggest that persistent type II endoleaks have clinical significance.

CLINICAL RELEVANCE

Endoleaks originating from retrograde flow in the side branch vessels of the aneurysm generate significant levels of intra-aneurysmal pressure, that is, 70% to 80% of systemic pressure. At least 2 patent side branch vessels appear to be necessary to cause persistent patency of type II endoleak in the canine model. Further studies will be necessary to enable more complete characterization of retrograde endoleaks and to extend these findings to allow clinical application. However, these results suggest that persistently patent type II endoleaks are clinical significance and may require more intensive follow-up intervention.

Abdominal Aortic Aneurysm: Contrast-enhanced US for Missed Endoleaks after Endoluminal Repair

PURPOSE

To evaluate contrast material-enhanced ultrasonography (US) for depiction of endoleaks after endovascular abdominal aortic aneurysm repair (or endovascular aneurysm repair [EVAR]) in patients with aneurysm enlargement and no evidence of endoleak.

MATERIALS AND METHODS

From November 1998 to February 2003, 112 patients underwent EVAR. At follow-up, duplex US and biphasic multi-detector row computed tomographic (CT) angiography were performed. In 10 patients (group A), evident aneurysm enlargement was observed, with no evidence of complications, at both CT angiography and duplex US. Group A patients, 10 men (mean age, 69.6 years +/- 10 [standard deviation]), underwent US after intravenous bolus injection of a second-generation contrast agent, with continuous low-mechanical index (0.01-0.04) real-time tissue harmonic imaging. Group B patients, 10 men (mean age, 71.3 years +/- 8.2) with aneurysm shrinkage and no evidence of complications, and group C patients, 10 men (mean age, 73.2 years +/- 6) with CT angiographic evidence of endoleak, underwent contrast-enhanced US. Digital subtraction angiography (DSA) was performed in groups A and C. Endoleak detection and characterization were assessed with imaging modalities used in groups A-C; at contrast-enhanced US, time of detection of endoleak, persistence of sac enhancement, and morphology of enhancement were evaluated.

RESULTS

In group A, contrast-enhanced US depicted one type I, six type II, one type III, and two undefined endoleaks that were not detected at CT angiography. All leakages were characterized by slow and delayed echo enhancement detected at longer than 150 seconds after contrast agent administration. DSA results confirmed findings in all patients; percutaneous treatment was performed. In group B, contrast-enhanced US did not show echo enhancement; in group C, results with this modality confirmed findings at CT angiography and DSA.

CONCLUSION

Contrast-enhanced US depicts endoleaks after EVAR, particularly when depiction fails with other imaging modalities.

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.

Preliminary Results

PURPOSE

To assess aortic wall compliance as a portent of rupture risk in patients with abdominal aortic aneurysms.

METHODS

In this pilot study, 38 patients (32 men; median age 78 years, range 63-95) underwent an ultrasound scan: 20 pre-repair and 24 post-repair (18 endovascular [EVR] and 6 open). Six patients from the pre-repair group were included in a post repair study after EVR. Cine loop images were analyzed offsite using wall tracking software, which measured aortic diameter changes during cardiac cycles. Brachial blood pressure was measured, and elastic modulus (Ep) and stiffness (beta) were calculated. Preop Ep and beta were determined at the neck, inflection points (IP), and mid sac levels. Postop Ep and beta were calculated in mid sac only for technical reasons.

RESULTS

Preoperative Ep and beta were significantly higher at IP compared with neck (median Ep 24.22 versus 12.95 N/cm(2), p<0.003; median beta 16.27 versus 8.65, p<0.003). At the mid sac, Ep and beta were also significantly higher compared with neck: Ep 26.41 versus 12.95 N/cm(2), p=0.001; beta 17.94 versus 8.65, p=0.001. The values for IP and mid sac were Ep 24.22 versus 26.41 N/cm(2), p=0.64; beta 16.27 versus 17.94, p=0.64. In the postop cases (n=24), Ep and beta in successful endovascular repair (n=12) were significantly higher than in open repair, respectively: median Ep 34.31 versus 12.33 N/cm(2), p<0.001; median beta 23.18 versus 8.24, p<0.001. Patients with endoleaks or endotension (n=6) had significantly elevated Ep and beta compared with those without endoleaks (n=12): median Ep 79.79 versus 34.31 N/ cm(2), p=0.002; median beta 51.52 versus 23.18, p<0.002. Six patients scanned before and after EVR showed a decrease of Ep and beta in 3, no change in 1, and an increase in 2. An increase greater than 2 fold was noted in a patient with a gross type II endoleak.

CONCLUSIONS

This pilot study shows that estimates of aortic wall compliance agree well with known values for wall stress distribution. EVR leaves patients with greater wall stiffness than those undergoing open repair, a situation accentuated by endoleaks. Wall compliance and stiffness measurement promises to be useful for the evaluation of success of endovascular repair.

Endovascular treatment of abdominal aortic aneurysm

BACKGROUND

Endovascular repair of abdominal aortic aneurysm has become widely used. Supporters claim high success rates, few complications and a dramatically reduced hospital stay. However, endoleak, endotension and reports of endoprosthesis rupture are causes of concern.

METHODS

A Medline search was undertaken to identify articles on endovascular repair of abdominal aortic aneurysm. Additional papers were identified by manual scanning of the references from key articles.

RESULTS AND CONCLUSION

Endoleak is a potentially serious complication of the endovascular technique and occurs in a significant proportion of patients. It is still not possible to judge whether the presence of an endoleak alone signifies failure of treatment, and the long-term durability of prosthetic covered stents is unknown. However, endovascular repair does appear to confer a degree of protection from rupture although patients must be advised of the need for life-long imaging surveillance and, perhaps, further intervention.

Endotension is Influenced by Wall Compliance in a Latex Aneurysm Model

OBJECTIVES

Even though endovascular aneurysm repair (EVAR) creates a closed chamber except for patent branches, the intra-sac pressure is never zero. This study was designed to investigate whether, and to what extent, aneurysm wall compliance influences intra-sac pressure.

DESIGN

In vitro experimental study.

METHODS

Aneurysm models with six and 12 latex layers were produced, resulting in elastic and stiff circumferential compliance (3.5 +/- 0.5 and 0.9 +/- 0.3%/100 mmHg, respectively). The models with an 18 mm internal neck and maximum aneurysm diameter of 60 mm were inserted into an in vitro circulation system. The systemic mean pressure (SPmean) was varied from 50 to 120 mmHg. After the aneurysm was excluded with a knitted polyethylene graft, aneurysm sac mean pressure (ASPmean) and aneurysm sac pulse pressure (ASPpulse) were measured. Data are presented as mean +/- SD. Statistics were performed using repeated measurements of variance; p<0.05 was considered significant.

RESULTS

In the model EVAR created a closed chamber without endoleak, but with an aneurysm sac pressure related to wall compliance. In the elastic aneurysm model with six latex coats the aneurysm sac mean pressure (ASPmean) and the aneurysm sac pulse pressure (ASPpulse) at all systemic pressures were significantly lower than they were in the stiffer model with 12 latex coats (p<0.05). At a SPmean of 90 mmHg, the ASPmean was 21.0 +/- 0.9 mmHg (six latex coats) and 26.0 +/- 0.2 mmHg (12 latex coats) (p<0.05), the ASPpulse was 5.7 +/- 0.2 mmHg (six latex coats) and 8.8 +/- 0.3 mmHg (12 latex coats) (p<0.05).

CONCLUSIONS

This in vitro model demonstrated that the aneurysm sac mean pressure (ASPmean) and the aneurysm sac pulse pressure (ASPpulse) were significantly influenced by the compliance of the aneurysm wall. These data highlight the need for further studies regarding endotension.

Endotension as a Result of Pressure Transmission through the Graft following Endovascular Aneurysm Repair—An In vitro Study

BACKGROUND

endovascular aneurysm repair (EVAR) significantly reduces, but does not abolish aneurysm sac pressure, possibly because of trans-fabric transmission.

OBJECTIVE

to investigate how blood pressure is transmitted through different types of grafts into the aneurysm sac.

DESIGN

experimental study, in vitro.

METHODS

a latex aneurysm was inserted into an in vitro circulation model. The systemic mean pressure (SPmean) was varied from 50 to 120 mmHg. The grafts used for aneurysm exclusion were: thin wall polyethylene (PE), thick wall polyethylene (PE) and thin wall ePTFE. Mean aneurysm sac pressure (ASPmean) was measured, as was pulse pressure (ASPpulse).

RESULTS

at an SPmean of 70 mmHg, the ASPmean was 34 +/- 0.8 mmHg (polyethylene knitted, thick wall), 30 +/- 1.0 mmHg (polyethylene woven, thin wall), and 17 +/- 0.6 mmHg (thin wall ePTFE). The ASPmean increased with SPmean, the relationship depending on the graft material. Stiffer grafts were associated with lower ASPmean and ASPpulse (p<0.001).

CONCLUSIONS

the relationship between aneurysm sac mean pressure and systemic pressure (SP) depends on the graft material. These data highlights the need for further studies regarding endotension.