Aortic Neck Dilation after Endovascular Abdominal Aortic Aneurysm Repair: Should Oversizing Be Blamed?

INFLUENCE OF PROXIMAL FIXATION ON ANEURYSM NECK EVOLUTION AFTER ENDOVASCULAR TREATMENT OF INFRARENAL ANEURYSMS

OBJECTIVE

We analyzed the long-term influence of fixation systems on proximal aortic neck (PAN) evolution by comparing two late-generation endoprostheses, Endurant (Medtronic Vascular, Minneapolis, Minn) with suprarenal fixation (SRF) and Excluder (W.L Gore & Associates, Flagstaff, Ariz) with infrarenal fixation (IRF).

METHODS

Our retrospective observational study included consecutive patients undergoing EVAR for aorto-iliac aneurysms (2011-2020). Primary end points: neck enlargement and freedom from significative PAN enlargement (5 mm). Secondary end points: neck-related reintervention, endoleaks and graft migration. Results were reported following the Society of Vascular Surgery reporting standards.

RESULTS

139 patients were included (97 in SRF group and 42 in IRF group). A difference in growth at 10 mm caudal to lowest renal artery at 2 years follow-up was found (mean growth of 1.92 ± 3.38 mm in SRF and 0.16 ± 6.86 mm in IRF; p <.001). A tendency to a major growth in SRF at 4 years follow-up at the lowest renal artery (1.27 ± 3.36 mm vs 0.63 ± 2.2 mm; p = .06), 5 mm distal to lowest renal artery (2.17 ± 3.52 mm vs 0.94 ± 2.76 mm; p =.001) and 10 mm distal to lowest renal artery (2.65 ± 3.86 mm vs 1.12 ± 1.5 mm; p <.001) was shown. Freedom from PAN enlargement was 96.65% and 88.20% in SRF and 100% and 94.4% in IRF at 2 and 4 years follow up respectively (log rank .041). A greater incidence of type II endoleaks in IRF was observed (40.48% vs 15.46%;p =.001). Oversizing > 15% showed to be a risk factor of PAN enlargement (OR 6.85; 95% IC 1.67 - 28.4; p =.007).

CONCLUSIONS

A small but significative percentage of patients after EVAR show a progressive PAN enlargement, being significatively greater in SRF, without increasing neck related complications four years after graft deployment.

Ultrasound elastography to quantify average percent pressure-normalized strain reduction associated with different aortic endografts in 3D-printed hydrogel phantoms

Objective

Strain has become a viable index for evaluating abdominal aortic aneurysm stability after endovascular aneurysm repair (EVAR). In addition, literature has shown that healthy aortic tissue requires a degree of strain to maintain homeostasis. This has led to the hypothesis that too much strain reduction conferred by a high degree of graft oversizing is detrimental to the aneurysm neck in the seal zone of abdominal aortic aneurysms after EVAR. We investigated this in a laboratory experiment by examining the effects that graft oversizing has on the pressure-normalized strain (ε ρ + ¯ /pulse pressure [PP]) reduction using four different infrarenal EVAR endografts and our ultrasound elastography technique. Approximate graft oversizing percentages were 20% (30 mm phantom-graft combinations), 30% (28 mm phantom-graft combinations), and 50% (24 mm phantom-graft combinations).

Methods

Axisymmetric, 10% by mass polyvinyl alcohol phantoms were connected to a flow simulator. Ultrasound elastography was performed before and after implantation with the four different endografts: (1) 36 mm polyester/stainless steel, (2) 36 mm polyester/electropolished nitinol, (3) 35 mm polytetrafluoroethylene (PTFE)/nitinol, and (4) 36 mm nitinol/polyester/platinum-iridium. Five ultrasound cine loops were taken of each phantom-graft combination. They were analyzed over two different cardiac cycles (end-diastole to end-diastole), yielding a total of 10 maximum mean principal strain (ε ρ + ¯ ) values.ε ρ + ¯ was divided by pulse pressure to yield pressure-normalized strain (ε ρ + ¯ /PP). An analysis of variance was performed for graft comparisons. We calculated the average percentε ρ + ¯ /PP reduction by manufacturer and percent oversizing. These values were used for linear regression analysis.

Results

Results from one-way analysis of variance showed a significant difference inε ρ + ¯ /PP between the empty phantom condition and all oversizing conditions for all graft manufacturers (F(3, 56) = 106.7 [graft A], 132.7 [graft B], 106.5 [graft C], 105.7 [graft D], P < .0001 for grafts A-D). There was a significant difference when comparing the 50% condition with the 30% and 20% conditions across all manufacturers by post hoc analysis (P < .0001). No significant difference was found when comparing the 20% and 30% oversizing conditions for any of the manufacturers or when comparingε ρ + ¯ /PP values across the manufacturers according to percent oversize. Linear regression demonstrated a significant positive correlation between the percent graft oversize and the all-graft average percentε ρ + ¯ /PP reduction (R 2  = 0.84, P < .0001).

Conclusions

This brief report suggests that a 10% increase in graft oversizing leads to an approximate 5.9% reduction inε ρ + ¯ /PP on average. Applied clinically, this increase may result in increased stiffness in axisymmetric vessels after EVAR. Further research is needed to determine if this is clinically significant.

A systematic review and meta-analysis of proximal aortic neck dilatation after endovascular abdominal aortic aneurysm repair

OBJECTIVE

To provide an updated systematic literature review summarizing current evidence on aortic neck dilatation (AND) after endovascular aortic aneurysm repair (EVAR) in patients with infrarenal abdominal aortic aneurysm.

METHODS

An extensive electronic search in major electronic databases was conducted between January 2000 and December 2021. Eligible for inclusion were observational studies that followed up with patients (n ≥ 20) undergoing EVAR with self-expanding endografts, for 12 or more months, evaluated AND with computed tomography angiography and provided data on relevant outcomes. The primary end point was the incidence of AND after EVAR, and the secondary end points were the occurrence of type Ia endoleak, stent graft migration, secondary rupture, and reintervention.

RESULTS

We included 34 studies with a total sample of 12,038 patients (10,413 men; median age, 71 years). AND was defined clearly in 18 studies, but significant differences in AND definition were evidenced. The pooled incidence of AND based on quantitative analysis of 16 studies with a total of 9201 patients (7961 men; median age, 72 years) was calculated at 22.9% (95% confidence interval [CI], 14.4-34.4) over a follow-up period ranging from 12 months to 14 years. The risk of a type Ia endoleak was significantly higher in AND patients compared with those without AND (odds ratio, 2.95; 95% CI, 1.10-7.93; P = .030). Similarly, endograft migration was more common in the AND group compared with the non-AND group (odds ratio, 5.95; 95% CI, 1.80-19.69; P = .004). The combined incidence of secondary rupture and reintervention did not differ significantly between the two groups, even though the combined effect was in favor of the non-AND group.

CONCLUSIONS

Proximal AND after EVAR is common and occurs in a large proportion of patients with infrarenal abdominal aortic aneurysm. AND can influence the long-term durability of proximal endograft fixation and is significantly related to adverse outcomes, often leading to reinterventions.

Effect of Stent-Graft Active Fixation and Oversizing on Aortic Neck Dilation After Endovascular Aneurysm Exclusion For Infrarenal Aortic Aneurysm

INTRODUCTION

Aortic neck dilation post endovascular aneurysm repair (EVAR) has been implicated in the long-term development of endoleak and the subsequent re-intervention. Optimal endograft sizing is a vital aspect to successful repair. This study looked at percentage of graft oversizing as well as type of fixation on aortic neck dilation.

METHODS

We retrospectively evaluated all EVARs completed at Loyola's University from 2006 to 2015 after IRB approval. Patients without follow-up scans within a year were excluded. We collected demographics, comorbidities, graft type, size, aortic neck diameter, maximum sac size diameters from the pre-operative and follow-up scans. We reviewed and collected data on 432 patients but analyzed 154. We measured the largest aortic diameter on axial images 1 cm above and 1 cm below the lowest renal artery. Change in supra and infrarenal aortic measurements were evaluated by calculating the mm difference from each scan compared to the pre-operative scan. Linear mixed effects models were used to estimate patients' mean differences over time.

RESULTS

We compared three groups of neck fixation grafts. Those with active suprarenal fixation had a significant change in suprarenal aortic diameter at four-year follow-up (1.86 mm, CI:0.65-3.06), compared to those with active infrarenal (0.22 mm, CI: -0.67 to -1.11) or passive suprarenal fixation (1.52 mm, CI: -0.11 to -3.15) (Fig. 1). Those with active suprarenal fixation were the only ones to have significant increase in suprarenal aortic diameter (P = 0.0026). Degree of oversizing was also divided into three groups. Oversizing by <10% had less impact on the suprarenal aorta than >15% oversizing at 4 years (0.41 mm, CI: -0.31 to -1.14 vs. 3.26 mm, CI: 1.63-4.88, P < 0.001) (Fig. 2). Oversizing had a more pronounced effect on the infrarenal aorta: 3.01 mm, CI: 2.18-3.83; 5.95 mm, CI: 3.26-8.64; and 5.05 mm, CI: 3.41-6.69 for <10%, 10-15%, and >15% oversizing at four years, respectively.

CONCLUSION

Stent-grafts with active fixation below the renal arteries as well as oversizing by <10% seem to have the least effect on aortic neck dilation over time. These factors should be considered when performing EVARs, as aortic neck dilation could lead to endoleak and need for further intervention. Further research defining the optimal stent-graft type, self-expanding versus balloon expandable, type of fixation and degree of oversizing.

A Five-Year Computed Tomography Follow-up Study of Proximal Aortic Neck Dilatation After Endovascular Aortic Repair Using Four Contemporary Types of Endograft

OBJECTIVE

This study analysed the progression of proximal aortic neck diameter in patients with asymptomatic abdominal aortic aneurysms, treated by endovascular aortic repair using four different, contemporary types of endograft.

METHODS

This is a retrospective study of four cohorts of 30 patients presenting with asymptomatic abdominal aortic aneurysms and treated with endovascular aortic repair using four different types of contemporary endografts, namely Endurant® (Medtronic), Excluder® (W.L. Gore), Zenith® (Cook Medical) and Ovation® (Endologix) endografts. Patients' demographics and aortic aneurysm measurements, including suprarenal aortic, proximal infrarenal neck and maximum aortic aneurysmal diameter, were gathered from the patients' electronic medical records, pre- and post-interventional computed tomography studies, respectively. Diameter measurements were modelled as a function of endograft type; an interaction test was used to test whether the evolutions over time were different between the four types of endograft.

RESULTS

Suprarenal aortic diameter increased over time (P = 0.0235) and maximum aortic aneurysm diameter decreased over time (P = 0.0008) in the four types of endograft. The progressive increase in proximal neck diameter from preoperative baseline up to five years of follow-up was 1.20 mm for Endurant (P = 0.0054), 1.72 mm for Ovation (P = 0.0006), 1.14 mm for Excluder (P = 0.0102) and 2.83 mm for Zenith (P < 0.0001), respectively. Five patients (4%) presented with a late-type 1a endoleak: Endurant (n = 1); Ovation (n = 2) and Zenith (n = 2).

CONCLUSION

All endografts were associated with a progressive dilatation of the proximal aortic neck over a time interval of five years and may be associated with late-type 1a endoleak.

Risk Factors, Dynamics, and Clinical Consequences of Aortic Neck Dilatation after Standard Endovascular Aneurysm Repair

OBJECTIVE

Aortic neck dilatation (AND) occurs after endovascular aneurysm repair (EVAR) with self expanding stent grafts (SESs). Whether it continues, ultimately exceeding the endograft diameter leading to abdominal aortic aneurysm (AAA) rupture, remains uncertain. Dynamics, risk factors, and clinical relevance of AND were investigated after EVAR with standard SESs.

METHODS

All intact EVAR patients treated from 2000 to 2015 at a tertiary institution were included. Demographic, anatomical, and device related characteristics were investigated as risk factors for AND. Outer to outer diameters were measured at a single standardised aortic level on reconstructed computed tomography (CT) images.

RESULTS

A total of 460 patients were included (median follow up 5.2 years, interquartile range [IQR] 3.0, 7.7 years; CT imaging follow up 3.3 years, IQR 1.3, 5.4). Baseline neck diameter was 24 mm (IQR 22, 26) and increased 11.1% (IQR 1.5%, 21.9%) at last CT imaging. Endograft oversizing was 20.0% (IQR 13.6, 28.0). AND was greater during the first year (5.2% [IQR 0, 11.7]) decreasing subsequently (two to four years to 1.4%/year [IQR 0.0, 4.5%], p ≤ .001) and was associated with suprarenal fixation endografts (t value = 7.9, p < .001) and oversizing (t value = 4.4, p < .001). AND exceeding the endograft was 3.5% (95% CI 2.2% - 4.8%) and 14.4% (95% CI 11.0% - 17.8%) at five and eight years, respectively. Excessive AND was associated with baseline neck diameter (OR 1.2/mm, 95% CI 1.05 - 1.41) while the Excluder endograft had a protective effect (OR 0.15, 95% CI 0.04 - 0.58). Excessive AND was associated with type 1A endoleak (HR 3.3, 95% CI 1.1 - 9.7) and endograft migration > 5 mm (HR 3.1, 95% CI 1.4 - 6.9).

CONCLUSION

AND after EVAR with SES is associated with endograft oversizing and radial force but decelerates after the first post-operative year. Baseline aortic neck diameter and suprarenal stent bearing endografts were associated with an increased risk of AND beyond nominal stent graft diameter. However, it remains unclear whether patient selection, differences in endograft radial force or the suprarenal stent are accountable for this difference.

Aortic Neck Dilatation Following Thoracic Endovascular Aortic Repair

OBJECTIVE

Thoracic endovascular aortic repair (TEVAR) has become a mainstay of treatment for a variety of thoracic aortic pathologies. Expansion of the proximal aortic neck after endovascular repair of abdominal aortic aneurysms has been demonstrated; however, dilatation of the proximal aortic neck after TEVAR has not been well described. We sought to describe remodeling of the proximal neck following TEVAR.

METHODS

This is a retrospective, single institution review of patients who underwent TEVAR for thoracic aortic aneurysm (TAA) and dissection with aneurysmal degeneration from 2010 to 2019. Postoperative computed tomography scans were reviewed and aortic diameter was measured in orthogonal planes using 3-dimensional centerline reconstruction software. The primary outcome was change in aortic diameter at the proximal aortic neck as compared to the initial postoperative computed tomography scan. Clinical and operative data were analyzed to identify factors associated with significant neck dilatation.

RESULTS

Of 87 patients who underwent TEVAR during the study period, 30 met inclusion criteria. Median follow up was 20.5 months. Median age was 67 years, and 15 patients (50%) were female. The proximal aortic neck experienced an overall increase over time in aortic diameter. Five mm distal to the graft showed the greatest rate of expansion, with a median increase of 1.3, 2.9, and 6.2 mm at one year, two years, and three years, respectively. When comparing patients who had mean expansion at this location of >2.0 mm/year to patients who did not, a higher percentage had dissection pathology (81.8% vs. 31.6%, P = 0.008), had graft placement at aortic landing zone 2 (36.4% vs. 5.3%, P = 0.028), and were smokers (100% vs. 52.6%, P = 0.006). Higher percent oversizing was shown to be associated with significant aortic neck dilatation for true aneurysms only.

CONCLUSIONS

Aortic neck dilatation occurs over time for the majority of patients following TEVAR with the distal neck experiencing the highest rate of expansion. Dissection pathology, aortic landing zone 2, and smoking were found to be associated with a higher rate of neck dilatation.

Predictors of Aneurysm Sac Shrinkage Utilizing a Global Registry

BACKGROUND

Aneurysm sac remodeling is a complex multifactorial process with unknown factors influencing sac regression after endovascular aortic aneurysm repair (EVAR). We sought to identify factors associated with this process by analyzing data obtained from patients treated with the GORE EXCLUDER endovascular aneurysm repair (EVAR) endoprosthesis from December 2010 to October 2016 enrolled in the Global Registry for Endovascular Aortic Treatment (GREAT).

METHODS

All patients enrolled in GREAT with three years CT angiography (CTA) follow-up in each of the three successive years after EVAR were included. The percentage of sac size reduction toward device diameter was calculated and used as a surrogate for sac regression with the formula used being: sac size reduction = ((AAA baseline diameter - AAA diameter at follow-up)/(AAA baseline diameter - device diameter))∗100. The cohort was divided into two groups in accordance with the percentage of aneurysm sac reduction at three years; one with the top quartile of patients and the other with the lowest three quartiles. Demographic and procedural variables were analyzed using univariate and regression modeling to determine factors predictive of sac regression.

RESULTS

There were 3265 subjects enrolled with follow-up as of May 2018 of which 526 (16.2%) had three years of CTA surveillance. Overall aneurysm sac size decreased from a mean of 58.0 mm (Std Dev: 10.4, range: 34.2, 100.0) to a mean of 49.3 mm (Std Dev: 14.1, range: 0, 140) for a percentage reduction toward device diameter of a mean 28.2% (Std Dev: 39.0, range: -103.7, 183.9). On multivariate logistic regression model; two factors proved to be statistically significant contributors to a larger percentage reduction in aneurysm sac: a conical neck (odds ratio [OR] = 1.64, P-value = 0.023) and a larger proximal device diameter (OR = 1.09, P-value = 0.023). On the other hand, two factors were negative predictors of sac shrinkage, namely: old age (OR = 0.96, P-value = 0.002) and larger baseline aneurysm sac diameter (OR = 0.98, P-value = 0.028).

CONCLUSIONS

Aneurysms with conical necks and larger proximal device neck diameters have an increased percentage change in sac size over time after EVAR. Older age and larger initial diameters of aneurysms were negatively associated with percentage change in sac size as well as sac regression. Further study is needed to determine the clinical utility of these observations and applicability across multiple endoprosthesis platforms.

Customized stent-grafts for endovascular aneurysm repair with challenging necks: A numerical proof of concept

Endovascular aortic repair (EVAR) is a challenging intervention whose long-term success strongly depends on the appropriate stent-graft (SG) selection and sizing. Most off-the-shelf SGs are straight and cylindrical. Especially in challenging vessel morphologies, the morphology of off-the-shelf SGs is not able to meet the patient-specific demands. Advanced manufacturing technologies facilitate the development of highly customized SGs. Customized SGs that have the same morphology as the luminal vessel surface could considerably improve the quality of the EVAR outcome with reduced likelihoods of EVAR related complications such as endoleaks type I and SG migration. In this contribution, we use an in silico EVAR methodology that approximates the deployed state of the elastically deformable SG in a hyperelastic, anisotropic vessel. The in silico EVAR results of off-the-shelf SGs and customized SGs are compared qualitatively and quantitatively in terms of mechanical and geometrical parameters such as stent stresses, contact tractions, SG fixation forces and the SG-vessel attachment. In a numerical proof of concept, eight different vessel morphologies, such as a conical vessel, a barrel shaped vessel and a curved vessel, are used to demonstrate the added value of customized SGs compared to off-the-shelf SGs. The numerical investigation has shown large benefits of the highly customized SGs compared to off-the-shelf SGs with respect to a better SG-vessel attachment and a considerable increase in SG fixation forces of up to 50% which indicate decreased likelihoods of EVAR related complications. Hence, this numerical proof of concept motivates further research and development of highly customized SGs for the use in challenging vessel morphologies.

Geometric Remodeling of the Perirenal Aortic Neck at and Adjacent to the Double Sealing Ring of the Anaconda Stent-Graft After Endovascular Aneurysm Repair

Purpose: To evaluate if the radial force of the double sealing ring of the Anaconda stent-graft induces dilatation in the perirenal aortic neck adjacent to the rings. Materials and Methods: This study evaluated the serial electrocardiogram-gated computed tomography scans of 15 abdominal aortic aneurysm patients (mean age 72.8±3.7 years; 14 men) who were treated electively using an Anaconda stent-graft. Follow-up scans were conducted before discharge and at 1, 6, 12, and 24 months after endovascular repair. Diameter and area were assessed perpendicular to the aortic centerline along the perirenal aortic neck, which was subdivided into 3 zones: the suprastent, the stent, and the infrastent zones. Measurements were performed independently by 2 experienced observers using dedicated 3-dimensional image processing software. Results: Between discharge and the 2-year follow-up the diameter and area remained stable in the suprastent zone [average diameter change: −0.1±0.4 mm (−0.4%±1.7%), p=0.893; average area change: −2.9±17.2 mm² (−0.7%±3.4%), p=0.946], increased in the stent zone [average diameter change: +1.9±1.0 mm (+7.3%±4.0%), p<0.001; average area change: +84.3±48.3 mm² (+15.5%±8.7%), p<0.001], and diverged in the infrastent zone [average diameter change: −0.8±2.2 mm (−2.3%±7.4%), p>0.99; average area change: −34.6±102.3 mm² (−4.1%±14.8%), p>0.99; increased in 4 patients, decreased in 9 patients]. Conclusion: After Anaconda implantation the infrarenal aortic neck accommodated to the expansion of the sealing rings at the stent zone. Below the stent zone the neck diameter decreased in the majority of patients, while an increase was related to downstream displacement of the main body. A decrease in size in the infrastent zone may contribute to durable sealing and fixation. A personalized follow-up scheme based on geometric neck remodeling should be feasible if our observations are confirmed in larger, long-term studies.

In silico study of vessel and stent-graft parameters on the potential success of endovascular aneurysm repair

The variety of stent-graft (SG) design variables (eg, SG type and degree of SG oversizing) and the complexity of decision making whether a patient is suitable for endovascular aneurysm repair (EVAR) raise the need for the development of predictive tools to assist clinicians in the preinterventional planning phase. Recently, some in silico EVAR methods have been developed to predict the deployed SG configuration. However, only few studies investigated how to assess the in silico EVAR outcome with respect to EVAR complication likelihoods (eg, endoleaks and SG migration). Based on a large literature study, in this contribution, 20 mechanical and geometrical parameters (eg, SG drag force and SG fixation force) are defined to evaluate the quality of the in silico EVAR outcome. For a cohort of n = 146 realizations of parameterized vessel and SG geometries, the in silico EVAR results are studied with respect to these mechanical and geometrical parameters. All degrees of SG oversizing in the range between 5% and 40% are investigated continuously by a computationally efficient parameter continuation approach. The in silico investigations have shown that the mechanical and geometrical parameters are able to indicate candidates at high risk of postinterventional complications. Hence, this study provides the basis for the development of a simulation-based metric to assess the potential success of EVAR based on engineering parameters.

Patient-specific in silico endovascular repair of abdominal aortic aneurysms: application and validation

Non-negligible postinterventional complication rates after endovascular aneurysm repair (EVAR) leave room for further improvements. Since the potential success of EVAR depends on various patient-specific factors, such as the complexity of the vessel geometry and the physiological state of the vessel, in silico models can be a valuable tool in the preinterventional planning phase. A suitable in silico EVAR methodology applied to patient-specific cases can be used to predict stent-graft (SG)-related complications, such as SG migration, endoleaks or tissue remodeling-induced aortic neck dilatation and to improve the selection and sizing process of SGs. In this contribution, we apply an in silico EVAR methodology that predicts the final state of the deployed SG after intervention to three clinical cases. A novel qualitative and quantitative validation methodology, that is based on a comparison between in silico results and postinterventional CT data, is presented. The validation methodology compares average stent diameters pseudo-continuously along the total length of the deployed SG. The validation of the in silico results shows very good agreement proving the potential of using in silico approaches in the preinterventional planning of EVAR. We consider models of bifurcated, marketed SGs as well as sophisticated models of patient-specific vessels that include intraluminal thrombus, calcifications and an anisotropic model for the vessel wall. We exemplarily show the additional benefit and applicability of in silico EVAR approaches to clinical cases by evaluating mechanical quantities with the potential to assess the quality of SG fixation and sealing such as contact tractions between SG and vessel as well as SG-induced tissue overstresses.

Comparative study of clinical outcome of endovascular aortic aneurysms repair in large diameter aortic necks (>31 mm) versus smaller necks

BACKGROUND

This study compares short-term (30 days) and intermediate term (3 years) clinical outcomes in patients with large (≥31 mm) versus small aortic neck diameters (≤28 and ≤31 mm).

METHODS

Prospectively collected data from 741 patients who underwent endovascular aortic aneurysm repair were analyzed. Some surgeons have reported the threshold for a large aortic neck for endovascular aortic aneurysm repair to be 28 mm, whereas for others it is 31 mm. Therefore, we classified aortic neck diameter into less than or equal to 28 versus greater than 28 mm; and less than or equal to 31 versus greater than 31 mm. Logistic regression and Kaplan-Meier analyses were used to compare outcomes.

RESULTS

There were 688 patients who had a defined aortic neck diameter: 592 with less than or equal to 28 mm, 96 with greater than 28 mm, 655 with less than or equal to 31 mm, and 33 with greater than 31 mm. The mean follow-up was 25.2 months for less than or equal to 31 mm versus 31.8 months for greater than 31 mm. Clinical characteristics were similar in all groups, except that there were more patients outside the instructions for use in the greater than 31 mm versus less than or equal to 31 mm group (94% vs 44%; P < .0001). There was a significant increase in early type I endoleak for patients with an aortic neck diameter of greater than 31 versus less than or equal to 31 mm (9 [27%] vs 74 [11%]; P = .01); late type I endoleaks (4 [14%] vs 18 [3%]; P = .01); sac expansion (5 [17%] vs 28 [5%]; P = .01); late intervention (5 [17%] vs 23 [4%]; P = .01); and death (9 [31%] vs 48 [8%]; P < .0001). There were no differences in outcomes between the patients with greater than 28 mm aortic neck diameters and the less than or equal to 28 mm diameters. Freedom from late type I endoleak at 1, 2, and 3 years were 96%, 88%, and 88% for patients with a neck diameter of greater than 31 mm versus 97%, 97%, and 97% for a diameter less than or equal to 31 mm (P = .19). The rate of freedom from sac expansion for patients with a diameter greater than 31 mm was 88%, 81%, and 81% at 1, 2, and 3 years versus 99%, 97%, and 92% for a diameter less than or equal to 31 mm (P = .02). Freedom from late intervention for 1, 2, and 3 years for patients with a diameter greater than 31 mm were 91%, 91%, and 91% versus 99%, 97%, and 96% for those with a diameter less than or equal to 31 mm. Survival rates at 1, 2, and 3 years for a diameter greater than 31 mm were 83%, 74%, and 68% versus 96%, 92%, and 90% for a diameter less than or equal to 31 mm (P < .001). Multivariate logistic regression analysis showed that patients with a diameter greater than 31 mm had an odds ratio of 6.1 (95% confidence interval [CI], 2.2-16.8) for mortality, 4.7 (95% CI, 1.4-15.5) for sac expansion, and 4.9 (95% CI, 1.4-17.4) for late type I endoleak.

CONCLUSIONS

Patients with large aortic neck diameters (>31 mm) had higher rates of early and late type I endoleak, sac expansion, late intervention, and mortality.

Outcomes of using endovascular aneurysm repair with active fixation in complex aneurysm morphology

OBJECTIVE

The ideal treatment option for patients with complex aneurysm morphology remains highly debated. The aim of this study was to investigate the impact of endovascular aneurysm repair (EVAR) with active fixation on outcomes in patients with complex aneurysm morphology.

METHODS

There were 340 consecutive patients who underwent EVAR using active fixation devices, 234 with active infrarenal fixation (AIF; Gore Excluder; W. L. Gore & Associates, Flagstaff, Ariz) and 106 with active suprarenal fixation (ASF; 85 Medtronic Endurant [Medtronic, Santa Rosa, Calif] and 21 Cook Zenith [Cook Medical, Bloomington, Ind]). Demographics, comorbidities, anatomic features, and outcomes were analyzed for patients receiving devices with active fixation. Outcomes of using active fixation in necks with <15-mm neck lengths, >60-degree infrarenal neck angle (β), >30-mm infrarenal neck diameter, severe aortic neck calcification or thrombus, and nonstraight neck morphology were evaluated.

RESULTS

Of the 340 patients, 106 (78 men; mean age, 74.5 ± 9.3 years at the time of surgery) received implants with ASF and 234 (191 men; mean age, 74.6 ± 8.9 years at the time of surgery) received implants with AIF. In comparing AIF and ASF devices, patients in the suprarenal fixation group had significantly shorter follow-up time (25 ± 17 months vs 44.3 ± 32 months; P < .0001). Patients in the ASF group had shorter aortic neck lengths (25.5 ± 15.1 mm vs 28.6 ± 14.9 mm; P = NS) and significantly larger infrarenal neck diameters (25.9 ± 6.3 mm vs 23.4 ± 3.2 mm; P < .0001) and aneurysm diameters (59.9 ± 11.6 mm v. 55.9 ± 10.0 mm; P = .002). Outcomes were similar between groups, with no significant differences in reintervention, proximal endoleak, sac growth, abdominal aortic aneurysm-related death, or rupture. Of the complex anatomic neck features investigated, neck diameter >30 mm and nonstraight neck morphology had the highest rates of reintervention in ASF devices.

CONCLUSIONS

In cases of hostile infrarenal neck morphology, ASF appears to be used more frequently. Our data suggest that ASF may be useful for certain patients but may be unfavorable for others, such as those with wide necks or several difficult neck features. Nevertheless, further research is needed to evaluate more optimal treatment options, such as fenestrated EVAR, branched EVAR, and endovascular adjuncts such as EndoAnchors (Aptus Endosystems, Sunnyvale, Calif), in dealing with high-risk anatomic characteristics that may not be optimally managed with standard EVAR devices with active fixation.

Clinical Outcomes of Endovascular Aneurysm Repair with the Kilt Technique for Abdominal Aortic Aneurysms with Hostile Aneurysm Neck Anatomy: A Korean Multicenter Retrospective Study

PURPOSE

We aimed to evaluate the clinical efficacy and short-term clinical outcomes of Kilt technique-based endovascular aneurysm repair (EVAR) with Seal^® stent-grafts for abdominal aortic aneurysms (AAAs) with hostile neck anatomy (angle > 60°).

MATERIALS AND METHODS

We retrospectively evaluated the pre-EVAR and follow-up computed tomography angiography findings of 24 patients (mean age 71 ± 11 years; age range 32-87 years; mean follow-up 50 ± 12 months) with hostile neck AAAs treated between 2010 and 2015. Serial change in aneurysmal neck angle was calculated using a standardized protocol. Relationships between clinical variables and outcomes were evaluated using univariate and multivariate Cox analyses and mixed-model regression. In addition, the Kaplan-Meier method was used to assess the cumulative rates of survival, endoleak, and reintervention.

RESULTS

The primary technical success rate (success within 24 h after EVAR) was 100% (24/24). The survival rate was 96 ± 8% at 1 month, 6 months, 1 year, and 3 years, and 87 ± 18% at 5 years. Endoleaks occurred in three patients. Four reinterventions were performed in three patients; no surgical revisions were required. Causes of post-EVAR mortality included intracerebral hemorrhage at 14 days and rhabdomyolysis at 32 months. The most remarkable change after Kilt-based EVAR was an acute decrease in the neck angle, which was observed between the pre-EVAR and first follow-up visits (at 1 month) (P = 0.001).

CONCLUSION

Kilt-based EVAR with Seal^® stent-grafts for AAAs with a severely angulated neck (angle > 60°) provided high technical success, low mortality, and low complication rates during short-term follow-up.

No Difference in Neck Enlargement for Patients Treated With Double Proximal Self-Expandable Suprarenal Fixation Endografting

INTRODUCTION

Neck enlargement is well described in patients treated with self-expandable endografts for abdominal aortic aneurysms. Double endografting (ie, overlapping of stent grafts) occurs in patients with proximal cuffs or bifurcated to monoiliacal configuration conversions. When the aortic neck of patients receives 2 suprarenal fixation endografts, it may behave differently in terms of radial force and interaction of additional suprarenal stents extending to the visceral aorta.

METHODS

We performed a retrospective study comparing 2 groups. Group 1 included 18 patients treated with 2 proximal self-expandable endografts. Group 2 included 17 patients treated with 1 self-expandable endograft who were consecutively treated during the period of treatment in group 1. Neck measurements were analyzed in both groups preoperatively and in the last computed tomography scan during follow-up. Suprarenal, interrenal, juxtarenal, and infrarenal (at 5 and 10 mm) diameters, as well as interrenal and infrarenal (5 mm) areas, were measured.

RESULTS

There was no significant difference in baseline characteristics, initial neck measurements, and aneurysmal sac evolution including endoleaks between the groups. Both groups showed neck enlargement. Group comparisons of all parameters in posttreatment neck measurements showed no statistical change. Univariate analysis showed oversizing to be significant in interrenal diameter and area and infrarenal at 10 mm diameter; however, 2-way analysis of variance analysis showed that the interaction between oversizing and the number of stent grafts was not significant.

CONCLUSION

Neck enlargement occurs in patients with self-expandable endografts with a tendency to reach the size of the endograft in the long term. Double endografting seems to interact in the same way as simple endografting in the aortic neck. Although the main limitation of our study lies in the small sample size, the presence of an additional "double" stent graft does not appear to result in any differences in aortic neck dilatation when compared to a single stent graft.

Proximal Aortic Neck Progression: Before and After Abdominal Aortic Aneurysm Treatment

Several risk factors including short or highly angulated proximal aortic neck have been associated with long-term outcomes after endovascular or open abdominal aortic aneurysm (AAA) repair. However, research data have emerged recently concerning the behavior of proximal aortic neck, and several authors have tried to evaluate this behavior after endovascular or open repair. Additionally, computed tomography angiography (CTA) remains the golden standard for detecting and observing the morphology of an AAA, both before and after treatment. Moreover, the question of whether the proximal neck’s progression independently affects postoperative morbidity and reintervention risks still remains. Therefore, this focused review aims to present all relevant data on the behavior of an AAAs neck, based on CTA imaging before and after repair, in order to produce useful conclusions for future clinical practice.

A Systematic Review of Proximal Neck Dilatation After Endovascular Repair for Abdominal Aortic Aneurysm

Purpose: To provide an updated systematic literature review and summarize current evidence on proximal aortic neck dilatation (AND) after endovascular aneurysm repair (EVAR). Methods: A review of the English-language medical literature from 1991 to 2015 was conducted using MEDLINE and EMBASE to identify studies reporting AND after EVAR. Studies considered for inclusion and full-text review fulfilled the following criteria: (1) reported AND after EVAR, (2) included at least 5 patients, and (3) provided data on AND quantification. The search identified 26 articles published between 1998 and 2015 that encompassed 9721 patients (median age 71.8 years; 9439 men). Results: AND occurred in 24.6% of patients (95% CI 18.6% to 31.8%) over a period ranging from 15 months to 9 years after EVAR. No significant dilatation of the suprarenal part of the aorta was reported by most studies. The incidence of combined clinical events (endoleak type I, migration, reintervention during follow-up) was higher in the AND group (26%) when compared with 2% in the group without AND (OR 28.7, 95% CI 5.43 to 151.67, p<0.001). Conclusion: AND affects a considerable proportion of EVAR patients and was related to worse clinical outcome, as indicated by increased rates of type I endoleak, migration, and reinterventions. Future studies should focus on a better understanding of the pathophysiology, predictors, and risk factors of AND, which could identify patients who may warrant a different EVAR strategy and/or a closer post-EVAR surveillance strategy.

Influence of Pulmonary Status and Diabetes Mellitus on Aortic Neck Dilatation following Endovascular Repair of Abdominal Aortic Aneurysms: A EUROSTAR Report

Purpose:

To elucidate the association of impaired pulmonary status (IPS) and diabetes mellitus (DM) with clinical outcome and the incidences of aortic neck dilatation and type I endoleak after elective endovascular infrarenal aortic aneurysm repair (EVAR).

Methods:

In 164 European institutions participating in the EUROSTAR registry, 6383 patients (5985 men; mean age 72.4±7.6 years) underwent EVAR. Patients were divided into patients without versus with IPS or with/without DM. Clinical assessment and contrast-enhanced computed tomography (CT) were performed at 1, 3, 6, 12, 18, and 24 months and annually thereafter. Cumulative endpoint analysis comprised death, aortic rupture, type I endoleak, endovascular reintervention, and surgical conversion.

Results:

Prevalence of IPS was 2733/6383 (43%) and prevalence of DM was 810/6383 (13%). Mean follow-up was 21.1±18.4 months. Thirty-day mortality, AAA rupture, and conversion rates did not differ between patients with versus without IPS and between patients with versus without DM. All-cause and AAA-related mortality, respectively, were significantly higher in patients with IPS compared to patients with normal pulmonary status (31.0% versus 19.0%, p<0.0001 and 6.8% versus 3.3%, p=0.0057) throughout follow-up. In multivariate analysis adjusted for smoking, age, gender, comorbidities, fitness for open repair, co-existing common iliac aneurysm, neck and aneurysm size, arterial angulations, aneurysm classification, endograft oversizing >15%, and type of stent-graft, the presence of IPS was not associated with significantly higher rates of aortic neck dilatation (30.6% versus 38.0%, p>0.05) and did not influence cumulative rates of type I endoleak, endovascular reintervention, or conversion to open surgery (p>0.05). Similarly, the presence of DM did not influence the above-mentioned study endpoints.

Conclusion:

In contrast to observations regarding the natural course of AAAs, impaired pulmonary status does not negatively influence aortic neck dilatation, while the presence of diabetes does not protect from these dismal events after EVAR.

Advanced Endovascular Approaches in the Management of Challenging Proximal Aortic Neck Anatomy: Traditional Endografts and the Snorkel Technique

Advances in endovascular technology, and access to this technology, have significantly changed the field of vascular surgery. Nowhere is this more apparent than in the treatment of abdominal aortic aneurysms (AAAs), in which endovascular aneurysm repair (EVAR) has replaced the traditional open surgical approach in patients with suitable anatomy. However, approximately one-third of patients presenting with AAAs are deemed ineligible for standard EVAR because of anatomic constraints, the majority of which involve the proximal aneurysmal neck. To overcome these challenges, a bevy of endovascular approaches have been developed to either enhance stent graft fixation at the proximal neck or extend the proximal landing zone to allow adequate apposition to the aortic wall and thus aneurysm exclusion. This article is composed of two sections that together address new endovascular approaches for treating aortic aneurysms with difficult proximal neck anatomy. The first section will explore advancements in the traditional EVAR approach for hostile neck anatomy that maximize the use of the native proximal landing zone; the second section will discuss a technique that was developed to extend the native proximal landing zone and maintain perfusion to vital aortic branches using common, off-the-shelf components: the snorkel technique. While the techniques presented differ in terms of approach, the available clinical data, albeit limited, support the notion that they may both have roles in the treatment algorithm for patients with challenging proximal neck anatomy.

Fate of Aneurysmal Common Iliac Artery Landing Zones Used for Endovascular Aneurysm Repair

PURPOSE

To determine outcomes of aneurysmal common iliac arteries (aCIA) used for landing zones (LZs) during endovascular aneurysm repair (EVAR).

METHODS

This single-center study retrospectively compared 57 EVAR patients (mean age 72±8 years; 56 men) with 70 aCIAs (diameter ≥20 mm) to 25 control EVAR subjects (mean age 73±7 years; 20 men) with 50 normal (≤15-mm) CIA LZs treated consecutively during the same time interval. The CIA LZ measurements were analyzed using random effects linear mixed models to determine diameter change over time. Life tables were used to estimate freedom from endoleak, reintervention, and all-cause mortality.

RESULTS

The mean maximum preoperative CIA diameter in the aCIA LZ group was 24.8±4.5 mm (range 20.0-47.3, median 23.9) vs 13.6±1.5 mm (range 9.2-15.0, median 13.9; p<0.001) in the controls. Nineteen aCIA LZs were treated outside the instructions for use of the device. Median follow-up in the aCIAs LZ cohort was 39.2 months [interquartile range (IQR) 15, 61] vs 49.3 months (IQR 36, 61) in the controls (p=0.06). The rate of aCIA LZ change (0.09 mm/mo, 95% CI 0.07 to 0.1) was significantly greater than controls (0.03 mm/mo, 95% CI -0.009 to 0.07; p<0.0001). No type Ib endoleaks developed in either group; however, aCIA LZ patients had 6 (11%) iliac limb-related reinterventions. There were significantly more endograft-related reinterventions in the aCIA LZ patients (n=10, 14%) compared with controls (n=2, 4%; p=0.06). There was no difference in mortality or freedom from any post-hospital discharge endoleak.

CONCLUSION

Aneurysmal CIA LZs used during EVAR experience greater dilatation compared with normal LZs, but no significant difference in outcome was noted in midterm follow-up. However, an increased incidence of graft limb complications or endograft-related reintervention may be encountered. Use of aCIA LZs appears to be safe; however, greater patient numbers and longer follow-up are needed to understand the clinical implications of morphologic changes in these vessels when used during EVAR.

Aortic neck enlargement after endovascular aneurysm repair using balloon-expandable versus self-expanding endografts

OBJECTIVE

This study evaluated changes in aortic neck diameter after endovascular aneurysm repair (EVAR) using a balloon-expandable stent (BES) endograft compared with a commercially available self-expanding stent (SES) endograft. We hypothesized that forces applied to the aortic neck by SES endografts may induce aortic neck enlargement over time and that such enlargement may not occur in aneurysm patients treated with a device that does not use a proximal SES.

METHODS

This was a retrospective quantitative computed tomography (CT) image analysis of patients treated with the Nellix (Endologix, Irvine, Calif) BES (n = 49) or the Endurant II (Medtronic, Minneapolis, Minn) SES (n = 56) endograft from 2008 to 2010. Patients with preimplant, postimplant, and at least 1-year serial CT scans underwent quantitative morphometric assessment by two independent vascular radiologists blinded to the outcome results. Changes in the infrarenal neck over time were compared with the suprarenal aorta for each patient.

RESULTS

Follow-up extended to 4.8 years for the BES and to 4.6 years for the SES, with no significant difference in median follow-up time (34 months for BESs and 24 months for SESs; P = .06). There were no differences in preimplant neck diameter (25.2 ± 0.9 mm vs 25.7 ± 1.1 mm; P = .54) or length (27.7 ± 3.7 mm vs 23.6 ± 3.7 mm; P = .12) between BESs and SESs at baseline. After implantation, neck diameter increased by 1.1 ± 0.5 mm in BES patients and 2.6 ± 0.5 mm in SES patients (P = .07) compared with the preoperative diameter. At 3 years, neck diameter increased by 0.5 ± 0.9 mm in BES patients and by 3.8 ± 1.0 mm in SES patients (P = .0002) compared with the first postoperative CT scan. The annual postimplant rate of increase in the infrarenal neck diameter was fivefold greater in SES patients (1.1 ± 0.1 mm/y) than in BES patients (0.22 ± 0.04 mm/y; P < .0001). There were no significant differences in the diameter of the suprarenal aorta at baseline or at 3 years and no differences in the annual rate of change in suprarenal aortic diameter between BES and SES endografts.

CONCLUSIONS

EVAR using SES endografts resulted in progressive infrarenal aortic neck enlargement, whereas EVAR using BES endografts resulted in no neck enlargement over time. These data suggest that infrarenal neck enlargement after EVAR with SES endografts is likely related to the force exerted by SES elements rather than disease progression in the infrarenal neck.

Endovascular aneurysm repair with the Ovation TriVascular Stent Graft System utilizing a predominantly percutaneous approach under local anaesthesia

OBJECTIVE

To present our experience with the Ovation Abdominal Stent Graft System (TriVascular Inc., Santa Rosa, CA) during endovascular aneurysm repair (EVAR) and compare results according to the type of anaesthesia.

METHODS

We conducted a single-centre retrospective study including patients who underwent EVAR using the Ovation endograft between May 2011 and July 2014. Outcome was evaluated regarding pre-, peri- and immediate postoperative and follow-up measures. Overall results are reported, while additional analysis was performed to compare the outcome between groups of patients undertaking either local or regional/general anaesthesia (LA vs RGA).

RESULTS

66 patients were included. Median follow-up was 13 months (range, 1-39 months). Median age was 72 years and median abdominal aortic aneurysm diameter was 58 mm (range, 54-100 mm). Technical success was 63 (95%), while there were 2 (3%) conversions to open surgery. A total percutaneous approach was used in 50/66 (76%) cases. Overall, 9/66 (14%) subjects suffered from any kind of morbidity. Median hospitalization was 3 days (range, 1-16 days). Immediate and midterm mortality rate was 0%. No endoleak Type I, III, IV or stent migration was observed. There were 8 (13%) Type II endoleaks. Overall, additional endovascular procedures were required in 6 (9%), while surgery was performed in 4 (6%) patients. 44 (67%) patients underwent LA and 22 (23%) RGA. Differences between groups were significant for procedural time (85 vs 107 min; p < 0.001), percutaneous access (91% vs 45%; p < 0.001) and systematic complications (2.3% vs 14%; p = 0.05).

CONCLUSION

EVAR with the use of the Ovation endograft shows promising short-term and midterm results regarding safety and effectiveness. Completion of the procedures under LA using a total percutaneous approach seems advantageous and may be used in routine practice.

ADVANCES IN KNOWLEDGE

The Ovation Abdominal Stent Graft System is an ultra-low profile stent graft system that allows percutaneous deployment for EVAR and offers excellent overall efficacy and safety. Totally percutaneous EVAR under LA seems advantageous and may be used as a routine with this specific endograft.

Role of graft oversizing in the fixation strength of barbed endovascular grafts

PURPOSE

The role of endovascular graft oversizing on risk of distal graft migration following endovascular aneurysm repair for abdominal aortic aneurysm is poorly understood. A controlled in vitro investigation of the role of oversizing in graft-aorta attachment strength for endovascular grafts (EVGs) with barbs was performed.

METHODS

Barbed stent grafts (N = 20) with controlled graft oversizing varying from 4-45% were fabricated while maintaining other design variables unchanged. A flow loop with physiological flow characteristics and a biosynthetic aortic aneurysm phantom (synthetic aneurysm model with a bovine aortic neck) were developed. The stent grafts were deployed into the aortic neck of the bio-synthetic aortic aneurysm phantom under realistic flow conditions. Computed tomography imaging of the graft-aorta complex was used to document attachment characteristics such as graft apposition, number of barbs penetrated, and penetration depth and angle. The strength of graft attachment to the aortic neck was assessed using mechanical pullout testing. Stent grafts were categorized into four groups based on oversizing: 4-10%; 11-20%; 21-30%; and greater than 30% oversizing.

RESULTS

Pullout force, a measure of post-deployment fixation strength was not different between 4-10% (6.23 +/- 1.90 N), 11-20% (6.25 +/- 1.84 N) and 20-30% (5.85 +/- 1.89 N) groups, but significantly lower for the group with greater than 30% oversizing (3.67 +/- 1.41 N). Increasing oversizing caused a proportional decrease in the number of barbs penetrating the aortic wall (correlation = -0.83). Of the 14 barbs available in the stent graft, 89% of the barbs (12.5 of 14 on average) penetrated the aortic wall in the 4-10% oversizing group while only 38% (5.25 of 14) did for the greater than 30% group (P < .001). Also, the stent grafts with greater than 30% oversizing showed significantly poorer apposition characteristics such as eccentric compression or folding of the graft perimeter. The number and depth of barb penetration were found to be positively correlated to pullout force.

CONCLUSION

Greater than 30% graft oversizing affects both barb penetration and graft apposition adversely resulting in a low pullout force in this in vitro model. Barbed stent grafts with excessive oversizing are likely to result in poor fixation and increased risk of migration.

[Aortic stent migration: a rare complication after endovascular repair]

Migration of an aortic stent is one of the most serious complications that can occur during follow-up after endovascular repair of an abdominal aortic aneurysm. We report the case of a 75-year-old man who underwent endovascular treatment for an infra-renal aortic aneurysm using an aorto-mono-iliac stent associated to a femoro-femoral bypass. The angiography performed at the end of procedure showed complete exclusion of the aneurysm. The postoperative course was uneventful. CT scans at 1, 6 and 12 months were normal. The CT scan at the 18th month showed a proximal migration of the stent, which was complicated by a type 1 endoleak and a stent disjunction with a type 3 endoleak. Revision surgery was indicated but the patient died from aneurismal rupture pending treatment. The migration of an aortic stent is a rare but serious complication of endovascular aneurysmal repair. Prevention requires a precise anatomical selection and adequate deployment of the stent graft.

Differential gene expression in the proximal neck of human abdominal aortic aneurysm

OBJECTIVE

Abdominal aortic aneurysm (AAA) represents a common cause of morbidity and mortality in elderly populations but the mechanisms involved in AAA formation remain incompletely understood. Previous human studies have focused on biopsies obtained from the center of the AAA however it is likely that pathological changes also occur in relatively normal appearing aorta away from the site of main dilatation. The aim of this study was to assess the gene expression profile of biopsies obtained from the neck of human AAAs.

METHODS

We performed a microarray study of aortic neck specimens obtained from 14 patients with AAA and 8 control aortic specimens obtained from organ donors. Two-fold differentially expressed genes were identified with correction for multiple testing. Mechanisms represented by differentially expressed genes were identified using Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. Some of the differentially expressed genes were validated by quantitative real-time PCR (qPCR) and immunohistochemistry.

RESULTS

We identified 1047 differentially expressed genes in AAA necks. The KEGG analysis revealed marked upregulation of genes related to immunity. These pathways included cytokine-cytokine receptor interaction (P = 8.67*10(-12)), chemokine signaling pathway (P = 5.76*10(-07)), and antigen processing and presentation (P = 4.00*10(-04)). Examples of differentially expressed genes validated by qPCR included the T-cells marker CD44 (2.16-fold upregulated, P = 0.008) and the B-cells marker CD19 (3.14-fold upregulated, P = 0.029). The presence of B-cells in AAA necks was confirmed by immunohistochemistry.

CONCLUSIONS

The role of immunity in AAA is controversial. This study suggests that immune pathways are also upregulated within the undilated aorta proximal to an AAA.

A computational framework for investigating the positional stability of aortic endografts

Endovascular aneurysm repair (Greenhalgh in N Engl J Med 362(20):1863-1871, 2010) techniques have revolutionized the treatment of thoracic and abdominal aortic aneurysm disease, greatly reducing the perioperative mortality and morbidity associated with open surgical repair techniques. However, EVAR is not free of important complications such as late device migration, endoleak formation and fracture of device components that may result in adverse events such as aneurysm enlargement, need for long-term imaging surveillance and secondary interventions or even death. These complications result from the device inability to withstand the hemodynamics of blood flow and to keep its originally intended post-operative position over time. Understanding the in vivo biomechanical working environment experienced by endografts is a critical factor in improving their long-term performance. To date, no study has investigated the mechanics of contact between device and aorta in a three-dimensional setting. In this work, we developed a comprehensive Computational Solid Mechanics and Computational Fluid Dynamics framework to investigate the mechanics of endograft positional stability. The main building blocks of this framework are: (1) Three-dimensional non-planar aortic and stent-graft geometrical models, (2) Realistic multi-material constitutive laws for aorta, stent, and graft, (3) Physiological values for blood flow and pressure, and (4) Frictional model to describe the contact between the endograft and the aorta. We introduce a new metric for numerical quantification of the positional stability of the endograft. Lastly, in the results section, we test the framework by investigating the impact of several factors that are clinically known to affect endograft stability.

Two-dimensional versus three-dimensional CT angiography in analysis of anatomical suitability for stentgraft repair of abdominal aortic aneurysms

BACKGROUND

The morphological analysis prior to endovascular abdominal aneurysm repair (EVAR) plays an important role in long-term outcomes. Post-imaging analysis of computed tomographic angiography (CTA) by three-dimensional reconstruction with central lumen line detection (CLL 3D-CTA) enables measurements to be made in orthogonal slices. This might be more precise than equal post-imaging analysis in axial slices by two-dimensional computed tomographic angiography (2D-CTA).

PURPOSE

To evaluate the intra- and interobserver variability of CLL 3D-CTA and 2D-CTA post-imaging analysis methods and the agreement between them in pre-EVAR suitability analysis of patients with abdominal aortic aneurysm (AAA).

MATERIAL AND METHODS

Anonymized CTA data-sets from 70 patients with AAA were analyzed retrospectively. Length measurements included proximal and distal aortic neck lengths and total distance from the lower renal artery to the higher iliac bifurcation. Width measurements included proximal and distal neck diameters, maximum AAA diameter and common iliac diameters just above the iliac bifurcations. The measurements were performed in random order by two vascular surgeons, twice per method with 1-month interval between readings. In the CLL 3D-CTA method we used semi-automated CLL detection by software and manual measurements on CTA slices perpendicular to CLL. The equal measurements in 2D-CTA were performed manually on axial CTA slices using a DICOM viewer workstation. The intra- and interobserver variability, as well as the agreement between the two methods were assessed by Bland-Altman test and bivariate correlation analysis.

RESULTS

The intraobserver variability was significantly higher in 2D-CTA measurements for both readers. The interobserver variability was significant in 2D-CTA measurements of proximal neck dimensions while the agreement in CLL 3D-CTA analysis between the two readers was excellent in all studied parameters. The agreement between the two suitability analysis techniques was poor for both readers, especially in measurements of proximal neck's dimensions and in total aortoiliac length (p = 0.001).

CONCLUSION

In pre-EVAR morphological evaluation of AAAs the CLL-3D CTA post-imaging analysis has better intra- and interobserver correlation than 2D-CTA and might represent a useful tool for the proper selection of endograft's type and size.

Long-term follow-up of neck expansion after endovascular aortic aneurysm repair

OBJECTIVE

This study determined the rate, extent, and clinical significance of neck dilatation after endovascular aneurysm repair (EVAR).

METHODS

The study included 46 patients who underwent elective EVAR using bifurcated Zenith stent grafts (Cook, Bloomington, Ind) and had at least 48 months of clinical and radiographic follow-up. Computed tomography images were analyzed on a 3-dimensional workstation (TeraRecon, San Mateo, Calif). Neck diameter was measured 10 mm below the most inferior renal artery in planes orthogonal to the aorta. Nominal stent graft diameter was obtained from implantation records.

RESULTS

Median follow-up was 59 months (range, 48-120 months). Neck dilation occurred in all 46 patients. The rate of neck dilation was greatest at early follow-up intervals. At 48 months, median neck dilation was 5.3 mm (range, 2.3-9.8 mm). The extent of neck dilation at 48 months correlated with percentage of stent graft oversizing (Spearman rho = 0.61, P < .001). No type I endoleak or migration >5 mm occurred.

CONCLUSIONS

After EVAR with the Zenith stent graft, the neck dilates until its diameter approximates the diameter of the stent graft. Neck dilation was not associated with type I endoleak or migration of the stent graft.

Size of the proximal neck in AAAs treated with balloon-expandable stent-grafts: CTA findings in mid- to long-term follow-up

PURPOSE

To determine the evolution of the proximal aortic neck diameter in mid- to long-term follow-up after endovascular aneurysm repair of abdominal aortic aneurysm (AAA) with a balloon-expandable stent-graft.

METHODS

Thirty patients (27 men; average age 71 years, range 56-87) with infrarenal AAAs were treated with the SETA-Latecba balloon-expandable stent-graft (6 aortomonoiliac and 24 bifurcated configurations). Follow-up ranged from 4 to 8 years (mean 73.4 months). Computed tomography was done systematically before the procedure, after implantation (1-3 months), at 1 year, and annually thereafter. The last follow-up scan was utilized to measure the proximal neck for purposes of comparison with baseline and the initial post-implant scans.

RESULTS

Five patients died during follow-up of causes unrelated to the procedure. No endoleaks or graft migrations were observed. The pre-deployment proximal neck diameter (a) averaged 23.4 mm (range 18-32), the diameter after deployment of the stent-graft (b) averaged 24.9 mm (range 18-34), and the most recent follow-up proximal neck measurement (c) averaged 23.8 mm (range 18-31). Comparing the last follow-up to the post-implant measurements (c-b), the neck diameter decreased in 15 (50%) patients [7 with short necks (i.e., <15 mm)] and remained unchanged (no variation) in 15 (50%) patients (4 with short necks). All patients treated with the SETA-Latecba balloon-expandable stent-graft showed stability of the proximal aortic neck diameter in mid- to long-term follow-up.

CONCLUSION

The study showed that the diameter reached at initial deployment did not increase further in the long term, which supports the safety and reliability of this modular balloon-expandable stent-graft and illustrates that this device does not produce dilatation of the proximal neck after deployment. Future dilatation of the aortic neck is unlikely, and consequently, migration or delayed type I endoleak are also unlikely.

A single-institution experience with the AneuRx Stent Graft for endovascular repair of abdominal aortic aneurysm

We report our experience of endovascular repair of infrarenal abdominal aortic aneurysms (EVAR) using the modular AneuRx Stent Graft System. We retrospectively reviewed the outcomes of 113 patients who underwent EVAR with the AneuRx system performed at our institution between October 1999 and August 2003. The mean age of this group was 72.5 years, with 71% (n = 80) over the age of 70 years and 95% (n = 107) males. Aneurysm diameter ranged 4.0-9.0 cm, with 33% (n = 37) >6.0 cm. The average duration of late follow-up was 32.6 +/- 24.8 months (median = 37). Successful deployment of the modular AneuRx system was noted in all patients. There were no immediate operative conversions, deaths within 24 hr of operation, or type I or III endoleaks observed at the completion of the procedure. Thirty-day mortality was 3.5% (n = 4). Acute deployment-related complications occurred in 10% (n = 13) of patients and included misdeployment, operative bleeding, arterial perforation/dissection, and access site complications. Acute systemic complications were present in nine patients, predominantly renal and cardiac complications. An endoleak noted at any time occurred in 25% of patients, with 40% of those requiring a secondary intervention. Two patients suffered late aneurysm rupture due to a type I endoleak and graft infection. Kaplan-Meier analysis revealed 5-year freedom from secondary intervention of 72.4%; freedom from aneurysm-related death of 93.9%; and probability of survival based on all-cause mortality of 60.1%. Endovascular treatment with the modular AneuRx Stent Graft System is safe and effective, producing acceptable rates of disease-free survival and mid-term clinical outcome.

Development of endovascular stent-grafts

The very first experiences in the early 1990s with endovascular aortic stent-grafts were associated with significant numbers of complications including an inability to deploy the stent-graft, conversion to open surgery, and aneurysm rupture. By the mid-1990s, improved home-made and commercially available stent-grafts started to appear. These devices could be successfully deployed in the aorta, achieving aneurysm exclusion with low morbidity and mortality. However, follow-up results raised concerns about the longer-term durability. Gradually, too, these problems have been addressed such that, in the recent UK multi-centre randomized controlled trial of endovascular versus open aneurysm repair, aneurysm-related mortality was 3 per cent less in the endovascular group four years following surgery. Currently the indications for aortic stent-grafts are being expanded. It is now possible to maintain perfusion successfully in aortic side branches and to treat aneurysms that would have once been thought untreatable. This review paper reviews the main developments in endovascular stent-grafting and the major role played by medical engineering and technology.

Aortic Neck Dilatation and Endograft Migration Are Correlated With Self-Expanding Endografts

PURPOSE

To compare self-expanding and balloon-expandable stent-grafts in terms of aortic neck dilatation and endograft migration.

METHOD

Two-hundred and forty-two patients (178 men; mean age 68 years, range 56-91) underwent elective endovascular repair of abdominal aortic aneurysm. Two-hundred self-expanding (115 Excluder, 48 Endologix, 23 Vanguard, 10 Anaconda, and 4 Talent) and 42 balloon-expandable (Lifepath) endografts were used. All patients underwent contrast-enhanced computed tomography (CT) prior to the intervention, at 1, 3, and 6 months after the procedure, and annually thereafter. Comparison was made between the first and the last follow-up CT scans.

RESULTS

Fifty-five (27.5%) of the 200 patients treated with self-expanding endografts had aortic neck dilatation compared to only 3 (7.1%) of the 42 patients treated with balloon-expandable endografts (p = 0.023). Forty-nine (24.5%) patients in the self-expanding group versus only 3 (7.1%) patients of the balloon-expandable group presented with endograft migration (p = 0.034); all had dilated necks. The difference between the means of neck dilatation for the Lifepath balloon-expandable stent-graft and the Excluder self-expanding endoprosthesis was statistically significant (p = 0.011, 95% CI 0.07 to 0.91).

CONCLUSION

Aortic neck dilatation following endovascular AAA repair appears to be correlated with self-expanding endografts, which may contribute to a higher incidence of graft migration compared to that occurring with balloon-expandable endografts.