Endograft platform does not influence aortic neck dilatation after infrarenal endovascular aneurysm repair with primary endostapling

Abstract

Objectives

Aortic endografts used for endovascular aneurysm repair (EVAR) are based on varying skeletal platforms such as stainless steel or nitinol stents, using radial force applied to seal at the aneurysm neck, and varying proximal fixation methods, applying either suprarenal or infrarenal fixation. This study assesses whether varying skeleton/fixation platforms affect neck-related outcomes after primary endostapling with Heli-FX EndoAnchors at EVAR.

Methods

Retrospective analysis of a prospective database of infrarenal EVAR undertaken at a single centre. Chimney-EVAR, secondary cases were excluded. Primary outcomes analysed included neck diameter evolution from pre-EVAR to latest imaging follow-up, including a comparison of stent platforms to see if there was any outcome difference between those using stainless steel or nitinol, as also freedom from type I endoleakage and migration. Secondary outcomes assessed included average number of EndoAnchors, and sac size patterns before and after EVAR.

Results

A total of 101 patients underwent endostapled infrarenal EVAR between September 2013 and March 2020. After exclusion of ineligible patients, 84 patients (76 male, 8 female, age 73.7 ± 7.8 years) were available for analysis. 57/27 endografts used suprarenal/infrarenal fixation, whilst 16/68 devices were based on stainless steel/nitinol platforms, respectively. Mean oversizing was higher for stainless steel/suprarenal fixation endografts (p = 0.02). A total of 582 EndoAnchors were deployed, averaging 7 ± 2 per patient. Median neck diameter was 25 mm (IQR 22–31) with 22 necks having non-parallel morphology (conical, tapered or bubble). Median follow-up period was 28.5 (IQR 12–43) months. Neck evolution studies suggested aortic neck dilatation of 5 ± 4 mm (p <0.001, paired T-test), independent of platforms employed (p = NS, ANOVA). There was no endograft migration; one immediate post-EVAR endoleak settled by eight weeks. There was a mean 5.7 ± 8.2 mm sac size reduction (p < 0.001, paired T-test).

Conclusion

Aortic neck dilatation occurs after EVAR with primary endostapling, but the process may be independent of stainless steel/nitinol platforms, possibly due to the attenuating effect of EndoAnchors. Adjunct aneurysm neck fixation by primary endostapling prevents migration regardless of whether suprarenal/infrarenal fixation is the primary fixative method. Device platform choice therefore may be left to the operator discretion if primary endostapling is applied at EVAR. Freedom from complications such as migration and endoleakage in the intermediate term suggests a higher level of ‘tolerance’ to aortic neck dilatation with primary endostapling. We would therefore suggest routine usage of EndoAnchors at EVAR when not otherwise contraindicated.

Keywords

Endovascular aneurysm repair EndoAnchors aortic neck dilatation stents endograft fixation

Introduction

Fixation and seal at infrarenal endovascular aneurysm repair (EVAR) for abdominal aortic aneurysms (AAAs) are key issues in preventing migration and type I endoleakage,¹ which lead to re-intervention or even AAA rupture. Such complications are a primary indication for surveillance after EVAR.² As the radial force gain from oversizing an endograft into the aortic neck does not alone fix the device securely, device manufactures have taken varying approaches to augment fixation, using either suprarenal fixation (SRF) or infrarenal fixation (IRF) using hooks/barbs to embed into the aorta to augment the pull-out resistance to forces that promote caudal displacement and migration. Radial force at the neck is also implied in contributing to late aortic neck dilatation (AND).³ It is conceivable that this may vary depending on whether the device skeleton is stainless steel (SS) or nitinol (NT), given that comparative studies suggest that NT-based endografts cause higher rates of AND compared to Co–Cr platforms⁴ for instance; the effect of tissue incorporation, particularly in the context of self-expanding, i.e. NT-based endografts and its effect on AND cannot be quantified as tissue incorporation of aortic endoprostheses itself is unpredictable, and not robust enough to prevent migration, thus reinforcing the need for basic fixation adjuncts as a part of aortic endograft design.²

Endostapling is a recognised technique for reinforcing fixation and seal,⁵ with terminology such as endosuture(d) aneurysm repair^6,7 recently used. This study therefore compares AND rates focusing on device skeleton types as there is evidence that endostapling using the Heli-FX EndoAnchor (EA) System (Medtronic Ltd., Minneapolis, USA) can attenuate or protect against the effects of neck dilatation.⁸ Whilst the risk of device migration is not insignificant, endostapling may reduce this risk even further;⁹ we therefore also examine whether the primary device fixation adjunct is relevant if primary endostapling is applied.

Methods

A retrospective analysis of a prospective database of patients who underwent planned EVAR using standard devices with primary endostapling for AAAs was undertaken in a single vascular centre with high endostapling experience at EVAR and TEVAR. The study was conducted in adherence to the principles of the Declaration of Helsinki; all patients provided written consent for inclusion into research, ethical approval was not required. Patients were selected for EVAR and endostapling with agreement at a multidisciplinary team meeting; all cases were included if there were no contraindications to use of EAs.

Endpoints

General outcomes

Device characteristics, length of stay and 30-day mortality are presented.

Primary outcomes

Primary outcomes assessed were infrarenal neck diameter changes comparing the pre-EVAR average neck diameter to that obtained at latest imaging, particular examining whether there was a difference based on whether SS/NT platforms were used, and also freedom from type Ia endoleakage and migration (defined as >5mm caudal displacement), and re-interventions for neck-related complications.

Secondary outcomes

Secondary parameters assessed include sac size changes comparing the pre-EVAR size against that obtained at the most recent scan, and EA deployment patterns.

Procedural and follow-up aspects

Patients underwent endostapling in a radial clockface fashion at the aortic neck as per the instructions for use (IFU); device selection was based on aortoiliac anatomy, with a focus on the neck characteristics. The number of EndoAnchors aimed to be used per case was >6, as per the author’s experience in line with recent studies that suggest usage of higher numbers;^10–12 all deployments were planned in advance. Follow-up imaging was undertaken on a standardised chronological protocol in the early post-procedure phase (<6 weeks), at six months and then annually thereafter. Neck diameter was assessed as the average of the inner-to-inner major and minor axis aortic diameters from the first-postoperative scan as described elsewhere,^12–14 and then for comparison against similar parameters (using matched and/or slice-linked images as appropriate at the level of circumferential EA deployment) in the most recent CTA or abdominal radiographs (as is standard practice in our institution),¹⁵ using the outer-to-outer diameter of the aortic endoprosthesis as these two designated measurement parameters would be the closest, as described before.¹² Measurements were all done by a single operator to minimise inter-operator variability, using local Picture Archiving and Communications System (PACS) software (Insignia Medical Systems, Basingstoke, UK).

Statistical analysis

Data were populated in Microsoft Excel for statistical analysis within Minitab 19.2 for Windows (Minitab LLC, Philadelphia, PA, USA). Categorical variables are presented as counts and percentages. Continuous variables are presented as mean/median ± standard deviation/range. Matched parametric data were analysed using paired T-tests, asymmetrical data using one-way ANOVA. The threshold of statistical significance was p < 0.05. A distribution analysis of the variable follow-up using a right-censored Kaplan–Meier method was undertaken to identify the numbers at risk at each annual follow-up interval, generating a life table-based time series plot to present freedom from type I endoleak and migration. Predictive discrimination of relevant variables such as the effect of neck profile and complications such as any type Ia endoleakage were assessed using logistic regression-based Wald Test.

Only patients undergoing EVAR with primary endostapling were assessed; non-standard devices/configurations (such as chimney-EVAR cases and secondary endostapling interventions with or without cuff usage) were excluded to avoid the confounding biomechanical effects of multiple/prior devices and/or increased oversizing. Patients with incomplete datasets were also excluded.

Results

A total of 101 patients underwent EVAR with standard devices and adjunct endostapling from September 2013 to March 2020 for infrarenal AAA. Seventeen patients were not eligible (ChEVAR, n = 3, lost to follow-up, n = 1, secondary interventions, n = 13), resulting in 84 patients (77 male, 7 females aged 76.8 ± 8.9 years) being available for analysis. Patients undergoing ChEVAR or secondary interventions were excluded to avoid the confounding effect of multiple devices at the neck or prior device ± cuff implantation. Median length of stay was 2 (IQR 1–4) days. Median follow-up period was 28.5 (IQR 12–43) months (Figure 1).

Figure 1.

Distribution analysis of follow-up patterns using the Kaplan–Meier method.

Devices (and platform details) used included Zenith Flex (SS/SRF, n = 14), Zenith LP (NT/SRF; n = 6) Alpha (NT/SRF, n = 24), aorto-uni-iliac (AUI, Cook Aortic Interventions, Bloomington, USA; SS/SRF, n = 2), Endurant (Medtronic, Santa Rosa, USA; NT/SRF, n = 8), Excluder C3 (WL Gore & Associates, Flagstaff, USA; NT/IRF, n = 27), Incraft (Cordis, Baar, Switzerland; NT/SRF n = 3). On a fixation platform basis this yielded 57 devices with SRF and 27 with IRF, whilst 16 skeleton platforms were SS-based and 68 NT-based.

Primary outcomes

Median neck diameter was 25 mm (IQR 22–31). Twenty-two (26.2%) necks were of nonparallel morphology (conical, tapered or bubble). Regression modelling indicated that varying neck profile was not a strong predictor of type Ia endoleakage (p = 0.97, Wald test, R-squared = 15.8%), thus excluding neck morphology as a potential factor that might be implicated in the early endoleakage noted in one patient.

There was no difference between the initial neck diameters or neck lengths when comparing device skeletons or fixation method (p = NS). Only 16.7% necks at EVAR were designated large applying the ≥29 mm cut-off,¹⁶ and thus further analysis comparing AND between large and small neck sizes was not undertaken. Mean endograft oversize was 23.4 ± 8%; this was statistically significantly higher for SS compared to NT devices (p = 0.02, ANOVA); a similar trend was noted for devices with SRF (p = 0.02, ANOVA). There was a trend towards continued aortic neck dilatation (median 4.6 mm, IQR 5.7), which was statistically significant (p < 0.001, ANOVA; Figure 2). Trends in neck dilation were not different between SS/NT platforms (p = 0.57, ANOVA; Figure 3(a)), or between fixation platforms (p = 0.17, ANOVA; Figure 3(b)).

Figure 2.

Aortic neck dilatation (AND) trends comparing the neck diameter pre-EVAR to that at the most recent imaging.

Figure 3.

Comparison of aortic neck dilatation (AND) trends between (a) skeleton and (b) fixation platforms.

Freedom from migration was 100%, and whilst there was one on-table endoleak (immediate freedom from type 1 endoleak 98.8%; Figure 4); this was noted to have eventually settled at the first post-operative scan.

Figure 4.

Time series plot indicating freedom from index complications.

Secondary outcomes

The mean pre-EVAR AAA size was 65.1 ± 12.2 mm, with significant shrinkage (mean AAA size at latest imaging 59.5 ± 13 mm; p < 0.001, paired T-test) notable in >65% of patients (Figure 5). Four (4.8%) patients had sac enlargement due to type II endoleakage – two had IMA embolisation, another patient had open sacotomy and IMA ligation for an acutely symptomatic AAA (with a shrinking sac prior), the remaining patient died of natural causes. One patient had a distal type I endoleak successfully treated with limb extension.

Figure 5.

Sac size trends after EVAR and endostapling.

A total of 582 EAs were implanted at a mean 7 ± 2 per patient. There were two EA losses into the aorta, which were retrieved by snaring and two hub fractures after deployment, also snared and retrieved, representing a low rate of EA loss (0.69%). There were no EA-related deaths or embolic complications.

These results are summarised in Table 1.

Table 1.

Overview of results.

Criterion	Outcome details	Comments	p
Patient details
Sex M/F	77/7	–	–
Age, years (mean, SD)	76.8 (8.9)	–	–
General/primary outcomes			–
Median LOS, days (IQR)	2 (1–4)	–	–
30-day mortality	0	–	–
Return to theatre within 30 days	0	^aIMA embolisation (n = 2), open IMA ligation (for type II endoleak, n = 1), late type Ib endoleak (n = 1)	–
Freedom from any intervention^a	96.4%		–
Freedom from persistent type I endoleak^b	100%	^bEarly type I endoleak, resolved (n = 1)	–
Freedom from migration	100%	–
EndoAnchor-related outcomes
Total deployed	582	–	–
EA deployed per patient	7±2	–	–
EA related complications (n, %)	4 (0.69)	Migration (n = 2), fracture (n = 2), retrieved	–

Neck characteristics			–
Diameter (mm, median/IQR)	25 (22–31)	–	–
Length (mm, median/IQR)	19 (13–28)	Shortest neck 8 mm	–
Parallel: non-parallel morphology (%)	62:22 (73.8: 26.2)	No correlation to endoleaks (R² = 15.8%)	0.67
Neck-related outcomes
Endograft oversize (mean, SD)	23.4%±8	–	–
AND (mm, median, IQR)	4.6 (5.7) ↑	–	<0.001
Sac size outcomes
Mean initial size (mm, mean, SD)	65.1 (12.2)	–	–
Final size (mm, mean, SD)	59.5 (13.3)↓	–	<0.001
Sac size reduction, n (%)	56 (66.7%)	Sac size reduction in majority	–
No change in sac size, n (%)	24 (28.6%)	–	–
Sac size increase,^a n (%)	4 (4.7%)	IMA embolised, n = 2
Endoskeleton comparison (mean, SD)	SS (n = 16)	NT (n = 68)
Device oversize (%)	27.5 (8.3) ↑	22.5 (7.8)	0.02
AND (mm)	4.6 (3.8)	5.3 (4.4)	NS
Fixation platform comparison (mean, SD)	SRF (n = 57)	IRF (n = 27)
Device oversize (%)	24.9 (8.2) ↑	20.3 (7.2)	0.02
AND (mm)	5.6 (4.5)	4.2 (4.0)	NS

LOS: length of stay; EA: EndoAnchors; AND: aortic neck dilatation; SS: stainless steel; NT: nitinol; SRF: suprarenal fixation; IRF: infrarenal fixation.

Discussion

In brief, this study – conducted in a real-world ‘all-comers’ setting – suggests that whilst AND occurs irrespective of primary endostapling or device platform, this does not result in higher rates of either migration or the development of type Ia endoleaks at least in the mid-term. Additionally, this study also confirms a high rate of sac shrinkage. A high number of EndoAnchors can be safely deployed in each patient with a low number of EA-related complications.

All devices using stent-fabric combinations for proximal seal seem to cause AND,¹⁷ likely due to the radial force of the sealing stent at the aortic neck.³ The annual dilatation rate quoted is 0.16 mm/year from smaller studies after open surgical repair (OSR).¹⁸ A median overall AND of 5.3 mm is noted at 48 months after EVAR in some studies;¹⁴ however, some small studies comparing OSR to EVAR found no significant differences in AND.¹⁹ The current literature implicates both oversizing and platform aspects, and though Tassiopoulos et al. indicated that SRF could be indicated as a risk factor for AND,⁸ this is contradicted by Cao et al. who found that SRF (and also oversizing >15%) did not correlate with AND in a similar cohort even without endostapling.²⁰

Excess oversizing is implicated in eventual neck failure and type I endoleakage and is to be avoided;² the higher oversizing noted with SS devices in the current study was largely due to the need to size for non-parallel necks. Both SS²¹ and NT^4,22 platforms have been associated with AND, but no study has undertaken a comparative study in this context particularly when adjunct EAs are used.

AND is a prevalent phenomenon after EVAR, and is linked to increased endoleakage, migration and reintervention rates,¹⁶ particularly as the resultant neck diameter exceeds the default endograft diameter²³ losing seal and fixation.¹³ Up to 4 mm of AND is designated as acceptable due to the redundancy created by oversizing;²⁰ however, our study seems to indicate higher values, which is also matched by a long-term study looking at AND at 48 months, which demonstrated AND of 5.3 mm,¹⁴ suggesting that such thresholds for defining what is ‘acceptable’; AND may need to be re-examined to determine if endostapling allows a greater degree of ‘tolerance.’ Neck-related complications are notable when undertaking EVAR for AAAs with large necks, where endoleak rates of 12% have been described,²¹ whilst other studies have looked focused on a >30% oversizing threshold as relevant to AND,²⁴ which is much higher than the average oversize described in our study. Generally, >15% oversize is recommended for large necks.²¹

EndoAnchors likely constrain the neck by achieving transmural aorto-prosthetic fixation, with suggestions that AND is attenuated by endostapling.^8,25 Furthermore, endostapling may also reduce subtle endograft surface movement, which has been implicated in the development of endoleaks,²⁶ and may be linked to the high incidence of sac shrinkage in this series as also noted in other studies.^27,28 The neck diameter-related results presented here echo that of other studies, which indicate that AND continues despite endostapling, the role of which may be thus to maintain endograft-to-aortic wall fixation/apposition in preventing both migration and endoleakage, which are the recognised ill-effects of AND, and this conforms to current hypotheses regarding how endostaples are protective.⁸ A ‘more is better’ approach to endostapling may also be relevant,^10,11 reflected in the high average number of EAs deployed in the presented series. Our results indicate a low rate of EA loss as also noted in the literature.²⁹

There seems to be no real difference between migration rates when comparing SRF to IRF even in short-necked AAAs.³⁰ Historical studies have compared the influence of SRF and IRF on neck dilatation and distal migration, indicating no real difference, though proximal migration was higher with a historical, now condemned device.^13,31 SRF has been shown to not contribute to AND.²⁰ Nevertheless, as our study indicates no difference in migration rate when primary EAs are used, device choice based on fixation becomes less important when primary endostapling is applied.

Interestingly, there was higher oversizing with SS and SRF platforms, and that may be a specific consideration for choice of endograft where both criteria are met. This is likely because of use of the 36 mm Zenith Flex aortic body, which is larger than counterparts by other manufacturers.

The presented study indicates that overall freedom from migration and type I endoleakage with a primary endostapling approach is low when applied to varying neck anatomy,^32,33 and may further attenuate device migration rates, which are described consistently from >8.5%^34,35 dropping to <4% with primary endostapling.³⁶ This supports bench studies that indicate high pull-out resistance when >6 EAs are applied,³⁷ which is now our current practice for all neck sizes.^10,11

Limitations

This study does not have full long-term follow-up for all patients beyond five years due to the failures in survival and loss to follow-up, as is typical of real-world data. However, the presented series is larger than most other single-centre^38–41 or even multicentre³² studies that have been presented outside of the ongoing ANCHOR registry,⁴² which examine primary endostapling and affirm good mid-term results. We have not assessed suprarenal AND because of a mix SRF/IRF devices being used, which do not provide comparable suprarenal aortic stressors. Similarly, device-specific analyses were not undertaken as this would likely lead to comparisons of small numbers. Other devices could not be tested as they do not form part of the author’s standard armamentarium. We specifically noted the low number of SS devices, which we acknowledge increase the possibility of a type II error so we cannot make a strong comment on the non-significant difference between the SS and NT platforms. Going forward, we feel this will be difficult to address in terms of getting larger sample sizes as the SS-SRF platform exemplified here is the Zenith Flex (bifurcated and AUI), use of which continues to diminish.

Neck thrombus and calcification (which is also felt to protect the neck from AND)⁸ are specifically not relevant as EA deployments were all planned pre-operatively as per IFU to ensure optimum aortic wall penetration, avoiding such areas, and we therefore feel such as aspects are not confounders where EAs can be used. Similarly, we could not compare this to a control group without EAs, as most operators may choose options such as excessively oversizing devices (out of IFU, potentially accelerating the risk of late neck dilatation,¹⁷ an approach that we discourage), or opt for super-complex options like fenestrated/branched/chimney (F/B/Ch)EVAR; however, endostapled EVAR can offer equivalent safety in this context to ChEVAR.⁴³

Conclusion

This study suggests that despite primary endostapling the rate of neck dilatation after infrarenal EVAR did not vary whether devices use a stainless steel as compared to a NT framework, and though the amount of AND noted was higher than in some other studies, this did not result in a higher number of seal-related complications. This may indicate a higher level of ‘tolerance’ to AND when primary endostapling is applied. We would therefore recommend routine endostapling where feasible. As migration rates are no different between devices using SRF or IRF, we suggest that it is up to the individual operator to choose such a device based on the aortic anatomy encountered. Aortic neck dilatation has implications for long-term freedom from complications, but further studies in larger numbers and of longer duration is needed to examine those aspects when primary endostapling is employed at EVAR, though it is likely that continued assessment of SS devices in this specific context will be difficult to realistically achieve.

Footnotes

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iDs

Arindam Chaudhuri

Ayman Badawy

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Stanley

Ballast

, et al. A comparison of endosuture aneurysm repair versus chimney stent grafts for treatment of short-neck infrarenal abdominal aortic aneurysms. J Vasc Surg 2019; 70: E147.