Endovascular aneurysm repair (EVAR) has gained wide acceptance as the preferred method of treating aortic aneurysms with suitable anatomy. The technique is associated with lower early mortality, morbidity, faster discharge and patient turnover by offering small incisions with minimal invasive nature [1, 2, 3, 4]. The adverse events in the endovascular procedures may be due to endograft, challenging aortic anatomy or iatrogenic. Endografts are dynamically in evolution according to the early and late results of the randomized studies to reduce the adverse events related to structural impairments.

Unibody bifurcated endografts have the advantage of reducing the operative time and avoiding iliac limb dislocation in the long term. The Endologix AFX$\mathrm{\circledR }$ (Endologix, Inc., Irvine, CA, USA) endograft system for endovascular abdominal aortic aneurysm repair is the only graft with anatomical fixation to the aortic bifurcation in comparison to most other endografts that use suprarenal neck as the main fixation point. In short and mid-term outcomes, the Endologix AFX$\mathrm{\circledR }$ endograft had a low-rate of device and procedure-related complication but there is not yet enough study that showed long-term results [5].

United States Food and Drug Administration (FDA) approval was originally granted for Endologix Powerlink system in 2004 [6], a modification to this device was introduced in 2011 as the AFX endograft, which used a lower profile 17F delivery system. A proximal and distal landing zone length of $\ge$15 mm, neck diameter between 18–32 mm and infrarenal angulation to the aneurysm of $\le$60 degrees were the recommended instructions for use [7, 8]. A change in the original IFU in 2013 recommended a minimum aortic component overlap of 30 mm to 40 mm which was followed in 2014 by introduction of the change of expanded polytetrafluoroethylene (e-PTFE) material from Strata to Duraply referring to a highly dense, helical wrap providing longitudinal strength. Finally, the instructors regarding the minimum length of overlap were further revised in 2016 as follows: overlap length equals half the maximum aortic aneurysm diameter plus 20 mm [9].

Endoleaks are defined by persistent blood flow within the aneurysm sac intraoperatively or following EVAR. During the follow-up, in a meta-analysis, type II, III or IV endoleak could be seen in 13.7% of patients [10]. Late type III endoleak is an uncommon but serious complication caused by fabric tears, disruptions or junctional separation of the endograft components.

We report our long-term experience of patients who underwent endovascular infrarenal abdominal aortic aneurysm electively with Endologix AFX$\mathrm{\circledR }$ endograft system.

EVAR is widely accepted treatment of choice for AAA. The superiority of EVAR over open surgery was seen especially in short-term outcomes [1, 2, 3, 4]. The use of the Endologix AFX$\mathrm{\circledR }$ endograft was associated with a low rate of device and procedure-related complications in this period [12, 13, 14, 15]. The Endologix AFX$\mathrm{\circledR }$ endograft system is a single-body bifurcation graft that is different from other grafts. Anatomic fixation in native bifurcation has the potential to reduce the risk of distal migration in long term. This advantage was also seen in our series. There was no migration.

In contrast to all other endografts, AFX stent frames are located inside to facilitate the aortic conformability. However, this endoskeleton can be challenging at reintervention times, especially for guidewire entrapment or the passage for the endograft bodies.

The texture is e-PTFE, located outside the skeleton, and only proximal and distal endings are sutured. Therefore, it provides flexibility and better adaptation to the irregular aortic neck in the proximal sitting area since the graft material can move freely in an “active seal” manner [16, 17]. This independent movement of the graft material from the stent may be a factor for uncoupling as the columnar strength may diminish when fixation is at the aortic bifurcation.

Besides long-term outcomes with abdominal aortic aneurysm (AAA) treated with unibody bifurcated endograft, our study demonstrated excellent short-term results, with no intra-procedural open surgical conversion and no 30-day mortality encountered. The first finding was related to the long-term prognosis of treatment of AAA with minimally invasive procedure. Cumulative survival was 54.0% at 5th year in this patient cohort. Because of the presence of CAD in 54.4% of our patient population, one can think that all-cause mortality was high in the long term due to diseases such as CAD and other vascular system disorders. Increasing malignancy rates with advanced age may also have caused this high mortality rate. Moreover, patients who are at high risk for surgery and older patients are now treated with endovascular intervention; in the long term, death due to non-aneurysm causes is more common. In Bahia et al. [18] meta-analysis, they showed no improvement in mortality, with a mean 69.0% rate, of elderly patients over the years. There is long-term follow-up of different endografts in the literature. In a recent study, overall survival at 7 years was 50.3% to 61.4% [19]. Therefore, this high mortality in long-term; it should be kept in mind that it is more dependent on additional issues like cardiac morbidity or malignity, not aneurysm related. In order to avoid extra nephrotoxic agent, we did not perform routine coronary angiography (CAG) on patients without cardiac symptoms. We routinely used transthoracic echocardiography and electrocardiogram. In cases where surgical stress was low and no cross clamp, we did not experience cardiac morbidities in the early period. In our series with high cardiac comorbidities, long-term cardiac mortality may have caused a significant reduction in survival.

As all designs carry their own pros and cons; there seems a component uncoupling problem, as the main body and aortic extension disconnection, tried to dissolve by the manufacturer’s suggestion as to maximize the overlap and some changes over the material used. Manufacturers’ material exchange does not seem to be sufficient for eliminating the type III endoleak, so proper patient selection, sufficient overlap are the key issues.

Endoleak type III due to fabric tears or disintegration of the endograft components has been a concern in EVAR. From study 701 EVAR patients treated with the Endologix Powerlink and Endologix AFX$\mathrm{\circledR }$ endograft, Skibba et al. [16] reported type III endoleak in 17 patients (2.4%). Welborn et al. [13] showed a similar incidence (2.3%) in 108 patients treated with the AFX endografts. Even though, the 30 mm and more overlap requirement was always applied in our clinic, six of the patients in our series had an endoleak type IIIa and one type IIIb, during long-term follow-up. It was 10.3% and close to 7.3% of Lemmon et al. [5]. Among the type III endoleak patients, five were already diagnosed with CT however the other two patients were detected firstly with CDUS and than confirmed by CT. This correlation leads us to another study concerning the primary tool for EVAR surveillance [20] where we found high correlation of type I and III endoleak detection with CDUS and CT.

The treatment of type III endoleak often employs an endovascular approach as first line. In case of failure open late conversion and repair are mandatory. Meticulous preoperative planning and proper choice of endograft for a sufficient overlap arevery important.

To avoid type III endoleaks, maximizing component overlap or more proper patient selection may be a choice. Proper patient selection for Endologix AFX$\mathrm{\circledR }$ endograft should include saccular aneurysms, infrarenal AAA with narrow aortic bifurcations and with short infrarenal-bifurcation lengths where modular endografts have technical disadvantages. Also older patients with ASA IV status necessitating a faster procedure may be proper candidates.

It is well established that the dominant forces on modular EVAR components are directed sideways and that such force increases along the greater curvature with aortic or endograft angulation [21, 22]. The resulting sideways displacement of the endograft is more prevalent in larger aneurysms with sufficient volume in the aneurysm sac to accommodate this conformational change and is associated with an increased incidence of type I and III endoleaks [23]. Long term integrity of the central overlap zone between the two modular components thus depends on appropriate outward radial force from the proximal extension, the sealing mechanism of the expanded PTFE endograft covering, adequacy of the overlap zone between the two aortic components and the degree of angulation.

The probability of type III endoleak was increased two-fold by 0.1 unit increase at ASI. Moreover, the interpretation that AAA larger than 60 mm and ASI over 3 had the possibility of type III endoleak may be revealed as the all patients with type III endoleaks were adjusted to these criteria.

Type II endoleaks were detected in the completion angiogram in 5 patients (7.4%). They were all followed up and three of them (60.0%) disappeared in the first year while the others were closely followed for the aneurysm sac enlargement. No aneurysm sac enlargement was seen and therefore no reintervention was necessitated.

No graft infection and post-implantation syndrome were seen. There are studies suggesting e-PTFE grafts are associated with a lower probability of postoperative fever, however there is no randomized clinical support [24].

Clinical reports confirm low limb occlusion rates [14, 18]. Stent grafts each have different variations in graft material, stent material and configuration. These differences are made for providing the perfect adaptation of graft and iliac artery anatomy, especially with angulated, calcified or nonuniform atherosclerotic landing zones. Clinical studies confirm low limb occlusion rates [9, 14, 18, 25]. Patients treated with the Endologix Powerlink and Endologix AFX$\mathrm{\circledR }$ endografts during an 8-year period, reported only three (0.4% of all patients) graft thrombosis that needed reintervention [16]. Limb thrombosis has low prevalence in patients with AFX endografts. In our long-term follow-up, the patients did not need to reintervention for limb issues. We only had periprocedural access site problems, resolved with femoral embolectomy and/or graft interposition.

Study limitations are the retrospective design, a single center experience with a relatively small patient population that may prevent statistical significance. There was no randomization as only Endologix AFX$\mathrm{\circledR }$ endograft for elective AAA were chosen. There is no actual comparison with other endografts.

Endologix AFX$\mathrm{\circledR }$ endograft does not require contralateral limb cannulation, therefore it enables a relatively fast procedure. Predisposition of performing with local anesthesia, it is more suitable for elderly and comorbid patients. This endograft has low reintervention rate even though all mandates reintervention. According to our results, aneurysms larger than 6 cm has more sideway displacement possibility and by this way type III endoleak. Especially in terms of type III endoleak, it should be closely monitored at follow-up. Manufacturers material exchange not seems to be sufficient for eliminating the type III endoleak, so proper patient selection, sufficient overlap are the key issues.

HZİ, MK, BBA and EUÜ conceived and designed the analysis; BBA, VB, GA, EK, BA collected the data; HZİ, BBA, GA, EK and EUÜ analyzed the data; HZİ, MK, BBA, VB, GA and EUÜ wrote the paper.

No informed consent was obtained because of the retrospective nature of data collection from hospital records in the study. The institutional review board of the Turkey Yuksek Ihtisas Hospital approved, code 29620911-929-1303.

We thank three anonymous reviewers for excellent criticism of the article.

This research received no external funding.

The authors declare no conflict of interest.