Indian Journal of Vascular and Endovascular Surgery

REVIEW ARTICLE
Year
: 2020  |  Volume : 7  |  Issue : 3  |  Page : 216--221

Endovascular aneurysm repair for infrarenal abdominal aortic aneurysm: How, why, and when!


Raghu Lakshminarayan1, Rakesh Kapur2,  
1 Consultant in Vascular Interventional Radiology, Hull University Teaching Hospitals NHS Trust, Hull, England
2 Consultant in Vascular Surgery, Hull University Teaching Hospitals NHS Trust, Hull, England

Correspondence Address:
Raghu Lakshminarayan
Consultant in Vascular Interventional Radiology, Hull University Teaching Hospitals NHS Trust, Hull
England

Abstract

Endovascular aneurysm repair is an established method for the treatment of infrarenal aortic aneurysms. The operator needs to remain abreast with evolving technology and be conversant with the proper use of pre and postoperative imaging and its interpretation, limitations of devices and of the technique itself, and the IFUs.



How to cite this article:
Lakshminarayan R, Kapur R. Endovascular aneurysm repair for infrarenal abdominal aortic aneurysm: How, why, and when!.Indian J Vasc Endovasc Surg 2020;7:216-221


How to cite this URL:
Lakshminarayan R, Kapur R. Endovascular aneurysm repair for infrarenal abdominal aortic aneurysm: How, why, and when!. Indian J Vasc Endovasc Surg [serial online] 2020 [cited 2021 Jan 20 ];7:216-221
Available from: https://www.indjvascsurg.org/text.asp?2020/7/3/216/294924


Full Text



 Introduction



Endovascular aneurysm repair (EVAR) has earned its place as an established method of treatment for infrarenal aneurysms over the last two decades. Stent and graft technology has improved over time making this a durable, safe, and acceptable procedure. However, unlike open aneurysm repair, EVAR needs regular follow-up to pick up endoleaks and other issues such as migration of graft over time. This does put a resource issue into the mix when deciding between EVAR and open repair. Further, expanding the anatomic considerations to difficult necks and iliacs has led to a decrease in long-term durability which has to be considered in present-day practice. A good understanding of the anatomy and consideration given to the instructions for use (IFUs) of each graft is paramount.

 Indications



It is a well-known fact that aneurysm rupture carries a high mortality. There is a wealth of literature addressing the need for intervention for abdominal aortic aneurysms (AAAs) based on their size and symptoms or growth rate.[1] All asymptomatic aneurysms >5.5 cm or an aneurysm that has shown rapid growth (aneurysms >4 cm increasing by 1 cm in a year) are considered appropriate for treatment. However, many other factors such as age, life expectancy at the time of treatment, aneurysm size, and morphology are actively considered, and a joint decision between the patient and the physician is arrived at. This is also complemented by discussions from multidisciplinary team meetings. The advantages of EVAR include reduced perioperative mortality and morbidity, reduced pain and a shorter inhospital length of stay, allowing some units to even offer day-case EVAR with same-day discharge in selected patients, and importantly, the fact that an intensive care unit bed is not usually needed for an EVAR patient.

The latest National Institute for Health and Care Excellence guidelines suggest that most people should be offered open repair, with EVAR being reserved for elderly patients with anesthetic risks or medical comorbidities reflected by lower fitness and situations of the hostile abdomen. This approach has been dictated by the fact that patients with EVAR need regular follow-up which provides strong economic and long-term outcome reasons in favor of open repair even with its slightly higher mortality. The European guidelines (ESVS)[2] suggest open repair for relatively young and fit patients, with EVAR being reserved for slightly more elderly patients with comorbidities. This is what we follow in our unit, with a typical 50-50 split between open and endovascular procedures for our population of patients with AAA, with excellent results.

 Anatomical Considerations



The anatomy of infrarenal aneurysm is a key factor in deciding the need for treatment (based on the size of aneurysm) and whether the AAA is amenable to EVAR. As mentioned before, the size of infrarenal aneurysm is a determinant for treatment. The size has traditionally been measured by ultrasound and is performed in an axial view with the largest diameter measured from the inner-to-inner wall [Figure 1].{Figure 1}

Once a decision to treat has been made and a consideration for EVAR is preferred as the treatment of choice and computed tomography (CT) done to assess whether the AAA is amenable to EVAR, a few key aspects of anatomy to be considered are access vessels, aneurysm neck and iliac sealing zones, presence of calcification, thrombus, and angulation.

Adequate imaging is the key to a good anatomical evaluation. This is obtained with a CT scan done in arterial phase of scanning (with bolus tracking) and scans reconstructed at subcentimeter slices which allow for good reconstruction. Once the CT is available, the scans are reconstructed using a software that allows for multiplanar reconstructions with the ability to look at orthogonal views for determining angulations of neck and iliacs which also allow for centerline reconstruction for length measurements. We would like all practitioners to thoroughly evaluate the raw data from axial, coronal, and sagittal scans before using the automated centerline measurements and automated multiplanar reformation views.

Access is defined by the size of the common femoral arteries, external and common iliac arteries, presence or absence of plaques/thrombus, and calcification and tortuosity of vessels.

Most grafts require around 18F access with a few low-profile grafts allowing a 14F access. Traditionally, a 7-mm smooth access vessel is considered an adequate size for EVAR [Figure 2]. The access for the contralateral iliac is generally around 12-16 F. Apart from size, tortuosity of iliac arteries is an important consideration, especially to advance a fairly large device to the neck of the aneurysm [Figure 3]. The greater the age of the patient, the more rigid the vessels would be. If the size of the vessels is 5 mm or less [Figure 4], the only option for an endovascular repair would be to place a conduit to the common iliac. However, if the external iliac arteries are very small, it is likely that common iliac arteries are also small in caliber. One of the long-term issues of endovascular repair is limb loss, and this should be considered during planning in the presence of small and tortuous iliacs.{Figure 2}{Figure 3}{Figure 4}

The neck of the aneurysm is a key factor in deciding suitability for endovascular repair. Most devices require a sealing zone of around 15 mm [Figure 5] with a few licensed for use at 10 mm. Obtaining a seal is defined as the ability of the graft to appose itself to the wall of the artery in a manner not to allow any leakage between the graft and the vessel wall. The aim is to place the graft in a healthy, nondissected, thrombus, or calcium-free parallel aortic segment. Necks might have different configurations (tapered, reverse taper, angulated, or a budge/penetrating ulcer [Figure 6]). Even in the presence of these complex necks, a defined sealing zone is a must for the success of the procedure [Figure 7].{Figure 5}{Figure 6}{Figure 7}

Neck angulation is another consideration for treatment. There are two angulations to be considered - first, that of the suprarenal aorta to the neck, and second, that of the neck to the aneurysm. Angulations above 60° are generally considered outside the IFUs for most grafts.

The iliac sealing zone should be viewed similarly to the sealing zone in the neck and has to offer a decent length and a healthy segment for sealing [Figure 8]. As mentioned before, iliacs with small diameter and tortuosity might predispose to limb loss, and iliac arteries with large diameter might continue to expand [Figure 9]. Many grafts will offer treatment of iliac arteries up to 23 mm. Consideration should be given to options of iliac branching or fenestration in large iliac arteries. Patients with lack of proper sealing zone either due to a short neck or extension of thrombus into the neck or aneurysm involving the visceral segment cannot have a conventional infrarenal EVAR. These patients will have to be considered for an open repair or other complex endovascular options such as a fenestrated or branched graft. Fenestrated grafts are traditionally considered to extend the sealing zone into the visceral segment in the absence of extensive dilatation of the visceral segment of the aorta. Branch grafts will have to be considered when the visceral segment of the aorta is dilated in which fenestrations will not offer a stable solution [Figure 10].{Figure 8}{Figure 9}{Figure 10}

 Devices and Technique



There has been a huge improvement in device technology over the last two decades. The initial problems associated with fabric tears and leaks with stent deformities have been largely overcome, and multiple devices have gained regulatory approval for use [Figure 11]. All traditional devices come with a sealing zone both for the neck and iliacs. Fixation with barbs is either suprarenal or infrarenal in position, which helps in preventing device migration. Although attempts were made to look at devices which worked on filling the aneurysm sac with polymers in endobags (Nellix device), this technology has not taken off. The present-day devices are off the shelf unlike the previous custom infrarenal devices. Most of them come with a body of the graft which also has the ipsilateral limb. The contralateral limb is then cannulated, and an iliac limb is placed. Iliac extensions in various dimensions are also available. Aortic cuffs are available which aid in increasing the sealing zone or increasing the radial force at the neck of the aneurysm.{Figure 11}

Most standard stent grafts require a 15-mm neck sealing zone such as the Gore C3 device, Jotec E-Tegra device, Lombard Aorfix device, or the Cordis Incraft device. The new conformable C3 device from Gore and Medtronic Endurant devices are now licensed for use at 10-mm neck lengths. Most devices are licensed for use for neck angulations of 60° or less. The Aorfix, Anaconda, and conformable C3 devices can be used in neck angulations up to 90°. Further advances have been made with the Endurant device with the use of endoanchors which help anchor the device and could be used in necks with shorter lengths. The Altura device is a bit different in that it has two stents (D stents) to seal at the neck leading into the two iliac limbs [Figure 12]. This graft system does not require contralateral limb cannulation. The choice of graft should be based on available expertise and anatomical patient characteristics. Most units work with two grafts, preferably one with suprarenal fixation and the other with infrarenal fixation.{Figure 12}

Along with graft selection, most units now work with percutaneous access using a variety of closure devices. The use of percutaneous access makes the procedure less invasive and can lead to early discharge.

 Postprocedure Follow-Up



The Achilles heel of EVAR has been the need for sustained follow-up as it is well known that various types of endoleaks can develop. Endoleaks refer to flow outside the graft into the aneurysm. There are various types of endoleaks. The Type 1 endoleak is when there is flow beside the neck of the graft (1a) or between the iliac limb seal at the bottom end of the graft (1b) [Figure 13]. This needs to be fixed as this direct flow into the sac will pressurize the sac and cause it to rupture [Figure 14]. Type 1 endoleaks are mostly due to either over- or undersizing of the graft or the presence of an angulated neck with thrombus and/or calcification. Unfavorable neck morphology should defer patients from being considered for an EVAR. Most Type 1a endoleaks can be fixed with an aortic cuff to get more coverage of the neck or increase radial force to get a better seal. This might also be achieved with a large Palmaz stent. Endoanchors have also been used to anchor the graft at the place of the endoleak. The most common type of endoleak is a Type 2 endoleak [Figure 15]. This is related to a re-bleed into the sac usually from a patent lumbar artery or the inferior mesenteric artery. Most Type 2 endoleaks are not treated and just followed up. The only Type 2 endoleaks that are treated are those which present with an increase in sac size of more than 1 cm on surveillance. These are usually treated with a transarterial or percutaneous approach. The underlying principle is to fill the endoleak “lake” with coils and liquid embolics such as onyx.{Figure 13}{Figure 14}{Figure 15}

Another common issue with EVAR grafts is related to limb occlusions which present with acute limb ischemia [Figure 16]. This can either be treated with lysis with alteplase or a femorofemoral crossover graft.{Figure 16}

Most units have follow-up protocols for EVAR. However, there is no consensus as to which protocol, if any, is the preferred one. Plain and contrast-enhanced CT is generally used in the 1st year of follow-up. Most units perform a CT in the immediate postprocedure period (within the month of EVAR or at discharge) followed by another at the end of a year. This is usually followed by yearly ultrasound follow-up, with contrast ultrasound[3] or CT used for resolving problems for the graft or aneurysm that might be noticed on the ultrasound examination.

The latest European guidelines,[2] if adopted, could reduce the burden of follow-up, as has been shown by a recent audit carried out in our unit. The European guidelines recommend early (within 30 days) CTA after EVAR to assess the presence of endoleak, component overlap, and sealing zone length. This aids in assigning the patients to one of three groups: low, intermediate, and high risk.

The low-risk group of patients are characterised by the following features: no endoleak, anatomy within IFU, adequate overlap, and seal of >10 mm proximal and distal stent-graft apposition to the arterial wall. These patients should have CTA once every 5 years.

The intermediate-risk group (adequate overlap and seal but the presence of Type II endoleak) patients require annual ultrasound to assess for sac expansion or shrinkage. Patients with sac shrinkage >1 cm in the presence of a Type II endoleak can be downgraded to the low-risk group (i.e., CTA every 5 years). Patients with sac expansion >1 cm need intervention.

The high-risk group of patients are characterised by the presence of Type I or III endoleak, inadequate overlap or seal <10 mm. Urgent re-intervention is recommended for patients with Type I or III endoleak or kinking. For patients with inadequate overlap or seal <10 mm, who do not show any signs of endoleak, surveillance is recommended with annual CTA.

 Conclusion



EVAR has established itself as a safe and durable procedure for the treatment of infrarenal AAA.[4] Proper patient and device selection is the key to a successful procedure. Long-term follow-up is mandatory.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

References

1Available from: https://www.nice.org.uk/guidance/ng156/evidence/f- thresholds-for-abdominal-aortic-aneurysm-repair-pdf-7087991155. [Last accessed on 2020 Aug 02].
2Wanhainen A, Verzini F, Van Herzeele I, Allaire E, Bown M, Cohnert T, et al. European Society for Vascular Surgery (ESVS) 2019 Clinical Practice Guidelines on the Management of Abdominal Aorto-iliac Artery Aneurysms. Eur J Vasc Endovasc Surg 2019;57:8-93.
3Jawad N, Parker P, Lakshminarayan R. The role of contrast-enhanced ultrasound imaging in the follow-up of patients post-endovascular aneurysm repair. Ultrasound 2016;24:50-9. [Last accessed on 2020 Aug 02].
4Available from: https://library.cirse.org/packages/latest-developments- in-evar. [Last accessed on 2020 Aug 02].