The Future of Abdominal Aortic Aneurysm Treatment and the Role of Totally Percutaneous Endografting

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Abstract

Endovascular abdominal aortic aneurysm repair (EVAR) has experienced a continuous spread worldwide as a result of the constant drive to develop innovative methods and devices that enable physicians to achieve therapeutic aims while reducing procedural risks and patient discomfort. Randomised controlled studies have demonstrated clear early benefits over open repair in terms of mortality and morbidity, but a high reintervention rate jeopardised the EVAR outcome. Complications in EVAR, such as endoleaks, separation of modular components, stent or hook fractures and distal migration of the endograft, can lead to aneurysm enlargement and thus to the native risk of aneurysm rupture. In order to prevent such complications and minimise potential re-interventions, new-generation stent grafts, low-profile delivery systems and new percutaneous closing devices have been developed and adopted, making a totally percutaneous approach possible and desirable. Nevertheless, operators must be aware and trained to face every complication that could possibly develop during and after the procedure. Given these circumstances, EVAR is under consideration as the first line of treatment for abdominal aortic aneurysms.

Disclosure
The authors have no conflicts of interest to declare.
Correspondence
Vincent Riambau, Professor and Chief of Vascular Surgery Division, Thorax Institute, Hospital Clinic, University of Barcelona, Villarroel 170, 08036 Barcelona, Spain. E: riambau@meditex.es; vriambau@clinic.ub.es
Received date
18 July 2010
Accepted date
10 August 2010
DOI
https://doi.org/10.15420/icr.2010.5.1.86

Since the first reported endovascular abdominal aortic aneurysm repair (EVAR) by Parodi in 1991,1 the approach to the treatment of aneurysmal pathology has changed. The old concept of substitution of the aneurysmal aorta has been replaced by the new and challenging concept of exclusion, in order to pursue the same aim of preventing or treating aneurysm rupture.

EVAR is a minimally invasive technique that involves placing a stent graft at the site of the aneurysm.2 The stent graft is inserted either percutaneously or through a small incision in the femoral artery in the groin, then carried to the site of the aneurysm using catheters and guidewires and placed in position under radiographic guidance. Once in position, the stent graft is deployed and anchored to the wall of the aorta using a variety of fixing mechanisms. The graft is stronger than the weakened aorta and allows blood to pass through it without placing pressure on the aneurysm. Nowadays, the main types of endovascular stent grafts are aorto-uni-iliac grafts and aorto-bi-iliac (bifurcated) grafts, with most procedures using bi-iliac stents. EVAR is carried out under general, regional or local anaesthesia.

The potential advantages of EVAR over open repair include reduced operative time, elimination of the pain and trauma associated with major abdominal surgery, reduced length of stay in the hospital and intensive care unit and reduced blood loss.3 The potential disadvantages include the development of complications requiring repeated interventions. Endoleak still represents the Achilles’ heel of EVAR. It often occurs when blood continues to flow through the aneurysm because the graft does not seal completely or because of backfilling of the aneurysm from other small vessels arising from the aneurysm wall.

In the early 1990s, EVAR was originally developed for patients who were considered to be physically ineligible for open surgical repair. However, new and interesting technologies have ensured the success of EVAR even in patients with favourable clinical conditions because of the minimal invasiveness. In 1996, an international register of EVAR was started and in 1999 data for 895 cases were reported, with a cumulative two-year survival rate of 85%.4 In this cohort of patients the 30-day mortality rate was low at 3%, but at discharge 14% of patients presented with an endoleak. In 18%, a new endoleak was reported during the first year of follow-up, and in 22% a continued expansion of the aneurysm was observed.

Since the motivation for aneurysm treatment is the elimination of the risk of rupture and death or else to prolong life, new standards for defining abdominal aortic aneurysm (AAA) treatment success have been set over the years. The first set of reporting standards for studies directed at the endovascular repair of the infrarenal aortic aneurysm was introduced by the Ad Hoc Committee for Standardized Reporting Practices in Vascular Surgery of the Society for Vascular Surgery/International Society for Cardiovascular Surgery in 1997.5 In 2002, new reporting standards were published by Chaikof et al.6 The success of EVAR remains dependent on a consideration of both clinical and radiographic criteria that differ from the historical standards established by conventional open repair. Before any surgical procedure is undertaken, the fitness of the patient needs to be assessed. As the aim of EVAR is the complete exclusion of the aneurysm from the circulatory system, technical success is achieved only if it can be performed using a remote site, the proximal and distal fixation is secure, no type I or III endoleak is detectable and the graft is patent without significant twists, kinks or obstructions that can be detected at completion angiogram.6 Clinical success requires deployment of the endovascular device at the intended location without death as a result of aneurysm-related treatment, type I or II endoleak, graft infection, thrombosis or migration, aneurysm expansion or rupture or conversion to open repair.6

Nowadays the presence of type II endoleak is not considered a failure in the absence of aneurysm expansion. In EVAR-treated aneurysms, changes in the dimension of the residual sac assist in defining the success or failure of aneurysm exclusion.7 Furthermore, long-term aneurysm exclusion and device stabilisation are dependent on the maintenance of an effective attachment or seal between the endograft and the aorta, while progressive angulation of the aortoiliac segment leading to distortions of the andograft may result in endograft disruption or limb occlusion.8–11 The success of EVAR is strongly influenced by pre-procedural planning, the experience of the operator, the technique used and the type and generation of endograft. Today, reporting standards on the clinical and cost-effectiveness of EVAR patients at varying levels of risk are based on the long-term results of randomised controlled trials (RCTs).

Evidence-based Practice

Concerning elective repairs, four RCTs have been carried out. The largest one, the EVAR trial,1 was undertaken to compare results between patients considered fit for open and endovascular repair.12–14 Patients at least 60 years of age with aneurysm diameter greater than 5.5cm and anatomically suitable for EVAR were randomly assigned to open or endovascular repair between September 1999 and August 2004 in 37 hospitals in the UK. Six hundred and twenty-six patients were assigned to each group and were followed for rates of death, graft-related complications, re-interventions and resource use until the end of 2009. The thirty-day operative mortality rate was 1.8% in the endovascular repair group and 4.3% in the open repair group. The endovascular repair group had an early benefit with respect to aneurysm-related mortality, but the benefit was lost by the end of the study, at least partially because of fatal endograft ruptures. By the end of follow-up there was no significant difference between the two groups in the rate of death from any cause, the rates of graft-related complications and re-interventions were higher with endovascular repair and new complications occurred up to eight years after randomisation, contributing to higher overall costs.14 The benefits of EVAR shown by the 2005 results13 faded away with an additional four years of follow-up.14 Similar outcomes have been obtained in the Dutch Randomised Endovascular Aneurysm Management (DREAM) study15,16 and in the American Open Versus Endovascular Repair (OVER) trial.17 Finally, a French RCT is already finished, but its results are still in press and will be published very soon.18

Nevertheless, the challenging matter remains the fitness of the patient. The design of the EVAR Trial 219,20 was drawn up to compare EVAR and continued non-surgical management of patients affected by AAA and considered unfit or unsuitable for open repair (an approach known as ‘watchful waiting’) in 404 patients enrolled between 1999 and 2004. The main results from this trial showed that the 30-day operative mortality rate was 7.3% in the endovascular repair group and the overall rate of aneurysm rupture in the no intervention group was 12.4 per 100 person-years. The endovascular repair of AAA was associated with a significantly lower rate of aneurysm-related mortality than no repair. However, endovascular repair was not associated with a reduction in the rate of death from any cause, as expected in a poorly fit population. Data from the EVAR 1 and 2 trials are summarised in Table 1.

The reported evidence related to EVAR applied in ruptured aneurysms is almost anecdotal. Nevertheless, the proportion of patients with ruptured abdominal aneurysms treated by EVAR is steadily increasing as most centres are adopting EVAR as a first-line therapy. However, the only short randomised trial failed to demonstrate any benefit of EVAR over open repair.21 A new multicentre randomised study named Endosvasculaire versus Chirurgie dans les Anévrysmes Rompus (ECAR) was set up in France with 160 patients to compare EVAR with open repair in ruptured aortoiliac aneurysms; it is still in the analysis phase.22

Endovascular Complications and Technique Improvements

When analysing the population of the two trials, the rate of re-intervention in patients submitted to EVAR was around 25%.14–20 Reported complications in EVAR are endoleaks,23,24 separation of modular components, stent or hook fractures and distal migration of the endograft. All of these complications can lead to aneurysm enlargement and so to the native risk of aneurysm rupture. Endograft migration and type I endoleak (inadequate seal at the proximal or distal end of endograft) significantly increase the incidence of rupture of AAA and the need for conventional surgical repair. Particularly challenging anatomy such as angulated and short infrarenal neck, large neck diameter, large maximal AAA diameter, neck thrombus and iliac tortuosity can cause high rates of post-EVAR complications.25–28

In order to prevent such complications, new-generation stent grafts, low-profile devices and new percutaneous closure devices have been developed. Recently, stent graft configuration, modularity, fabric, support system and fixation components have been improved together with peri-operative adjuncts or adjunctive manoeuvres. Since aorto-iliac tortuosity is a major cause of concern when performing EVAR, management of the access site and introduction of the delivery system play important roles in technical improvement. Several manufacturers have modified their original designs to make the endograft more flexible or repositionable29,30 or to provide an ‘anatomical fixation‘ so that the endograft bifurcation rests on the aorto-iliac bifurcation.31 To enhance fixation to the aortic wall, barbs, spikes or hooks have been integrated into the devices30,32 and clips and staples have been used as adjuncts.33 In patients with complicated infrarenal aortic neck anatomy, a bare-metal stent (BMS) could be deployed in the infrarenal neck before or after the endograft positioning, or an aortic cuff could be deployed in the distal infrarenal seal zone before the main body deployment (the ‘kilt technique’)34 in order to improve proximal neck sealing.

Adjunctive manoeuvres to treat anatomically challenging aortic aneurysms include bending the guidewire or using a superstiff guidewire to align the endograft with the axes of the aneurysm and the neck, or the ‘endowedge technique’, which enables a proximal scalloped endoprosthesis to be wedged against a temporarily ballooned renal artery.34

Totally Percutaneous Endografting

To reduce the invasiveness of EVAR, percutaneous closure devices have been developed and tested in some series.35–40 New, smaller introduction devices allow operators to avoid the conventional surgical femoral approach in most procedures. These benefits could translate to a potential decrease in hospital stay and early discharge following totally percutaneous endovascular procedures. In EVAR, suture-based vascular closure devices can be used. They achieve arterial haemostasis by deploying sutures that are tied to form a surgical knot to close the arteriotomy so repeat arterial access or immediate surgical exploration of the same artery can be safely performed. Although these closure devices are approved for the closure of arteriotomies created by a 10Fr sheath size, several studies have reported various off-label applications following percutaneous interventional procedures of sheaths up to 24Fr in size,35–38 with success rates ranging from 88 to 96%. It is worth noting that the larger sheaths (>18Fr) had the lowest technical success rate at 92.8%, as reported by Lee et al.39 Indeed, a technical requirement of the use of closure devices is the assessment of the femoral artery to determine its diameter and eventual wall calcification, which can be responsible for access-site complications. Moreover, in addition to the increase in procedure costs, the use of closure devices requires a learning curve, so complications must be taken into account when considering a totally percutaneous EVAR procedure and the operator must be trained to deal with such complications. Nevertheless, with proper patient selection and increased operator experience, endovascular aortic procedures can be performed using a percutaneous approach using suture-based closure devices with high success rates.40

Conclusions

There is a constant drive to develop innovative methods and devices that enable physicians to achieve therapeutic aims while reducing procedure-related risks and patient discomfort. New devices have been designed to improve the previous late outcomes and reduce re-intervention rates. The anatomical limits of EVAR can nowadays be overcome in many cases by the use of several adjunctive techniques during stent graft deployment. A totally percutaneous approach is now possible and will be widespread in the future due to technological improvements. Nevertheless, this technique and overall aortic aneurysm care should be approached by a multidisciplinary team with a vascular surgeon as leader to assure the best global treatment.

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