NDT Advance Access originally published online on July 21, 2006
Nephrology Dialysis Transplantation 2006 21(9):2362-2365; doi:10.1093/ndt/gfl264
© The Author [2006]. Published by Oxford University Press on behalf of ERA-EDTA. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org
Editorial Comment
Endovascular abdominal aortic aneurysm repair and renal function
Peter R. Taylor1,
John Reidy2 and
John E. Scoble3
1 Department of Vascular Surgery, 2 Department of Radiology and 3 Department of Nephrology, Guy's & St. Thomas' NHS Foundation Trust, London SE1 7EH, UK
Correspondence and offprint requests to: Dr J. E. Scoble, 6th floor, New Guy's House, Guy's Hospital, London SE1 9RT, UK. Email: john.scoble{at}gstt.nhs.uk
Keywords: aortic stent; renal artery stenosis
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Introduction
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Post-operative renal failure is relatively common following
aortic aneurysm surgery and is associated with a poor outcome
[
1,
2]. The interdependent relationship of aneurysms and renal
failure is well-known to clinicians, leading to close working
relationships between vascular surgeons and nephrologists. The
traditional method of surgical repair for abdominal aortic aneurysms
involves open access to the aorta, the application of vascular
clamps and the replacement of the aneurysmal segment by a synthetic
graft manufactured from either polyester or polytetrafluoroethylene
(PTF) which is sutured into place. In patients with short necks,
the clamps may compromise renal blood flow as they have to be
applied immediately below, or occasionally above, the level
of the renal arteries. There is some evidence that the application
of clamps distally to the iliac arteries before clamping proximally
may increase the number of atheroemboli detected in the renal
arteries. The length of ischaemic time to the limbs may also
cause the ischaemia–reperfusion syndrome resulting in
a deterioration in the renal function post-operatively. Pre-existing
renal failure and renal artery stenosis due to aortic atheroma
will increase the incidence of renal failure associated with
open surgical aneurysm repair.
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Endovascular aortic aneurysm repair
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The endovascular revolution in treating abdominal aortic aneurysms
started with Volodos
et al. [
3] and Parodi
et al. [
4]. They
used stent grafts consisting of a metal stent covered with fabric
contained within a sheath, which was inserted through the femoral
artery. The stent graft was deployed in the neck of the aneurysm,
i.e. a healthy segment of the normal calibre aorta below the
renal arteries, by withdrawing the sheath and allowing the self-expanding
stents to open. The stents were oversized compared with the
diameter of the aorta and were held in place by the radial force.
The early experiments showed that both the proximal and distal
stents were required to exclude the aneurysm. The term endoleak
was introduced to describe the continued leak of contrast material
into the aneurysm sac outside the device. Aortic tube grafts
had an unacceptable incidence of distal endoleak and it quickly
became apparent that bifurcated devices were required with the
distal landing zones in the common iliac arteries. Home-made
aortouni-iliac devices became popular as they were able to treat
a wider range of anatomical variations, the drawback being that
the contralateral iliac artery had to be occluded and a femoro–femoral
crossover graft inserted to revascularize that limb. Commercially
manufactured bifurcated stent grafts were developed which were
either manufactured in a single piece or had a modular configuration.
Single piece devices required that the contralateral limb had
to be pulled down into the contralateral iliac artery. This
could lead to twisting of the graft material with consequent
occlusion of that limb. Modular devices were developed with
the contralateral limb being inserted via the contralateral
femoral artery, and then positioned in a gate in the main body
of the device to form a seal. Several early devices had unacceptable
rates of limb occlusion, modular disconnection and migration.
The long-term results were relatively poor, with the combination
of metal and fabric disintegrating causing pressurization of
the sac and subsequent rupture [
5].
The current generation of stent grafts consists of either nitinol or stainless-steel stents covered with either polyester or PTF. Most employ hooks or barbs to prevent distal migration. Some employ suprarenal fixation which consists of having a bare or uncovered part of the stent in the suprarenal aorta. The aorta at the level of the visceral and renal arteries is recognized as the most resistant to dilatation. It is also usually free of atheromatous disease. The evidence for suprarenal stents causing a deterioration in renal function is not supported by the literature. Many studies show that this is a safe procedure [6–9]. A detailed analysis has recently been published comparing open repair with endovascular repair using suprarenal fixation in a non-randomized study [10]. The endovascular group had better results initially using serum creatinine concentrations as a marker of renal function, however, there were no differences at 1 year. Interestingly, the incidence of renal artery occlusion was 1% in the endovascular group compared with 1.4% in the open surgery, and the incidence of renal infarction was 1.5 and 1.4%, respectively. A reduction in creatinine clearance was shown in both the groups over 1 year which then stabilized or improved by 2 years for the endovascular group.
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The renal artery ostia and aortic stent placement
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Placing the most proximal part of the covered device as close
to the renal arteries as possible is associated with good results
to affect a good seal around the upper neck of the aneurysm.
Figure 1 illustrates how close the stent is placed to the renal
arteries in a patient with renovascular disease. The use of
an uncovered suprarenal stent also reduces distal migration
as seen in
Figure 1. Distal migration is a disaster and is the
main factor associated with subsequent aneurysm rupture. It
is clear, therefore, that the renal arteries may be compromised
by stents and by graft material placed unwittingly over the
ostia. This can be minimized by the use of excellent imaging
in high-quality endovascular suites. Occasionally, proximal
migration of a device may occur, especially in a conical neck.
Most of the hooks and barbs are designed to prevent distal migration
and do not prevent proximal migration of the device. One device
with a suprarenal stent has the markers signifying the start
of the material 2–3 mm below the edge, thereby allowing
inexperienced users to deploy the fabric over the lower part
of the renal orifice. The completion angiogram may not show
any compromise, but follow-up computerized tomographic (CT)
scans will show poor renal perfusion, often within 3 months
of insertion. The inadvertent deployment of the device over
both renal arteries can occur if the branches of the coeliac
artery are misinterpreted as renal arteries. However, if the
stent graft is secured with hooks and barbs proximally, these
may damage the aorta with disastrous consequences. Immediate
conversion to open repair may be the only option in this clinical
scenario.
Even with optimum placement of a stent graft, renal malperfusion
may occur after the procedure.
Figure 2A and B show an aortic
stent placed and follow-up CT scans 6 weeks and 1 year after
placement. The angiogram shows that renal artery occlusion has
occurred in the year after aortic stent placement. The deployment
of ostial stents may reperfuse renal arteries that have been
partially compromised by suprarenal stents or graft material.
Figure 4 illustrates how difficult this can be. The balloon
is being deployed through the side of the uncovered part of
an
in situ aortic stent. This is obviously a technically challenging
procedure.
The nephrotoxic nature of the contrast material may contribute
to renal failure at the time of implantation of the endoluminal
devices and during their continued follow-up. There is little
evidence for the use of N-acetylcysteine to prevent this [
11,
12].
However, this problem may be overcome by the use of carbon dioxide
as a contrast material and intravascular ultrasound as an imaging
modality [
13,
14]. Follow-up using duplex ultrasound and plain
abdominal radiography has been shown to be as effective as computed
tomography with contrast [
15].
New devices are being developed which will allow aneurysms with short necks to be treated. These include fenestrated and branched stent grafts [16,17]. Most fenestrated devices require an uncovered stent to be placed within the renal artery orifices to ensure correct alignment. Branched stent grafts will allow the endovascular treatment of suprarenal and thoracoabdominal aneurysms.
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Outcomes with endovascular aortic aneurysm repair
|
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Level I evidence for the use of stent grafts to treat abdominal
aortic aneurysms is sparse. However, the multicentre EVAR trials
were performed in the UK and the 30 day results have been published
for EVAR 1 [
18]. The EVAR 1 trial is a randomized prospective
trial of endovascular compared with open surgical repair in
patients considered fit for surgery. The EVAR 2 trial compares
the best medical treatment with best medical treatment and endovascular
repair in patients considered unfit for open surgery. The DREAM
[
19] trial has reported an operative mortality of 4.6% for open
repair and 1.2% for endovascular repair, although this was not
statistically significant. The trial showed no difference in
the change in renal function pre- and post-intervention between
the two groups. This, however, was only for the pre-operative
and day 2 post-operative values, and not long-term data.
The interesting recent data is that of Azizzadeh et al. [20], who have shown that the estimated glomerular filtration rate (eGFR) is a predictor of mortality in endovascular abdominal aortic aneurysm repair. These authors used the Cockroft–Gault equation and quartile segmentation. The actuarial survival was 61.5% for eGFR 7–45 ml/min vs 85.7% for eGFR of >80 ml/min at 4 years. The effect of renal function on the outcome in arterial surgery is not a lesson lost on vascular surgeons.
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Implications of endovascular aortic aneurysm repair for the nephrologist
|
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These developments are clearly going to impact upon nephrologists.
Up to 50% of infrarenal abdominal aortic aneurysm can now be
treated with the current devices and this percentage will increase
as advances in technology occur. The long-term effect of endoluminal
repair on renal function will be one of great interest. With
open repair, any renal damage will be due to peri-operative
damage. With endoluminal repair, as discussed, the stent position
or aneurysm's size may alter over time. This may alter the relationship
to the renal artery ostium and thus, its patency. Trans-renal
stent placement offers another differential diagnostic problem
in older patients with impaired renal function and an aortic
stent. There still remains the dilemma of whether or not an
individual with renal artery stenosis needs renal stent placement
prior to aortic stent placement. This is technically much easier
than when the aortic stent graft is in place and partially covering
the renal artery ostium. Renal stent placement through the side
of the
in situ aortic stent is a challenging procedure. There
remains no evidence base for this decision. As always, the interaction
between vascular surgeons and nephrologists is stimulating.
Conflict of interest statement. None declared.
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References
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- Hertzer NR, Mascha EJ, Karafa MT, O’Hara PJ, Krajewski LP, Beven EG. Open infrarenal abdominal aortic aneurysm repair: the Cleveland Clinic experience from 1989–1998. J Vasc Surg 2002; 35: 1145–1154[CrossRef][Web of Science][Medline]
- Volodos NL, Karpovitch IP, Troyan VI et al. Clinical experience of the use of self-fixing synthetic prostheses for remote endoprosthetics of the thoracic and the abdominal aorta and iliac arteries through the femoral artery and a intraoperative endoprosthesis for aorta reconstruction. Vasa Suppl 1991; 33: 93–95[Medline]
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- Lau LL, Hakaim HG, Oldenburg WA et al. Effect of suprarenal versus infrarenal aortic endograft fixation on renal function and renal artery patency: a comparative study with immediate follow-up. J Vasc Surg 2003; 37: 1162–1168[CrossRef][Web of Science][Medline]
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- Fishbane S, Durham JH, Marzo K et al. N-acetylcysteine in the prevention of radiocontrast-induced nephropathy. J Am Soc Nephrol 2004; 15: 251–260[Abstract/Free Full Text]
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- Verhoeven ELG, Tielliu IFJ, Prins TR et al. Frequency and outcome of re-interventions after endovascular repair for abdominal aortic aneurysm: a prospective cohort study. Eur J Vasc Endovasc Surg 2004; 28: 357–364[CrossRef][Web of Science][Medline]
- Verhoeven ELG, Tielliu IFJ, Prins TR et al. Treatment of short-necked infrarenal aortic aneurysms with fenestrated stent-grafts: short-term results. Eur J Vasc Endovasc Surg 2004; 27: 477–483[CrossRef][Web of Science][Medline]
- Chuter TAM, Schneider DB, Reilly LM et al. Modular branched stent graft for endovascular repair of aortic arch aneurysm and dissection. J Vasc Surg 2003; 38: 859–863[CrossRef][Web of Science][Medline]
- The EVAR trial participants. Comparison of endovascular aneurysm repair with open repair in patients with abdominal aortic aneurysm (EVAR trial 1), 30-day operative mortality results: randomised controlled trial. Lancet 2004; 364: 843–848[CrossRef][Web of Science][Medline]
- Prinssen M, Verhoeven ELG, Buth J et al. A randomized trial comparing conventional and endovascular repair of abdominal aortic aneurysms. N Eng J M 2004; 351: 1607–1617
- Azizzadeh A, Sanchez LA, Miller CC et al. Glomerular filtration rate is a predictor of mortality after endovascular abdominal aortic aneurysm repair. J Vasc Surg 2006; 43: 14–18[CrossRef][Web of Science][Medline]
Received for publication: 6. 4.06
Accepted in revised form: 9. 4.06
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Introduction
Endovascular aortic aneurysm...
