Endoluminal Treatment of AAA
Endovascular repair of abdominal aortic aneurysms (AAA) is performed at OHSU by a multidisciplinary team, some of whom have 10 years of experience with these devices. The team, comprised of interventional radiologists and vascular surgeons, have a collective experience with over 500 endograft procedures.
repair of infra-renal AAA with stent-grafts is an alternative
to surgical repair. Aortic stent-grafts are available
in 3 basic configurations. [Fig
1] Patients must meet anatomic criteria involving
the proximal and distal attachment sites, angulation
and tortuousity of the aorta and pelvis,
and the presence of calcification and occlusive disease
in the access arteries. The specific requirements vary
for each manufacturer. The majority
of devices are modular in construction; i.e the endograft
is assembled in the patient. The materials used in
construction of endografts are
bio-compatible metals such as nitinol, stainless steel,
and elgiloy, and proven vascular graft materials. Endografts
function by depressurizing
the aneurysm sac. Two critical differences from surgery
are the absence of sutured anastomoses to blood vessels,
and the continued patency of
branch vessels from the sac such as lumbar arteries
and the inferior mesenteric artery. Most patients treated
with current devices receive bifurcated endografts.
In general, only ½ to 2/3rds of patients with AAA amenable to
surgery can be managed with current endografts. Up
to 1/3rd of these patients required pre-implantation
embolization of an internal iliac
or accessory renal artery, or other percutaneous intervention
in order to become anatomically suitable for an endograft.
As many as 30% of patients
who undergo internal iliac artery embolization develop
transient buttock claudication.
|Fig.1 a) Bifurcated extending into
either the common or external iliac arteries. This
is the most common type of endograft. b) Aorto-unilateral
iliac (AUNI) graft with surgical femoral-femoral
bypass. This type is used when the
patient’s anatomy is not suited to a bifurcated graft. c) Tube
graft. This is rarely used due to the lack of adequate
distal landing zones in the aorta below the aneurysm.
(Reproduced with permission from
Kaufman JA, Geller SC, Brewster DC, et al. Endovascular
repair of abdominal aortic aneurysms: current status
and future directions. Am J Roentgenol
The exact technique of endograft placement varies with each device,
but certain commonalities exist. Most important is
careful pre-procedural planning, especially device
selection, as none are retrievable. For most
manufacturers, the diameters of the device at the attachment
sites should be at least 10-15% greater than the artery.
Excellent intra-procedural imaging is mandatory. Precise
localization of critical
such as the renal and internal iliac arteries prevents
inadvertent occlusion by graft overlay. In general,
an aortogram is obtained centered on the
renal arteries, followed by deployment of the proximal
portion of the device. Once this has been accomplished,
the distal portion is deployed
after localization of the internal iliac arteries.
Most modular bifurcated devices require catheterization
of at least on limb, usually from the
opposite common femoral artery, to complete construction
of the endograft. The device delivery systems range
in size from 4 to 8 mm in diameter.
Large diameter introduction systems require surgical
exposure of the common femoral arteries.
Placement of endografts is successful in more than 95% of attempts, provided patients are carefully selected. In approximately 15-30% of patients additional endovascular procedures are necessary to improve the technical and clinical success of the procedure. The major complication rate is less than 5%, with most complications related to the vascular access. Patients usually are discharged home by the 2nd or 3rd post-procedure day.
Continued opacification of the aneurysm sac by contrast
following endograft placement (termed “endoleak”)
is found on CT scans in 30-40% of patients acutely,
and 20-40% during follow-up. [Fig 2] This
finding correlates with sub- or systemic pressures
in the aneurysm sac. The etiology of the majority
of early and late sac perfusion is Type II, although
Types I and III can occur at any time. Type IV perfusion
generally resolves spontaneously within 48 hours
of endograft placement. Many endoleaks can be treated
with percutaneous methods, such as insertion of endograft
extensions for Type I leaks, embolization of branch
vessels or the sac for Type II leaks, insertion of
endograft “patches” for type III leaks.
The most important outcome of endografts is freedom from AAA rupture. Delayed rupture is reported in fewer than 0.1% of patients. Most patients have stabilization or decrease in the volume of the aneurysm sac. However, continued sac growth is seen at least 5% of patients. Shrinkage of the peri-aneurysmal fibrosis after endograft placement has been reported in patients with inflammatory aneurysms.
Plain films as well as CT scans (or some other reproducible imaging
technique) are essential parts of the follow-up of these patients.
Patients must be studied at regular intervals for the remainder of
their lives after endograft placement. As the AAA sac decreases in
volume, the endograft may become distorted, with limb kinking, separation,
and even disengagement from attachment sites. The incidence of complications
is increasing as longer follow-up is accumulated. The future role of
endografts for AAA remains to be determined as these late outcomes become
Link to article: A Northwest First: Aortic Aneurysm Pressure Sensors Implanted (May 4, 2006)