Endoluminal grafting is an exciting new technology that holds the promise of significantly reducing the morbidity and mortality associated with open repair of abdominal aortic aneurysms. From primitive beginnings with untested ideas and homemade prototypes, endografting has become a clinical reality. This article provides an overview of the development of this technology up to the present time.
Dr. Bromley is a senior interventional fellow at the Dotter
Interventional Institute, Oregon Health Sciences University,
The placement of an endoluminal graft under radiological
guidance is the latest advance in the treatment of aneurysmal
disease of the abdominal aorta. Endografting represents a logical
extension of endoan-eurysmorrhaphy, which has been the accepted
surgical therapy for abdominal aortic aneurysms since the 1960s.
In this latter procedure, the aneurysm is exposed surgically and
opened longitudinally after proximal and distal hemostatic control
has been obtained by surgical clamps (figure 1A). A synthetic
fabric tube is then sutured to nondilated segments proximally and
distally from within the aneurysm, and the sac is closed over the
prosthesis (figure 1B and C). By avoiding resection of the aneurysm
sac, aneurysm surgery was simplified significantly and the
complication rate improved.
The technique of endografting strives to further this end by
means of specially designed "endografts," which can be introduced
into the aneurysm lumen from a remote and minimally invasive access
site (typically the common femoral arteries). These devices are
positioned and deployed with radiological guidance. Proximal and
distal fixation are obtained in nonaneurysmal segments by
sutureless endoluminal fixation devices. The aneurysm sac is
excluded from the circulation by a procedure performed from small
groin incisions with minimal blood loss, no exposure of the
aneurysm, and no need for aortic cross clamping.
Since the first radiologically guided, endoluminal repair of an
abdominal aortic aneurysm in a human by Parodi and Palmaz
in 1990, there has been an explosion of academic and commercial
activity in this arena. Far more than arterial occlusive disease,
endografting of aneurysmal disease has propelled the development of
the new field of endovascular therapy. Continued advancement in
this field is best served by cooperative efforts between those with
the advanced training and expertise in the various radiological,
endoluminal, and open surgical techniques necessary for procedural
success and good patient outcome. This article will discuss the
historical development of endografting and the clinical status of
current technology and will also touch on endografting's future
In the beginning there was wire
As a remarkable testament to human ingenuity, endoluminal
approaches to the treatment of aortic aneurysms can be found as far
back as the mid-19th century. The English surgeon Moore, in an
effort to stimulate thrombosis, inserted 75 feet of fine iron wire
into a thoracic aortic aneurysm in 1864. Unfortunately, the patient
died from sepsis a few days later.
Wire placement was first used to treat an aneurysm in the United
States in 1866 by Ranoshoff.
In 1879, the Italian physicians Buressi and Corradi
inserted wire into an aneurysm and attempted to induce coagulation
with an electric current. In the first half of the 20th century
in England, and Blakemore,
in the United States, were proponents of the "wiring" method. These
techniques, sometimes using up to 900 feet of wire,
produced mixed results and remained controversial. In cases of
fusiform infrarenal aneurysms, the intent appeared to be to
"strengthen" the aneurysm while maintaining a flowing channel
through the middle.
In fact, complete thrombosis was felt to be undesirable since it
not infrequently led to fatal gangrene of the lower extremities.
Nonetheless, reports appeared sporadically until the 1970s (figure
It was not until Dubost reported on the successful resection and
in-situ bypass of an abdominal aortic aneurysm in Paris, on March
19, 1951, that the era of surgical cure of abdominal aortic
aneurysms was truly born.
The initial flurry of enthusiasm for this new procedure, however,
was later tempered by the identification of serious late
complications resulting from degeneration of the cadaveric human
aortic allografts (homografts) used to perform the bypass.
The 1950s became a period of intense investigation to identify a
suitable synthetic material that could be handled easily and cut to
length in the operating room, sutured to a blood vessel, and
trusted to withstand the stress of the circulation in the patient
for many years. Many different materials were investigated,
including parachute silk, Vinyon-N, Orlon, Dacron, and Teflon, with
the latter two ultimately proving to be quite suitable for arterial
The availability of commercially produced synthetic grafts allowed
surgical abdominal aortic aneurysm repair to become more widely
applied but did nothing to reduce the severity of the surgery. The
first step in this direction came in the form of an in-situ bypass
without resection, attributed to Creech.
His modification of the original endoaneurysmorrhaphy, described by
Matas in 1902, allowed the bypass graft to be placed within the
aneurysm lumen and ended the need for lengthy and difficult
resection of the aneurysm sac from the retroperitoneum. This
technique has been the standard since that time.
From today's perspective, it seems a logical next step in the
progression of this therapy to introduce a graft into the lumen of
the aneurysm from a remote access site without the need for
exposing and opening the aneurysm. This moment arrived in September
of 1990 when Parodi and associates
performed, in Argentina, the first successful transfemoral
endoluminal grafting of an abdominal aortic aneurysm in a human.
The crude but innovative device used in this procedure was born of
a melding of synthetic graft with catheter, stent, and imaging
technology pioneered by interventional radiologists.
In 1964, Dotter and Judkins introduced the concept of
catheter-mediated minimally invasive therapy for arterial disease
when they reported a new technique for treating arterial stenoses
with dilating catheters.
Searching for a means to improve on the results of his new
"transluminal catheter dilatation" procedure, Dotter conducted
experiments using tubular endovascular prostheses in the femoral
arteries of dogs. Although all of the devices made of impervious
plastic tubing resulted in thrombosis, he had encouraging results
with coilspring prostheses made of stainless steel wire (figure 3),
and introduced the concept of percutaneously placed endarterial
tube grafts in 1969.
Little activity occurred in this area for nearly 15 years when both
Dotter and colleagues
in Oregon, and Cragg et al
in Minnesota, published simultaneous reports on nitinol-based
coilspring grafts, again in a dog model. Nitinol is a special alloy
of nickel and titanium that is highly kink-resistant and possesses
the characteristic of thermal shape memory. Exploiting these
properties, these investigators were able to pass nitinol wire
through the lumen of a catheter and have the wire shift to a
coiled-tube state in the arterial lumen by exposure to body
temperature or by flushing the delivery catheter with heated saline
(60° C). The ability to pass the device as a straightened form (in
the catheter lumen) and have it revert to a coiled tube of
predetermined diameter (in the arterial lumen) meant that the
diameter of the artery treated was no longer restricted by the size
of the introducer catheter, as was the case in 1969.
The following year, Maass and coworkers
in Switzerland reported on a series of experiments they had begun
in the early 1980s using a similar spiral-spring vascular
endoprosthesis made of stainless steel. These devices became known
as stents in a somewhat abstruse reference to Charles Stent, an
English dentist who in the 19th century devised a splint to
stabilize skin grafts.
Numerous publications followed throughout the 1980s as a variety of
self-expanding and balloon-expanded metal endoluminal prostheses
were developed and utilized in the treatment of arterial occlusive
disease. In 1984, percutaneously introduced coiled wire experienced
a brief reincarnation as a potential therapy for abdominal aortic
aneurysms. That year, Cragg and associates
published further work on their nitinol coil grafts. In an article
entitled, "Percutaneous Arterial Grafting," they reported the first
percutaneous treatment of an experimental abdominal aortic aneurysm
with a stent composed of a tightly wound tubular coil of nitinol
It was not long before wire and fabric were united and the
stent-graft was born.
The stent-graft concept
Who was truly the first to conceptualize a stent-graft for the
treatment of an aneurysm may never be known. The archives of the
U.S. Patent Office contain a document entitled, "Method For
Performing Aneurysm Repair" that describes a device created by M.
Hasan Choudhury, which was filed in 1977 and patented in 1979
Choudhury's device was to be composed of a single tube of surgical
graft material, such as Dacron. It would be introduced into the
body in a collapsed form on a catheter placed via a peripheral
artery, such as the common femoral artery, and maneuvered into
position to span the normal arterial segments proximal and distal
to the aneurysm. This would be performed under fluoroscopic
guidance. The catheter would contain channels to inject
radiographic contrast. A guidewire was not mentioned. At the
proximal and distal ends, "convoluted expansion rings" containing a
"plurality of radially spaced anchoring pins" provided a means for
attachment. Choudhury felt that "once in place, hemodynamic
pressure [would] assure a continued fluid tight seal between the
graft and the healthy vessel wall."
Juan Parodi, meanwhile, was a resident in vascular surgery at
the Cleveland Clinic under Alfred Humpheries and Edwin Beven. In a
retrospective article published in 1997, Parodi recalled fondly
"the expression on Ed Beven's face when I told him that I foresaw a
day when patients with aneurysms could be treated under local
anaesthesia in the outpatient department."
Parodi apparently conducted some experiments in 1979 on a tubular
polyester device with expandable stainless steel wire rings at the
ends, using dogs, but abandoned the project because of
disappointing initial results.
In 1986, Balko and associates
of New York were apparently first to describe in a scientific paper
a device having the characteristics of a stent-graft for the
treatment of an abdominal aortic aneurysm. These investigators
created artificial aneurysms in the abdominal aortas of sheep using
large Dacron patches and then several weeks later inserted their
prostheses. These were composed of a constrainable wire metal
framework (resembling Gianturco Z-stents) with a polyurethane
coating. Cessation of sac pulsation and absence of bleeding when
the aneurysm wall was lacerated purposefully determined successful
acute exclusion of the aneurysm. Long-term follow-up was not
obtained. The devices were inserted from femoral artery cutdowns,
but the lack of fluoroscopic equipment necessitated they be
positioned by direct palpation of the aneurysm neck during
laparotomy. In their discussion, the authors mentioned the
potential for collaboration between angiographers and vascular
surgeons in the possible clinical application of such technology.
Ultimately, radiologically guided aortic stent-graft placements
were reported in experimental animals with very encouraging results
on long-term follow-up.
At about the same time, Palmaz was reporting the results of his
newly designed balloon-expandable stent. Parodi met Palmaz in 1988
and immediately realized that this stent was the component he
needed to achieve anchoring and sealing of an endoluminal graft.
Their collaboration resulted in a series of 62 canine experiments
in Buenos Aires and culminated in the implantation of a device in a
patient on September 7, 1990.
In another parallel development, Harrison Lazarus, a vascular
surgeon from Utah, had begun working on an endograft for abdominal
aortic aneurysms during the mid-1980s.
His early concept would ultimately evolve into a Food and Drug
Administration (FDA)-approved device (discussed in the following
Early devices were constructed from a piece of straight surgical
tube graft, like Dacron, and modified by the addition of some form
of endovascular attachment system. Lazarus experimented with and
patented a device having an attachment system composed only of
staples, at the proximal end, that would be driven into the vessel
wall at the attachment site by a balloon device built into the
Stent technology was progressing rapidly during this period,
however, and soon all devices incorporated some form of stent into
the attachment sites. Lazarus's attachment device evolved into a
self-expanding metal system similar in design to Gianturco Z-stents
but with large anchors derived from the initial staple system.
Parodi's group initially constructed devices with large balloon
expandable stents for proximal attachment. The surgical approach
was to modify the graft so that it could be attached from within
the vessel. Interestingly, neither of these prototypes had a distal
attachment mechanism. In fact, the first three patients in the
clinical series that Parodi reported on in 1991 lacked any form of
distal attachment device.
Meanwhile Gianturco's group was building Z-stent devices long
enough to span the infrarenal aorta and then covering the stents
with graft material (figure 6).
These stents came with or without wire barbs. Three separate design
dichotomies were apparent from the outset and have persisted into
current devices. One involves the method of obtaining device
attachment within the vessel--radial force producing friction
versus positive attachment with hooks or barbs. Another is the
issue of structural support over the length of the graft material
with stents. Finally there is the issue of utilizing stents that
are self-expanding or balloon-expanded. The superiority of one
approach over the other has not yet been resolved. Furthermore, it
quickly became apparent during the initial clinical application of
this technology that few patients could be treated successfully
with a straight tubular graft.
New devices, new challenges
By 1995, Parodi
was reporting on a series of 50 patients in whom he had performed
endograft procedures and was being referred to as the father of
transfemoral abdominal aortic endografting.
In Sydney, Australia, White et al
were accumulating a similar quantity of patients. By February of
1993, the EVT device (Endovascular Therapeutics, Inc., Menlo Park,
CA), derived from Lazarus's work, had already entered Phase I FDA
clinical trials in the United States, and Moore
from UCLA was reporting on the first 10 patients in 1994. Although
Parodi was able to implant a significant number of straight tubular
devices in Argentina, the experience in the United States indicated
that <15% of patients with abdominal aortic aneurysms would be
suitable for such grafts.
Parodi's approach to patients without a suitable distal neck was to
extend a tapered aortomonoiliac device into one iliac, embolize the
contralateral side, and perform a femoral-to-femoral bypass.
The Sydney team also utilized this technique.
The impetus for a completely endovascular solution was strong,
however, and as early as 1993, Chuter
had constructed a bifurcated device and delivery system and used it
successfully in dogs. He then made the first report of successful
use of his device in a human in February 1994.
This was followed, in September, by a report of 5 patients
successfully treated at the University Hospital in Nottingham,
United Kingdom, using Chuter's bifurcated device.
The Sydney group published the preliminary results of their
bifurcated device in 1994 as well,
and EVT introduced a bifurcated device late that same year.
Interestingly, the 5 patients in the Nottingham series represented
only 17% of the 29 consecutive patients screened for possible
As experience was gained, a problem list of challenges to be
overcome in the development of new devices was developing. For all
devices, the femoral and iliac arteries represented potential
obstacles to the introduction of the bulky delivery systems either
from atherosclerotic stenoses or from severe tortuosity. The latter
could sometimes be overcome by stiff guidewires or by surgical
traction on the arteries. Angioplasty of focal atherosclerotic
lesions could be performed, but was of little help in diffuse
disease or in patients with intrinsically small arteries (often the
case in women). Parodi
developed the approach of anastomosing a graft to the iliac
arteries above the restrictive segment to provide a conduit for
device delivery, but this approach is somewhat contrary to the
minimally invasive theme of the endovascular paradigm. In 1994, the
sheath used to introduce the EVT device was 28F and the Sydney
device was 24F. The devices themselves needed to become smaller and
According to the Sydney group, in general, patients requiring
bifurcated grafts seemed to have larger and more complex aneurysms
than those suitable for straight-tube grafts.
Early in their experience, they deployed both limbs of a bifurcated
device into the ipsilateral iliac artery on two separate occasions,
necessitating conversion to open procedures in both patients.
Although the details behind the "technical errors" are not
discussed in their report, these mishaps highlight the need for
accurate measurements of parameters never before considered in open
surgery. Custom fitting of devices to individual patients required
detailed preoperative analysis of computed tomography (CT) and
angiographic data. Devices made too short would need to be rescued
by open surgery or modular extension components, and devices made
too long could result in confinement of the contralateral graft
limb (as described above) or could cover and occlude internal iliac
Continued perfusion or late "reperfusion" of the aneurysm sac
were also recognized quickly and led to the characterization of a
new entity, the endoleak. This is defined as the persistence of
blood flow outside the lumen of the endoluminal graft but within
the aneurysm sac.
A variety of endoleaks can develop and have been classified by a
fairly uniformly accepted scheme (Table 1). However, continued
expansion of aneurysmal sacs after endografting in the absence of
identifiable endoleaks has led to the development of an additional
Whether this is a separate notion or an additional form of endoleak
has led to some controversy over its definition and the endoleak
Although most authorities seem to agree that Type I and Type III
endoleaks should be addressed by further endovascular procedures or
conversion to open surgery, the question of what to do with branch
perfusion leaks (Type II endoleaks) remains controversial.
The identification of hemodynamic pressures in these reperfusion
circuits, comparable to those in the systemic circulation, has
raised the level of concern, particularly among radiologists.
By early 1995, investigators began reporting the first instances
of device deterioration. Hook fractures, and later frame breaks,
were identified in follow-up of the EVT device resulting in a halt
to enrollment in the FDA trial.
The attachment system and hook configuration were redesigned, and
the second generation of EVT grafts was subsequently introduced at
the end of 1995.
No new fractures have been reported since the design change, but
other devices have developed similar metal fatigue problems, as
well as disintegration of sutures and fabric erosions.
Device migrations have developed particularly in short angulated
necks as well as late disconnections of modular components.
Two cases have been described in which patient positioning during
subsequent (and unrelated) surgical procedures may have contributed
to separation of modular components.
Furthermore, longitudinal shrinkage of the aneurysm after
successful exclusion may contribute to detrimental structural
distortion of the grafts.
Along a similar line, studies have demonstrated continued
dilation of the infrarenal neck in some patients following
endograft placement, raising the concern that Type I endoleaks
could develop, possibly years after a graft has been implanted.
Evidence has also appeared that little tissue incorporation occurs
at the attachment site with these devices in humans, despite
evidence to the contrary in experimental animals.
Device migrations and dilating necks have fostered the use of
positive fixation devices and suprarenal fixation elements in newer
generation devices. Their value, however, remains theoretical until
long-term follow-up data on their use becomes available. So it
appears that, in the foreseeable future, patients implanted with
abdominal aortic endografts will be subjected to a lifetime of
Another unique set of challenges that has arisen out of this
evolving field includes the questions of who should perform these
procedures and where they should be performed. Since the size of
the delivery system required to implant an aortic endograft
necessitates surgical exposure at the access site, surgical skills
have been obligatory from the onset and remain so. The potential
for completely percutaneous systems, however, is on the horizon
(see below) and will no doubt significantly alter the playing field
in the future. Although some vascular surgeons choose to ignore the
unique skills and experience of their colleagues in interventional
radiology and set out to rediscover basic catheter and wire
techniques on their own,
this cannot be of any benefit to the patient or the field of
An interventional radiologist would not be surprised to hear that
surgeons implanting the large and stiff early EVT device in a
tortuous aneurysm without an over-the-wire technique deployed a
device into the thrombus necessitating open repair.
Collaborative teams of experts in vascular surgical and endoluminal
techniques, such as the archetypal Miami Vascular Institute, are to
be applauded. This cooperative approach has also been fostered at
the Dotter Interventional Institute where we evaluate endograft
candidates and perform endograft procedures in conjunction with the
vascular surgeons (figure 7).
Nearly 50 years ago, pioneers of aortic synthetic graft surgery
employed a seamstress to construct a suitable fabric tube for a
patient after the abdomen had been opened and measurements obtained
in the operating room.
The graft was then autoclaved and sewn into place. Similarly, the
first stent-grafts were handmade for each patient out of available
materials, although modern cross-sectional imaging techniques
obviated the need to open the patient's abdomen. As was the case
with synthetic grafts, it was not long before dedicated endografts
for the repair of abdominal aortic aneurysms were being
manufactured commercially. In the United States, the marketing of
these devices is subject to regulations enforced by the FDA.
Endografts are included in the regulations for Class III devices
and are subject to a premarket approval system that requires
clinical testing to establish safety and efficacy prior to
marketing. Two bifurcated devices have completed this process and
are marketed in the United States for the treatment of abdominal
aortic aneurysms. These are the Ancure endografting system
(previously the EVT graft; Guidant Cardiac and Medical Division,
Menlo Park, CA) and the Aneurx stent-graft (Medtronic Inc.,
Minneapolis, MN). Both of these devices received FDA approval in
September 1999. There are at least nine other devices currently in
various stages of premarket development. Table 2 summarizes many of
the features of these devices.
Despite that fact that both contain self-expanding stent
components, the Ancure (figure 8) and Aneurx (figure 9) devices are
products of very different design philosophies. The unibody design
of Ancure mimics that of a standard surgical graft, while the
Aneurx design is modular. The modular design permits greater
versatility in matching a patient's anatomy, as the device is
constructed inside the patient, but the junctions between
individual parts provide potential places for early and late graft
failures (see the discussion of endoleaks above). The stent
skeleton provides support against compression over the entire
length of the Aneurx device but reduces its mechanical flexibility.
Conversely, although the Ancure device boasts greater flexibility,
particularly in angulated necks, the unsupported iliac limbs have
been subject to a greater number of thromboses. This has been
improved through the liberal use of Wallstents (Boston Scientific,
Boston, MA) by many interventionalists.
Finally, the self-expanding stents at the ends of the Ancure device
provide a means to initiate deployment of the anchoring pins, but
otherwise do little to hold the device in place. Once the graft is
released from the delivery catheter and the pins have contacted the
wall, they are driven into place by the operator with a balloon.
The pins provide the primary means of securing the graft. In
contrast, the Aneurx device relies entirely on the force of
friction between the self-expanding stents and the vessel wall.
There is only one other unibody design among the devices listed
in Table 2. The PowerLink System (Endologix Inc., Irvine, CA) is a
single-piece bifurcated graft created from polytetrafluoroethylene
(PTFE) with an endoskeleton of self-expanding stainless steel wire
(figure 10). The main body stent is composed of a single wire,
which is purported to eliminate any potential for stent separation.
The company states that the long body, reaching to the aortic
bifurcation, will reduce the chances of late migration. Cuffs are
available to extend the device proximally and distally to
accommodate challenging anatomy. Experience with the device is
limited in the United States, but Phase II FDA Trials have been
ongoing since July 2000. The device is marketed in Europe and South
All of the other devices in Table 2 are modular designs and are
fully supported by stents or stent-like elements. The Excluder
(W.L. Gore and Associates, Flagstaff, AZ), Talent (Medtronic World
Medical, Sunrise, FL), and Zenith (Cook Inc., Bloomington, IN) have
all completed Phase II FDA trials in the United States. The aortic
segment of the Talent device is available in diameters up to 36 mm.
This is the largest diameter of any of the devices. The Zenith
device derives a significant amount of its design from the
extensive experience developed in Perth, Australia. It is notable
for the high suprarenal attachment combined with positive fixation
elements present on all versions of the devices (figure 11). The
Zenith, Talent, and Ancure devices are also available in
aortomonoiliac configurations. The Lifepath AAA graft system
(Baxter Edwards Lifesciences LLC, Irvine, CA) is the only device on
the list to rely on balloon-expandable stent elements (which the
company refers to as "wireforms") that are present in the upper
segment of the bifurcate body and throughout the other modular
components. Only the limbs of the bifurcate body have
self-expanding stents. The wireforms are also woven into the graft
fabric to remove the need for sutures. Wireform fractures
identified during long-term follow-up led to a halt of Phase II
trials with this device in April 2000. These fatigue issues have
been addressed, and the company anticipates restarting clinical
trials before 2002. The Excluder also avoids sutures and suture
holes by attaching the nitinol to the PTFE with polyethylene tape.
Of the devices that have completed Phase II trials, the Excluder
currently has the lowest profile at 18F.
What does the future hold?
In 1999, the Health Services Research and Development Service of
the Veterans Health Administration's Office of Research and
Development released a 22-page report assessing the effectiveness
of endovascularly placed grafts for the repair of abdominal aortic
This group reviewed the data available up to May 1998 to address
issues such as the establishment of VA referral centers for
minimally invasive vascular surgery procedures. Specifically, they
wished to address the lower morbidity, mortality, and/or healthcare
costs offered by endovascular treatments. Their report concluded
the "currently available literature represents studies that are
methodologically inadequate to answer the questions addressed in
this report." The only proven benefits of endoluminal grafting for
abdominal aortic aneurysms, to date, are less blood loss and a
shorter hospital stay.
The risk of aneurysm rupture has not yet been eliminated since late
ruptures have occurred during the follow-up of both of the
While efforts will undoubtedly continue to make technical advances
like fully percutaneous abdominal aortic endografting a reality
(Figure 12) and to extend the range of patients who can be treated,
carefully controlled trials are needed to prove this technology
alongside the gold-standard open procedure. Attention must also be
directed at better defining the need for "sac management" since it
is becoming clear that, in many cases, the endograft itself is
insufficient to exclude the aneurysmal sac from the systemic
circulation (see the discussion of endoleaks in the previous
Techniques for the treatment of abdominal aortic aneurysms have
evolved dramatically from the first primitive attempts to coil the
lumen with wire in the 19th century. The mid-20th century saw the
historic first open resection and in-situ grafting of an abdominal
aortic aneurysm. Now, at the beginning of the 21st century,
transfemoral endoluminal grafting has become a reality. Although
the technology for endoluminal repair has developed through the
contributions of both vascular surgeons and interventional
radiologists, these groups have often worked in isolation. Since
the shared expertise of these groups is greater than the sum of
their separate parts, the evolution of the field of endovascular
therapy and the future treatment of patients will be best served by
cooperation. The first decade of the 21st century provides an
exciting opportunity for these two specialties to prove the
benefits of this promising technique. *