Stent Grafts for Minimally
Invasive Aortic Aneurysm Repair: Two Studies Published in New England
Journal of
Medicine EVAR I -- No Difference in
Mortality between Endovascular and Open Surgical Repair at 5-10
Years;
EVAR II -- Endovascular
Procedure Shows Significant Reduction in Aneurysm-Related Mortality
for Patients Ineligible for
Open Surgery
Example of an Abdominal
Aortic Stent
Graft
(photo
courtesy Medtronic)
April 11, 2010 --
Two important trials that studied the long-term outcomes of the endovascular
repair of aortic aneurysms using stent grafts were published online
first today by The
New England Journal of Medicine to coincide with a presentation
at the Charing
Cross International Symposium in London.
The studies were conducted by the investigators of the United Kingdom
Endovascular Aneurysm Repair (EVAR) trial and they give us one of the
first glimpses of the long-term safety and efficacy of a minimally invasive
procedure first performed two decades ago by Argentinean surgeon Juan
Parodi, MD.
Whether or not the results of these two studies
are a "plus" for the use of stent grafts compared to open surgery
for the repair of aortic aneurysms depends upon one's perspective.
The first endovascular repair was done only 20 years ago, whereas
the surgical technique has been around three times that long.
Historical Perspective of Aortic Aneurysm Repair
An aortic
aneurysm occurs at a weakened segment of the aorta, the body's main artery.
Due
the the pressure of the
blood flow, the weakened vessel wall begins expanding and ultimately
over time may rupture,
fatal 80% of the time. It is estimated that 15,000 people die annually
in the U.S. from a ruptured aortic aneurysm. The surgical repair of an aortic
aneurysm was first
described in 1951, and it required a significant
and traumatic "open" surgical
procedure, due to the location of the aorta which is underneath
many other anatomic structures and organs.
The aorta would be isolated, the aneurysmal sack often excised,
and
an artificial
graft sewn
into place. One of the problems with this procedure was that many
patients suffering from aortic aneurysms are elderly, often with
co-morbidities that
made such an invasive open surgical procedure risky, if not impossible.
In the 1990s,
the concept of repairing these aneurysms from the inside
out became a reality, due to the advancements of stent technology
and the imagination of pioneering surgeons, radiologists
and cardiologists. Argentinean surgeon Dr. Juan Parodi collaborated
with his
fellow countryman Dr. Julio Palmaz (co-inventor of the Palmaz-Schatz
coronary stent)
who was at the University of Texas Health Science Center
in San Antonio, and ultimately developed the first successful
AAA
endograft
device. (See
video clip from Angioplasty.Org's documentary,
"Vascular Pioneers: Evolution of a Specialty --
you can also buy
the DVD online.)
Parodi utilized
the concept of the body's
circulation
as
a "highway" for
the delivery of therapy (first used in angioplasty to open
blocked
arteries
with a balloon). He threaded his stent graft into the body
in much the same way as an angioplasty, through the femoral
artery in the leg
and then up into the aorta. The stent graft was expanded
inside of the aneurysmal segment, providing a new "pipe"
for the blood
to flow through.
The First
Endovascular AAA Repair, from the documentary,
"Vascular Pioneers: Evolution of a Specialty" (6:22)
Results of EVAR I and II
The first study (EVAR I) compared endovascular repair with the "gold standard" of
open surgical repair in patients with large (> 5.5cm) abdominal aortic
aneurysms. EVAR II looked only at patients who were judged ineligible for
the open surgical procedure
(too sick or elderly
to withstand
a major operation) and compared
endovascular repair to doing nothing.
In EVAR I, the investigators enrolled 1,252
patients at 37 hospitals
in
the
United
Kingdom
during 1999-2004,
randomizing
them to
either
procedure.
These patients had large aneurysms of the abdominal aorta
and were followed until 2009, so the follow-up period was between five and
ten years. The early results favored the stent graft approach: 30-day
operative mortality was more than double in the surgical cohort: 4.3% in
the open-repair group vs. 1.8% in the endovascular-repair group -- not
a surprise,
since open surgery
is
a
riskier
procedure. This early benefit, however, disappeared over the long term and
at the end of the study, five to ten years out, the difference in the death
rate from aneurysm rupture, as well as from all causes (including non-cardiac),
was insignificant between the two procedures. Additionally, endovascular
repair was associated with increased rates of graft-related complications
and reinterventions and was more costly.
When interpreting these results, it is important to take a few
facts into consideration. When the EVAR study enrollment was begun,
the endovascular approach was less than a decade old. The devices
used were first generation and were found subsequently to have
a number of shortcomings -- issues that have been addressed by
a whole new generation of stent grafts. Moreover, with operator
experience of 20 years, the technique itself has improved. Nevertheless,
when endovascular stent graft repair was first described, the surgical
community looked upon it with extreme skepticism. The fact that
this major study has shown the mortality outcomes to be equivalent
to the "gold standard" of surgery, even with the handicap of first
generation equipment and technique, is a milestone in the story
of minimally invasive treatment.
The EVAR II study is particularly interesting, since Dr. Parodi
invented the endovascular technique specifically to address a
patient population too sick for surgery. 404 patients were
enrolled in this trial, with 197 randomized for endografts and
207 to no intervention. The endovascular approach certainly had
an impact in preventing death from a burst aneurysm: at the end
of the trial there were more than twice as many deaths in the
cohort
that
had
no intervention. But there was no difference in all-cause mortality.
As was the case in EVAR I, endovascular repair was associated with
increased
rates of graft-related
complications and reinterventions and was more costly.
However, the results
of EVAR II need to be parsed carefully. The median age of patients
in EVAR II was 77 years old and a number of patients died before
the end of the study, five to ten years later. Also 41% of the
deaths in the endovascular group were
from respiratory illness
or lung
cancer,
one of the
major reasons why a patient would be considered ineligible for
open surgery to begin with. Most interestingly, 34% of the
patients randomized to no intervention crossed-over to the endovascular
repair group during the trial period when it became clear that
their aneurysm was at risk of bursting, which the authors noted,
resulted
in a
"loss
of equipoise."
All in all, these two studies show that the use of a catheter-based
procedure using stent grafts is a viable option certainly for patients
in whom surgery is not possible -- as for whether it should be
the preferred treatment over open, as Dr. Takao Ohki told Angioplasty.Org,
"If you give patients the choice of surgery or no surgery, they
will pick no surgery every time."