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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

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Example of an Abdominal Aortic Stent Graft
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."

Reported by Burt Cohen, April 11, 2010