AAA Stent Grafts: Current Developments
It has been just over 10 years since Dr. Juan Parodi performed a successful endoluminal graft (ELG) exclusion of an abdominal aortic aneurysm (AAA) in Buenos Aires, Argentina using a customized tube graft made of Dacron and a Palmaz-type stent on the cephalad end. While Dr. Parodi's procedure was the first recorded endovascular AAA surgery of its kind, the very first aneurysm exclusion was actually done in Russia a number of years before. Certainly though, Dr. Parodi deserves credit for initiating important clinical study of ELGs and has made a number of contributions that have advanced the technology considerably in the last decade.
Indeed, it was Dr. Parodi's early work that demonstrated straight tube grafts without distal stent fixation failed uniformly. When he went on to apply a distal stent with a straight tube graft, the results were considerably more favorable. Unfortunately, as he and other investigators soon discovered, probably fewer than 10% of aneurysms can be successfully treated using the straight tube prosthesis. The majority of aneurysms require interventional treatment involving the aortic bifurcation, and for that reason, most investigators and corporate sponsors are concentrating on developing bifurcation devices.
The first commercially available bifurcated ELG was the Mintec device, which was produced in a rather crude fashion in the Bahamas. This technology was eventually transferred to Europe, where Mintec sales began. Boston Scientific Corporation subsequently purchased the Mintec graft, design changes were made, and the device was reintroduced in Europe under the name Stentor, and later as Vanguard.
In the U.S., investigational device exemptions (IDEs) were necessary before clinical assessment of devices could begin. The first two commercial products approved in the U.S. were not Vanguard products, but the Ancure device by Guidant (Menlo Park, California) and the AneuRx device by Medtronic (Sunnyvale, California). These two companies took their products to the FDA (Food and Drug Administration) panel on the same day, and both received approval in September 1999. At present, the products have had worldwide sales of over 10,000 grafts each. Another device, the Talent graft by World Medical/Medtronic (Sunrise, Florida), actually has the largest number of implantations worldwide (~ 20,000 at present). Other companies, such as Cook (Zenith graft, Bloomington, Indiana), Endologix (Endologix graft, Irvine, California), Edwards (Lifepath graft, Irvine, California), WL Gore (Excluder graft, Flagstaff, Arizona), and Cordis Endovascular (Warren, New Jersey) all have products in clinical trials; most of these grafts have already received a CE mark (European Commission approval) and are being sold outside the U.S.
While we have yet to demonstrate long-term success with ELGs for treatment of AAAs, a growing number of manufacturers and clinicians are advancing the technology worldwide. As experience has been gained, a variety of difficulties have been encountered. Fabric erosion, fractures of stents and grafts, perforations, and actual ruptures of grafts resulting in death have been reported. The current data, which are being collected by EUROSTAR, generally reflect early Stentor implants. This product was removed from the market because of a variety of problems seen on implantation and the high incidence of adverse clinical events in follow-up. The AneuRx graft (Medtronic), one of the two ELGs available in the U.S., has also been associated with adverse events -- in particular with AAA rupture. At least 10 ruptures have been reported; most (n = 6) were associated with phase I devices, which were a stiff, bifurcated design. Additional cases of aneurysm rupture, although unpublished, have been reported to the manufacturer as well.
Such difficulties have placed ELG technology in a gray light. Early enthusiasm has been tempered, and some investigators who, as recently as three years ago, were advocating the use of the devices in all patients are now much more reluctant to suggest them in younger, asymptomatic patients. This change in philosophy accompanies the universal opinion that surveillance following implantation of the ELG is mandatory. Unlike the surgical patient, in whom the follow-up after resection and graft replacement is minimal, those who receive ELGs require much closer long-term surveillance. Indeed, a number of adverse events have occurred as late as two years following device implantation.
The advantages and disadvantages of current ELG configurations are being debated from continent to continent -- a discussion that is likely to continue for a number of years -- and we have yet to answer questions about the usefulness of suprarenal fixation of ELGs. As we consider treating patients with ELGs, we must continue to optimize our selection criteria, examine success rates with available devices, study the problem of endoleaks (a leading complication), and assess outcomes from an economic and quality-of-life perspective.
Introduction
It has been just over 10 years since Dr. Juan Parodi performed a successful endoluminal graft (ELG) exclusion of an abdominal aortic aneurysm (AAA) in Buenos Aires, Argentina using a customized tube graft made of Dacron and a Palmaz-type stent on the cephalad end. While Dr. Parodi's procedure was the first recorded endovascular AAA surgery of its kind, the very first aneurysm exclusion was actually done in Russia a number of years before. Certainly though, Dr. Parodi deserves credit for initiating important clinical study of ELGs and has made a number of contributions that have advanced the technology considerably in the last decade.
Indeed, it was Dr. Parodi's early work that demonstrated straight tube grafts without distal stent fixation failed uniformly. When he went on to apply a distal stent with a straight tube graft, the results were considerably more favorable. Unfortunately, as he and other investigators soon discovered, probably fewer than 10% of aneurysms can be successfully treated using the straight tube prosthesis. The majority of aneurysms require interventional treatment involving the aortic bifurcation, and for that reason, most investigators and corporate sponsors are concentrating on developing bifurcation devices.
The first commercially available bifurcated ELG was the Mintec device, which was produced in a rather crude fashion in the Bahamas. This technology was eventually transferred to Europe, where Mintec sales began. Boston Scientific Corporation subsequently purchased the Mintec graft, design changes were made, and the device was reintroduced in Europe under the name Stentor, and later as Vanguard.
In the U.S., investigational device exemptions (IDEs) were necessary before clinical assessment of devices could begin. The first two commercial products approved in the U.S. were not Vanguard products, but the Ancure device by Guidant (Menlo Park, California) and the AneuRx device by Medtronic (Sunnyvale, California). These two companies took their products to the FDA (Food and Drug Administration) panel on the same day, and both received approval in September 1999. At present, the products have had worldwide sales of over 10,000 grafts each. Another device, the Talent graft by World Medical/Medtronic (Sunrise, Florida), actually has the largest number of implantations worldwide (~ 20,000 at present). Other companies, such as Cook (Zenith graft, Bloomington, Indiana), Endologix (Endologix graft, Irvine, California), Edwards (Lifepath graft, Irvine, California), WL Gore (Excluder graft, Flagstaff, Arizona), and Cordis Endovascular (Warren, New Jersey) all have products in clinical trials; most of these grafts have already received a CE mark (European Commission approval) and are being sold outside the U.S.
While we have yet to demonstrate long-term success with ELGs for treatment of AAAs, a growing number of manufacturers and clinicians are advancing the technology worldwide. As experience has been gained, a variety of difficulties have been encountered. Fabric erosion, fractures of stents and grafts, perforations, and actual ruptures of grafts resulting in death have been reported. The current data, which are being collected by EUROSTAR, generally reflect early Stentor implants. This product was removed from the market because of a variety of problems seen on implantation and the high incidence of adverse clinical events in follow-up. The AneuRx graft (Medtronic), one of the two ELGs available in the U.S., has also been associated with adverse events -- in particular with AAA rupture. At least 10 ruptures have been reported; most (n = 6) were associated with phase I devices, which were a stiff, bifurcated design. Additional cases of aneurysm rupture, although unpublished, have been reported to the manufacturer as well.
Such difficulties have placed ELG technology in a gray light. Early enthusiasm has been tempered, and some investigators who, as recently as three years ago, were advocating the use of the devices in all patients are now much more reluctant to suggest them in younger, asymptomatic patients. This change in philosophy accompanies the universal opinion that surveillance following implantation of the ELG is mandatory. Unlike the surgical patient, in whom the follow-up after resection and graft replacement is minimal, those who receive ELGs require much closer long-term surveillance. Indeed, a number of adverse events have occurred as late as two years following device implantation.
The advantages and disadvantages of current ELG configurations are being debated from continent to continent -- a discussion that is likely to continue for a number of years -- and we have yet to answer questions about the usefulness of suprarenal fixation of ELGs. As we consider treating patients with ELGs, we must continue to optimize our selection criteria, examine success rates with available devices, study the problem of endoleaks (a leading complication), and assess outcomes from an economic and quality-of-life perspective.
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