Advertisement
Advertisement
February 2011 Supplement
A Practical Look at EVAR Fixation
Ross Milner, MD, discusses the properties of fixation for endovascular abdominal aortic stent grafts, including their strengths and weaknesses and how the technology has evolved.
What are the properties of fixation for
endovascular aneurysm repair (EVAR)
devices, and how do they relate to sealing?
Dr. Milner: Fixation is designed to prevent distal migration
of an endograft and can be accomplished by passive
and active mechanisms. Generally speaking, passive fixation
is provided via the radial force of the endograft,
whereas active fixation is provided by such mechanisms as
barbs and hooks, etc. The difference between fixation and
sealing is commonly misunderstood. Fixation relates to
migration but does not directly relate to sealing, which is
accomplished via radial force in some approved devices.
In the case of the EXCLUDER Device (W. L. Gore &
Associates, Flagstaff, AZ), sealing is accomplished with
both radial force and a sealant ring at the proximal end of
the device, which is very useful in causing the device to
stick to the inner wall of the aorta. The only correlation
that exists between fixation and sealing is that poor fixation
can result in migration of a device, which would
then obviously affect sealing, but there is no direct correlation
between the fixation properties of the various
endografts and sealing.
How would you summarize the milestones
in the evolution of fixation for EVAR
devices from the first uses of the procedure
through the current generations of
devices?
Dr. Milner: The first two devices approved by the US
Food and Drug Administration, Ancure (Abbott Vascular,
Santa Clara, CA, formerly Guidant Corporation) and
AneuRx (Medtronic, Inc., Minneapolis, MN), accomplished
fixation by different means. The Ancure had
active fixation with hooks, whereas the AneuRx relied on
passive fixation alone. Both devices encountered difficulties.
The Ancure device had delivery system malfunctions1,2
but excellent prevention of migration.3 The
AneuRx device struggled with distal migration.4 This is
especially true when treating challenging aortic neck
anatomy.4
The next generation of devices included the Zenith device (Cook Medical, Bloomington, IN), which uses suprarenal fixation with barbs, the EXCLUDER Device, which uses infrarenal fixation with barbs, and the Powerlink device (Endologix, Inc., Irvine, CA) uses what they like to call “anatomical fixation” because the device is designed to sit on the iliac bifurcation. The Talent endograft (Medtronic, Inc.) is unique in that it uses passive suprarenal fixation.
There are currently no other endografts being marketed within the United States. One of the investigational devices, the Aptus endograft (Aptus Endosystems, Inc., Sunnyvale, CA), used staples to achieve fixation. The device had some issues regarding limb thrombosis, but that was not related to the staple fixation. I suspect that devices are evolving to incorporate the benefits of a combination of passive and active fixation mechanisms, but at present, the EXCLUDER Device is the only device that uses both passive and active fixation.
What are the possible risks associated with different
types of fixation?
Dr. Milner: Any device is subject to fatigue. All devices
have shown some element of fracture or fabric issues, and
fixation has not been exempt from fatigue problems. All
active fixation materials (stainless steel, nitinol, and cobaltchromium
alloy) have all shown fracture events and are
still prone to this type of problem. It is not clear that fractures
lead to significant device issues, such as migration,
but this concern exists.5
In your practice,have you seen examples of when a
particular type of fixation created issues?
Dr. Milner: I have seen a clinical trial device with
suprarenal fixation develop a separation from the main
body device. However, this did not lead to a migration
event. When working in Europe, I did see an example in
which oversizing of a passive fixation device led to aortic
neck dilatation. I believe that we have seen less of that in
recent years, and I don't know if that is because of device improvements or if endovascular specialists have learned
to do a better job of sizing devices for the anatomical
measurements.
How does the type of fixation used by a
device affect the delivery/deployment of
various EVAR devices?
Dr. Milner: I think it does not significantly change the
delivery/deployment of the device. For some devices, it
adds one or two additional steps during the main body
deployment. In addition, I always take great care in
removing the main body device delivery system when a
suprarenal fixation system has been deployed.
What are the proven benefits of different
types of fixation? In short necks? In angulated
necks?
Dr. Milner: I do not think there are data to support
that different fixation means (ie, passive vs active,
suprarenal vs infrarenal) allow for improved treatment
in general or in short or angulated necks. This is based
on the Instructions For Use (IFU) and my own clinical
experience. Some specialists have assumed that devices
with suprarenal fixation are better suited for treating
shorter aortic necks, even though the devices' IFU were
identical to that of other devices using infrarenal fixation.
It may well be that those suprarenal devices are
able to treat shorter necks but neither the clinical data
nor the IFU have supported that conclusion. The Talent
device differs slightly in that it is approved by the US
Food and Drug Administration for a 10-mm aortic
neck length.
I believe that the best option for treating challenging aortic necks is to use a debranching procedure, chimney/ snorkel stent placement, or branched/fenestrated devices. All of these types of repair have been reported to be successful, but they have also had significant complications. 6-8
Finally, open repair is still an appropriate option in physiologically suitable patients.
Are there misconceptions about the different
types of fixation?
Dr. Milner: I think the main misconception is that
suprarenal fixation allows the user to treat a shorter aortic
neck. The suprarenal fixation devices can be deployed
successfully in challenging anatomies, but I am always
concerned about the durability of this approach.
What do you see as the short- and long-term
future for fixation of EVAR devices?
Dr. Milner: In the short-term, the benefit of the new C3
Delivery System for the EXCLUDER Device (W. L. Gore &
Associates) is that you can be exceptionally accurate in placing
the device with active fixation because you will have the
ability to deploy it and reposition it during the procedure.
This device is available in Europe and recently FDA approved.
In the long-term, I think stent grafts will always need some amount of active fixation to prevent migration, and I do not think that improvements in fixation will change our ability to treat difficult anatomy.
Ross Milner, MD, is Associate Professor and Division Chief, Vascular Surgery and Endovascular Therapy, and Vice Chair for Clinical Trials/Site-Based Research, with Loyola University Medical Center in Maywood, Illinois. He has disclosed that he is a consultant for W. L. Gore & Associates. Dr. Milner may be reached at (708) 327-3431; rmilner@lumc.edu.
Advertisement
Advertisement
