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"*Failures of endovascular grafts that have been observed clinically*"

By Geoff White, MD

DR. WHITE: Okay. We are moving now from theory to reality, and as far as
technology is concerned, this is where East meets West; California
method here, and East Coast over here.

What I am going to do is just show some slides illustrating failure
modes that have been encountered clinically in our own practice and
elsewhere, using some of our own slides, and some that I have stolen
from various publications.

So if I use your slide here, thank you very much. Then I am going to go
to the computer slides and just give a quick summary as to what I see as
being the most important issues.

To start with the most common failure mode we have encountered is
probably endoleak, and I think it is a good place to start because it
illustrates one very important feature, and that is endoleak may occur
because of device failure.

It may occur because of poor patient selection, and what somebody
recently termed as patient failure. It may occur because of a procedural
failure by the implanting physician, and it may occur because of
diverse, anatomic variations within the patient, as we have already
touched on.

And just a quick summary of the current classification that we have been
using, Type One of the attachment slides; and Type Two, any retrograde
type of flow from side branch vessels, and Type Three, a defect in the
graft wall or disconnection.

This type probably mainly depends on the patient, but it obviously can
also occur because of anatomic factors. To confuse all of this, we have
variations in graft construction, which can give the appearance of
endoleak, and with the earlier version of the endograft, we have this
mixture of perhaps porosity of the graft fabric, and little channels
through the graft where the sutures go through, which on early CT scans
gave it this appearance of like a jet of blood coming out form the
graft.

And this we had termed Type Four endoleak, because it seemed to close
reliably within at least a month, and often quite earlier, but we are
still not quite sure whether there may be long term consequences of
these little channels.

This is an illustration of another type of endoleak, and I am going to
run through these fairly quickly. This is one of the earlier seam
separations, and I think this was the stentograph, where the seam was
sewn and the suture broke with perforation of the graft limb.

Here is another similar one, again with either the stent or the
vanguard, showing leakage outside the graft, and this is the appearance
after explant of the graft, and after attempted repair with another
graft inside. And again you can see the separation of the sutured seam.

Here is another type of graft erosion, or tear, or hole, a fairly subtle
appearance on this view, but when you hold it up to the light, you can
see the holes within the graft, which obviously can become significant
channels, and can lead to repressurization of the graft, and much of the
aneurysm.

And I think it was Juan Parodi earlier who emphasized the fact that once
the aneurysm is deemed depressurized, it may be far more liable to early
rupture when it is repressurized.

In the direction of the metal components, and the fabric components,
they obviously can have the same effect. And with all modular grafts
which are constructed inside the body by connecting various pieces, we
can later have disconnection.

This is a typical CT scan appearance, where one of the graft limbs is
appearing sideways, like somebody crossing their knees, with the
endoleak associated as you see here. Here is the thrombus and here is
the leak within the aneurysm sac.

This is how it appears on the plain x-ray, which is extremely valuable
for diagnosing this kind of dislocation, and where you see the limb here
and the trunk here and these two points should be in contact with each
other.

And here is the angiographic appearance with contrast coming down and
appearing in the aneurysm sac at that disconnection point. Here is
another form of disconnection, where approximal extension has become
disconnected from the graft, and you see the two similar sized fragments
here.

These are both the approximal ends of the graft and not limbs, and here
they are laying side by side, instead of one inside the other. Another
common form of graft failure or complication is this kink of the limb
seam, where the metallic fragments are angulated and very close
together.

And this typically would lead to occlusion of thrombosis of a graft
limb, and or in some cases partly thrombosis, following by embolization,
leading to trash foot and other complications.

There have been attempts made to define this more scientifically if you
like; buckling and any increase in angulation, kinking and acute
localized angulation, and this comes from a publication of Peter Harris,
the Journal of Endovascular Surgery.

Importantly, they showed that late complications, that is, endoleak or
lumen collusion, developed in 19 percent of the cases, all of whom
exhibited graft buckling or kinking in a series of Vanguard grafts.

So it was a very important association with those early signs, with late
adverse effects on the patients. Here is another example of graft
buckling or kinking from our own practice, associated with displacement
of the graft from the distal or the approximal neck of the aneurysm.

And you can see that it slipped down 5 or 6 centimeters from the neck.
There is still good blood from the channel, and here is the plain x-ray
of that patient showing you the angulation of the metallic components of
the graft.

We have also shown and published a variety of these grafts shortened
considerably during the implant procedure, and with both the Vanguard
and the aneurylextial (phonetic) stent, we observed a shortening of more
than 10 percent, and close to 50 percent of case, probably caused by the
forces needed to push the graft out of the deployment system so that the
graft in the loader is this long, and in the patient is this long.

And that is another possible cause for acute or light device failure.
This slide was meant to demonstrate the fracture of a Y-Form, and I
think it illustrates why it is an important point about Y-Form
fractures, and those can be very difficult to detect.

And in this case, we see that a tubular graft has dislocated from the
distal aspect of the makeup of the so-called distal makeup on an
aneurysm. This is one of our early cases from about 1993, and I will
come back to this later on the computer slides just to discuss some of
the complexities of diagnosis and analysis.

The other thing that is important to stress on these is variations in
the angle between the various wires, which we feel may be associated
with external pressure, but it may also be associated with variations in
the compliance or the oscillations, or whatever you like to term it.

This slide was just meant to show that analysis and searching for these
Y-Form fractures can be extremely difficult. Here is an electro x-ray of
a patient with one of the Baxter endografts in place, and you can see
the individual Y-Forms.

And to look at these is a very painstaking effort to determine whether
or not these are actually fractured or not. So a lot of these are
probably being missed on diagnosis today for all graft types.

And it is far more difficult to see the ones made of nyanom (phonetic).
In some cases, poor apposition of the graft, either because it has been
placed too low, or because of thrombus, may lead to the complication
which we now term endo-tension.

And that is defined as continued or recurrent pressurization of the
aneurysm sac without any evidence of endoleak. And here you see a
patient whose aneurysm was slightly more than five centimeters at the
time of implant.

And two years later the aneurysm is now close to seven centimeters in
diameter, with no evidence of endoleak on any of the imaging studies
that have been done.

So persistent or reoccurring pressurization without endoleak, and here
is that same patient with an open surgical conversion, and these are the
typical appearances we found now in seven cases.

And with liquified thrombus, or semi-liquid, or plasma-jelled type
thrombus, surrounding the graft, and this liquified component, and in
most cases we feel that this is due to an endoposed layer of thrombus at
the neck, and this thrombus, which you can see here after the graft
being removed, probably transmits pressure in males who have osmotic
effects leading to activity within the thrombus and within the sac.

Whether or not this can be tested in a pre-clinical means is very
doubtful. However, the factors that lead to it may be identified, and
perhaps can be tested.

We have heard a lot about variations in anatomy, and I would just like
to finish off the slides just by talking a little bit about causal
factors in variations in anatomy.

Somebody asked earlier about the relevant incidents of the taper or
reverse taper in a series of patients that we analyzed last year, and
this was in 8 percent of the cases that we actually treated with an
endograft, and probably far higher than in those that are not treated.

We have defined six different types of neck, and we have shown that in
almost every case it can be fitted with this classification. And we have
used that to define what we feel is a practical anatomic risk grading.

And in essence this depends on the neck and the iliac arteries, or the
sac, with all favorable necks being defined \-- correction, with all
favorable necks being defined as Grade I, and unfavorable necks as Grade
II, and severely unfavorable as Grade III.

Whereas, if the iliacs or the sac are unfavorable, that led to it being
changed from 1A to a 1B. And another way to put this, Grade IA, the neck
was favorable, and the iliacs and sac were favorable.

And Grade 1B, the neck favorable, and iliacs and the sac unfavorable;
and we come down to Grade III, the neck was severely unfavorable, and
the iliacs and the sac were unfavorable.

Now,I mentioned this because I think this might have relevance to
pre-clinical testing, because I believe that we should have difficult
grades of difficulty in the models that we use for our pre-clinical
testing.

We should be testing grafts in the Type 1-A anatomy as most of us have
seen today, but we also should have different degrees of difficulty
within the anatomic testing to simulate the human variation that we see.

Now, these ones would not fit the criteria for any graft at present, and
you can see in Grade III the incidents of earlier outcome failure; that
is, endoleak was 50 percent. But in fact all of these were sealed and
were cured by subsequent removals.

And we are now awaiting the long term results of studies such as this. I
would quickly now just kind of like cross to the other screen, because I
would like to try and bring together what I have said from the clinical
situation, to how it pertains to this meeting today. If we could have
the next slide.

In an outline, I am just going to reiterate the frequent modes of
endograft failure, and state which I think are the most critical modes
of failure, and thereby come to some form of classification.

And talk a little bit about causing factors, and emphasize the
relationship of device failure to patient, and any other factors, and I
will try to do all of that in about three minutes. Next slide, please.

The classification of failure may be according to many factors, and we
can classify according to the component or device affected, and we can
classify according to the cause, and we can differentiate device factors
versus patient factors.

We can talk about the timing, early versus late, the severity, and
particularly with respect to clinical effects, and there are probably
many other ways of classifying device failure.

To date, most testing has really been relevant to acute device failure.
That is, being able to deploy the graft and analyze acute failure within
the model, usually with fairly simple anatomy.

And the things that are tested there, first, whether or not the device
will deploy, which we are not ready to discuss today; and failure of the
device to attach to the aortic wall; and failure of the device to seal
or exclude the aneurysm; disconnection of modular components; and
occlusion or thrombosis of the graft.

So I think that this represents a useful framework for a subsequent
discussion. Next slide. If we now look at the chronic or long term modes
of device failure, these are the ones which we really have difficulty in
devising preclinical testing for, because it really pertains to device
durability.

But these same factors really come up here. The failure of the device to
maintain its fixation to the aortic wall, and leading to displacement,
loss of device seal, or it may have been previously sealed,
disconnection of modular components, and again occlusion, or thrombosis
of the graft again.

And now device materials failure or durability rears its ugly head. Next
slide. And when we are looking particularly at those device and
materials durability factors, we are coming back to most of the things
that we have already talked about today.

Fractures of the stents, or Y-Forms, and which hasn\'t really been
mentioned too much, either due to fatigue or corrosion, or to most
likely a combination of these.

Breakage or disconnections of sutures, which I didn\'t illustrate on
those slides, but it has also been a frequent failure mode. Graft fabric
or material tears, metal erosion through the fabric, and device
angulation or kinking. Next slide.

The critical effects of device failure are really those that affect the
patient in the most critical ways, and causes, such as failure of the
seal, or fabric tears, or device shift, or stent fractures, are really
only relevant to the patient if they cause either an aneurysm
enlargement, or aneurysm rupture.

Likewise, device kinking, buckling, and so on, is also only relevant to
the patient if it is a precursor to these factors, or if it causes
arterial blockage, or embolus.

So in looking at the critical effects, we are really talking about the
effects on the patient rather than the bench top testing. But naturally
we need to devise bench top testing which can lead to earlier
recognition of these potential failure modes. Next slide, please.

I would like to just quickly give a patient illustration, which I also
used at the recent conference in Ireland, because I think it really
shows the multifactorial nature very nicely.

This is a true case, and it involves a 73 year old male, who we
initially treated in 1993 for an abdominal aortic aneurysm. At that
time, we only had two grafts available in a workable fashion, and so he
received the tube endograft.

And not surprisingly, two years later, he presented with distal
endoleak, and the graft had pulled out of the distal end, and it was
similar to that slide that I showed you where the graft had pulled out
distally.

And we put a second redistal tube extension in to seal it off. Two years
again later, he had a Type I distal endoleak, which occurred during an
exercise test for his cardiac status, and this was treated by a third
endograft. Next slide.

It may on the face of it seem very simple on what caused failure in this
case, but here are the factors that really need to be analyzed in
determining that, and I think that is part of the problem that we are
struggling with here, because it is a very multifactorial question.

The patient selection and device type obviously paid a role, because we
think that distal disconnection may not have occurred if we used
bifurcated graft rather than a tube graft.

However, they weren\'t available. Changes in the patient\'s anatomy may
have contributed because the distal nick may have expanded, leading to
that disconnection.

Activity and reactions in the aneurysm sac seemed to be an important
component, because the patient actually developed a coagolapathy at the
time of his second endoleak.

Endoleak forces, and the effect of exercise and extraneous factors, and
perhaps there was also a device material failure, and interaction of the
metal, and the fabric, and the graft. Next slide.

The patient factors, I think, we have done to death already, and so I
won\'t dwell on those. Next slide. Device materials failure. Again, all
of these are the things that can lead to long term failure in the
durability of devices. Next slide.

And to finish off, there have been some attempts within the various
bodies to try and define these failure modes in a mode that is relative
to reporting.

One is to classify endograft deformity, and you see an initial attempt
here, which is due to be published in the SVS standards document
hopefully later this year in the Journal of Vascular Surgery, with a
grading of angulation or kinking of the graft from zero to three.

And on the final slide, a further classification of device failure
according to clinical severity, which from the patient\'s point of view
is obviously the most relevant.

And with Grade Zero being no adverse or clinical effects, and down to
Grade Three, resulting in conversion, rupture, major complications, or
death of the patient.

So I hope that will serve as a useful introduction to this section on
modes of failure that have been observed in practical and clinical
experience to date. Thank you.