Biomedical Engineering Reference
In-Depth Information
freedom among the patients treated with AneuRx (passive fixation) and Zenith
(active fixation) and found that overall rate of migration occurrence was 67.4 %
versus 90.1 % respectively at 4 years of follow up. The prevalence of losing
positional stability in devices with passive fixation of up to 15.9 % (stringent
criterion) has been documented in [
57
]. Similarly, Heikkinen et al. [
87
] have
observed 10 % incidence of post-implantation movement of
10 mm with respect
to superior mesenteric artery with a mean follow up of 2 years. Zarins et al.
carried out a review of multicentre trial and identified that overall percentage of
migration was 19
:
8 %
;
after 3 years of surveillance [
88
].
However, in current designs with a number of novel methods devised to engage
proximal and distal aortic neck, high rate of migration is now contained. These
novel method include use of barbs and hooks, fenestrated and branched limbs,
extended bare metal stents, high columnar strength, bifurcated device, and iliac
fixation. As documented by Thompson [
11
] and Won et al. [
82
] that migration
may occur in up to 3 % of the patients with a follow-up at 18-24 months.
Migration is a highly time dependent phenomenon. In a comparative study, it has
been reported that at a 1 year follow up of patients who received Zenith device,
there was no migration, whereas, by the end of 4 years 2.4 % of the patients have
shown migration of at least 10 mm [
86
].
Migration is also correlated with type-I endoleak, which is a primary cause of
device failure and rupture [
10
]. Proximal stent graft failure should not be judged
on the basis of caudal movement of device as it has been observed that pure
migration is less likely to occur. It is rather always accompanied by aortic neck
dilatation, shortening and elongation. Lintwinski et al. have reported outcomes of
a study, where migration occurred, without causing patients to lose proximal
fixating zone and hence no EVAR failure was observed [
57
].
The importance of iliac fixation has not been considered in detail as a con-
tributing factor in developing late migration. Nonetheless, currently, a number
studies exist, showing that it is also equally important in inhibiting migration.
Heikkinen et al. [
57
] have noticed that short proximal aortic neck length can be
compensated by deploying devices having more columnar support (AneuRx) and
by achieving proximity to iliac bifurcation at the distal site. Benharash et al. [
89
]
reported that in patients with good iliac fixation, in addition to suprarenal and
infrarenal fixation, no migration was observed. Waasdrop et al. [
84
] have carried
out a study with the Zeinth device to establish a relationship between fixating
length and migration, and found that vast majority of migrations were observed in
the group having short distal and proximal fixation zones.
4.2.1 Management of Migration
Management of migration involves following considerations.
• Oversizing of stent grafts by 10
20 % to counteract aortic neck dilatation in the
follow up [
10
].
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