Abstract
OBJECTIVE: We reviewed the incidence of stent-graft migration after
endovascular aneurysm repair in a prospective multicenter trial and
identified factors that may predispose to such migration. METHODS:
All patients who received treatment during the course of the multicenter
AneuRx clinical trial were reviewed for evidence of stent-graft migration
over 5 years, from 1996 to 2001. Post-deployment distance from the
renal arteries to the proximal end of the stent graft and the proximal
fixation length (length of the infrarenal neck covered by the stent
graft) were determined in patients for whom pre-procedure and post-procedure
computed tomography scans were measured in an independent core laboratory.
RESULTS: Stent-graft migration was reported in 94 of 1119 patients,
with mean time after device implantation of 30 +/- 11 months. Freedom
from migration was 98.6\% at 1 year, 93.4\% at 2 years, and 81.2\%
at 3 years (Kaplan-Meier method). Subset (n = 387) analysis revealed
that initial device deployment was lower in 47 patients with migration,
as evidenced by a greater renal artery to stent-graft distance (1.1
+/- 0.7 cm), compared with 340 patients without migration (0.8 +/-
0.6 cm; P =.006) on post-implantation computed tomography scan. Proximal
fixation length was shorter in patients with migration (1.6 +/- 1.4
cm) compared with patients without migration (2.3 +/- 1.4 cm; P =.005).
There was significant variation in migration rate among clinical
sites (P <.001), ranging from 0\% to 30\% (median, 8\%), with a greater
than twofold difference in migration rate between the lowest quartile
(6\%) and the highest quartile (15\%) clinical sites. Univariate
and multivariate analysis revealed that renal artery to stent-graft
distance (P =.001) and proximal fixation length (P =.005) were significant
predictors of migration, and that each millimeter increase in distance
below the renal arteries increased risk for subsequent migration
by 5.8\% and each millimeter increase in proximal fixation length
decreased risk for migration by 2.5\%. Pre-implantation aortic neck
length, neck diameter, degree of device oversizing, correct versus
incorrect oversizing, device type (stiff vs flexible), placement
of proximal extender cuffs at the original procedure, and post-procedure
endoleak were not significant predictors of migration. Migration
was treated with placement of extender modules in 23 patients and
surgical conversion in 7 patients; 64 patients (68\%) with migration
have required no treatment. CONCLUSIONS: Stent-graft migration among
patients treated in the AneuRx clinical trial appears to be largely
related to low initial deployment of the device, below the renal
arteries, and short proximal fixation length. Significant variation
in migration rate among clinical sites highlights the importance
of the technical aspects of stent-graft deployment. Advances in intraoperative
imaging and deployment techniques that have been made since completion
of the clinical trial facilitate precision of device placement below
the renal arteries and should increase proximal fixation length.
Whether this, together with increased iliac fixation length, will
result in lower risk for migration remains to be determined in long-term
follow-up studies.
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