Biomedical Engineering Reference
In-Depth Information
(a)
(b)
(c)
8.4 Serial plain X-rays (images (a), (b) and (c) were taken one year
apart) of the same patient. The top end of the stent-graft has migrated
caudally in relation to vertebral bodies. The top end of the stent-graft
can be seen to have expanded since it migrated into the aneurysm
and is therefore no longer constrained by the aneurysm neck.
Distortion of the stent-graft also occurred as a result of migration.
fi xation (see Fig. 8.4). Fixation relies upon the radial force exerted by the
stent-graft against the aortic wall, frictional forces between the stent-graft
and the aorta and the strength of hooks or barbs which may be added to
the proximal stent. Experimental studies, however, reveal that the fi xation
strength of any model of stent-graft is considerably lower than that of a
surgically anastomosed graft (Malina et al. , 1998, 2000).
Secure fi xation of the endograft relies on the radial force of the stents
and the presence of hooks and barbs. Barb fracture often occurs in vivo .
Different methods are used to secure the barbs to the endograft. For
example, they can be wrapped around and soldered to the proximal bare
stent or fi rmly sutured to the graft component. The latest devices, such as
the Medtronic Endurant endograft, are provided with stent that is fabri-
cated with integral hooks, a design that may result in reduced incidence of
fracture.
Proper healing of the device at the proximal and distal attachment points,
with infi ltration of cells into the graft wall, would create a secure and reli-
able seal and help to anchor the device to the vessel. However, this does
not appear to happen with either Dacron or ePTFE grafts (Malina et al. ,
2000, McArthur et al. , 2001). The use of basic fi broblast growth factor incor-
porated into the graft component has been shown to enhance healing and
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