Vascular implants for peripheral arterial bypass and aortic aneurysm repair - Biomaterials and Devices for the Circulatory System - page 221

this might contribute to the development of IH. In an attempt to clarify the
infl uence of compliance mismatch, Ballyk et al. (1998) utilised a mathemat-
ical model to calculate the stress along the suture line of end-to-end (ETE)
and ETS anastomoses. They found that the presence of a suture line
increased the mean stress compared with an undisturbed artery, irrespec-
tive of geometry or conduit compliance. They also reported greater stress
in ETS than in ETE models, and signifi cantly higher mean stress with a
compliance mismatch in an ETS model. They speculated that the concen-
tration of stress at the toe might correlate with the known propensity for
intimal deposition at the toe of an ETS anastomosis. Bassiouny et al. (1992)
investigated the location and severity of distal anastomotic hyperplasia in
13 dogs and found increased suture line hyperplasia in ePTFE grafts com-
pared with vein. They accept, however, that caution must be applied in
attributing such fi ndings solely to compliance mismatch. Trubel et al. (1994)
compared elasticity and IH in venous grafts and vein grafts constricted with
an external Dacron mesh implanted into 12 sheep. Elasticity was signifi -
cantly lower and distal anastomotic IH signifi cantly greater in the mesh-
constricted group, a fi nding they attributed to the compliance mismatch
between graft and native vessel.
The confounding issues of previous studies, however, were recognised by
Wu et al. (1993) as ambiguous defi nition of IH, pharmacological infl uences,
poor control groups and short follow-up periods. They designed an in vivo
study to examine the direct and sole effect of compliance mismatch. They
discerned between 'true' IH and intimal thickening as a result of mural
thrombus organisation. In addition, they recognised the undesirable infl u-
ence of anticoagulant and antiplatelet agents used in other studies, since
these compounds, such as heparin and aspirin, are known to inhibit IH
(Bush et al. , 1988; Clowes and Clowes, 1989). They created ETE and ETS
carotid bypass grafts in opposing arteries of 11 dogs using pre-clotted
5 mm supported Dacron grafts. A group of autologous carotid artery grafts
interposed end-to-end into a section of femoral artery served as a control.
Flow rates in all vessels were equal, no anticoagulant or antiplatelet agents
were administered, and follow-up was performed at 6 and 12 months. They
found that compliance in the Dacron graft was 1/300 that in the arterial
conduit; however, there was no difference between the two groups in terms
of thickness of anastomotic neointima. The neointimal thickness did not
signifi cantly change between 6 and 12 months. This important and well-
conducted study indicates that compliance mismatch alone is not suffi cient
to explain the development of neointimal hyperplasia at the anastomotic
interface. Similar conclusions were reported by Okuhn et al. (1989) who
compared virgin and externally banded iliac arteries in dogs and found no
difference in intimal thickness when such a compliance mismatch was
applied.

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