Vascular implants for peripheral arterial bypass and aortic aneurysm repair - Biomaterials and Devices for the Circulatory System - page 223

corroborated in a study by Keynton et al . (2001) who reported that OSI
within ePTFE bypass grafts in carotid arteries of mongrel dogs provided a
stimulus for the development of anastomotic IH. An anastomosis with high
outfl ow resistance may have signifi cant retrograde fl ow during the diastolic
phase of the cardiac cycle. The resultant OSI would be high, and the anas-
tomosis at risk of IH and subsequent occlusion. Such a scenario may be
observed in the clinical situation.
The patterns of fl ow within the distal anastomosis are responsible for
the haemodynamic profi le, with areas of low fl ow, turbulence and fl ow
separation associated with low WSS or high OSI. Bassiouny et al. (1992)
studied the distribution of IH within the distal anastomosis of explanted
ePTFE and vein grafts to the ilio-femoral arterial segments of dogs. Equal
quantities of IH were found along the arterial fl oor irrespective of conduit
material; however, increased hyperplasia was reported in the anastomotic
suture line of ePTFE grafts. Flow visualisation studies in models recreating
the morphological features of each anastomosis identifi ed secondary fl ow
patterns within a sinus created along the suture line. They speculated that
such a fl ow phenomenon might interact with other biomechanical and
humoral factors to modulate suture line intimal thickness. They further
postulated that this process might be self-limiting and abate once the
remodelling has eliminated the morphological anomalies that generate the
fl ow patterns. The non-compliant ePTFE may be expected to create a
more pronounced anastomotic sinus than autologous vein, resulting in the
increased degree of observed IH. In addition, however, fl ow patterns
may directly contribute to endothelial trauma and result in IH. Sottiurai
(1990) described the 'shingle effect' whereby the distal aspect of an endo-
thelial cell overlaps the adjacent downstream cell. Flow separation as seen
at the heel and toe of an ETS distal anastomosis may lift this overlapping
process, exposing the underlying sub-endothelium and facilitating access
of blood-borne elements known to infl uence the formation of IH, such as
platelets.
The presence and nature of distal anastomotic IH in ETS anastomoses
has led to theories describing different types of IH with differing aetiologies
and sequelae (Fortunato et al. , 1999). Suture line IH may represent a com-
bination of vascular healing and remodelling in response to mechanical
injury, local haemodynamics and compliance mismatch. As it is a ubiquitous
and potentially self-limiting feature of any anastomosis, it may not repre-
sent a poor prognostic factor (Sottiurai et al. , 1989; Bassiouny et al. , 1992).
Conversely, a more sinister form may be the juxta-anastomotic IH seen at
the toe, heel and along the recipient artery fl oor, which may be attributed
to the haemodynamic forces and blood-borne products. When considering
arterial reconstruction to crural vessels of 3 mm diameter or less the accu-
mulation of only small amounts of hyperplasia at these critical points will

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