Biomedical Engineering Reference
In-Depth Information
In patients with lower-limb occlusive disease balloon angioplasty and
stenting are commonly applied in the iliac, femoral and infrapopliteal arter-
ies depending on the pathology and morphology of the lesions. Since ste-
notic lesions are usually localised and short, angioplasty or primary stenting
with a self-expanding stent perform well. Femoropopliteal lesions tend to
be long and diffuse and the results are therefore worse than bypass surgery
with a suitable autologous vein (Ruef
et al.
,
2004; Beard, 2008). Stents
placed in the femoropopliteal segment are exposed to large repetitive
mechanical stresses that can lead to stent compression, distortion and frac-
ture (Kroger
et al.
,
2004; Schillinger and Minar, 2007). These mechanical
stresses are associated with high restenosis rates and the transient nature
of a bioresorbable stent may potentially overcome some of these problems
(Peeters
et al.
,
2005).
8.3
Bypass grafts
The materials and techniques used for bypass vary with anatomical site,
availability and the surgeons' preference. Clinical evidence acquired over
several decades demonstrates that polyethylene terepththalate (PET or
more commonly known as Dacron) and expanded polytetrafl uoroethylene
(ePTFE) perform well when used to replace large diameter vessels. These
materials are stable and inert and are resistant to chemical degradation and
mechanical failure (van Damme
et al.
, 2005). The main complication is
infection, accounting for between 1 and 6% of cases (Mussa
et al.
,
2007;
Zetrenne
et al.
,
2007). However, when it occurs, it is extremely challenging
to treat and with aortic graft infection, mortality rates range from 25 to
88%.
For peripheral arterial bypass where the graft used is 6 mm or less in
diameter, the overwhelming evidence identifi es autologous vein as the gold
standard in achieving optimum graft patency, but, if unavailable, prosthetic
alternatives are available although the results are considerably poorer. This
chapter will focus on the characteristics of materials for lower limb periph-
eral arterial bypass.
8.3.1 Critical limb ischaemia
Throughout the western world critical limb ischaemia (CLI) has become a
progressively more common manifestation of atherosclerosis, which places
the limb at imminent risk, especially in the presence of diabetes and tissue
necrosis. The outcome of CLI can be summarised by the data presented by
Wolfe (1986), whose one year estimates were that 25% of patients would have
at least one leg amputated, 55% would retain both legs, and 20% would
have died. Its fi nancial demands on the health service are profound, and
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