Study design
The use of no-touch techniques during preparation of saphenous veins for
CABG has been advocated for decades based on evidence from experimental
studies.[5] However, efficacy in terms of reduced early graft
occlusion and less neointimal thickening has not been evaluated in
clinical trials, except for the studies of Souza and colleagues using
grafts surrounded by a pedicle.[11, 22] The HArVeST trial is the
first adequately powered RCT comparing the efficacy of low vs.
high-pressure testing of saphenous vein and of harvesting with and
without a pedicle. Histological measurements of lumen size and wall
thickness in samples of prepared veins were taken to examine the acute
effects of distension. Wall thickness is a more sensitive measure of
neointima formation after grafting than luminal encroachment.[6, 10]
In time course experiments, lumen area increases by 33% between one and
six months of implantation, whereas graft wall thickness increases 2-3
fold.[23] Vein wall thickening occurs rapidly within the first 2
months, stabilising at 6-9 months.[5, 24] Hence, by 12 months early
fluctuations have abated, establishing the choice of primary endpoint,
although atherosclerosis within 12 months is rare.[2, 3, 5] Owing to
its effect on bulk fluid transfer and lipoprotein retention, total wall
thickness is thought to be a key predisposing factor for subsequent
graft atherosclerosis and late occlusion. Wall thickness may be
considered a surrogate for long-term patency, although this remains to
be investigated directly.