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.