INTRODUCTION
Saphenous vein remains the most commonly used conduit for coronary
artery bypass because of its predictable handling qualities and ready
availability.[1] However, as many as 40% of vein grafts become
occluded at 12 years post-surgery.[2, 3] Early thrombosis occurs in
up to 10% of vein grafts due to spasm or technical error.[4, 5]
Late vein graft failure occurs as a consequence of early neointimal
hyperplasia with later superimposed atherosclerosis.[5] Therefore,
the clinical implications of any intervention to improve long-term graft
patency are significant.
Surgical preparation of the harvested vein is often overlooked but may
be an important contributor to vein graft failure. Typically, the
harvested vein is distended at uncontrolled high pressure with blood or
fluid using a syringe to test for leaks and relieve spasm prior to
grafting; this has been shown to result in endothelial loss and medial
disruption.[6, 7] Our group proposed an alternative protocol that
tests for leaks by connecting the harvested vein to a side branch of the
aortic return cannula on the cardiopulmonary bypass circuit.[8] In
this way, the grafts are then distended at the patient’s own systemic
pressures. We hypothesised that this should attenuate medial disruption,
platelet adherence, the release of mitogenic growth factors and
subsequent neointima formation, as supported by our observations that
avoiding high pressure distension reduces medial damage and preserves
release of prostacyclin and nitric oxide (NO), both of which have
potential antiproliferative actions.[6-8] Our technique has also
been shown to reduce neointima formation in cultured human saphenous
vein grafts in vitro compared to conventional harvest.[9] However,
while avoiding pressure distension increases graft patency in vivo in a
porcine saphenous vein to carotid artery interposition model, this
appears to be due to a reduction in early thrombosis rather than an
effect on neointima formation.[10] Furthermore, it is not known
whether avoiding high-pressure distension by our method improves
long-term graft patency.
Souza and colleagues described a non-traumatic vein harvesting technique
that combines avoidance of pressure distension with preservation of the
surrounding adventitia and fat or ‘pedicle’, which is stripped during
conventional vein harvesting.[11] The pedicle has been shown to
preserve wall architecture and endothelial function in vitro and
experimental studies have shown that the preserved fat tissue is a rich
source of NO.[12, 13] It has been hypothesised that preservation of
the adventitial microcirculation may reduce subsequent atherogenesis by
improving wall oxygenation and reducing oxidative stress.[14]
Until recently clinical trials of therapies designed to prevent vein
graft disease were limited by the large sample sizes required to measure
changes in the lumen (i.e. new lesions) or patency rates by
postoperative angiography. Intravascular ultrasound (IVUS) accurately
and reproducibly measures vein graft wall dimensions and quantifies
levels of plaque and wall fibrosis.[15-17] Using this technology, we
set out to determine the effects of the vein graft harvesting technique
and pressure distension on the development of vein graft wall thickness
in a factorial randomised controlled trial (RCT), which allowed both
techniques to be evaluated in the same trial.