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.