Saphenous vein: advances
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Although the saphenous vein (SV) is a widely used conduit for coronary artery bypass graft surgery (CABG), lower long-term graft patency rates and worse clinical outcomes have been reported after CABG performed with SV grafts compared with CABG performed with internal thoracic artery (ITA) grafts. Of various efforts to overcome the limitations of SV that are resulting from structural and functional differences from arterial conduit, recent improvement in harvesting techniques including no-touch technique, surgical strategy of using the SV as part of a composite graft over an aortocoronary bypass graft, and external stenting of the SV will be discussed in this topic.
KeywordsCoronary artery bypass graft surgery Saphenous vein Composite graft
Since the introduction of the saphenous vein of the SV as an aortocoronary bypass graft in early 1960s , the SV has been widely used for CABG. However, atherosclerotic failure, lower long-term patency rates and worse clinical outcomes have been reported after CABG performed with SV aortocoronary grafts compared with CABG performed with ITA grafts [2, 3, 4, 5].
Of various strategies, pharmacologic relaxation of the SV after harvest and strict medical therapy, including administration of antiplatelet and lipid-lowering agents after surgery, were suggested to improve SV graft patency [6, 7]. Further efforts to improve patency of the SV included external support using stents, intraoperative gene transfer, and improvement in harvesting technique [8, 9, 10, 11]. Improvement in harvesting techniques including no-touch technique, alternative surgical strategy of using the SV as a composite graft, and external stenting of the SV will be discussed in this topic.
Improvement in harvesting techniques and alternative grafting strategies
No-touch technique for SV harvesting
Clearly, tissue or cellular damage to each separate layer of the SV may affect its performance as a graft in patients undergoing CABG. However, preservation of the surrounding tissue that remains intact in NT SV grafts influences the effect of harvesting, having both direct and indirect actions on each of the vein’s layers, thus contributing to the various mechanisms underlying the improved performance of NT SV grafts. Therefore, the presence of the surrounding tissue may contribute to the significantly higher long-term patency rate of NT SV grafts compared with conventionally harvested SV grafts; CABG performed with NT SV aortocoronary grafts showed a high patency rate (83%) that was comparable to left ITA graft patency at a mean time of 16 years postoperatively [18, 19]. Concerns have been raised regarding the issue of increased leg-wound complications in NT technique. Preoperative mapping of the SV course using an ultrasonographic Doppler assessment is essential in NT technique because this procedure allows for a rapid and accurate location of the SV without causing excessive soft tissue injury and the creation of tissue flap. Future aim will be developing an endoscopic or minimally invasive NT technique.
Minimally manipulated SV as a composite graft based on ITA
NT SV with surrounding pedicle tissue as a composite graft based on ITA
Although no differences in the 1-year patency rates between the SV and right ITA composite grafts were demonstrated in a previous study, the SV composite grafts showed a trend toward a lower patency rate in the right coronary artery territory than in the other coronary artery territories (early vs. 1-year patency rates: right coronary artery territory, 97.4% vs. 93.4%; left coronary artery territory, 99.4% vs 98.8%, respectively) . One recent observational study demonstrated that the NT SV conduits with surrounding pedicle tissue further improved the early and 1-year patency of SV composite grafts compared with those of NT SV composite grafts without surrounding pedicle tissue, which might result from improving patency of the competitive SV conduits by maintaining pulsatility of the cushioned graft . Insertion of a Jackson-Pratt drain in the SV harvest site and careful closure of the leg wounds could decrease the possibility of wound complications .
External stenting of the SV
The concept for external stenting of saphenous veins was first proposed more than 50 years ago ; the rationale was that external supports would reduce diameter mismatch between the vein and target vessels and reduce the tendency of vein to dilate when exposed to arterial pressures. It was also postulated that they might reduce intimal hyperplasia and the risk of thrombosis.
The initial studies to examine the potential benefits of external stents were all conducted in animal models using femoral or carotid arteries but did not involve coronary implantation. The first study of using external stents in the coronary circulation was a proof of principle study in 2013 in a sheep model . This demonstrated a reduction in risk of graft thrombosis, degree of intimal hyperplasia, and improved lumen regulatory at 12 weeks. Despite the encouraging results in animal models, the initial results of external stents for vein grafts in coronary artery bypass grafting produced uniformly poor results with patency rates of 0 to 30% up to 1 year after implantation [33, 34]. Potential explanations for the poor results were due to excessive stent rigidity, oversizing of the stents, and the potential of kinking of the grafts at the proximal or distal anastomosis.
These failures led to the development of second-generation external stents, including the venous external stent (VEST) (Vascular Graft Solutions, Tel Aviv, Israel). VEST is a cobalt-chromium braid with axial plasticity (which allows elongation) and radial elasticity (resulting in a kink and crush resistant stent). After the encouraging animal results with this stent , the first clinical trial (VEST I) was of 30 patients where each patient in addition to receiving an internal mammary artery to the left anterior descending coronary artery received two vein grafts that were randomized to act as a control vein graft or to receive a stent . All vein grafts underwent transit-time flow measurement assessment before chest closure and all were widely patent with no technical failures. At 1 year angiographic follow-up, all ITA grafts were patent, but there was an overall failure rate of vein grafts, defined as occlusion or > 50% narrowing, of approximately 30% in both groups. It was noted that there was a higher failure rate of vein grafts, particularly to the right side, when metallic clips had been used to secure side branches within the stent and also if and there had been fixation of stent to the proximal or distal anastomosis. This raised the possibility of disturbance of the geometrical alignment of the anastomosis after chest closure. In the vein grafts that remained patent, the perfect patency was 80% with the stent versus 50% for the controls with significantly reduced intimal hyperplasia . Simultaneous studies showed that in the patent stented vein graft there was considerably superior hemodynamic flow and less oscillatory shear index resulting in lower intimal hyperplasia . Likewise, optical coherence tomography findings confirmed superior luminal regularity and less intimal hyperplasia in the stented vein grafts .
A second study examining the use of stents to the vein grafts to the right coronary artery but without fixation to proximal or distal anastomosis and securing side branches with sutures rather than metallic clips, resulted in an almost 90% patency at 6 months .
A number of randomized clinical trials are now under way including the VEST III study (180 patients randomized as in in VEST I), and the results of this will be available in 2019 with a primary endpoint of perfect vein graft patency at 2 years. Similarly, a study is underway sponsored by the Food and Drug Administration in the USA of 220 patients using the same methodology as VEST I.
Recent advances in SV harvesting techniques including no-touch technique, grafting strategy of SV as a composite graft based on the in situ ITA and external stenting of the SV may improve long-term patency of the SV conduits in CABG. Preserved SV endothelial wall structures and exposure to substances of the in situ ITA may lead to favorable negative remodeling of the SV. With pre-existing advantages of the SV conduit, such as ease of access, enough length, and short-operation time by simultaneous harvesting with the ITA, the improved SV patency will make this conduit more valuable for CABG.
Compliance with ethical standards
Conflict of interest
Prof. David Taggart states that he has received research funding, speaking, and traveling honoraria from Vascular Graft Solutions (VGS), and also has share options in VGS.
Ki-Bong Kim, Ho Young Hwang, and Domingos Souza state that they have no conflict of interest.
Human and animal rights and informed consent
This article does not contain any studies with human participants or animals performed by any of the authors.
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