Saphenous Vein Grafts

Anatomy and Physiology

In discussing SVG, it is essential to distinguish the GSV from the short saphenous vein (SSV). In most saphenous vein grafts the GSV is utilized, however, in select circumstances, the SSV may also be a suitable option.

The GSV exists as the prominent superficial lower extremity vein emptying into the common femoral vein. Bounded between a layer of muscular fascia and dermis, the GSV begins its course anterior to the medial malleolus, crosses the tibia, and traverses medial to the knee and ascends in the medial-posterior aspect of the thigh as it passes into the groin. It receives tributaries from accessory saphenous veins and enters the fossa ovalis 4 cm inferolateral to the pubic tubercle, at which point it joins the superficial circumflex iliac, superficial epigastric and external pudendal veins to create the saphenofemoral junction along the anterior surface of the common femoral vein.

The SSV forms initially at the confluence of the lateral aspect of the dorsal venous network of the foot, passes behind the lateral malleolus of the foot and proceeds superiorly in the subcutaneous tissue of the calf. After passing through the calf, it perforates the fascia lata and drains into the popliteal vein at the popliteal fossa. During its course, it has small communicating branches with the GSV and the deep venous system via numerous perforating branches.

Indications

Current indications for saphenous vein grafting in the setting of coronary artery disease include indications for coronary artery bypass grafting as outlined by the American College of Cardiology and the AHA. Given its high maintained patency rate, LIMA has been considered the bypass vessel of choice, especially to the LAD. Historically saphenous vein grafts have been used as additional grafts beyond the LIMA or have been utilized in circumstances that the LIMA is unavailable, however recent data has led to the Society of Thoracic Surgeons recommending a radial artery (RA) graft as the vessels of choice over saphenous vein grafts given the significant increase in arterial graft patency over vein.[4] Currently, saphenous vein grafts should be used as adjuncts to LIMA grafts in circumstances in which RA conduits are not suitable or viable for coronary artery bypass grafting.

In addition, saphenous vein grafts are often used for peripheral bypass surgeries particularly in the lower extremities. For example, a saphenous vein may be mobilized and utilized for a femoral to the popliteal artery for occluded vessels not amenable to conservative treatment or angioplasty. The saphenous veins (both GSV and lesser saphenous vein) can also be used to increase vascular pedicle length in free tissue transfer reconstruction, especially of the head and neck.

Contraindications

Contraindications to use of saphenous vein graft include factors that may compromise the quality of the saphenous vein, including local cellulitis/thrombophlebitis, venous thrombosis, or previous vein stripping/vein manipulation. Also, increased vein branching, varicosities, wall thickness and decreased diameter all confer a higher likelihood of graft failure.[5]

Equipment

Equipment required for saphenous vein grafting depends on whether an open vein harvest (OVH) or endoscopic vein harvest (EVH) is in use. An open vein harvest requires a tray of standard surgical instruments as used in any vascular case. Ultrasound guidance can also be a valuable tool when location is uncertain avoiding unnecessary incisions and dissection. Additionally, nonabsorbable and monofilament sutures, as well as clips, are used to ligate tributary vessels. Heparinized saline and a vessel cannula are also requirements for harvest.

In addition to these set of standard surgical instruments and suture, EVH requires additional instruments including a carbon dioxide insufflator, balloon tip trocar with a camera for videoscopic dissection, conical dissector, and bipolar cautery to achieve endoscopic hemostasis.

Personnel

Personnel required for saphenous vein harvest and grafting includes a surgeon with technical skill capable of carefully dissecting out and handling the vein graft without causing significant injury. A trained cardiothoracic surgeon is required to sew the graft from its new origin at the aorta to a suitable arterial landing zone. A vascular surgeon is trained to perform this procedure when bypass is required of the peripheral circulation. 

Preparation

While historically not required for SVG harvest, imaging modalities may augment and decrease complications arising from excessive dissection. Historically, the GSV and less commonly the SSV may be identified and dissected using anatomic landmarks intraoperatively, with veins from both limbs available for dissection until encountering a suitable vein segment. More recently, ultrasonography and pre-operative vein mapping have shown utility in identifying suitable vein segments in a non-invasive manner and may decrease unnecessary vein exposure and dissection.[6]

Technique or Treatment

Several techniques have been described for reversed or valvotomized saphenous vein graft harvesting for coronary artery bypass grafting. Reversed vein grafting negates the function of the venous valves inherent to the saphenous vein whereas valvotomized veins lose their valvular function.

Initial identification of the saphenous veins can be performed by identifying anatomic landmarks and palpating a thrill with one hand while milking the vein with the other hand; additionally, preoperative ultrasonography can directly visualize and mark the saphenous vein.

Historically, an open approach to SVG harvest has been the method of choice, in which an incision is made following the course of the saphenous vein and continued down until the identification of the vein. Sequential, step-ladder, incisions can also be used, rather than a single, parallel incision. Dissection continues along the length of the vein with care to manipulate the vein as minimally as possible. Tributaries are identified and clipped or tied. On obtaining a suitable length of vein, the proximal and distal aspects of the vein are clamped, the vein is ligated and removed. The vein is carefully cannulated to avoid endothelial damage, and heparinized saline is used to insufflate the vein to assess for any points of extravasation that can be addressed with clips, ties or by oversewing with monofilament suture. This specimen is then placed in a heparinized saline bath until used for implantation.

More recently, a less invasive approach to saphenous vein harvesting has been implemented—the endoscopic saphenous vein harvest (EVH). EVH of the saphenous vein begins by making a small incision just above the medial aspect of the knee to obtain ~ 35 cm of graft, or by making an additional incision 2-3 cm above the medial malleolus to capture the entire ~70 cm length of the vein. A balloon tip trocar is then inserted into the incision in the direction of the groin, and a tunnel around the saphenous vein is created by insufflating the fascial canal along the length of the vessel. A conical dissection cone is then advanced towards the groin along the anterior aspect of the vessel free from tributaries. Circumferential dissection of the vein is then performed carefully identifying any tributaries along the lateral and posterior aspects of the wall; these undergo ligation with bipolar electrocautery. Once the vessel is isolated entirely, a stab incision is made at the groin and the vessel is removed. Similar to open harvest, the vein is then cannulated and any remaining branches or points of injury are clipped, tied or oversewn.

Whether performing open or endoscopic harvest, extreme care is necessary to avoid unnecessary trauma and damage to the vessel, as increased manipulation of the vein is associated with higher rates of thrombosis and atherosclerosis, and decreased vessel patency.

Complications

The two most common and most significant complications arising from saphenous vein grafting in the setting of CABG are thrombosis and atherosclerosis.  Both complications result in significantly decreased duration of vessel patency–graft failure is as high as ten to twenty-five percent after twelve to eighteen months postoperatively, with a 5 percent increase in failure rate for each year beyond five years post-bypass.[7] Early graft failure (up to 18 months) is thought to result from intimal hyperplasia secondary to endothelial injury and decreased production of nitric oxide, platelet aggregation, growth factor secretion, inflammation, and intraluminal foam cell accumulation which has associations with increased manipulation and mechanical trauma of the vessel during harvest.[8][9][10][11] Late graft failure (greater than 18 months post-op) occurs as intimal hyperplasia creates a progressive atherosclerotic-like occlusive plaque.[12]

Beyond concerns for long-term patency, additional complications may relate to the harvest itself at the harvest site. These include, but are not limited to, persistent post-operative pain/paresthesias, surgical site infections, development of lower extremity varicosities and lower extremity swelling secondary to reduced venous outflow after vein removal. OVH, in particular, may result in increased postoperative pain and persistent paresthesias related to incision length and incidental nerve injury during dissection and are at an increased risk of developing surgical site infections given the length of the incision.[13] While EVH reduces the risk of developing many of these complications as compared to OVH, critics of EVH have shown data that its utilization results in increased vessel trauma during dissection and thus may be at an increased risk of graft failure postoperatively,[14]although large meta-analyses recently have suggested otherwise.[15]

Clinical Significance

Initially, the conduit of choice for coronary artery bypass grafting, the saphenous vein has been supplanted by the LIMA, the RA and increasingly the RIMA as bypass conduits of choice given its high rate of failure compared to arterialized grafts. More and more evidence is accumulating regarding additional arterial grafts such as the gastroepiploic artery; these have not demonstrated clear superiority to SVG, however, and are used less frequently[16]. The rising use of arterial grafts over vein is related to the morphologic benefit of arterial grafts as they accommodate to their role as coronary bypass grafts. While postoperatively are prone to progressive intimal hyperplasia and subsequent atherosclerosis, thrombosis, and failure, the improved patency of arterial grafts suggests that this progressive intimal hyperplasia is not as prevalent in arterial conduits. To prevent accelerated atherosclerosis of coronary bypass grafts, post-operative lifestyle modifications, a and antiplatelet agents, and occasional percutaneous coronary intervention and even redo bypass grafting may be necessary to maintain perfusion of at-risk segments of myocardium.[17]

Despite new evidence supporting the use of arterial over vein grafts in coronary artery bypass grafting, utilization of the GSV remains a mainstay of the current treatment of coronary revascularization; this may be in part to surgeon comfort with SVG and a thorough understanding of SVG progression after revascularization as compared to its arterial competitors. While the LIMA remains the vessel of choice for coronary artery bypass grafting, the relative ease of harvest, length of usable vessel and comfort in its use make the SVG an indispensable tool in any cardiothoracic surgeon’s armamentarium in coronary revascularization.

Enhancing Healthcare Team Outcomes

More and more data is being compiled regarding the patency of different conduits in different settings.  While it is essential to understand the trend in current literature suggesting a benefit of arterial over venous grafts, it also remains important to understand the history of saphenous vein grafts, technical considerations regarding their grafting, potential complications related to the graft and its utility.