Autogenous Grafts (Including Vein Harvest, Surgical and Endoscopic)

Background

Autogenous vein remains the conduit of choice for infrainguinal revascularization and has been shown to be superior to alternatives above and below the knee in patients with claudication and chronic limb-threatening ischemia (CLTI). ^, The first report on the use of autogenous vein for the treatment of arterial occlusive disease came in 1944 by Dr. Dos Santos, who performed a vein patch during a superficial femoral endarterectomy, and then soon after by Dr. Kunlin, who utilized reversed great saphenous vein as a conduit to bypass a superficial femoral artery occlusion. Kunlin’s techniques were continued in the United States by the likes of Drs. Linton and Darling, who replicated his earlier success with autogenous vein grafting. From there, great saphenous vein use was extended below the knee to tibial and inframalleolar targets. Interest in extending the use of autogenous vein in these locations was furthered by the observation of poor outcomes with prosthetic graft use below the knee. Other autogenous options have been explored including arm vein and small saphenous vein, with mixed results. With these options available, an autogenous conduit is possible in most patients. A detailed review of venous biology including the anatomy of these options as well as the histology and physiology can be found in Chapter 3 (Vessel Wall Biology).

Preoperative Vein Mapping

Preoperative assessment of autogenous vein is essential in planning an arterial reconstruction. Its value has been recognized since the 1970s when preoperative assessment was performed with venography. In the 1980s ultrasound was introduced. Ultrasound offers the advantage of being noninvasive, and also better characterizes vein diameter, depth, and location relative to surrounding structures, while still providing important information on anatomic variation, varicosities, fibrosis, calcification, and areas of extensive branching that may prohibit use as a conduit. With advances in technology and increased familiarity with its use, along with reports on its accuracy and predictive value, ultrasound has become the gold standard in venous imaging. In addition to its role in preoperative planning, duplex vein mapping has been shown to decrease the rate of surgical site infection, frequency of readmission, and cost. This is presumably due to avoiding unnecessary or excessive vein exploration. ^, CT angiography is sometimes already available for patients being planned for revascularization, and has also been shown to be a reliable method of measuring GSV diameter that correlates well with duplex. CTA has good specificity but relatively poor sensitivity for this indication, therefore if CT shows inadequate vein it should be followed up with an ultrasound exam.

Diameter measurements of the great saphenous vein should be taken from inner wall to inner wall at multiple levels; high thigh near the saphenofemoral junction, mid-thigh, low thigh, knee, high calf, low calf, ankle. Anatomic variation, varicosities, fibrosis, calcification, and areas of extensive branching should be noted.

There are numerous reports on the relationship between vein diameter and graft function, and the minimum acceptable vein diameter for bypass grafting has been debated. In PREVENT III, vein grafts <3 mm (along with non-GSV) were designated as high-risk conduits, comprising 24% of conduits used. These grafts demonstrated 1-year primary and secondary patency rates of 44% and 69%, respectively, as compared to 72% and 87% in grafts with a diameter >3.5 mm. ^, ^, Wengerter et al. showed superior patency with veins >3 mm compared to those <3 mm (1-year patency rates of 53% and 20%, respectively). In a prospective multicenter study, Buth et al. found that vein diameter <3.5 mm was the only factor that significantly correlated with subsequent graft stenosis. A designation of high risk or sub-optimal becomes relative when considering the alternative options (prosthetic graft, cryopreserved vein) in the open surgical management of patients with CLTI. While inferior, the results in high-risk conduits in PREVENT III still showed reasonable secondary patency of 69% with no difference noted in limb salvage of 84.7% at a year. Slim et al. extended the use of reversed vein to as small as 2 mm in patients with CLTI and they have shown acceptable patency rates. The use of grafts as small as 2 mm has also been reported to be acceptable with in situ bypass. These results highlight that with close surveillance and secondary intervention for threatened grafts, successful outcomes are feasible even with marginal conduit diameter. Ultimately, every effort should be made to use an autogenous conduit when feasible. Each patient presents with unique circumstances and the most appropriate conduit will depend on the clinical scenario, patient-specific risks factors, and their anatomy.

Vein Graft Preparation

Vein Handling Considerations

As is the case in most areas of surgical technique, precise, atraumatic dissection is critical in vein handling during harvest. Minimal direct handling of the vein helps avoid injury to endothelial cells, which function as a barrier between blood and the highly thrombogenic subendothelial tissue, and also house and produce a number of vasorelaxant, anti-inflammatory, and antithrombotic factors. Traumatic dissection and loss of endothelial integrity can expose subendothelial tissues, which not only induces platelet deposition, but can alter the media and lead to the elaboration of growth factors that cause smooth muscle cell proliferation and production of a fibrous matrix. This environment, coupled with the recruitment of inflammatory mediators, has the potential to develop an occlusive arterial lesion. Study of animal models support this notion by demonstrating that smooth muscle cells are maintained in a contractile (nonproliferative) phenotype and that leukocyte infiltration is reduced when endothelial injury is avoided. ^, Direct evidence linking endothelial integrity to improved clinical outcomes is lacking, however given the indirect evidence and limited downside, the general consensus is to strive for precise, atraumatic dissection and minimal direct manipulation of the vein. This can be performed via a “no-touch” technique, which has been demonstrated to reduce endothelial damage during harvest ( Fig. 65.1 ). Though somewhat a misnomer, the “no-touch” technique involves limited handling of the vein without direct application of forceps or vascular clamps. Major branches should be ligated away from the wall to avoid narrowing of the lumen or crimping of the endothelium and to promote outward remodeling after implantation, but not too far away as to leave a long stump, which may be a nidus for thrombus formation. ^, ^,

Figure 65.1, “No-Touch” Technique Used in the Harvest of Autogenous Vein.

Distention Pressure

Cannulation of the vein is required before implantation to evaluate the potential diameter of the graft, assess for leaks, and identify adventitial bands impinging on the lumen. A number of investigations have examined the effect of distention pressure on endothelial integrity and almost uniformly have observed that pressure in excess of 100 mm Hg causes patchy endothelial denudation and that pressure in excess of 500 mm Hg leads to disruption of the media. ^, The intrinsic biomechanical properties of the graft are negatively impacted, with a resultant decrease in wall compliance secondary to disruption of the elastic elements within the wall. Biologic function is also influenced, with distention injury initiating an increase in c-fos expression, an upstream regulator of platelet-derived growth factor production. Use of a standard small-volume syringe can produce intraluminal pressure in excess of 700 mm Hg. A variety of pressure-sensing devices have been developed to allow the surgeon to monitor or control distention pressure. Ranging from syringes with intrinsic pressure transducers to reservoir inflation bulbs that generate a fixed pressure, these devices have undergone only sporadic testing and have not yet been accepted into widespread clinical use. Improving outcomes by minimizing vein graft intimal hyperplasia via external mechanical support or altering the makeup of the vessel wall is an area of ongoing research.

Irrigating Solution

A number of preservation solutions continue to be used for temporary storage after vein harvest, and include crystalloids, autogenous blood, and solutions containing ions for pH buffering with different pharmacologic additives. Current opinions and use of these solutions still vary. The bulk of the literature suggests that unbuffered, isotonic crystalloid solutions are most damaging to the endothelium and can increase the likelihood of graft failure. Simple buffered and modified crystalloid solutions have demonstrated reductions in endothelial denudation and improvements in both cell viability and contractility when compared with an unbuffered solution. ^, Using data from PREVENT IV, researchers found that in patients undergoing coronary bypass, veins that were preserved in a buffered solution had a lower likelihood of graft failure at 1 year compared to the saline group (OR 0.59; CI 0.45–0.78; P <0.001) or blood group (OR 0.62; CI 0.46–0.83; P <0.001). For these reasons, buffered crystalloid seems to be the best option for short-term storage of excised vein, however institutional availability, cost, and previous practices vary as evidenced by the high rate of continued use of saline and blood in PREVENT IV, at 44.4% and 32.2%, respectively.

Temperature

With conflicting experimental evidence, delineation of the most favorable storage temperature is difficult, and reasonable arguments for either cold- or room-temperature treatments can be crafted. Although no definitive recommendation can be proposed, the increased effort required to supply and maintain cold perfusate in the operating suite has prompted most clinicians to favor the use of room-temperature solutions.

Pharmacologic Adjuncts

Unfractionated heparin has universally been included in most vein harvest solutions. Aimed at reducing fibrin deposition and the formation of microthrombi, doses ranging from 4 to 10 U/mL are typically used. Pharmacologic agents have been used in vein harvest in an attempt to prevent vasospasm and maintain an intact endothelium. The most widely studied vasodilator for this purpose is papaverine. Percutaneous injection of papaverine (120 mg/L) along the outside of the vein before skin incision has been described as a step to minimize spasm, although this can prove challenging in all but the thinnest patients. Application of papaverine along periadventitial tissues and within the lumen perfusate is more easily accomplished and continued throughout vein harvest. Though not rigorously studied as an independent variable, most regimens containing papaverine have shown reduced endothelial injury in comparison to controls. ^, Other vasodilators have been examined, and a combination of glyceryl trinitrate (8.3 mg/L) and verapamil (16.7 mg/L) appears to be particularly beneficial. In direct comparison to papaverine, glyceryl trinitrate/verapamil demonstrated notable improvement in endothelial coverage.

The majority of published regimens have sought to optimize variables to maintain an intact endothelial monolayer or reduce smooth muscle cell injury at the time of implantation; few reports have challenged their techniques to extended exposure in an in vivo environment. Among the clinical investigations in this area was the PREVENT III trial, which was a prospective, randomized controlled trial that sought to evaluate the efficacy of an edifoligide, an E2F inhibitor expected to block cellular proliferation, in improving vein graft patency following infrainguinal revascularization for CLTI. Ultimately, they concluded that treatment of vein grafts with the E2F inhibitor prior to bypass did not confer protection from clinically meaningful outcomes such as reintervention for graft failure. ^,

Though extensive research has been conducted in this area, no consensus has been reached regarding the optimal techniques for vein graft harvest, with each variable demonstrating unique advantages and shortcomings. Box 65.1 provides a practical summary protocol for the preparation of autogenous vein conduit.

BOX 65.1

Recommended Vein Graft Harvest Protocol

Handling

Precise atraumatic technique
Ligation of tributaries away from the wall
Lysis of adventitial bands
Minimization of time from vein excision to implantation

Solution

Buffered isotonic crystalloid (e.g., Plasma-Lyte)

Temperature

No definitive recommendation

Distention

Maximum pressure of 100–150 mm Hg

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