888-552-5792 info@ct-assist.com

CT Assist Blog

Preservation of the Adventitia of the Greater Saphenous Vein during Endoscopic Vein Harvest

Posted by Liza Szelkowski, PA-C on Nov 24, 2016 11:04:00 AM

History

The greater saphenous vein (GSV) has long been a standard of coronary artery bypass grafting surgery.  Since the 1960’s, surgeons have been performing this operation with the help of both the internal mammary artery, and the GSV.  While the internal mammary artery, and other arterial conduits, have proven to be reliable grafts, the GSV has continued to undergo scrutiny regarding long-term patency.  The GSV has traditionally been harvested with an open technique, with direct visualization, and minimal need for vein manipulation, stretching, or electrocautery in close proximity to the vein.  Endoscopic vein harvesting (EVH) has now become the standard of care in most institutions.  This technique has become a focus of discussion regarding its possible role in decreasing the patency of the graft, since there can be more manipulation of the GSV in inexperienced hands.  Greater manipulation of the vein can include harming the adventitial layer, which newer research demonstrates can be a detriment to the graft.  Since one of the major duties of the cardiac surgery PA is to harvest vein, it is important to understand the current literature regarding preservation of the GSV, since this is directly related to its patency rate.

latex-free-surgical-gloves-img1.jpg

Histology and Pathophysiology

The internal mammary artery possesses properties that give it an advantage, as a conduit, over the GSV.  It is, generally, resistant to the development of atherosclerotic plaque, its endothelial layer is less fenestrated, and this layer produces a higher level of nitric oxide (Otsuka, Yahagi, Sakakura, & Virmani, 2013).  Nitric oxide plays an important role in graft patency, not only because it is a vasodilator, but also because it inhibits platelet aggregation, which may prevent occlusion of a graft (Cable, O'Brien, Schaff, & Pompili, 1997).  That being said, the GSV does have a number of practical advantages that make it a favorable conduit.  It is easily accessible to the harvester, it is expendable since the venous drainage of the leg can be accomplished by the deep system, and its length provides a means for creating multiple grafts (Hashmi et al., 2015).  Given this information, the question that remains is what can be done while harvesting and preparing the GSV to ensure its greatest patency. 

The Adventitial Layer

Recent literature has focused on the development of techniques that preserve the adventitial layer of the GSV.  Traditionally, and especially with EVH techniques, the adventitial layer of the vein can be stripped off, or damaged.  This can contribute to graft dysfunction since this layer not only provides structural support for the vein, but also contains a micro vascular network of vasa vasorum that help in the exchange of gasses and with the supply of nutrients to the wall of the vein (Hashmi et al., 2015).  In addition, the adventitial layer and peri-adventitial fat provide nitric oxide which improves graft patency (Hashmi et al., 2015).  When the vasa vasorum is interrupted, vein wall ischemia can occur.  This contributes to intimal hyperplasia and, thus, graft closure (Papakonstantinou, Baikoussis, Goudevenos, Papadopoulos, & Apostolakis, 2016).  When this layer is stripped away, these protective benefits are lost.

What Can We Do?

The evidence is clear that damaging the adventitial layer of the GSV is not only harmful to the vein; it also decreases the patency rate of the graft itself.  Studies are still conflicting as to whether EVH is harmful to GSV patency rates or not.  Lopes and colleagues, in their 2009 study, presented data that demonstrated that veins harvested with EVH technique had lower patency rates than those harvested with open technique (Lopes et al., 2009).  Alternatively, a 2011 study by Dacey and colleagues showed that EVH was not associated with any harm (Dacey et al., 2011).   There are several studies providing arguments on each side, making the data confusing.  Clarity will be provided with a forthcoming study.  The National Institutes of Health is currently recruiting participants for the REGROUP Trial.  This study, The Randomized Endo-Vein Graft Prospective Trial, aims to investigate the impact of GSV harvesting techniques by evaluating open versus endoscopic vein harvesting, and its effect on graft patency (The randomized endo-vein graft prospective trial.2013).  It is with a randomized clinical trial that we may finally get concrete answers regarding EVH.  Until then, PAs harvesting vein need to continue to go with what is known.  Preserving the adventitial layer of the GSV is paramount.  Practicing clean technique while harvesting vein is of the utmost importance.  Handling the GSV with care is essential.  Treating each vein with care ensures that we are doing all we can as clinicians to obtain a maximal rate of patency for the grafts we provide for an operation, thus, providing the greatest chance of success for the patient.

References

Cable, D. G., O'Brien, T., Schaff, H. V., & Pompili, V. J. (1997). Recombinant endothelial nitric oxide synthase-transduced human saphenous veins: Gene therapy to augment nitric oxide production in bypass conduits. Circulation, 96(9 Suppl), II-173-8.

Dacey, L. J., Braxton, J. H.,Jr, Kramer, R. S., Schmoker, J. D., Charlesworth, D. C., Helm, R. E., et al. (2011). Long-term outcomes of endoscopic vein harvesting after coronary artery bypass grafting. Circulation, 123(2), 147-153.

Hashmi, S. F., Krishnamoorthy, B., Critchley, W. R., Walker, P., Bishop, P. W., Venkateswaran, R. V., et al. (2015). Histological and immunohistochemical evaluation of human saphenous vein harvested by endoscopic and open conventional methods. Interactive Cardiovascular and Thoracic Surgery, 20(2), 178-185.

Lopes, R. D., Hafley, G. E., Allen, K. B., Ferguson, T. B., Peterson, E. D., Harrington, R. A., et al. (2009). Endoscopic versus open vein-graft harvesting in coronary-artery bypass surgery. New England Journal of Medicine, 361(3), 235-244.

Otsuka, F., Yahagi, K., Sakakura, K., & Virmani, R. (2013). Why is the mammary artery so special and what protects it from atherosclerosis? Annals of Cardiothoracic Surgery, 2(4), 519-526.

Papakonstantinou, N. A., Baikoussis, N. G., Goudevenos, J., Papadopoulos, G., & Apostolakis, E. (2016). Novel no touch technique of saphenous vein harvesting: Is great graft patency rate provided? Annals of Cardiac Anaesthesia, 19(3), 481-488.

The randomized endo-vein graft prospective trial.(2013). Clinicaltrials.Gov: NCT01850082,

 

 

Topics: Cardiac PA, CT Surgery