Overview of Arteriovenous Grafts

AVG or prosthetic bridge grafts are surgically created artificial conduits that connect an artery to a vein and are superficially tunneled under the skin to allow easy cannulation1. The conduit can be straight or looped and ranges between 4 to 8 mm in diameter2. A common configuration for AVG is the forearm loop graft which connects the brachial artery and the cephalic vein in the antecubital fossa. The forearm loop graft is generally preferred to a straight configuration because it is thought to have better patency,2,3. AVG are also frequently placed in the upper arm from the brachial or axillary artery to the brachial or axillary vein. Creative surgeons have placed grafts in such diverse locations as the thigh, across the chest in a necklace configuration, loops from the axillary or subclavian artery to the jugular vein and axillary- femoral placement1.

Historically, the most commonly used material for construction of AVG was polytetrafluethylene or PTFE. This synthetic material was utilized in preference to other synthetic or biologic materials, based on its availability, ease of implantation, structural integrity, ease of cannulation, longer patency and lower risk for disintegration with infection3. Other organic, semi-organic or synthetic materials that have been used to create prosthetic bridge grafts include bovine carotid or mesenteric vein, ovine collagen with mesh, homologous saphenous vein, polyurethane (PU), silicon and Dacron3,4. None of these has shown improved survival or better patency than PTFE grafts. PTFE grafts can typically be cannulated in 2-3 weeks. The composite/PU graft has the advantage of a self-sealing property which allows it to be cannulated in as little as 24-48 hours and even within hours of placement, if necessary, for dialysis3,5. As a result, the composite/PU graft can be placed in some cases without having to use a catheter for initiation of dialysis therapy.

Primary failure rates can vary significantly between AVG and arteriovenous fistula (AVF)2,5,6. Primary failure is defined as an access that never provided reliable hemodialysis2. Though primary failure rates correlate with demographic factors, comorbidity and anatomical position, AVG primary failure percentage of approximately 15% is considerably lower than the approximate upper limit of primary failure percentage of 40% for AVF2,5,6. However, AVG have serious long term disadvantages including more frequent thrombosis and infection than AVF. Thrombosis is the major cause of graft failure accounting for approximately 80% of cases5. A meta analysis encompassing 1849 AVF and 1245 AVG abstracted from 34 studies demonstrated that AVF had significantly better unassisted (primary) patency (72% at six months, 51% at eighteen months) then AVG (58% at six months, 33% at eighteen months). Assisted (secondary) patency was also superior in AVF (86% at six months, 77% at eighteen months) than in AVG (76% at six months, 55% at eighteen months)7. PTFE grafts have a significantly higher infection rate than AVF1 and are associated with a 41% higher risk of death in prevalent diabetic patients.8 Repeated cannulation of AVG in combination with proximal stenosis may result in the development of pseudoaneurysms that can leak or become infected. These troublesome and expensive complications have increasingly relegated AVG to select patients who are poor candidates for AVF and have placed an emphasis on access surveillance and the development of new technologies. One recent development is the Hemodialysis Reliable Outflow (HeRO™) vascular access device. This device merges graft and catheter technology. Arterial blood is shunted from the brachial artery through a superficial graft segment and subsequently into the central venous system, via a catheter like segment that enters the internal jugular vein with discharge into the right atrium9,10. Although it is too early to evaluate its complication rate and long term patency, preliminary results with this technology have shown promise.

References

  1. Huber TS, Carter JW, Carter R, Seeger JM. Patency of autogenous and polytetrafluoroethylene upper extremity arteriovenous hemodialysis accesses: A systematic review. J Vasc Surg 38:1005-1011, 2003
  2. Oliver MJ. Chronic hemodialysis vascular access: Types and placement. Retrieved from www.uptodate.com on January 14, 2008
  3. KDOQI Clinical Practice Guidelines for Vascular Access. Am J Kidney Dis 48(Suppl 1):S176-S273, 2006
  4. Berardinelli L, Vegeto A. Lessons from 494 permanent accesses in 348 haemodialysis patients older than 65years of age:29 years of experience. Nephrol Dial Transplant 13(Suppl 7):S73-S77, 1998
  5. Maya ID and Allon M. Core curriculum in nephrology vascular access: Core curriculum 2008. Am J Kidney Dis 51:702-708, 2008
  6. Polo JR, Tejedor A, Polo J, Sanabia J, Calleja J, Gómez F. Long-term follow-up of 6-8mm brachioaxillary polytetrafluorethylene grafts for hemodialysis. Artif Organs 19:1181-1184, 1995
  7. Sands JJ. Vascular access 2007. Minerva Urol Nefrol 59:237-249, 2007
  8. Dhingra RK, Young EW, Hulbert-Shearon TE, Leavey SF, Port FK. Type of vascular access and mortality in U.S. hemodialysis patients. Kidney Int 60:1443-1451, 2001
  9. Katzman HE. The HeROTM vascular access device: A new long-term dialysis access option for access challenged patients. 36th Annual Symposium for the Society for Clinical Vascular Surgery, Las Vegas, NV, March 2008
  10. Hemosphere product information. Retrieved from www.hemosphere.net on February 2, 2008

P/N 101041-01 2/2009