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J Thorac Cardiovasc Surg 2007;134:504-505
© 2007 The American Association for Thoracic Surgery
Brief Communication |
Bristol Heart Institute, Bristol Royal Infirmary, Bristol, United Kingdom.
* Address for reprints: Mr GJ Murphy, Bristol Heart Institute, Bristol Royal Infirmary, Marlborough Street, Bristol BS6 5SJ, United Kingdom. Telephone: 0044 117928 3145, Fax: 0044 1179299737. (Email: Gavin.Murphy{at}bristol.ac.uk).
The success of coronary artery bypass grafting is limited by poor long-term graft patency. Despite the superior patency of arterial grafts, saphenous vein remains the most commonly used conduit for coronary artery bypass because of its predictable handling qualities and ready availability.1
Over 40% of vein grafts are thrombosed at 10 years postoperatively,2 largely as a consequence of vein graft disease that is characterized by neointima formation, atherosclerosis, and plaque rupture. Graft failure results in recurrent angina, myocardial infarction, or death and leads to repeat revascularization procedures with their associated morbidity and costs. To date, with the exception of aggressive lipid lowering, no therapy has been shown to improve long-term vein graft patency in clinical studies. In porcine saphenous vein to carotid artery interposition graft, placement of a loose-fitting external macroporous Dacron sheath inhibits vein graft disease in the long term.3,4 The aim of this phase I randomized pilot study was to evaluate the effects of placement of the external Dacron stent, or Extent (Vascutek Ltd, Inchinnan, Scotland), on vein graft disease in patients undergoing elective coronary artery bypass grafting.
Between March and September 2005, 20 patients undergoing isolated on-pump coronary artery bypass grafting, and who had given informed consent, were randomized to have an Extent placed to either a right coronary system graft or left coronary system target graft. The Extent is an incomplete tube of knitted polyester reinforced with polytetrafluoroethylene ribs at approximately 1-cm intervals to maintain rigidity (Figure 1). The edges of the incomplete tube form a flange. The stent was so designed to maintain the circular cross section of the graft and to facilitate placement after completion of both distal and proximal anastomoses, with the flange preventing migration or kinking of the vein graft through the side of the graft. Two graft sizes were used, 8 mm and 6 mm. Graft sizing was intended to be nonrestrictive with up to 1-mm clearance around the circumference of the vein graft. Patients were eligible if they were to receive a reversed long saphenous vein graft to both the right and left coronary systems in addition to a pedicled left internal thoracic artery graft to the left anterior descending coronary artery. The Extent was placed on the vein graft after the proximal and distal anastomoses had been completed and protamine administered. Where possible, the proximal and distal ends of the graft were sutured to the epicardium distally and to the aortic adventitia to prevent migration; however, in 9 of the grafts, postdeployment trimming of the proximal or distal anastomoses to optimize the graft lie prevented this. The flange was allowed to lie as appeared optimal to the graft curvature around the heart. The study had received local ethical review board approval, and all patients gave informed consent to the procedure. The primary end point of the study was a 20% reduction of wall thickness as assessed by intravascular ultrasound at 6 months after surgery relative to the untreated contralateral vein graft.
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Key demographic, operative, and postoperative data are listed in Table 1. One patient randomized to a left-sided Extent had the stent placed on a graft to the posterior descending, inasmuch as the left-sided target was heavily calcified. Two patients refused to attend for follow-up and 1 subsequently reported an allergic reaction to iodinated contrast. At follow-up angiography (9 conventional, 8 computed tomographic) all 17 Extent grafts were thrombosed. All left internal thoracic artery and non-Extent vein grafts were patent.
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The most likely explanation for the universal thrombosis of Extent vein grafts in this phase 1 study is that stent rigidity, oversizing, or the incomplete tube design resulted in grafts kinking, either at the anastomoses or within the middle part of the graft. This could have occurred as a consequence of stent or graft movement on chest closure or patient repositioning or at some later time. The potential for this to occur was not foreseen. Preclinical studies had been performed in the end to end or end to side porcine carotid artery interposition model where the vessels are shorter and the potential for graft movement and kinking is less, although the degree of graft oversizing was similar.
Despite the poor results of the Extent study, the dramatic and sustained effectiveness of external sheaths in experimental studies suggests that continued research is warranted. One alternative is a nonrestrictive, flexible, biodegradeable, macroporous polyglactin (Vicryl; Ethicon, Inc, Somerville, NJ) external sheath. These features overcome many of the limitations of the rigid Dacron stent and have also demonstrated long-term inhibition of vein graft disease in the porcine model.5
Footnotes
Funded by the British Heart Foundation.
1 Andrew Newby and Gianni Angelini are employees of the University of Bristol, which holds a patent on the concept of the external vascular stent. 
References
This article has been cited by other articles:
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  T. Rajathurai, S. I. Rizvi, H. Lin, G. D. Angelini, A. C. Newby, and G. J. Murphy Periadventitial Rapamycin-Eluting Microbeads Promote Vein Graft Disease in Long-Term Pig Vein-Into-Artery Interposition Grafts Circ Cardiovasc Interv, April 1, 2010; 3(2): 157 - 165. [Abstract] [Full Text] [PDF]
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